787 Batteries and Chargers - Part 1

[Machaca]

The Washington Post reports (http://www.washingtonpost.com/lifestyle/travel/overcharging-of-batteries-likely-culprit-in-boeing-787-fires-aviation-and-battery-experts-say/2013/01/18/a701daea-61bf-11e2-81ef-a2249c1e5b3d_story.html):

Overcharging of batteries likely culprit in Boeing 787 fires, aviation and battery experts say


Here are some details and images of the 787 chargers and batteries:

http://i337.photobucket.com/albums/n385/motidog/787batt01_zps460c4d50.jpg

Thales is the power system general contractor for the 787.

The chargers are made by Securaplane (a Meggitt company), who state (http://www.securaplane.com/products/power-conversion):

Securaplane has developed a method for accurately detecting the inflection point which has eluded battery experts for years and is critical in reducing an overcharge condition. This patented method of charging ensures that the battery receives the optimum amount of charge for all temperature conditions combined with various battery states of charge.

Securaplane battery chargers store every fault including battery over-temperature, cell unbalance, defective temperature sensors, defective charger/battery connection and GMT time/date of fault period. Our chargers possess extensive diagnostics such as charger microprocessor status and permanent memory of faults...

http://i337.photobucket.com/albums/n385/motidog/787batt05_zps78dfa924.jpg


The batteries are made by GS Yuasa, and are the Lithium Cobalt variety.

http://i337.photobucket.com/albums/n385/motidog/787batt06_zps4e0b43e6.jpg

http://i337.photobucket.com/albums/n385/motidog/787batt07_zps0a7c2262.jpg

http://i337.photobucket.com/albums/n385/motidog/787batt02_zps393f8581.jpg

Result of overcharge:

http://i337.photobucket.com/albums/n385/motidog/787batt08_zps856057b4.jpg

[gums]

Thank you, Mach

The whole battery thing reminds me of many software and iPhone/Droid folks that always want the latest and greatest apps.

No doubt that the Li-ion batteries have a greater power/density/weight capability than some of the not-so-old batteries like the nickel-metal-hydride ones. Funny, but Toyota sticks with those nickel ones for their Prius.

In a plane that weighs as much as the 787, a few pounds for an "older", but more safe battery seems a good trade-off.

My friends who served in the 'stan and Iraq told me war stories about those "new" batteries. The temperatures and charging systems did not help, so they went back to older batteries.

In my mind, it ain't worth the extra battery capacity to require expensive charging systems and such. Then there's the requirement to have a good fire extinguishing system if one of the suckers goes into thermal runaway.

[hetfield]

@gums

I agree with every word.

Nevertheless, the almighty FAA had a different opinion.....

[kilomikedelta]

The Thales Li-ion battery unit shown has a mass equivalent to 13.5 two litre bottles of cola. Perhaps restricting the drinks mixer selection and adding a few battery packs might moderate the transient draw of the 1 megawatt load of the aircraft. No doubt the marketing suits would be in high dudgeon regarding this suggestion. I suspect the electrical system weights and redundancy decisions were made by MBA's, which like papal pronouncements in catholicism, are infallible in the corporate religion.

[Romulus]

The whole battery thing reminds me of many software and iPhone/Droid folks that always want the latest and greatest apps.

No doubt that the Li-ion batteries have a greater power/density/weight capability than some of the not-so-old batteries like the nickel-metal-hydride ones. Funny, but Toyota sticks with those nickel ones for their Prius.

In a plane that weighs as much as the 787, a few pounds for an "older", but more safe battery seems a good trade-off.

...

In my mind, it ain't worth the extra battery capacity to require expensive charging systems and such. Then there's the requirement to have a good fire extinguishing system if one of the suckers goes into thermal runaway.

So who else do you give an extra weight allowance to so that you stick with older technology? Hindsight is a nice easy game to play but can you do it prior to the event? And how much extra weight allowance are you going to make for that "good fire extinguishing system"?

What about that new fangled carbon fibre stuff - better make sure they put double the amount of that on or perhaps just stick with aluminium. But heck, where did that aluminium stuff come from!!?? Back to wooden frames and fabric covering I say!!

Progress is progress. Undoubtedly Boeing did their testing and decided the new batteries were safe and yielded significant benefits, primarily weight saving. Now there's a problem. So they will go back and fix it.

That's how progress works.

[RR_NDB]

Mach,

Thanks for technical thread. Important issue.

The information you bring us shows there are software involved. :8

And the tracing to the root cause could be more complex and not deterministic in the short term.


Securaplane has developed a method for accurately detecting the inflection point which has eluded battery experts for years and is critical in reducing an overcharge condition. (http://www.securaplane.com/products/power-conversion)

May be a tweaking is necessary to the algorithms to allow a safer pass of teething period.

The marketing information make us confident. After reading the caput information we may wonder what happened.

The days difference between similar incidents is just coincidence?

Battery subsystems now have their own FDR.:)

Could you comment something on the graph?

[RR_NDB]

Romulus:

Boeing did their testing (http://www.pprune.org/tech-log/505695-787-batteries-chargers.html#post7643602)

The Testability issue is showed during the products teething phase and even much later, sometimes. Examples in aviation are dramatic.

When designing innovative and complex machines the Testability issue is a big concern. And the plane testing phase may miss important details only detectable by time.

[PJ2]

Romulus;
Undoubtedly Boeing did their testing . . .
I expect that that question will be part of the investigation prior to re-certification of the B787. From the NYT this morning (http://www.cnbc.com/id/100392765) (Jan 19, 2013 10:54 EST:
The government approved Boeing's use of lithium-ion batteries to power some of the plane's systems in 2007, but special conditions were imposed on the plane maker to ensure the batteries would not overheat or ignite. Government inspectors also approved Boeing's testing plans for the batteries and were present when they were performed.

Even so, after the episode in Boston, the federal agency said it would review the 787's design and manufacturing with a focus on the electrical systems and batteries. The agency also said it would review the certification process.
The FAA approval of Boeing's use of Li-Ion batteries is in the following document. One would expect that Boeing's testing and results will be examined against the FAA approval.
Special Conditions: Boeing Model 787–8 Airplane; Lithium Ion Battery Installation
AGENCY: Federal Aviation Administration (FAA), DOT. (http://www.gpo.gov/fdsys/pkg/FR-2007-10-11/pdf/E7-19980.pdf)

[RR_NDB]

gums:

In a plane that weighs as much as the 787, a few pounds for an "older", but more safe battery seems a good trade-off.

My friends who served in the 'stan and Iraq told me war stories about those "new" batteries. The temperatures and charging systems did not help, so they went back to older batteries.

In my mind, it ain't worth the extra battery capacity to require expensive charging systems and such. Then there's the requirement to have a good fire extinguishing system if one of the suckers goes into thermal runaway. (http://www.pprune.org/tech-log/505695-787-batteries-chargers.html#post7643497)

The grounding of the 787 fleet an it´s consequences strongly supports your rationale.

It´s unclear to me the size of the gain in using these batteries. We need to understand better the trade-offs and quantify.

The designers probably required to use them in the 787. We need to check why. Which were/are the dominant reasons?

May be the very high peak current of the new batteries (due low internal resistance) were important for the high energy consumption of the 787?

On maintenance aspects and risks it´s clear Boeing heard the promises of the suppliers (Batt and chargers) installing it close to Electronic Equipment without elaborated safety schemes in case of major failures like the ones that occurred.

[RR_NDB]

Hi,

The government's approach, while prudent, worries industry officials who fear it does not provide a rapid exit for Boeing. (http://www.cnbc.com/id/100392765)

IMO FAA aggravated the problem with this political attitude (e.g. 1000%).

...It will happen when all are confident they have a good solution that will contain a fire or a leak."



This opens a new front.

Government inspectors also approved Boeing's testing plans for the batteries and were present when they were performed.

The Testability again must be remembered after the problems in BOS and TAK.

[Booglebox]

Lithium-cobalt, lithium-poly and lithium-ion batteries can be very unstable even under normal conditions; only the power management chip in your laptop battery stops it from bursting into flames when charging. Some have, even when not charging.
Enormous pressure on battery makers to increase energy density and decrease weight/volume, for phones / laptops / tablets etc. (and now for airplanes!) has resulted in increasingly daring & unstable designs being produced. In aerospace, this is all pretty new tech. The massive electric requirements of the 787 compared to other a/c only compound the problem.
Before the 787, I have never heard of any lithum-tech batteries being used for anything mission-critical in aerospace (please enlighten me if I am wrong).

As a previous poster points out:
Funny, but Toyota sticks with those nickel ones for their Prius.
Yep. Heavy and large by comparison, but well-known, predictable, proven tech.

[gums]

TNX, boogle

Weight and form factor not a biggie.

It's the charging system and batt monitering system, plus a fire extinguishing system.

I like the Li-ion batts for small stuff, but not big ones for mission-critical power supplies.

[kbrockman]

Might I suggest switching over to a Plutonium-238 battery, works by means of radioactive decay ,have a very long life, good energy density and at the end of the plane's life-cycle can be sold on the second hand black market for 'alternative' uses.

See, problem solved.

[ZAGORFLY]

It woul be nuclear flying devices, not very ideal concept to accept...

[green granite]

Securaplane had a major fire back in 2006, there's a discussion about it here (http://www.airliners.net/aviation-forums/general_aviation/read.main/3091319/) it has been suggested that it was due to a lithium battery catching fire while being charged or used. Unfortunately I can find no other contemporary accounts of the fire which destroyed a entire building apparently.

[Jetstream Rider]

Before the 787, I have never heard of any lithum-tech batteries being used for anything mission-critical in aerospace (please enlighten me if I am wrong).

Apparently the International Space Station, the F22 and F35 and the A380 all have LiIon batteries.

The same ones fitted to the 787 have "1.3 million hours of flight time" according the Boeing - so they are used in other places. I would suggest anything on the ISS is "mission critical" as its not easy to land if something goes wrong! ;)

[green granite]

According to Leeham News and Comment:
The Airbus A380 uses lithium batteries to power its emergency lighting system. The US FAA set special conditions when certifying the aircraft. Airbus says “the batteries are small, limited, and are not in a frequently-active charging/discharging function.”

rest of article: A380 has, A350 will have lithium-ion batteries « Leeham News and Comment (http://leehamnews.wordpress.com/2013/01/14/a380-has-a350-will-have-lithium-ion-batteries/)

[hetfield]

The battery that caught fire on the Japan Airlines 787 in Boston was the second main battery. This unit’s primary purpose is to electrically start the APU when neither of the engines is running and the aircraft is not connected to external ground power. In this case, the battery energizes the right hand of the two starter/generators connected to the APU. The aft battery also provides another minor role, namely power to the navigation lights during battery-only towing operations. The unit in the second incident, which forced an ANA 787 to make an emergency landing in Japan on Jan. 16, involved the main battery in the forward E/E bay. In this case, there was less damage, though spilled electrolytes, fumes and minor thermal damage indicated signs of overheating.(Aviation Week)

So the Main battery as well as the APU battery catched fire..., hhmmm.

Here a small example what to expect....

-DcpANRFrI4

[saptzae]

The charger manufacturer got a patent Patent US5780994 - Detection of inflection point in secondary-battery charging process (http://www.google.sk/patents/US5780994), which they claim as per Innovative Inverter Technologies and Main Ship Battery Chargers for Power Conversion (http://www.securaplane.com/products/power-conversion) to apply with the 787 charger. Last sentence from the abstract: Accordingly, the voltage response is no longer monitored and the time remaining to reach the inflection point is used to complete the fast-charge operation. _If_ they really charge like that, without the monitoring the cell voltage, the problems seen are to be expected, as even a minor mismatch (caused amongst others by aging) of the assumed inflection point to the actual cell would lead to overcharge. Lithium cells will degrade fast with minor (trickle) overcharge and absolutely will not not tolerate any overcharge at fast-charge current. NiCd and Pb cells would be much more tolerant.

[archae86]

Here are some details and images of the 787 chargers and batteries:
http://i337.photobucket.com/albums/n385/motidog/787batt02_zps393f8581.jpg
Could you comment something on the graph?

I happen to know the man who took the data, made the graph, and presented it to more than one conference--ballpark a decade ago. I discussed it with him extensively a few hours ago.

The graph subject is heat released during a thermal runaway event, with the actual vertical axis being rate of temperature rise observed in a specialized adiabatic test fixture. In the tests, thermal runaway is obtained by very slowly heating a disconnected battery in the test fixture, it taking a couple of days to reach the beginning of appreciable heat release from the battery. This first phase uses externally supplied heat--but when self-heating is detected the test assembly switches to adiabatic mode (i.e. heat is neither added to nor allowed to escape the battery under test). From that point the test progresses up the temperature scale extremely rapidly, as is hinted by the self-heating rate scale.

Obviously different cathode compositions are being compared here. Comparing the curves by essentially integrating the area under them, one can see that the total energy released per unit volume by the lithium cobalt cathode (as used in the Yuasa batteries of interest here) is quite substantially the highest in the comparison.

However, this has relevance to heat released--and thus possibly collateral damage--after the battery has already expired, which in all cases occurs tens of degrees cooler than the beginning of the thermal runaway shown. So this graph has nothing to do with why there was failure, though it does have something to do with the aftermath.

The comparison curves were all measured on 18650 cells--a size and form factor often used inside those black brick laptop batteries we have all seen.

One other point he mentioned: in their automotive application, Tesla uses these very small cells in very large numbers--but they are located in a sort of honeycomb structure. One must either design hoping never to have failure (in reality, extremely improbable), or design in a way so that failure causes acceptable harm. It appears Tesla decided that could not count on their lithium cells never failing, so took good care (it involves both physical and electrical considerations) to assure that the likely failure mode of a single cell would not cascade to adjacent cells. The cells they use are small enough that the energy release from a single one should not endanger crew or vehicle.

Looking at the Thales/Boeing design and the FAA special considerations, it appears that the approach was to assure cell failure would never occur--as it seems self-evident that no serious measures to avert propagation to adjacent cells were employed, nor were serious measures to contain damage to nearby systems.

Even if the specific cause of these events is determined and mitigated, I wonder if all concerned will remain convinced that all other possible causes of cell failure are sufficiently unlikely to make this approach prudent.

I'm not a pilot, and my design and reliability careers were not in aviation, but this all reminds me of the pair of risk mitigation approaches found in, I believe, every modern turbofan engine regarding bits of engine flying away and causing harm when they hit something important. For some parts, such as fan blades, the assumption is that they will indeed fly off sometimes, and an adequate shield is required to protect the rest of the airplane (and a spare engine to keep it aloft). Call this Tesla-like. For other parts, such shielding is deemed "impossible" (which really means too heavy and otherwise expensive), so the approach is to assure it will "never" happen. Call this Thales/Boeing-like. It is awkward when "never" happens anyway, as happened with the IPT disc on a Rolls-Royce Trent 900 on Qantas flight 32, and has happened on these two 787 episodes.

[TURIN]

Comparing the curves by essentially integrating the area under them, one can see that the total energy released per unit volume by the lithium cobalt cathode (as used in the Yuasa batteries of interest here) is quite substantially the highest in the comparison.



My information is that the batteries are Lithium Manganese. (From Boeing Training Notes). :confused:

[archae86]

My information is that the batteries are Lithium Manganese. (From Boeing Training Notes).

I think not.

The GS Yuasa site (http://www.gsyuasa-lp.com/aviation-lithium-ion-markets) story on 787 batteries points to GS Yuasa parts LVP10 and LVP65.

GS Yuasa "spec sheets" for the LVP10/65 (http://www.s399157097.onlinehome.us/SpecSheets/LVP10-65.pdf) appear to match characteristics at hand here.

The MSDS posted by GS Yuasa for LVP65 (http://gsyuasa-lp.com/SpecSheets/LVP65-MSDS.pdf) expressly specifies that it is Lithium cobalt dioxide/carbon.

Many, many of the stories on this topic assert that they are Lithium cobalt (as did Machaca in the post starting this thread).

Any more evidence than a recollection of training notes? I certainly don't want to help propagate an error, but I'm not yet convinced of my error here.

[syseng68k]

Just had a look at that patent. Fwics, at the inflexion point, the remaining time to
full charge is calculated and applied to the battery, but the voltage is not monitored
after that ???. I would have thought that voltage should be monitored continuously,
irrespective of charge or discharge conditions. Also, does the standard reference,
ie: the software battery model, take account of battery aging, where the curve may
change ?. The patent must be only part the story for this application.

Soemone else have more info ?...

[Speed of Sound]

Battery subsystems now have their own FDR.:)

As do iPods and Apple Mac laptop batteries!

I took my iPod to an Apple store about 5 years ago to have them check out an intermittent fault. They told me that I hadn't used it for over 18 months and when I asked how they could possibly know that, they told me that prior to a full charge that day, it had not been charged since 3 March 2006 at 18.23.

Apparently every charge/discharge cycle during the life of the battery is logged with the battery itself. :-)

[RR_NDB]

saptzae

Welcome aboard; Thanks for important information.

:ok:

[RR_NDB]

Speed of Sound.

Apparently every charge/discharge cycle during the life of the battery is logged with the battery itself. :-)


I hope they could, at least trace voltages of ea. cell in the charred batteries. Next step would be put the memories far from the battery. We may never understand what happened with the BOS and TAK batteries. This would be bad. The FDR analysis probably will not reveal anything useful.

[FlightPathOBN]

From Boeing land today...

WASHINGTON (Reuters) - U.S. safety investigators on Sunday ruled out excess voltage as the cause of a battery fire last month on a Boeing Co 787 Dreamliner jet operated by Japan Airlines Co (JAL) and said they were expanding the probe to look at the battery's charger and the jet's auxiliary power unit.

Dreamliner probe widens after excess battery voltage ruled out - Yahoo! News (http://news.yahoo.com/ntsb-rules-excess-battery-voltage-boston-787-incident-114146853--finance.html)


Thats all fine, but one of the batteries was in the front EE Bay, not at the APU...

[RR_NDB]

syseng68k,

Could you provide the link? If so, insert the link instead to paste on the post. To reduce the chance to be edited by the robot. (or PM it)

One of the batteries i used in a Dell mini latched a warning sign that later after investigating the reason i traced to voltage cell mismatch. An important condition that affects the battery performance. And even safety during the charging. For example: You could be able to limit the charging current when a given cell increases it's internal resistance. With higher current one cell can "suffer". (thus increasing it's voltage and consequently overheating)

This may happened in both incidents. A mere cell mismatch.

The outsourcing of new high tech items (capable to ground an airliner) could be well managed (understood, etc.) by a plane manufacturer. This would require experts not working in this environment. The sophistication of the planes and the amount of innovation creates a very difficult situation.

[RR_NDB]

FPO:

Thats all fine

This info shows they don't know failure mechanisms of these batteries. The external voltage is just one parameter. There are other 8 VERY IMPORTANT parameters (the voltage of each cell).

[sgs233a]

I posted this earlier in another thread - really just a bystander here, but I found it quite interesting:


Interesting article from 2008, seems to be saying that the specific type of Li-Ion batteries fitted to customer delivered aircraft differed from those originally fitted to test/certification aircraft:

Boeing looks to boost 787 lithium ion battery service life (http://www.flightglobal.com/news/articles/boeing-looks-to-boost-787-lithium-ion-battery-service-life-224663/)


Excerpt from above link:

"Boeing will move away from its original lithium ion battery design for its main and auxiliary power units, flight-control electronics, emergency lighting system and recorder independent power supply. Instead, Boeing is investigating the incorporation of manganese inside the lithium ion battery to boost service life.

Boeing has not determined which 787 will be the first to receive the new battery modifications, although multiple programme sources have told Flight's FlightBlogger affiliate that the new battery could be introduced as early as Airplane Seven, the first production 787 scheduled for delivery to All Nippon Airways in the third quarter of 2009."

[FlightPathOBN]

RR,

I didnt mean anything was fine...far from it...

I agree with you...not only dont they appear to know the failure mechanism...the process of self-cert is in jeopardy...

[RR_NDB]

sgs233a:

I found it quite interesting:

Important information! :ok:

[pull-up-terrain]

I havent read every post in this thread. But i know on the 747-400 there is a thermal cut off switch preventing this from happening. I know nothing about the 787 but does the 787 have a thermal cut off switch (im assuming not)?

[flyhuzaifa_a380]

Machaca : :):ok:Nice Efforts

[Speed of Sound]

If_ they really charge like that, without the monitoring the cell voltage, the problems seen are to be expected, as even a minor mismatch (caused amongst others by aging) of the assumed inflection point to the actual cell would lead to overcharge.

I assume that they do monitor individual cell voltages though.

From the pics of the damaged battery, we can see that the individual cells are strapped together with steel bars and there is a loom sitting over the top of the cells that sits in a rectangular 'grid' over the top of the cells.

Surely these are the conductors which carry individual cell voltage information to the charging/monitoring system? :confused:

[hetfield]

I havent read every post in this thread. But i know on the 747-400 there is a thermal cut off switch preventing this from happening. I know nothing about the 787 but does the 787 have a thermal cut off switch (im assuming not)? pull-up-terrain

To my knowledge, 747-400s have NiCd batteries.

They behave totally different compared to LiIon types.

NiCd have ONE charge current for all cells.
LiIon are more complex, every cell has to be charged seperately and within certain limits. Don't know if their "runaway temperature" is monitored in 787 chargers/controllers.

Regards

[wbclay]

@green granite: The fire that destroyed the Securaplane headquarters is very interesting and relevant for at least two reasons:

1. While under test, the battery assembly being developed for the 787 by Securaplane exploded and caught fire, setting off the three-alarm building fire that destroyed Securaplane's lab and production facility.

2. The technician running the test later became a whistle-blower, asserting the Securaplane battery/charger assembly was unsafe for use in aircraft. He was subsequently fired by Securaplane.

A bit of additional information on the fire is contained on page 2 of the OSHA Administrative Law Judges'
Decision and Order (http://www.oalj.dol.gov/Decisions/ALJ/AIR/2008/LEON_MICHAEL_v_SECURAPLANE_TECHNOLO_2008AIR00012_%28JUL_15_2 011%29_172333_CADEC_SD.PDF) ,which found the technician's firing to be for valid cause. Given recent developments, looks like the judgement of a tech regarded as highly competent was ultimately ignored as a consequence of his less impressive diplomatic skills.

I'm not a pilot and haven't read the FAA documents cited elsewhere in this thread, but the OSHA findings recounting the circumstances of the Securaplane technician's firing do not encourage me to become a 787 passenger.

[Lyman]

hetfield

If as SoS explains, the loom above the cells is sensory, they are connected to each indvidual cell. They are perhaps copper, and appear to be insulated in pretty standard fashion. Once enough heat is acquired, and the insulation fails, don't we have "Inter connectivity"? This eliminates the ability to monitor in isolation, and if the loom also carries the charging current, doesn't this exacerbate the possibility for fire, and explosion? Should the "Loom" be better protected against this type of failure? With diodes, or at least segregated leads?

[hetfield]

@Lyman

I'm afraid if the cell temperatur exceeds a certain level (140 deg Celsius?) nothing will stop the internal reaction with known results.

IMHO it would make more sense to have the cells seperated and well canned. So eight small cells instead of one big. They don't :mad: up at the same time.

To make it even more safe I suggest to put a single cell under the bed of CEO Boeing, CEO securaplane and CEO Yoasa.


thermal runaway
"Lithium-ion cells with cobalt cathodes should never rise above 130°C (265°F). At 150°C (302°F) the cell becomes thermally unstable, a condition that can lead to a thermal runaway in which flaming gases are vented."

[fuelevaporator]

why should boeing not learn from teslamotors.com
electric cars manufacturers from all over the world ar knocking at their doors.
no, am not working for them nor have I shares but am following them for some time...

[EEngr]

If I were running the forensic program, I'd be asking some of the airlines to provide samples of their batteries with varying service histories (together with the charger's history records) for some lab testing. Surely the cost of 100 new batteries (whoever picks up the tab) has got to be a drop in the bucket compared to the cost of aircraft down time being incurred.

Anyone know (or can say) if the regulatory agencies have requested battery samples to be sent to their labs?

[grebllaw123d]

EEngr,

Don't you think that flight recorder readouts of the battery system performance from a number, or from all, of the grounded 787s would do the job?

Easy and not very expensive.

[EEngr]

Don't you think that flight recorder readouts of the battery system performance from a number, or from all, of the grounded 787s would do the job?Not if there is some deficiency in the parameters read or the battery model inherent in the system. The goal is to compare what the charger/controller/FDR sees to the actual internal state of the batteries.

[kilomikedelta]

Perhaps grebllaw123d is one of the many who believe that whatever you read out from a computer is 1000% accurate to unlimited significant figures. No need to get your hands dirty (yecch!) with the actual physics and you can always wear a suit and look corporate.

[gums]

Adding to the above.....

Go look up the "off the grid" folks' charging systems. Many turn off the charging and look at the batteries. Maybe apply a small discharge mechanism, even as simple as a resistor.

As I posted on another thread, sometimes it's the simple things versus the high-tech, latest and greatest stuff that gives you problems. Like the charging system.

The Li-ion batteries are great for power density, size and such. But ya gotta be careful when using them without good monitoring systems for charge and such.

One biggie is the failure mechanism of the Li-ion batteries when they decide to go "thermal". They are not like the older batteries, including the nickel-metalic ones that are not that old. No need to go back to Ni-cad or lead-acid car batteries. The item of concern is what the Li-ion batteries do when they go into thermal runaway.

The FAA rules on shipping large amounts of the Li-ion batteries seem to take into account the catastrophic effects of a problem with those suckers. And do I need to remind all of the infamous Value Jet crash due to the emergency oxygen bottles starting to burn? Still cry about that one.

[syseng68k]

Gums,

Pulling sources together, summary, to be confirmed of course:

1) The cells look much like the rectangular cells found in the traditional
nicad aircraft batteries, as does the overall enclosure.

2) It doesn't look like there is temp monitoring for each cell. I would
think that this less than optimal, as the cells have little thermal
mass and would heat up very quickly. This may not be detected in time
with a single / global enclosure sensor.

3) It does look like there is individual voltage monitoring for each cell.

4) It doesn't look like there is a separate charge circuit for each cell,
perhaps not ideal for such a sensitive application.

5) Very high charging currents are being used, together with a patented
charge algorithm based around a model of the actual cell. Not
clear if this takes account of cell aging over time, which could
invalidate the model. Also, cell production spreads and how the set of
8 is matched / selected / toleranced. If all cells are charged in series,
at high current, matching is not a trivial issue.

That's about it at the mo, but perhaps you can add more...

[syseng68k]

RR_NDB:

Google US patent 5780994. On google patents, among others...

[gums]

As with any design and the components and the manufacturing and finally the actual implementaion/fielding, things show up that nobody had considred.

Apparent;y, the Boeing warning system alerted the crew (Nippon emergency landing) that the battery was getting hot.

I have no problem with the Li-ion batteries. OTOH, I also believe that using them in an airliner should have really good charging systems and monitoring systems.

The only problems I have are related to the effects of the thermal runaway characteristics. Saw a BMW or similar catch fire one night after a fuel leak caused the driver to pull over and then grab a fire extinguisher. I couldn't do much and neither could he ( no cell phones back n late 70's). Next thing you know is the transmission casing start to burn - aluminum/magnesium alloy. Fire department showed up, but once that metal started to burn all was lost.

So my feeling is Boeing will add some fire protection capability and also look long and hard on the battery charging/monitoring circuits.

[sevenstrokeroll]

gums

value jet had oxygen generators in cargo section, not bottles.

on a DC9 the oxgyen bottles are actually at the 4 o'clock position to the copilot...one for crew one for pax with valves in reach on top of bottles.

AS to the 787...someone will work out the problem...it is interesting to me that both offending batteries are/were in japanese operated airplanes. perhaps mx issues? we shall see...

of course the japanese planes were in the first batch and there might be nothing to really understand except that the batteries might have to be changed every six months as part of the solution.

[DozyWannabe]

value jet had oxygen generators in cargo section, not bottles.

And a tyre in the same cargo hold - not good.

...it is interesting to me that both offending batteries are/were in japanese operated airplanes. perhaps mx issues? we shall see...

I can't think of an issue with Japanese MX in recent times. As you say, far more likely to be simply that ANA was the launch customer and they've had more airframes for longer than anyone else.

[Machaca]

The worse-case scenario -- an in-flight battery meltdown -- did occur on the ANA aircraft and the safety systems all performed as designed to allow a safe landing and pax to deplane.

http://i337.photobucket.com/albums/n385/motidog/ANAbatt0.jpg

The containment is designed to sustain the duration of a battery burn down. It did prevent damage to the surrounding equipment, nothing else caught fire, the smoke was evacuated via the venturi port, and the hull wasn't breached.

[sb_sfo]

Sevenstrokeroll,
The JAL airplane is line #84 and delivered in December. The ANA airplane is about a year older.

[Machaca]

The battery in the ANA aircraft was replaced in October, so there is a greater chance of having cells from the same production batch in both.

[hetfield]

Boeing Warned Of Battery Safety In 2006 (http://www.aero-news.net/subsite.cfm?do=main.textpost&id=66f459f8-4d6b-452b-961a-6b80dc4830a1)



Aviation reporter and blogger Ben Sandilands writes in Plane Talking that while employed at Securaplane, which brought together mission critical battery assemblies for the 787, Leon wrote a report on the battery technology planned for the 787 saying it was a flight of safety risk and that substitute battery technology should be used. A month later, Securaplane's main buildings were burned to the ground when a battery test went wrong. Leon was injured in the blaze. Securaplane reportedly tried to force Leon out of the company when he refused to ship what he considered an unsafe battery assembly to Boeing for use in the 787. That assembly later malfunctioned when installed in a prototype airframe.

[syseng68k]

hetfield

That's pretty serious stuff if true and there was a similar report in
this week's Sunday Times business section.

So what are the options ?.

Revert to nicad batteries, which would add weight (100lbs ?), need
different charge electronics, may not meet the rapid charge requirements
(why did they need this anyway ?) and may have to be recertified.

Stick with the current li batteries, but rework the battery assembly and
charger design to be a bit more proactive in terms of temperature sensing,
recovery and shutdown.

Both option involve a lot of work and it doesn't look like a 5 minute
fix...

Regards,

Chris

[Lyman]

Maybe Boeing should have purchased Securaplane at that point, just as it later "bought Vought".....

There was an industry wide evolution in manufacturing to offshore, or at least "SUB contract" the actual work, and retain "Project Management". Capital investment was deferred, then eliminated, and the cream of the project, "management" stayed in house.

So how much is "Control" worth? Fracturing any part of the construction of an airliner and scattering it to remote and iconoclastic regions is a problem.

There is nothing more important in a complicated, technologically complex project than "integration".

Starting a project by eliminating success friendly paradigm (integration) at the outset is problematic.....

Is Thales a "BUY".....?

syseng68k..... Another option? Lithium technology remains certified until it is decertified. It is merely grounded (sic).

Why does it have to be "on-line" in flight? Does it? It is down the chain of redundancy merely by virtue of the 787's electrical architecture, having plugged the bleeds, and added a genset to each engine.

The argument then becomes (if I am airframer), why must the 787 be super redundant in the first place? two extra generators, and the RAT, how much is the Battery requirement just "overkill"?

:ok:

[hetfield]

@syseng68k


If I were Mr. Boeing I would revert to NiCd.

Why?

- proved for decades
- simple chargers (one current for all cells)
- bad publicity for LiIon


Nobody would understand if, for whatever reason, another LiIon incident happens after these two....

BTW, NiCd batteries and their reliable proved chargers may be cheaper, but I'm not sure.


But I'm sure, I have overseen/not considered some facts...., therefore I'm not Bill Boeing:\

[DozyWannabe]

NiCds have been supplanted by NiMH for some time now, as Cadmium is very difficult and expensive to dispose of.

[hetfield]

@Dozy

You are right, nevertheless 747-400 an T7 have Ni-Cd.

[syseng68k]

Gums:

If you have a load of vendors, it's the gaps in the specs shared between
them that cause the problems. In one company I worked for many years ago,
the alternatives and feasability studies and initial specs to the client
always specified what was *not* going to be done, as well as what was. It
was quite good at catching stuff the client hadn't considered. Even then,
there's stuff round the edges and misalignment in understanding of the
specs that either no one thought of, or never considered relevant. The more
complex the project, the worse it gets.

I would stick with the li batteries. Why ?, because it's a proven and
reliable technology that's been around for years, despite the occasional
duff batch of laptop batteries, which is really just noise in the terms
of the numbers shipped. In some ways, the consumer electronics use is a
much greater engineering achievement, in that they are built down to a
price, shipped in millions, take hundreds os charge / discharge cycles
and cause very few problems. Aviation, on the other hand, throws
thousands, perhaps millions of $ at the problem and still can't get it
right. Amazing really...

Regards,

Chris

[DozyWannabe]

@Chris - agreed, though I'd argue that aviation subjects the batteries to a far wider variety of operating temperatures and humidity levels than domestic use, which probably took a lot of time to engineer around...

@hetfield - Correct, but the 744 and T7 have been in service now for nearly 24 and 18 years respectively. Christ, that makes me feel old...

[syseng68k]

Doze:

Greater temp range is just an engineering problem, but to have such
failures so early in the life cycle suggests a design issue / inadequate
development and testing. I would be surprised if this comes down
to a "bad batch of batteries".

I think gums said something about li being used in some mil a/c. It's
also used in some Airbus models, fwih. Wonder what their experience is
and if they have had any problems ?.

Regards,

Chris

[grebllaw123d]

I just found a very interesting British website with all the information worth knowing about batteries and associated subjects.

It contains over 140 web pages of information and explanations, so just go ahead!

Electropaedia, Energy Sources and Energy Storage, Battery and Energy Encyclopaedia and History of Technology (http://www.mpoweruk.com/index.htm)

[wbclay]

@hetfield & @syseng68k re. your posts 54 & 55 this thread:

Electronic tech Leon was fired by Securaplane after he blew the whistle to the FAA that this battery/charger assembly was unsafe for use in an aircraft. A US Department of Labor Administrative Law Judge's report found Leon's firing justified, but the story it tells leaves lots of reason to wonder if this technology was adequately vetted before it flew.

My post #37 earlier in this thread provides a link to the ALJ's report that provides additional detail beyond what was cited from Plane Talking.

[DozyWannabe]

Greater temp range is just an engineering problem, but to have such failures so early in the life cycle suggests a design issue / inadequate development and testing.

Sure. Given prior art when it comes to introducing new technologies to aviation, I suspect it will be some combination of factors, possibly related to environment and power/charging regulation that somehow either slipped through the cracks when the certification specs were drawn up or was hitherto unknown.

I think gums said something about li being used in some mil a/c. It's
also used in some Airbus models, fwih. Wonder what their experience is
and if they have had any problems ?.

Given that even the most modern US military jets were specified and designed upwards of two decades ago, I suspect that the LI batteries were a proposed modification that came later in the development lifecycle. Airbus do use LI batteries on some later models, but as far as I recall to nowhere near the same degree. I'm sure someone will correct me if I'm mistaken. :)

[gums]

Salute!

Yeah, syseng, the lithium types are presently being used in military systems. Only problems I have been told about were from folks in the "sand box", and temps there were getting really high, and many units went back to Ni-cads for ground-based systems. I share your opinion that we had a "bad batch", as the failures happened in short order and not spread out over months or years.

As I mentioned on another thread, our original Viper electrical systems were primitive by today's standards. So it turned out that our "last ditch" emergency power system was the most simple - PMG's and some coils, driven by engine bleed air or the hydrazine generator like the ones you see on the space shuttle ( that pffft, pffft, sound you hear after roll out). So uncommanded activation of the bleed air doofer cranked out too many volts because the basic system had not switched over to safe voltage output.

"normally", heh heh, when the system went to back-up it provided AC/DC and hydraulic power. So we had a basic design fault and corrected it after several losses and one fatality.

Secondly, those lithium batteries need high-tech monitoring for the charging system. And if all they are used for is back-up power, then there's no need to charge them all the way to max capacity constantly. Even the Prius does not charge its NiMH batteries to 100%, and they leave about 20% for regenerative charging when braking.

Finally, despite claims about no pure lithium in the batteries, physical and chemical actions could result in catastrophic thermal runaway. So I plan to take my old cell phone ( kids bought me an iPhone for Christmas) and break the sucker with a hammer and throw it in a pail of water. As with other metals of the same class, they react violently with water. Will report back.

[EEngr]

syseng68k (http://www.pprune.org/members/302789-syseng68k), I'd stick with the LiON batteries for the short term (excuse that 'short' remark :E). If it can be determined that these failures are related to battery age, number of load cycles or some other condition, an accelerated maintenance and replacement program can get the dodgy batteries out of the planes before they become a risk. That would be cheaper than keeping the fleet parked. And Boeing may have to pick up the tab (no cost to operators).

In the long term, a battery/charger/smart load controller may have to be developed and certified. This will be done with far more outside scrutiny by independent experts.

[DozyWannabe]

So I plan to take my old cell phone ( kids bought me an iPhone for Christmas) and break the sucker with a hammer and throw it in a pail of water. As with other metals of the same class, they react violently with water. Will report back.

Blimey, gums - not that I'd presume to teach you how to suck eggs, but - if you're really going to try that - then for heavens' sake wear eye protection, heavy-duty gloves and an apron - those things really don't like heavy impact shocks!

[syseng68k]

Gums:

>> the hydrazine generator

/anorak on

Jeez, such exotic technology in aircraft. I'd love to get my hands on
something like that, though sourcing the hydrazine might attract unwanted
attention here in the uk, even if you could find someone to sell it to you.

The uk Lightning a/c used an IPN (Isopropyl Nitrate), a fairly unstable
monopropellant starter. Apparently, back in the day, the RAF used to keep
the stuff sloshing around in unsealed plastic buckets, ready to fill the
small starter fuel tank. You can still find the starters on the surplus market
and are light enough to lift with one hand. They consist of a small turbine
and reduction gearbox and generate ~100hp short term. It would make an
interesting project to fit one in a car for instant additional acceleration.

As for the mobile, do it. Reminds me of all the kitchen and garden substances
we used to mix together to make "fireworks" when we were at school. You would
get locked up for years now for that sort of thing, such is the security
paranoia, health and safety, control culture, ad nauseum.

/anorak off

I think you misread the line about batteries in that I doubt if the problem
will be as simple as a duff batch. Sticking neck out, from info thus far,
looks like an overall charger / battery system design issue...

Regards,

Chris

[DozyWannabe]

Jeez, such exotic technology in aircraft. I'd love to get my hands on something like that, though sourcing the hydrazine might attract unwanted attention here in the uk, even if you could find someone to sell it to you.

The pre-production and first two (non-service) production Concordes had what were known as a MEPU, or Monofuel Emergency Power Unit - powered by hydrazine. Obviously there was no way they could have a substance that unstable on a line aircraft - and that was back in 1976!

Reminds me of all the kitchen and garden substances we used to mix together to make "fireworks" when we were at school. You would get locked up for years now for that sort of thing, such is the security paranoia, health and safety, control culture, ad nauseum.

Don't forget that H&S legislation boomed at the behest of corporate donors in order to minimise their exposure to litigation. Left to their own devices I'm sure the powers that be would have been more than content to simply continue scaring the bejeezus out of us with Public Information Films from an early age!

[bsieker]

archae86,

Looking at the Thales/Boeing design and the FAA special considerations, it appears that the approach was to assure cell failure would never occur--as it seems self-evident that no serious measures to avert propagation to adjacent cells were employed, nor were serious measures to contain damage to nearby systems.

I'm not aware of any damage to nearby equipment. I agree with Machaca here that apparently the safety systems (or call it hazard mitigation) did their job.

Also, having designed the venting system apparently so that it can prevent damage to nearbt equipment even in case of a thermal runaway and burn-down of a battery, I don't think the engineers just assumed it would "never happen".

The other issue is, of course, that the battery properties did quite obviously not conform to the special conditions set out by the FAA, in particular I cannot see how any Lithium Cobalt (or even Manganese ...) type battery could fulfil No. 2:
(2) Design of the lithium ion batteries must preclude the occurrence of self- sustaining, uncontrolled increases in temperature or pressure.

It is likely that condition no1 ...
(1) Safe cell temperatures and pressures must be maintained during any foreseeable charging or discharging condition and during any failure of the
charging or battery monitoring system not shown to be extremely remote. The lithium ion battery installation must preclude explosion in the event of those failures.
... was agreed to be fulfilled by the FAA, but is now obiously violated. It is hard to see how the described failures of the charger could be seen to be "extremely remote", taken to mean with a probability of less than once in 10 million operating hours, but more frequent than once per billion op-hours. The qualitative specification of "extremely remote" is "not anticipated during the operational life of a single airplane, but may occur a few times in the lifetime of the entire fleet." (paraphrased from CS.25, similar in FAR Part 25.)


Bernd

[gums]

Salute!

No problem with my test, Doze. I'll let all know manana. I may be brave and fearless, but not all that brave!

From the Gums' archives.......

GD thot that the hydrazine EPU was a light, compact source of backup electricity and hydraulics. If we lost our motor, then the sucker had to provide at least one of our hydraulic systems and a very reduced amount of electricity. We paved the way for the space shuttle. That sucker used the same hydrazine doofer that we had, but bigger. If you look at the launches you can tell when the sucker starts to move the flight control surfaces and so forth. On landing, you can hear the thing and see the IR images as it puffs out gases, mostly ammonia. Big deal was our EPU only did that for about 5 minutes unless we had the motor still running and it could run off of bleed air. Shuttle was screwed, as it need the hydrazine power for takeoff and landing.

From my perspective, I see a batch of bad batteries or a design problem with the charging/monitoring system.

I do not advocate the hydrazine EPU that we had or that the shuttle used on a normal mission.

I also think that Ni-MH batteries could satisfy the Boeing requirement and have less problems. Look at Toyota and the Prius versus the Tesla and Volt.

I am glad to discuss the battery problem considering my experience in the first "electric jet". We learned a lot and we passed on our lessons to later and greater planes. There's just something about being "the first", and I was honored to be in the cadre of that neat little jet.

[chris weston]

Dozy, like most things chemical .... it depends.

I've spent a lifetime with Group 1 metals and showing their reaction with water to students.

If gum's pail is big enough and full of tap water at ambient temperature (say 10C and 1 or 2 gallons?) the whole event will be a non event. The Li will just effervesce. Yes I know about H2(g) ignition issues.

I would bet folding money that a pail of water with an iPhone battery would be a big enough thermal sink to keep the thermal runaway of the Li and the resultant kinetics under control.

But do wear full face protection and gloves. Li2O/LiOH in the eye, like that of any alkali, is properly serious

You have to push Li to get it to go "crack". Careful use of English.

If the temperature gets up, the rate of oxide formation on the metal substrate of Li2O (+Li2O2 for the pedants) will form a protective coating that eventually bursts with semi random explosive force/rapid combustion zones. For the record, you get crimson streamers radiating in parabolic curves from the point of release.

CW

[Lyman]

If these are STANDBY BATTERIES (back UP), why are they being charged inflight in the first place? Charging a Battery by definition means the power that the batteries supply can be provided by the charging system alone.

They have to have the juice to start the APU, and then the charging system carries the load. Once the APU starts, the Batteries are done. If the Batteries are charged by the APU, then obviously the APU is powering the system, not the Batteries.

Why even equip the aircraft with a BATTERY CHARGING SYSTEM? If the APU does not start, and the batteries need to power emergency lighting, they will, the APU, having not started, will be unable to charge (power) the system by definition. If the MAIN ship battery powers instruments and cockpit area lighting, same thing, if it needs to be charged, then the charging system (APU) will charge it, if it cannot, the batteries need to have the capacity to satisfy ETOPS, and if they do, they don't need charging....in the first place.

This applies if the BATTERIES are STAND ALONE. If provision for BATT/Charge together is to satisfy the safety reg, then the charger and BATTERIES constitute a dual (interdependent) system.

[gums]

Salute!

Yeah, I'll be very careful. I still remember my high school teacher dropping a tiny amount of phosphorus or whatever into a jar of water and seeing the reaction. Years later I dropped munitions using the same metal to set off the napalm. No ignitor required, the stuff caused an immediate fire and poof!

I still stick to my story that the charging/monitoring systems need to be examined.

Nothing wrong with the NI-Mh batteries, and they are less susceptible to thermal runaway and such. No need to go back to "car batteries".

As a systems engineer and un-employed fighter pilot, I fully appreciate the advances in many systems. I am not a dinosaur.

The shuttle and Viper hydrazine systems were developed about the same time. Unlike the shuttle, ours had only a few pounds of the nasty stuff. Nevertheless, we had a great emergency system that worked regardless of altitude/air density and speed. Only had about 5 minutes or so to do something, but better than an immediate ejection.

[archae86]

I'm not aware of any damage to nearby equipment. I agree with Machaca here that apparently the safety systems (or call it hazard mitigation) did their job.

First, I'm honored to have earned a comment from you.

But, second, I think the "no harm done" view voiced by some here is rather too optimistic. The electrolyte in these batteries is itself a hazardous substance. In particular, it is itself flammable (or inflammable in proper English before the insurance companies decided we would not figure out what that meant), corrosive, and conductive. Second, the very high energy production by a cell which reaches thermal runaway practically guarantees that electrolyte will exit at high temperature and high pressure.

While photos of the ANA battery case might suggest that just a little seepage occured at seams, multiple press accounts describe a more energetic event. Recent articles in the Wall Street Journal assert that both incidents included both leaking electrolyte and smoke damage to "nearby portions of the aircraft". An early Seattle Times story described this of the ANA incident: Hot chemicals sprayed out of the battery on the 787 Dreamliner in this week’s emergency landing in Japan, leaving a gooey dark residue and suggesting a different malfunction than last week’s 787 battery fire in Boston, according to two people with knowledge of the situation.

The residue covered the battery and splattered over nearby instruments inside the forward electronics bay. It left a 12-foot-long dark streak from the battery to an outflow valve through which some of the spray vented overboard during the flight.

I don't think that outer battery case was designed to contain a full thermal runaway event without hazard to surroundings, and I don't think we'd want to see many repetitions to see whether we continue to be lucky with that particular hot fluid spraying about in an electronics bay.

My friend who has blown up a great many lithium ion batteries, in addition to more gentle means of assessing their behavior, does not think a pressure vessel for full containment is practical. His tests are on single cells tiny compared to these, in custom chambers capable past 3000 psi, and he has had chamber failures. Possibly if this is to be designed to fail safely to the degree of all-cell thermal runaway, the outer battery chamber needs to guide the inevitable electrolyte spray to a safe exit channel.

[bsieker]

archae86,

thanks for the reply.

I didn't mean to downplay the event(s). This is serious stuff and it is not supposed to happen. And for all we know, there could be worse battery fires.

Just saying that it was an event that was considered during risk analysis, and they seem to have gotten the mitigating measures not totally wrong: chanelling and dumping of hot gases and fumes, instead of trying to contain them.

I don't think that outer battery case was designed to contain a full thermal runaway event without hazard to surroundings, and I don't think we'd want to see many repetitions to see whether we continue to be lucky with that particular hot fluid spraying about in an electronics bay.

I fully agree. I wouldn't want to play my chances on another similar event.

We'll see, but I wouldn't be surprised if Boeing was going back to Ni-Cd, with all the redesign that requires. Airbus may then have to rethink their A350 battery system, as well. I don't see Ni-MH happening here: they cannot deliver discharge currents anywhere near what Li-Ion or Ni-Cd can deliver.


Bernd

[MurphyWasRight]

They have to have the juice to start the APU, and then the charging system carries the load. Once the APU starts, the Batteries are done. If the Batteries are charged by the APU, then obviously the APU is powering the system, not the Batteries.



While simple and atractive as a concept I suspect that restricting battery charging to the ground would have ripple effects.

For example what % of the APU battery charge is used by a single start cycle? How long does it take to "top off" after that and how many start attempts must be avaialable in non-nominal flight?

While these factors might have been fairly easily accounted for if "ground charge only" was in play early on, retrofitting it would probably take a signifiicant amount of effort to revisit all the analysis that assumed fully charge batteries, even assuming the basic capacities where adequate.

Of course this also assume that the actual fault involves the charging system rather than an internal battery fault.

[Chris Scott]

MWR,

I agree with all that.

Lyman,

I don't understand your argument, but you might like to see my reply (http://www.pprune.org/rumours-news/505455-faa-grounds-787s-17.html#post7649675) to your post on the "FAA Grounds 787s" thread. Hope it helps, as I'm turning in now.

[Lyman]

Hi Chris

Thanks for the reply in the other thread. Some of my comment probably tips a worry that the LITHIUM ION Back up makes a good 'single use' safety system, not ready for prime time....

I think for whatever reason will prevail, current events suggest it is "not suitable for use in aircraft...."

:{

[RR_NDB]

Hi,

Sadly Boeing is suffering a serious setback. What´s important now:

787 Back in the skies with batteries within “aviation standards”

Considering it could take long to precisely know what caused one or both incidents and above all, timing is very important for all players, the best path seems to return ASAP to the current “standard”: Ni Cd´s. A third case is inconceivable.

Any implication like weight penalties, etc. IMO are "becoming small" compared to prolonged grounding. So the business could not wait too much.

It seems wiser to start again the effort to adopt these wonderful but dangerous items in airliners. The 787 program is paying a high price. Even the use of them in the A380 emergency lighting would require a closer look. Not to mention the A350 and other. (Mil not included here)

Despite the current use of electronics “inside the case” of the Thales used in 787, a battery is a simple device. A Lead Acid or Ni Cd may have just cells to work properly. You may “protect” any battery internally, externally or in both ways.

A charger is also a simple device even for Lithium. In the later the operation just requires monitoring and control of each cell voltage and temperature to keep the cells inside the envelope. (Monitoring the individual cell temperature adds extra safety to properly manage the cells and monitor the unit.) The circuitry required to accomplish this is also “simple”. (a closed loop system). And with the protections ideally derating the battery for airliners application, the advantages of Lithium versus Ni Cd will certainly be reduced.

I am a technician, love high performance items but the management of the crisis demands a sound managerial decision making.

With safety first, looking to the people and the business involved.

Mac

bsieker:

...with all the redesign that requires.
(http://www.pprune.org/tech-log/505695-787-batteries-chargers-4.html#post7649624)
Easily affordable, IMO.

[MrDK]

No doubt that the Li-ion batteries have a greater power/density/weight capability than some of the not-so-old batteries like the nickel-metal-hydride ones. Funny, but Toyota sticks with those nickel ones for their Prius.

@gums
You might want to do a little research.
ALL Prius vicheles sold outside of North America feature Li-Ion batteries.
The US "pluck-in" version also featurs Li-Ion.

[A33Zab]

Even the use of them in the A380 emergency lighting would require a closer look. Not to mention the A350 and other.


Why? If you already have the answer at hand.


In the later the operation just requires monitoring and control of each cell voltage and temperature to keep the cells inside the envelope. (Monitoring the individual cell temperature adds extra safety to properly manage the cells and monitor the unit.)


A350 Spec:

The charging, monitoring, and protection functions are integrated in each battery.

[bsieker]

MurphyWasRight,

For example what % of the APU battery charge is used by a single start cycle? How long does it take to "top off" after that and how many start attempts must be avaialable in non-nominal flight?

The only thing I found on this is that the APU battery is designed for two consecutive start attempts, after which a 5 minute cooling period must be observed before a third starting attempt. I don't know if that means 5 minutes from then on after every start attempt, or if a maximum of 3 attempts is permitted, and if the limiting factor is only the battery or perhaps also the starter motor. (Starting from other sources, the starter motor used can be alternated, but the APU battery can only power the right starter motor.)


RR_NDB,

I agree that a redesign for Ni-Cd would almost certainly be cheaper than another (serious) incident or accident.


Bernd

[Chris Scott]

Quotes from bsieker:

(1) “The only thing I found on this is that the APU battery is designed for two consecutive start attempts, after which a 5 minute cooling period must be observed before a third starting attempt. I don't know if that means 5 minutes from then on after every start attempt, or if a maximum of 3 attempts is permitted, and if the limiting factor is only the battery or perhaps also the starter motor.”

It sounds a very familiar, conventional limitation, typical of APU starting limitations since the 1960s, where the batteries have been lead-acid or NiCd. My understanding was always that it was to stop the starter overheating, and/or time for unburned (sorry, pun not intended!) fuel to drain away. But within these factors, an unwritten battery-protection measure may have been contained, as you seem to be suggesting might be the case with these Li-Ion ones.

As you know better than I, the peak battery load on starter engagement is massive (just as it is on a car battery during engine start). The A320 uses its 2 main (NiCd) batteries for APU start if no external power is available. In the 1990s, when starting the APU using external power, I was able to monitor the two TR loads. Initially, they would be off-scale but, IIRC, they reappeared as the current was falling through 350 amps (each). So the peak current delivered by the TRs was in excess of 700 amps. But the main (NiCd) battery was also contributing, so this suggests a peak starter load of the order of 1000 amps.

(When the A320 entered service, it only employed one TR for APU start. This led to an embarrassing incident on a demonstration flight for the French President, during which the relevant TR failed during APU start, resulting in considerable DC load-shedding.)

(2) “(Starting from other sources, the starter motor used can be alternated, but the APU battery can only power the right starter motor.)”

I’ve never used an APU that had more than one starter motor, AFAIK. When you say the “right” starter motor, do you mean “R/H” or “correct”? (The English word “right” can be ambiguous, which is why many of us old pilots replace it with “starb’d”.) Are there two APU starter motors on the B787?

[lasernigel]

You'd think even a giant like Boeing would have heeded a warning in 2011 when Cessna CJ4's were grounded by the FAA.

"In 2011, the Federal Aviation Administration temporarily grounded the CJ4 and issued an airworthiness directive because of battery fires in the Lithium-Ion original equipment:
We are adopting a new airworthiness directive (AD) for certain Cessna Aircraft Company (Cessna) Model 525C airplanes. This emergency AD was sent previously to all known U.S. owners and operators of these airplanes. This AD requires replacing certain lithium-ion batteries installed as the main aircraft battery with either a Ni-Cad or a lead acid battery. This AD was prompted by a report of a battery fire that resulted after an energized ground power unit was connected to one of the affected airplanes equipped with a lithium-ion battery as the main aircraft battery. We are issuing this AD to correct the unsafe condition on these products."

[bsieker]

Chris Scott,

yes, I meant "right hand". I was aware of the ambiguity when I sent it, but decided to leave it like that, because that is the wording used.

On the Dreamliner, being the "more electric plane", both main engines and the APU each have two starter/generators. The APU's SGs are designated "left" and "right".

A single dedicated starter would probably suffice, but since they are starter/generators, and two generators are installed for redundancy, one ends up with two starters as well.


Bernd

[Chris Scott]

Quote from bsieker:

“...both main engines and the APU each have two starter/generators. The APU's SGs are designated "left" and "right".
A single dedicated starter would probably suffice, but since they are starter/generators, and two generators are installed for redundancy, one ends up with two starters as well.”

Thanks for the clarification, Bernd, and for reminding me that they are starter/generators. I’m disappointed with Boeing’s left/right terminology in this instance.

The twin starter/generator configuration is shown in the only document that I have seen, entitled “B787 Systems and Performance”, which dates from 2005. In addition to being at least six years ahead of actual entry into service, it has the look more of a publicity document than a technical overview, so I’ve been taking its contents with a large pinch of salt. The fact that it schedules certification and delivery in 2008 does little to inspire confidence in the currency of its information.

The document also shows both APU gennies, together with the 4 ED gennies, supplying a common, nebulous “230Vac Distribution”. I presume you must have a more detailed, authoritative source?

Somewhere in the multitude of PPRuNe threads (is it 5?) started since the APU battery failure in Boston earlier this month, I’ve picked up the idea that the APU battery can only be charged by energy from its dedicated APU charge circuit; not by the main electrical system. So, bearing in mind what you have said, I tentatively conclude that the R/H starter/generator feeds the APU battery charge circuit, while the L/H starter/generator feeds the main 230Vac system. Is that correct?

The APU battery and the Main battery seem to be identical in themselves, each rated at only 65Ah. Unlike the B777, it seems there is only one Main battery unit. There has been speculation on whether the separate APU and Main battery failures were similar or not, and whether they were under charge or under load. It seems unlikely that the ANA aircraft’s Main battery would have been subject to a high load, although the same cannot be said for the APU battery in the JAL case. If the failures were from a common cause, it would probably be the chargingsystem?

Chris

[Lyman]

I am viewing what I think is the same source as Chris Scott re: schematic. So let me display a risk of appearing thick...

Aren't the SG's on all the turbines AC? Simply from a weight standpoint, how could they be DC? Obviously the APUBATT is 28vDC?

I 've peeped the APU, and it seems a bit massive for its DC power (EMER) source?

So how is APUBATT integrated to the APU/start? Inverter, or separate (dedicated) and DC SG?

layman

[sb_sfo]

From the study guide, circa 2010:
The Start Power Unit (SPU) takes 28v dc from the battery and changes it to 115v ac. The 115v ac is sent to the R2 Autotransformer Rectifier Unit (ATRU) where it is changed to +/- 135v dc and then sent to the Common Motor Start Controller (CMSC) which then changes it back to 115v ac (!) to start the APU if 4 or so other things have happened in the meantime.

As I understand it, 115v ac is used to turn the ASG (which normally puts out 230v ac) and the generator neutral relay must be open.

The right-hand ASG is used to start from battery power. From ship or ground power, they alternate.

[Lyman]

Dangit, that is just the thing...


Thanks sfo :ok:

My very first a/c was a 1966 J model Cessna 182. I obviously am weak in the technoELEC.

Having noticed an architecture in the 787 that mimics fifty (sixty?) year old technology, as to back up systems, how behind the times are regs, and FAA?

For all the flak Boeing are taking, it must be grating to put a battery in their electric jet.

Aside. LiH is what makes the Hydrogen bomb go boom, no?

For my money, a sufficient amount of compressed air and a small turbine would be safer and more dependable than Lithium, imo. At least to start the APU.

thanks, Bernd :ok:

[bsieker]

Chris, Lyman,

The "235 V AC distribution" consists of 4 buses, L1, L2, R1, R2. Normally each is powered by one main engine generator, but there seems to be some crossbar switching, so if generators fail, the associated buses are powered from other buses.

The APU can power all four buses, or those buses not powered by main engine generators. As far as I can see, in practice, the buses can be switched onto different generators dynamically, as load and available generation requires.

They are all variable frequency AC, depending on generator rpm, so I guess it's not a good idea to try to power one bus from two different sources at the same time.

(I don't know how authoritative my source is. It says "do not use for flight" and appears to be from 2010.)


Bernd

[hetfield]

@RR NDB

As a technician and Ex airline pilot I agree fully with your post #81.

I'm kind of nosy what actions Boeing will take.....

[RR_NDB]

Hi,

The battery has ~ 1/1000 of the mentioned ~ "1.5 MW" plane design. I´ve heard of a diode in the main battery circuitry. We will be able to understand the approach used.

A very low internal resistance together a highly critical battery in a bus (i am looking for the main battery) is another concern. You naturally have "discharge spikes" to batteries in buses. Lead acid and Ni Cd´s are much more tolerant.

I hope transient loading (a design parameter of the electric circuit) to the main battery allows Boeing to replace to Ni Cd without further considerations. (A battery in a bus also acts as a "capacitor" reducing the ripple in the DC level).

In APU battery fire (BOS) we may say this was not a factor. It started the APU and being recharged as we imagine.

IMO what saved the day in TAK was just how fast the crew landed. I also think Machaca put a "lighter" scenario on Japan incident.

Question: The battery case cover is flat or has the geometry showed in the picture of destroyed main battery?

Mac

[RR_NDB]

@ hetfield # 93

IMHO: Imediate change to Ni Cd.

Rgds

[grebllaw123d]

RR_NDB,

I also agree 100% with your post#81.

As you say: A third case is inconceivable - so right and BOEING knows that!

Therefore I think they will have to go back to the "old" battery technology as the best option for getting this very important project on track again.

In any case before the type will be allowed to fly again, BOEING "must demonstrate to the FAA that the battery system is safe" - not an easy job with the current system, bearing in mind the many known causes of Lithium-ion battery failures.

[RR_NDB]

A33Zab,

It seems not feasible/possible integrate an effective protection inside the battery.

It allows even remove the battery from the bus?

I could limit the discharge spikes current?

This sounds "marketing talk".

Will comment on that in subsequent posts. And also your first question.

Mac

I´m posting using the mobile between meetings.

[Lyman]

The image Machaca posted from ANA shows top cover attached, and exhibiting the results of "rapid expansion" of contents. It is higher resolution, but does not show as extensive display of dripping electrolytes on front cover.

The JAL (APU) BATT shows evidence of a pry tool to remove damaged top cover.
(Anyone able to report on the health and whereabouts of the injured firefighter?)

From RR_NDB....

"I think Machaca put a "lighter" scenario on Japan incident. Question: The battery case cover is flat or has the geometry showed in the picture of destroyed main battery?"

Another thank you to Machaca for such helpful imagery...

[A33Zab]

"marketing talk".

The information is from the A350 spec jun '11 not from last week.

Withholding information is also a 'marketing strategy'.

You are seriously worried about A380 emergency lighting?

What about the installed but - not mentioned - approx. 40! wireless emergency lighting Li-Ion batteries, 2 Li-Ion Flight Control BackUp batteries and the 2 Li-Ion indepent power supplies to the recorders in B787?

[Machaca]

The Chicago Tribune reports (http://www.chicagotribune.com/business/sns-rt-us-boeing-dreamlinerbre90m0zo-20130123,0,4295551.story):

Japan: overcharging unlikely cause of Dreamliner woes

TOKYO/WASHINGTON (Reuters) - Japanese regulators have joined their U.S. counterparts in all but ruling out overcharged batteries as the cause of recent fires on the Boeing Co 787 Dreamliner, which has now been grounded for a week worldwide.

Solving the battery issue has become the primary focus of the investigation, but with excess voltage more or less off the table, investigators are still hunting for a possible cause.

Last weekend the U.S. National Transportation Safety Board said the fire on a Japan Airlines Co Ltd 787 in Boston was not due to excess voltage, and on Wednesday, Japanese officials all but ruled it out for the incident on an All Nippon Airways Co Ltd plane there.

"On the surface, it appears there was no overcharging," said Norihiro Goto, chairman of the Japan Transport Safety Board, at a media briefing.

[hetfield]

Wasn't the Boeing PR about "not overcharged" BEFORE their "visit" to securaplane (funny in context BTW)?

So if no overcharge, why talks/inspections with the manufactor of the chargers?

[Lyman]

Don't Securaplane supply the integrated system/monitoring?

hetfield, I don't know about you, but the name "Securaplane" makes me think of a chain and padlock on the Nosewheel?

:ok:

[Chris Scott]

Quote from Bsieker:

“They are all variable frequency AC, depending on generator rpm, so I guess it's not a good idea to try to power one bus from two different sources at the same time.”

Thanks for that, and the list of 4 AC distribution buses. No constant-speed drives (reminiscent of the B707). Sounds like a flight-engineers dream, so they must have a very good automatic load-transfer system to do the job for mere pilots...

sb_sfo,

Can you confirm you are saying that the R/H APU starter/generator (as well as the L/H) can receive 115Vac from either the ship’s or external? So would it be true to say that the R/H APU starter/generator can receive 115Vac from any of the 3 potential power sources, including the APU battery (via its Start Power Unit), but the L/H one can only get it from ship’s or external?

I wonder what the initial load is on the 28Vdc APU battery, and if it is modulated. As I’ve noted elsewhere, the initial (28Vdc) load on the A320 starter (for example) is about 1000 amps, which is shared between two NiCd batteries if the TRs are not powered.

Can you tell me the possible source(s) of power to the APU battery charger? And please confirm that the APU battery is able to power lighting for towing and maintenance purposes, but otherwise is dedicated to APU start?

Sorry for such a lot of questions!
Chris

[hetfield]

"Securaplane" makes me think of a chain and padlock on the Nosewheel?
lol, me too....

In context with burning batteries it's kind of sarcasm:ouch:

[Lyman]

IAM WAGing, the APU starter motor draws 25-30 amps, at 115vAC, 2-3 horsepower?

The DC cables at the APUBATT are copper braid (for surface area) and perhaps ten times the weight of indexed AC wires? I saw similar cabling on automobiles from the thirties and forties.

Dinosaur. At least in that position.

[gums]

Salute!

Well, I didn't die and sure enough the battery got hot.

I wimped out and cracked the case and then used a garden hose from 15 feet away ( 3 meters for you other guys).

It started to smoke about a minute into the run. And then it stopped smoking and cooled down in about 3 more minutes.

Only conclusion I can justify from the rough test is that a mechanical crack and exposure to high humidity could cause the Li-ion to get real hot. this was only a 1 amp-hour doofer, but I couldn't hold it in my hand.

Anyway, was fun to run a test, however ill-conceived and planned.

[MurphyWasRight]

Sorry all but can not stop myself from posting this clip from the current "google ads" at top of the page:

Energizer® Batteries (http://googleads.g.doubleclick.net/aclk?sa=L&ai=CgrjxUUkAUcmRD4Oa6gGorIDYD9Og_LIDu5DWhUPAjbcBEAEggZKMEFD0 _uTTAWDJ5uqIhKSAEcgBAagDAaoElQFP0JuDV2uIsHQNNult7mZrO2QP1OEW WPs_HgOzPd-o00sIvXz1jdFhkSWcdwJo7WINb8zApEJ_VLwenVt-7FP035JIKbclEk3PcyX8h_hhDSA7vMqEYKlaNiTke9DqG_EslIPW2w1-wFfWQSgpWUPH0-lR9ixVKrHWOybUUKhISj1Pm4ls4WOIG5JB9hU3FHCG--tAy4AHm8G5HQ&num=1&sig=AOD64_1mBenuUcgcFODX9BL0ezq3_fhlmg&client=ca-ib_employment_sede_1&adurl=http://bs.serving-sys.com/BurstingPipe/AdServer.bs%3Fcn%3Dccs%26ebcmp%3D10143117%26ebkw%3D84680779% 26advid%3D65560%26ebag%3D2401687%26sead%3D17917725323%26ccsu rl%3D%24%24http://1168.xg4ken.com/media/redir.php%3Fprof%3D13%26camp%3D1881%26affcode%3Dkw29326%26ci d%3D17917725323%26networkType%3Dcontent%26url%5B%5D%3Dhttp%2 53A%252F%252Fwww.energizer.com%252Fbatteries%252FPages%252Fd efault.aspx%24%24)
Everyone Needs a Battery They Can Rely On. Find Yours Today.

[Lyman]

gums

15 feet = 3 meters (for the rest of us guys......)


How are things working in your world?

:D

[saptzae]

It was reported that no overcharging of the battery as a whole may have occurred. This may have been derived from FDR recording of the bus voltage.

A weight loss of 4kg of (one) of the batteries was also reported. This amount is indicative of substantial loss of electrolytic and insulator material of multiple cells.

All this happened very quickly, perhaps faster then thermal runaway by conduction of thermal energy amongst cells.

In a possible scenario, a single cell short would result in the battery voltage dropping, which would have to be detected and the battery quickly disconnected by a means in order to prevent the bus (or charger) driving remaining good cells into redline above 4.3V, which could result in a cascading increase of cell voltages as more cells reduce voltage and leading to the rapid destruction of all cells.

Thus it would be interesting to know whether some cells are shorted and how the battery is decoupled/protected from tied buses.

[hetfield]

It was reported that no overcharging of the battery as a whole may have occurred. This may have been derived from FDR recording of the bus voltage. Yes, but this is just sugar for the public/press.

An individual overcharge MAY have occurred, 'cause every single cell (8) has to be charged and controlled seperatly. I'm afraid, this is not recorded...


Why is BOEING visiting secuaraplane......?

[saptzae]

Cells are rated for max discharge at 5C, thus 325A. Inner resistance is 3milliohm, which seems a fairly high inner resistance for this capacity.

At 300A load, the internal voltage drop would be 900mV and the power dissipation 270W per Cell, or 2160W per battery. Thats really stressful.

At 1000A, power dissipation would be 3000W per cell.

It would be prudent for the starter not to pull more than 150A (5KW) sustained.

[sb_sfo]

The other specific answers are gonna have to wait a while- don't have the material handy. But I noticed one thing- you seem to be under the impression that 777s have more than one main battery. The ones I work on have a main and APU battery, and unless you want to count the fuel spar valve batteries, I know of no others.

As to the rest, yes the APU battery can only send power to the R/h ASG. The APU battery charger is powered through the F/O instrument bus, and the APU battery supplies lights when towing.

More later

[RR_NDB]

@ saptzae #109 and 111

Touching the core of the (probable) main issue.

I suspect they didn´t design means to "remove" the battery from the bus.

Important comments from HK!

Question: Who produces these big cells in China?

[YRP]

hetfield wrote:
Why is BOEING visiting secuaraplane......?

Do you mean rather than the NTSB or FAA?

[RR_NDB]

hetfield,

Ideally the charging would be controlled to each cell. (because they are not identical. And Temp and Aging are extra factors). In the config of the Thales battery the charging current SEEMS TO BE THE SAME* for all cells). The control of the voltage just allowing a derating during the charging (extending the time). But when discharging (APU start, etc.) voltage control is useless. Just for recording, if so.
If the internal data recorder is not properly designed we may never know what led to BOS and TAK incidents.

The plane FDR certainly is not used to look inside a battery. Should be. If airliners would use these batteries for HIGH CURRENTS. It´s relatively simple.

This comment is also to answer A33Zab question on my concerns on other Li Ion applications in 787 and 380. Problems are much likely with high current (specially charging). Trickle charging (to keep the cells "floating" to a safe value is not dangerous.

There are other considerations on the use of Li Ion on an airliner. Location can be critical, in case of a catastrophic failure.

I actually have objections on the positioning of them in the 787. Specially the APU battery. (Nearby electronics).

(*) There is a possible charger architecture with controlled currents (closed loop) for each cell. It allows quick charge "respecting the personality of each cell during her aging and under different temperatures". I will assembly it for my electric bike pack. I would like to know if what A33Zab commented on A350 was with this concept. We may find this in Patents Database. (USPTO, SPACENET, etc.) The concept is one charger for each cell. I assume the designers put everything possible (for safety) in the 787 subsystems design. The same i imagine in A380 Li Ion application and A350 (that will benefit from 787 teething issues).

[Chris Scott]

Quote from sb_sfo:
"But I noticed one thing- you seem to be under the impression that 777s have more than one main battery. The ones I work on have a main and APU battery, and unless you want to count the fuel spar valve batteries, I know of no others."

You are right, I did post that the B777 had two main batteries, plus the APU one. My Google search for "B777 electrical system" had produced a nice clear schematic with two, which I now see is for a generic system. Thanks for setting me straight on that, and I look forward to more info on the B787 points.

(EDIT)
Have now found and amended my post (http://www.pprune.org/rumours-news/504572-another-787-electrical-smoke-incident-ground-13.html#post7641927). Looks like all currently-operating Boeing types have one main battery, plus a dedicated APU battery?

[Lyman]

My opinion of the APUBATT and EE bays location is that it is optimal. It cannot go in the tail cone (unpressurized), and would be too far from its best position, the forward most area of the cargo hold just aft of the wing box. This is equi-distant from the TWO main engines, and co locates generated and usable power. Wiring is resistance, so the APUBATT belongs closest to the APU but equidistant from #1 and #2 engines.

The Main battery serves systems that are closer to the cockpit, instruments and flight controls, so belongs just aft the cockpit and in the hold closest to the nose wheel structure. This affords best use of the hold's volumes, shortens conductor runs optimally, and affords accessibility from outside.

bear

[RR_NDB]

archae86 (http://www.pprune.org/members/118881-archae86):

(http://www.pprune.org/tech-log/505695-787-batteries-chargers.html#post7645496)Thank you very much for your elaborated answer. (http://www.pprune.org/tech-log/505695-787-batteries-chargers.html#post7645496)

My apologies for the delay in commenting.

I discussed it with him extensively a few hours ago.

Indeed, make us very interested.

The comparison curves were all measured on 18650 cells--a size and form factor often used inside those black brick laptop batteries we have all seen.

Did you use or tested the protected 18650´s?

The cells they use are small enough that the energy release from a single one should not endanger crew or vehicle.

The big adjacent cells in the Thales battery concerns me.

Looking at the Thales/Boeing design and the FAA special considerations, it appears that the approach was to assure cell failure would never occur--as it seems self-evident that no serious measures to avert propagation to adjacent cells were employed, nor were serious measures to contain damage to nearby systems.

TAK incident and specially BOS showed dramatically they failed.

...I wonder if all concerned will remain convinced that all other possible causes of cell failure are sufficiently unlikely to make this approach prudent.

This error is being paid by Boeing with threatening consequences.

Call this Tesla-like.

Tesla just used the perhaps the most important characteristic of a good design:

Fault Tolerance and Graceful Degradation.

It is awkward when "never" happens :{

...as happened with the IPT disc on a Rolls-Royce Trent 900 on Qantas flight 32, and has happened on these two 787 episodes. Examples everywhere. :}

Thanks again for excellent post and answer.

[mm43]

15 feet = 3 meters (for the rest of us guys......)

Now I understand how you guys are sooooo... tall.

Make Google your friend ....

"15 feet = meters" will get you down to size.:ok:

[Romulus]

:

15 feet = 3 meters (for the rest of us guys......)
Now I understand how you guys are sooooo... tall.

Make Google your friend ....

"15 feet = meters" will get you down to size.

As I tell female acquaintances, this <------------------------>

is 8 inches or 300millimetres...

Ok, OK, I'll make sure the door doesn't hit it on the way out...

[saptzae]

Looking at the Thales/Boeing design and the FAA special considerations, it appears that the approach was to assure cell failure would never occur--as it seems self-evident that no serious measures to avert propagation to adjacent cells were employed, nor were serious measures to contain damage to nearby systems. Imho, they did not bother to mitigate cell failure spreading to other cells as this would be weight and size prohibitive (likely worse then NiCd and not near certain to work either).

Rather, the approach seems to be to contain a _rare_ failure inside a solid box and mitigate over pressure by an elaborate venting system out the pressurized vessel.

It worked, twice, resulting in a fart out of the tail pipe and some leakage and one bent box likely due to internal arcing ignited oxygen fed combustion after breakdown of the electrolyte.

All that seems acceptable for a rare failure. It is by no means the equivalent of a hub failure.

What is unexpected and not reasonable is that 2 out of 100 or so batteries in service fatally fail within about year. Two points really do not add up to a curve, but the fact still is of great concern

[hetfield]

Do you mean rather than the NTSB or FAA? @YRP

You are right, my bad.
NTSB, not Boeing visited securaplane.

BTW, just found this:
Securaplane said it makes two battery charging units used on the 787, one for the APU battery in an aft bay, and one for the main ship battery used in a forward bay, which provides backup power for flight critical controls.U.S. NTSB reviewing whistleblower claims in 787 case - chicagotribune.com (http://www.chicagotribune.com/business/sns-rt-us-boeing-787-ntsbbre90n08s-20130124,0,2349989.story)

So, the chargers are not identical.

[hetfield]

For those who never heard about Lithium batteries, and if the RC guys are taking it seriously..........

Complete Guide to Lithium Polymer Batteries and LiPo Failure Reports - RC Groups (http://www.rcgroups.com/forums/showthread.php?t=209187)

9RGwoDacW2A

[specificimpulse]

The Yuasa battery being used in the 787 and what appears to be its prismatic cells are unfamiliar to me but our experience with all Li batteries is that there is a threshold vibration level that will cause rapid cell damage and lead to shorting behavior. In our aerospace application we've tested pretty much every cell type and none of them are particularly tough. Our application has a considerably higher vibration level than most transport aircraft however. I am sure that the battery in question was qualification vibration tested before it ever flew but I wonder if the actual in-service vibration level of that battery installation is what was expected. Our experience is that if the vibration threshold is exceeded the failure is prompt. The operating temperature of these cells is a issue as well. Just how hot does that compartment get when the aircraft is on the ground?

[saptzae]

@Hetfield,

Securaplane said it makes two battery charging units used on the 787, one for the APU battery in an aft bay, and one for the main ship battery used in a forward bay, which provides backup power for flight critical controls. Very interesting, would have thought both are identical. Guess these are customizations of the same basic design.

From page 15 of www.oalj.dol.gov/Decisions/ALJ/AIR/2008/LEON_MICHAEL_v_SECURAPLANE_TECHNOLO_2008AIR00012_%28JUL_15_2 011%29_172333_CADEC_SD.PDF (http://www.oalj.dol.gov/Decisions/ALJ/AIR/2008/LEON_MICHAEL_v_SECURAPLANE_TECHNOLO_2008AIR00012_%28JUL_15_2 011%29_172333_CADEC_SD.PDF)
The root cause study also showed failure to use the signal harness was one of the possible causes of the fire.Various types of signals transmit between the battery and BCU, and they operate almost together. As Leon used the battery in the test, he didn't have the signal harness connected; thus, he couldn't monitor the internal workings of the battery.
Improper to work with the battery "open loop".

Good to look again into the charger history. Also the history of the batterie's installation, was the main battery ever used as an APU battery? Can a bus "charge/reverse flow" the battery without the chargers involvement?

The charger is only part of the story. The installation should have prevented the mess by protecting the battery from any charge.

Other than electrical management failure, thermally induced thermal runaway of many cells without electrical involvement after one cell failed (for any cause) seems less likely but is not impossible.

What makes cells fail? Design/manufacture, storage, overload or deep discharge or overcharge or the bus reverse flowing. The investigation will determine which.

Overcharge of individual cells seems a more likely scenario to me than the cells itself. But it does not have to be the charger, it could also be the bus.

[Chris Scott]

saptzae,

Thanks for your interesting post. Could you possibly, however, help me translate this clause into intelligible English for us laymen?

" ...resulting in a fart out of the tail pipe and some leakage and one bent box likely due to internal arcing ignited oxygen fed combustion after breakdown of the electrolyte."

:{

Do you mean something like:
"...resulting in a fart out of the tail pipe; and some leakage and one bent box, due to internal arcing-ignited, oxygen-fed combustion, after breakdown of the electrolyte."?

What a difference punctuation can make. Or, if that's difficult (as it often can be); shorter, simpler sentences. There are no hard and fast rules, of course, but a degree of logic can make the difference between understanding and misunderstanding.

As you may know, a lady called Lynne Truss once wrote a book called "Eats, shoots and leaves", which might describe the actions of a gangster in a restaurant. The gunman, however, is a panda. Asked by the waiter to explain the carnage he has created, he produces a badly-punctuated wildlife manual and says: "I'm a panda, look it up." Finding the relevant entry in the manual, the waiter reads:
"Panda. Large black-and-white bear-like mammal, native to China. Eats, shoots and leaves."

Sorry to pick on yours, because PPRuNe is jam-full of ambiguous and/or unintelligible posts: many written by intelligent, experienced pilots and engineers whose first language appears to be some kind of English!

Regards,
Chris
[With apologies to John Tullamarine for the thread-drift.]

[A33Zab]

Shipping details of B787 Main,Apu & FCS batteries states:


- IATA Dangerous Goods
- Transport not allowed on passenger aircraft

[hetfield]

@A33Zab


There were at least two fires on UPS freighters with Li-Ion loaded.

One (747F) was a hull loss, both pilots died.

[sb_sfo]

You've got it right on the APU starting- the l/h ASG can get power from either ship power or external only. The r/h can get it from 3 sources.

The APU battery provides power for external lights when towing, and can also provide power for manual RAT deploy, and, of course, APU start. Its charger is powered by the F/O instrument bus. The main battery provides brakes, captains audio control panel and a dome light when towing.

I have no idea of the current draw when starting the APU.

[BARKINGMAD]

Hi moderators, is there any reason why this subject is running in Tech Log and Rumours also?

For those trying to learn from all this very valuable info, surely it makes it harder to follow? :confused:

[Lyman]

For my dough, this thread carries the weight. Here are pilots, engineers, and experience. This thread is Platinum, R+N, Copper.

The topic deserves both, but if it's FAA, politics, or scuttlebutt, R+N seems like the proper spot.

Here be the real deal.

[gums]

Salute!

Thank you, Lyman.

In my quest to find out more about AF447 I found this site a few years back.

We have many experienced folks here that have survived due to training, innate skill, and learning from those who went before. .Not just pilots, but engineers and wannabes

We have had many spirited exchanges here, but I have yet to see a lack of respect for the posters' thoughts and theories and explanations of how things work in the real world.

[etudiant]

The JAL incident seemed a lot more potent than 'a fart out of the tailpipe'.
An equipment fire that takes the Logan Airport fire dept 40 minutes to put out is a safety of flight issue, imho.

[DozyWannabe]

One (747F) was a hull loss, both pilots died.

As yet there has been no confirmation or denial that the LI cargo was responsible for the fire. Any recommendations have been precautionary only.

[Lyman]

etudiant ....... The JAL incident seemed a lot more potent than 'a fart out of the tailpipe'.
An equipment fire that takes the Logan Airport fire dept 40 minutes to put out is a safety of flight issue, imho.


The NTSB report from the "Grounded" thread states the fire department fought the fire from 10:49 to 12:15.

Eighty Six Minutes.

etudiant? mois aussi.... :ok:

[hetfield]

As yet there has been no confirmation or denial that the LI cargo was responsible for the fire. Any recommendations have been precautionary only.

True!

Why?

Revenue?
Money?

Who got the balls to exlude Li-Ion on airplanes?

[RR_NDB]

Hi,

In a first analysis we may see they discarded failures (like a major short circuit) in the DC busses as causes of the problems.

This means:

The problem was not due catastrophic load to the batteries (excessive current draw)

My comment is because considering certainly there is no discharge control (perhaps will be required for Li Ion in aviation) the analysis is concentrating in:

1) Cell issues (defect, etc.)
2) "Circuitry" like protections, charger including design, algorithms, etc.

There are other points to comment. I´m further analysing.

E.g. the point on cell overcharge is intriguing. Are the cells charged individually in this design? IMO should be for airliners batteries.

With over "US$ 10 billion grounded" and other costly consequences the briefing shows we are distant from a solution (using Li Ion).

An immediate decision to revert to Ni Cd´s appears urgent and inevitable.

Can be implemented? Surely yes. Implications? We would need data not publicized, to estimate. Certainly less costly than the current situation.

Very serious issue. Painful teething! And a "virtual stalemate" (If Li Ion usage insisted).

[rottenray]

RR NDB writes:
My comment is because considering certainly there is no discharge control (perhaps will be required for Li Ion in aviation) the analysis is concentrating in:I'm pretty sure there is, it would be inconceivable to connect an uncontrolled load (ie DC starter motor, etc) directly to any Li battery. All of the "big" loads on the 787 are AC or driven from the +/- 270V DC bus and have no direct connection to the battery buses. The APU starter is a starter/generator which has its own (load-limiting) controller when using the APU battery for start power.

The simplified graphic in this post shows high-power distribution. (http://www.pprune.org/rumours-news/505348-ana-787-makes-emergency-landing-due-battery-fire-warning-13.html#post7651761)

We're getting closer to the reason for at least one of the failures. Flightglobal writes that a short was found in cell # 5 of the JAL battery.

Story with pix here. (http://www.flightglobal.com/news/articles/ntsb-finds-signs-of-short-circuit-thermal-runaway-in-jal-787-battery-failure-381464/)

[misd-agin]

They don't know if the short was the chicken or the egg(cause or effect).

They have the results. They don't know what the triggering event was or the sequence of events.

[syseng68k]

rottenray:


We're getting closer to the reason for at least one of the failures.
Flightglobal writes that a short was found in cell # 5 of the JAL battery.
If a cell grossly overheated, it wouldn't be surprising to find that the
separator material broke down eventually, whatever it's made of.

What they are also saying is that they are not sure if an overcharge
condition occured in a single cell, which would have caused thermal
runaway affecting the rest of the battery.

Still early days, but my money is still on the charger or temperature
sensing within the battery. Yuasa have been shipping these cells for
years and they are even used for space applications, so find it difficult
to believe there's a fundamental design fault in that area...

Regards,

Chris

[rottenray]

Sys writes:
Still early days, but my money is still on the charger or temperature
sensing within the battery.Some time in the past, a poster (here or somewhere else) mentioned that an inspection showed wiring errors.

I wonder what they were and where they were at.

If a harness was mis-wired so that charge sensing was swapped between two cells - cell A being read as cell B and vice versa - it would eventually lead to an overcharge situation.

If the swap happened on cell temp, then a cell going into thermal runaway would be allowed to do so as the corrective action would be applied to the wrong cell.

Wow.

[RR_NDB]

rottenray

I'm pretty sure there is, it would be inconceivable to connect an uncontrolled load (ie DC starter motor, etc) directly to any Li battery. (http://www.pprune.org/tech-log/505695-787-batteries-chargers-7.html#post7655296)

On inconceivable look to the battery picture. Certainly the design doesn´t control the CHARGING current independently in each cell. :{

This may explain BOTH INCIDENTS!

And on discharge control:

1) How you would design it? What kind of part to perform it?

2) We will learn soon to confirm. I suspect there is not this feature in 787 main battery (main one is my bigger concern)

Mac

This picture just shows the high current cell conections (strips) and the sensors wiring. There is no provision for independent cell charging! :{

http://www.flightglobal.com/Assets/GetAsset.aspx?ItemID=49342

[syseng68k]

Rottenray:


Some time in the past, a poster (here or somewhere else) mentioned that an inspection showed wiring errors.

I wonder what they were and where they were at.

If a harness was mis-wired so that charge sensing was swapped between two cells - cell A being read as cell B and vice versa - it would eventually lead to an overcharge situation.

If the swap happened on cell temp, then a cell going into thermal runaway would be allowed to do so as the corrective action would be applied to the wrong cell.
I didn't see that post, but it seems unlikely, since the manufacturing
process for such an item would have have visual inspection and test rigs
to ensure that the wiring was correct. and that it functioned as expected.

If voltage sensing were swapped between two cells, i'm not sure it would
make that much difference if all the cells are charged in series, since
you can only vary the overall charge rate for all cells, not individually.
Would make a lot of difference if there were a charging circuit for each
cell, though from the pics of the internals, doesn't look like that is
the case.

There's another point that may be relevant as well: It's not clear from the
pics if there is a temperature sensor per cell, or a single sensor for
the enclosure. I don't have figures, but the cells could have significantly
less thermal mass than say lead acid or nicad. ie: they might heat up much
faster than the latter. They also have a fairly low max operating temp of
65 C. If you have a single sensor at one side of the enclosure and a cell
starts to overheat at the opposite side, would that single sensor detect the
overheat condition in time to shutdown the battery ?.

May be irrelevant, if there's a temp sensor per cell, but the failure also
raises the question of whether they tested the overall system for all
fault conditions, including that to destruction...

Regards,

Chris

[rottenray]

RR NDB writes:
On inconceivable look to the battery picture. Certainly the design doesn´t control the current independently in each cell. http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/boohoo.gif

I wasn't aware you were referring to independent current control. And I'm not aware of any multi-cell Li battery packs which do limit current on a cell-by-cell basis.


Sys writes:
There's another point that may be relevant as well: It's not clear from the
pics if there is a temperature sensor per cell, or a single sensor for
the enclosure. I don't have figures, but the cells could have significantly
less thermal mass than say lead acid or nicad. ie: they might heat up much
faster than the latter. They also have a fairly low max operating temp of
65 C. If you have a single sensor at one side of the enclosure and a cell
starts to overheat at the opposite side, would that single sensor detect the
overheat condition in time to shutdown the battery ?.

I read somewhere that temp sensing is overall, rather than cell by cell.

Given the relatively "light" weight of these cells, and the corresponding lower rate of thermal inertia, I'd guess that a cell could overheat in one area before a sensor located on the opposite side could sense the climb. Perhaps thermal curves could be modeled to predict this, but if I were designing the bugger I'd certainly have at least 2 sensors per cell.

Cheers!

[RR_NDB]

rottenray:

I wasn't aware you were referring to independent current control. And I'm not aware of any multi-cell Li battery packs which do limit current on a cell-by-cell basis.

Before editing i made implicit first point was on CHARGING. I consider a safer design to charge the cells INDEPENDENTLY. Why not?

Another point on safer design. There are certainly better locations for this DANGEROUS battery.

http://regmedia.co.uk/2013/01/25/boeing_787_fire.jpg

[Lyman]

syseng68k

From published data, it certainly appears that testing to destruction was not done. That is inconceivable; Boeing certainly would have done that, if only to know what solutions were available to conform to the regs. If there was fire...

That was Boeing's position, initially, that the battery performed as designed.

If they hadn't done the testing to arrive at a default solution to failure that did conform, they would not have pleaded to FAA: "give us instructions on a fix..."

Which suggests they don't have one, ergo, they did not test the system to failure that did not comply.

Scary

[saptzae]

I apologize for my earlier analogy, it is a lot worse than a fart out of the tail pipe.

Parallel charging
There will be differences between cells, a few %. The cell of the lowest capacity determines the total charge-able and discharge-able battery capacity. Cells age, available capacity diminishes over time and varies more and more amongst cells.

Parallel charging enables to micro-manage the charge per cell in particular when cells are individually loaded (battery tapped). Very rare scenario in this day and age.

Here, batteries are discharged in series. Discharging must be stopped when the cell of the lowest charge is empty and charging must be stopped when it is full. Parallel charging would have little if any practical benefit beyond micro-management.

Parallel charging would require one isolated inverter per cell, capable of the maximum fast charge current + associated heavy wiring. 4V 30-60A x 8. Please consider size, weight, connection, cooling and reliability.

Actually, switching and rectifying losses depend mostly on the current and in practice would be almost same for a single 4V inverter and a 32V series charger.

Electrically, a parallel charge arrangement here would have 1/8th of the efficiency of the current 32V charge arrangement.

Then, these eight chargers must be managed and monitored!

No thanks, KISS :)

Overload
Generally, Li based cell chemistries will tolerate transient overload less than others. Au, Ni or Pb based cells can handle lots of abuse as these do not chemically deteriorate, at least not very quickly.

Important to all batteries is that the cells match, by effective inner resistance, throughout the event. Gross mismatch could even reverse a weak cell. The result would be rapid cell deterioration or outright destruction.

A partial cell failure, resulting in capacity loss or effective inner resistance increase, could trigger this scenario.

Mis-wiring
Swap of monitoring connections would identify the wrong cell to the management system, but would likely be detected by a production test.
This is a serial charge and discharge arrangement. Operationally, the weakest cell counts. Mis-wiring by swapping amongst cells would have no effect on charge/discharge management.

[saptzae]

Temperature would be used to limit fast charge current. Management system will lower max charge current at higher temperature.

Cell voltage change precedes temperature change. Once the temperature rises substantially, it will be too late to manage.

When a cell arcs internally or shorts, the voltage will fluctuate a lot and reduce to near zero.

When a cell electrically opens, voltage across it will revert and the battery shows a high inner resistance.

Important is to keep individual cell voltages in the allowed range at _all_ times, or disconnect the battery.

Thus, per cell temperature monitoring would not be a big benefit to battery management.

Important is that charge current be reduced quickly when any cell's voltage approaches it's limit, and that it never increases the design limit.

When _any_ cell over/under/reverse voltage is detected, the entire battery must be taken off-line (disconnected) within a very short time to prevent secondary damage to it.

[saptzae]

There three main management issues.

a) Cell production quality
b) Cell operational management
c) Cell failure handling.

It was reported that a cell was found shorted. We do not know whether this was the initial failure, or whether due to a) or b). It does not really matter because c) should have worked better, and may be what did the real damage.

If short was the initial failure, from an electrical perspective:


A cell fails and shorts - (reason either a) or b) above
Cell voltage drops, removing (most) of its 4V share of the 32V
Bus voltage remains essentially the same at 32V
Other cells take up 4V / 7, thus are subjected to severest over-charge in terms of voltage and current
More cells fail in a cascading manner
Combined per-cell energy and the bus feed battery destruction

Shorting

It is not going to be a solid short from one moment to the next. The energy is just too great. Cell could not ever dissipate it's 200 - 300 Watt hours quietly. It would short, arc, burn out the short and do more damage along the way. There would be over pressure, relieve valves opening, electrolyte blown out. More shorting as separators fail by the heat. The whole cycle continues until energy is dissipated and some spot shortened can not be burned out.

Throughout all this, terminal voltage will fluctuate and other cells be subjected to voltage and current spikes, until the next one fails and the cycle repeats itself even faster.

[hetfield]

Then, these eight chargers must be managed and monitored!

No thanks, KISSThere is no need for parallel charging if you have a battery management system (e.g. balancer etc.).

Battery Management System (BMS)

One of the main functions of the BMS is to keep the cells operating within their designed operating window (the green box above). This is not too difficult to achieve using safety devices and thermal management systems. As an additional safety factor some manufacturers set their operating limits to more restricted levels indicated by the dotted lines.
There is however very little te BMS can do to protect aginst an internal short circuit. The only prevention action that can be taken is strict process control of all the cell manufacturing operations (http://www.mpoweruk.com/battery_manufacturing.htm).
Lithium Charged but Not Guilty?

The cause of many fires has been attributed to Lithium batteries and there is a fear of Lithium because of its well known vigorous reaction with water. Under normal circumstances, most (but not all) batteries do not contain any free Lithium. The Lithium content is combined into other compounds which do not react with water. The amount of Lithium deposited during the Lithium plating when cells are damaged as described above is very small and not usually responsible for the fires which have occurred. Furthermore, many of the reported fires are due to burning electrolyte rather than the Lithium compounds.
The guilty party
Although investigation has shown that some Lithium fires are due to internal short circuits as described above, many, if not most fires are caused by abuse by the user. This may be "deliberate or negligent" abuse such as overcharging or operating in a high temperature environment or physical damage due to mishandling, but quite often it is unconscious abuse. Surprisingly many of the most serious fires have been initiated by inadvertent short circuits caused by careless disposal of cells in the rubbish. While strict regulations for transporting Lithium batteries (http://www.mpoweruk.com/shipping_regs.htm) by air have been implemeted, the sources of several aircraft / transport fires have been identified as spare laptop batteries being carried in passenger luggage shorting against other items packed with them.
Note: Large batteries such as those used in automotive applications usually incorporate short circuit protection, but smaller laptop batteries do not usually have this facility.
Lithium Battery Failures (http://www.mpoweruk.com/lithium_failures.htm)

[saptzae]

@Hetfield

Yes, serial management is sufficient. All it must do is to keep cell voltages in range. It's important for any battery chemistry. It's critical for Li based cells, which are sensitive also to short-term over-discharge.

Importantly, when cell management fails, failure mitigation must kick in. It seems that it did not.

[syseng68k]

rottenray:

I read somewhere that temp sensing is overall, rather than cell by cell.
A temp sensor per cell becomes more important where fast charging is used.
There will be significant temperature rise and that coupled with a low
max temp of 65 C means that a single temp sensor to cover such a large
area is not enough. From what i've read, the fast charge timescale is about an hour
30mins.


Given the relatively "light" weight of these cells, and the
corresponding lower rate of thermal inertia, I'd guess that a cell could
overheat in one area before a sensor located on the opposite side could
sense the climb. Perhaps thermal curves could be modeled to predict
this, but if I were designing the bugger I'd certainly have at least 2
sensors per cell.
2 would provide redundancy, but if the temp and voltage sensing were
combined into a single chip device, it could be embedded into the cell
casing at very little cost and have enough diagnostics to detect either
the voltage or temp sensor's failure.

There's another point as well: It looks like there are printed circuit
boards inside the battery casing. Hmm: pcb's + electrolyte = trouble,
even if the boards have a conformal coating. You only need a single cell
case to split, for whatever reason and you have electrolyte and vapour
which could play havoc with electronics. Inside a battery casing is
the last place I would put a pcb, especially if that is handling the
sensors

Regards,

Chris

[grebllaw123d]

syseng68k,

Quote from your post#143:

If you have a single sensor at one side of the enclosure and a cell
starts to overheat at the opposite side, would that single sensor detect the
overheat condition in time to shutdown the battery?

How do you shutdown a battery that is experiencing a thermal runaway? I thought that a runaway in a lithium-ion battery cell could not be stopped.

By the way, thanks for all your very informative posts!

[Chris Scott]

Saptzae,

Thanks for your latest posts. For a layman like me, they seem to summarise the issues facing Boeing, Securaplane, Thales, and (perhaps) Yuasu very clearly; particularly your description of the cascade effect following the shorting of one cell during charging.

Could you just clarify the last sentence of this part of your penultimate post (http://www.pprune.org/tech-log/505695-787-batteries-chargers-8.html#post7656854), please (my bold)?

“Shorting
It is not going to be a solid short from one moment to the next. The energy is just too great. Cell could not ever dissipate it's 200 - 300 Watt hours quietly. It would short, arc, burn out the short and do more damage along the way. There would be over pressure, relieve valves opening, electrolyte blown out. More shorting as separators fail by the heat. The whole cycle continues until energy is dissipated and some spot shortened can not be burned out.”

Also, do you think that a manganese (spinel) type of Li-ion battery would have been a safer choice than the cobalt type, and would its performance be adequate for the task? If so, could its retrofit be one of the options currently under consideration?

[syseng68k]

grebllaw:

Once there's a runaway condition, it's probably too late. The whole
idea is to have accurate and timely info from the cells, to allow the
electronics to stop the charge or dump the load before runaway happens.
If the battery is managed correctly, it should never happen, other
than from gross component failure.

LI is far more fussy about operating temperature range and min / max
cell voltages than either lead acid or nicad and both need to be
continuously monitored to ensure safe operation. It doesn't mean there's
anything inherently wrong with the technology, but the overall system
design of battery, charger and load profile need to be to be much
better matched and to a tighter spec.

Analysis of this problem is interesting, even if we are stumbling
around in the dark a bit :-)...

Regards,

Chris

[syseng68k]

grebllaw:

Thanks for the encouragement as well. Interest will probably subside soon,
until more info is available...

Regards,

Chris

[Machaca]

saptzae - thank you for your excellent contributions! :D:D:D

[Machaca]

The Chicago Tribune reports (http://articles.chicagotribune.com/2013-01-25/business/chi-dreamliner-circuit-boards-012513_1_lithium-ion-gs-yuasa-corp-main-battery):

Burnt circuit boards snag Japan Boeing 787 probe

Circuit boards that control and monitor the performance of the plane's lithium-ion battery unit were charred and may be of little use to the teams investigating why the battery effectively melted, forcing safety investigators to scramble for possible clues from other components in the plane's electronics...

Japanese safety officials plan to take the damaged circuit boards to the manufacturer, Fujisawa-based Kanto Aircraft Instrument, for a detailed inspection.


http://i337.photobucket.com/albums/n385/motidog/GSYuasa7871.jpg

The PCB's are large and possess significant monitoring/management capability. As has been stated, the protections failed to prevent thermal runaway.

Let's hope the ANA units are testable and yield good information.

Best outcome may be discovering a bad batch of PCB's.

[syseng68k]

Lyman:


Scary
Perhaps, but let's put it into perspective: After arguably the most serious
level of battery failure possible, the fire was contained within the battery
enclosure, even if the contents did leak out and make a bit of a mess. The
smoke was discharged as per design. Inconvenienced, but no one in any
serious danger, nor lost their life, which is the most important thing..
It's what actually happens, not what might.

These events should provide a lot of new data, even if it is a bit expensive and
whether they were expecting it or not :E...

Regards,

Chris

[hetfield]

Thx Machaca.

So,

- "GS Yuasa" is the manufacter of the Li-Ion cells
- "Kanto Aircraft Instrument" deliver the "circuit boards",
- "Securaplane" the chargers (two different models)
- "Thales" put it all together, besides the chargers


The "circuit boards" are very important. To my knowledge, they do the "balancing" and monitoring of each of the 8 cells which is crucial.

Outsourcing at its best....

[syseng68k]

Machaca:

Thanks for that pic, much easier to get some idea of the topology. There
are a lot of sensing wires, but again, no evidence of individual cell
temperature sensors / monitoring.

Looks a serious amount of analog and digital processing on those boards
and they aren't protected from cell contents in any meaningfull way other
than a possible conformal coating. The connectors look molex'ish and
are exposed as well.

All in all, not impressed. Boards and connectors of that type should
never be located anywhere near cells and their contents...

Regards,

Chris

[hetfield]

All in all, not impressed. Boards and connectors of that type should
never be located anywhere near cells and their contents...

Exactly!

Even the hobby RC guys doing better....

[saptzae]

@Chris Scott.

Could you just clarify the last sentence of this part of your penultimate post (http://www.pprune.org/tech-log/505695-787-batteries-chargers-8.html#post7656854), please (my bold)?

“Shorting
It is not going to be a solid short from one moment to the next. The energy is just too great. Cell could not ever dissipate it's 200 - 300 Watt hours quietly. It would short, arc, burn out the short and do more damage along the way. There would be over pressure, relieve valves opening, electrolyte blown out. More shorting as separators fail by the heat. The whole cycle continues until energy is dissipated and some spot shortened can not be burned out.”
I look at it at the cell level, from an electrical perspective, which I understand and which is the initial trigger of the destructive cycle. I disregard secondary effects of fire sustained by chemical reactions and thermal runaway.

A cell consists of stacks of Anode-plate Separator Cathode-plate. A short circuit occurs when any part of anode touches part of cathode. It could be caused by plates deforming or separator deterioration or contamination due to chemical reactions.

That process starts at a spot, the area of which is a quite small part of total cell area. Short results in a large current density at that spot leading to arcing and local heating. The effect of arcing is increased current flow and more heat. Once the spot is hot enough, it evaporates and the short may weaken. Also, resulting pressure increase may push plates apart and weaken or open the short.

However, the damage has been done and another spot will fail. 200-300 Watt hours is a lot of energy to dissipate within seconds. The short-arc-open cycle goes on until the cell is discharged or ceases to function for lack of electrolyte.


Also, do you think that a manganese (spinel) type of Li-ion battery would have been a safer choice than the cobalt type, and would its performance be adequate for the task? If so, could its retrofit be one of the options currently under consideration?
There are two problems on my mind, two separate things to resolve. 1) What caused the initial failure. 2) Was the failure mitigated by disconnecting the battery immediately from all power.

Changing cell chemistry or manufacturer would be effective only if 1) is caused purely by bad cell. IMHO, a cell management issue is much more likely than bad cells. The investigation will figure it out.

If cell management is the problem, "Safer cells" would not make a significant difference. Safer cells mismanaged would break too with quite similar effects due to high energy density.

What makes cells fail is imbalanced charge or load, it does not have to be the charger, it can be the bus, or the interaction of both.

IMHO, other batteries in service, will already show detectable symptoms of impeding failure.

What one could do is to inspect batteries from all over the fleet using CT to look for anomalies such as distortion or contamination and then track back to cell quality or cell management.

[syseng68k]

hetfield:

The assumption they possibly made was that the cells are sealed, but they
are not. With age, vibration and pressure changes from internal heating &
cooling, they will leak vapour which will accumulate within the enclosure.
Vapour meets electroncis = corrosion and it wouldn't need much deposited
on the pcb to cause measurement error in sensitive analog electronics.

I was going to make some comment about consumer electronics quality in a
billion $ a/c project, but I suppose i'd better not :uhoh:...

Regards,

Chris

[Machaca]

The individual cells of the incident batteries have been subjected to CT scans, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and physical inspection after being disassembled.

CT of the JAL incident battery:

http://i337.photobucket.com/albums/n385/motidog/GSYuasa7872.jpg

[hetfield]

The assumption they possibly made was that the cells are sealed, but they
are not. With age, vibration and pressure changes from internal heating &
cooling, they will leak vapour which will accumulate within the enclosure.
Vapour meets electroncis = corrosion and it wouldn't need much deposited
on the pcb to cause measurement error in sensitive analog electronics.

If this is the case, it's just poor engineering.

[saptzae]

@Machaca

CT of the JAL incident battery
Yes, seen that, I am interested in random in-service batteries.

I believe it is gradual degradation already present elsewhere and want to see whether there is any anomaly such as cell distortion and then track back to what causes it.

Gradual: At least as long as these batteries were in service. 100 hours?

[Chris Scott]

saptzae,

Thanks again for that. I now understand that the cell failure involves a complex series of temporary shorts at different spots, progressively destroying the cell.

The fact that the first cell-failure inevitably leads to the application of a higher charging voltage to the remaining 7 cells - unless the monitoring system detcts the problem - represents a potentially fail-hard situation. Not something you want to be happening under the cabin floor...

[TacomaSailor]

I highly recommend “Lithium-Ion Batteries Hazard and Use Assessment”+:

http://www.nfpa.org/assets/files/pdf/research/rflithiumionbatterieshazard.pdf

for those of you who really want to understand the chemical, electrical, and mechanical aspects of these batteries. This report was mentioned in one of the first dozen or so posts about this problem but, based on the many questions and comments here, I suspect many participants have lost track of the report.

It was published in July 2011 at the request of “The Fire Protection Research Foundation” and was produced by two professional engineers and two PhD engineers. The research group reports they have been studying Li-ion battery failures and conducting destructive testing for over a decade.

The report was not focused only on aviation use of the battery but rather the general fire hazard, fire containment, and fire fighting issues associated with Li-ion batteries. The report does contain a great deal of FAA and UN regulatory data and information. The report is clear, concise, easy to read, and contains a lot of good photographs and detailed test data.

The report tested many Li-ion batteries to total destruction and carefully documents the many aspects of Li-ion battery fire initiation and spread.

Key characteristics of the batteries that I noted in the report that might be important are shown below:

1) The susceptibility to minor point impact on the battery case and the resultant internal damage that leads to individual and then battery wide conflagration. (page 71)

2) Mechanical damage to a cell case “perpendicular to the electrode edge is likely to result in high impedance shorting between electrode layers and initiate thermal runaway.” (page 57)

3) “Mild” mechanical damage can lead to thermal runaway over multiple cell discharge/charge cycles; caused by lithium plating (dendrites?) or mechanical creation of a small internal hole in the electrode. Failure is most likely to occur during charging or just after charging. (page 72)

4) “The vast majority of thermal runaway reactions that occur in the field occur during or shortly after cell charging.” (Page 84)

5) Cells that are below 50% of their full charge will seldom experience thermal runaway (page 84)

6) A single cell that is in thermal runaway mode will vent gas at over 650°C which is far above the Auto-ignition flash temperature of the electrolyte. (page 85)

7) FAA burn tests in an contained space show temperatures of 1000° F to 1400° F at 12” above the burning cells. (page 107)

8) No significant amount of oxygen is found in the gases vented by an overheated cell (page 63) and there must be a sufficient oxygen present from an external (not vented gas) source to sustain combustion (page 66)

9) Multi-cell batteries can be designed to minimize cell-to-cell heat transfer during a single cell thermal runaway by adjusting cell spacing and the orientation of the cell ejection path. (page 67)

10) “Thermal runaway can occur significantly after flame suppression” – a coolant must be applied to prevent subsequent ignition. (page 110)

11) Extensive tests by the US Navy show plain water to be an effective flame suppressant and coolant. (page 112)

12) There are several significant unknowns (“Gap Analysis”) regarding Li-ion fire hazards: Limited understanding of vented gas composition and flammability and Limited data on the effectiveness of suppressants. (page 116)

[saptzae]

@Machaca
Thank you for the picture of #158. It shows bypass connections which could be used to divert small part of the charging current across individual cells. Bypass can be used to fully charge all cells and also lower voltage of individual cells. This contributes to explaining why there is lots of stuff on the PCB's.

In the lower right, at the bus bar, there seems to be a breaker used to disconnect the battery from the bus. If so, I wonder whether it was opened and remained open after the initial failure.

[RR_NDB]

Hi,

saptzae:

Parallel charging would have little if any practical benefit beyond micro-management. (http://www.pprune.org/tech-log/505695-787-batteries-chargers-8.html#post7656754)

Parallel charging is the safer way one can charge an stack of critical cells. And it´s easy to design a highly reliable and dependable charger. There are some, IMO important benefits:

1) You fully respect the characteristics of each cell charging it with the proper current to attain the proper charge. Sensing it´s voltage and temperature during the charging allow us to improve the cell reliability keeping them bellow a safe specified temperature. (Remember the failure rate is correlated to temperature.)
2) You can even "help" a given cell to avoid to be transformed in a load (during heavy discharging) maintaining it´s within a safe voltage. (Something possible from energy of the DC bus itself). A dangerous polarity reversal would be practically impossible.
3) You can detect, register and inform on impending cell failures by a better characterization of the cell, instead of just doing this during the discharging. (Batteries for Av. application should have it´s recording capability)

Parallel charging would require one isolated inverter per cell, capable of the maximum fast charge current + associated heavy wiring. 4V 30-60A x 8. Please consider size, weight, connection, cooling and reliability.


All these factors were seriously considered and weighted before posting. IMO parallel charging is easily justifiable for an improved design.

Electrically, a parallel charge arrangement here would have 1/8th of the efficiency of the current 32V charge arrangement.


No problem with current high efficiency inverters.

Then, these eight chargers must be managed and monitored!

No problem!

Mac

PS

I am here trying to show a way to increase the safety when using these dangerous cells. I yet adopted this approach in a (cost sensitive) design.

PS2

No thanks, KISS :)

I love the k.I.S.S. design approach. When it´s possible. In this case every reasonable feature to save the reliable use of these dangerous cells are being considered. There are big advantages with Lithium batteries. I´m trying to feel better and more confident when relying (if possible) on her.

PS3

The old approach of charging ("open loop") stacked cells directly from the bus in my mind is being seriously questioned. it´s too simple to be safe with dangerous cells.

PS4

To a better analysis of the 787 Batt/chrgr issue (thread focus) we would go beyond block diagrams (boxes) and must look to schematic diagrams (wiring, etc.)

[RR_NDB]

Hi,

syseng68k:

Vapour meets electroncis = corrosion and it wouldn't need much deposited
on the pcb to cause measurement error in sensitive analog electronics.

(http://www.pprune.org/tech-log/505695-787-batteries-chargers-9.html#post7657720)

In digital circuitry could be catastrophic too. :{

I was going to make some comment about consumer electronics quality in a
billion $ a/c project, but might I suppose i'd better not ...

:sad:


Bear:

scary (http://www.pprune.org/tech-log/505695-787-batteries-chargers-8.html#post7656651)

I agree! (organizational problems are potentially more dangerous than Li Ion batteries). :E

[RR_NDB]

saptzae:

Generally, Li based cell chemistries will tolerate transient overload less than others...Important to all batteries is that the cells match, by effective inner resistance, throughout the event. Gross mismatch could even reverse a weak cell. The result would be rapid cell deterioration or outright destruction...A partial cell failure, resulting in capacity loss or effective inner resistance increase, could trigger this scenario. (http://www.pprune.org/tech-log/505695-787-batteries-chargers-8.html#post7656754)

Question:

The ANA main batt. geometry mismatch was likely due what kind of abuse? During charging cycles?

(BOS incident had APU start then charging) JAL APU battery had CT possibility?

http://i337.photobucket.com/albums/n385/motidog/GSYuasa7872.jpg

[RR_NDB]

Hi,

syseng68k:

There are a lot of sensing wires, but again, no evidence of individual cell temperature sensors / monitoring. (http://www.pprune.org/tech-log/505695-787-batteries-chargers-9.html#post7657661)

There are more connections in some terminals. In the battery terminals you can see 12 (6 in each strip) what is this? :confused:

[syseng68k]

saptzae:


Thank you for the picture of #158. It shows bypass connections which
could be used to divert small part of the charging current across
individual cells. Bypass can be used to fully charge all cells and also
lower voltage of individual cells. This contributes to explaining why
there is lots of stuff on the PCB's.
Assuming that they are bypass connections, not just voltage sensing. The
cable thickness is no guide. That technique is used on ups systems
and balances out the differences in individual cell residual leakage
current, which tends to float some cell voltages upwards at the expense
of the others. The question is, how much control range would be needed
under fast charge conditions, arguably the worst case ?.


In the lower right, at the bus bar, there seems to be a breaker used to
disconnect the battery from the bus. If so, I wonder whether it was
opened and remained open after the initial failure.
Well spotted. A breaker of that type would have a normally open contact,
to maximise contact pressure when closed. It may be driven via a
driver and logic level from the charger, or direct. If via a driver on
the logic board and there was an overheat condition, the driver could
fail and the battery remain connected.

Interesting forensics, but we still don't have enough data :-)...

Regards,

Chris

[RR_NDB]

Chris:

The fact that the first cell-failure inevitably leads to the application of a higher charging voltage to the remaining 7 cells - unless the monitoring system detcts the problem - represents a potentially fail-hard situation. (http://www.pprune.org/tech-log/505695-787-batteries-chargers-9.html#post7657795)

During the charging cycle this may be well managed. But there are threats: The internal resistance of the failing cell during the charge (and discharge) may be situated in a range of values capable to generate high heat (Joule effect, like a resistor). And polarity reversal during the discharge is another threat.

Parallel charging eliminates the above problems.

Not something you want to be happening under the cabin floor...

We engineers MUST imagine everything POSSIBLE (not just probable) and provide means to allow the pilots "manage accordingly". Surprises with these dangerous cells nearby PCB´s inside EE bays nearby electronic modules are potentially threatning issues and a surprise to me.

A battery like the one we are seeing seems an absurd. Boeing had luck.

[syseng68k]

RR_NDB:


There are more connections in some terminals. In the battery terminals you
can see 12 (6 in each strip) what is this ?.
No idea, but probably something to do with measurement accuracy. For
example, if you need to measure voltages of a cell in a string of cells in series,
you must use a differential input amplifier from the cell terminals to
cancel out the common mode voltage and any charge/ load current related
effects. Analog stuff often uses kelvin leads or a single common point for this
reason...

Regards,

Chris

[RR_NDB]

syseng68k:

No idea, but probably something to do with measurement accuracy.

Measurement accuracy at this degree with a PCB in the same environment of the cells is :{

On bypass i am preparing to comment on that.

Question: How many amps the thin white wires could carry without being transformed in fuses? 1 amp? By pass?

[RR_NDB]

saptzae (http://www.pprune.org/members/366005-saptzae)

It shows bypass connections which could be used to divert small part of the charging current across individual cells. (http://www.pprune.org/tech-log/505695-787-batteries-chargers-9.html#post7657863)
This contributes to explaining why there is lots of stuff on the PCB's.
Did you see this approach used before? How many amps to be shunted? Voltage control loading a charging (or charged cell) through by pass?

With these thin wires seems just impossible to control cell voltages during the charging. A likely scenario (during charging) JAL BOS fire.

Again, parallel charging is the only way i can imagine to adequately manage cell voltages during charging.

In the lower right, at the bus bar, there seems to be a breaker used to disconnect the battery from the bus. If so, I wonder whether it was opened and remained open after the initial failure. After loosing control of a given cell voltage, thermal effects will kick in (may be impossible to revert the runaway) and the opening of the main battery connection to the bus may not help at all. I heard on the use of a diode in the main battery circuitry. Anyway means of disconnection of the battery to the bus seems mandatory with Li Ion.

[RR_NDB]

saptzae (http://www.pprune.org/members/366005-saptzae);

3. Bus voltage remains essentially the same at 32V (http://www.pprune.org/tech-log/505695-787-batteries-chargers-8.html#post7656854)

Where is the source of information that sez the battery is charged by the bus. I´ve heard of a diode.

The direct connection of a Li Ion stack of cells to a bus seems very dangerous. A much safer approach would be:

1) Batteries being monitored and kept charged.

2) Batteries going to the DC bus only when necessary. A diode in the main battery path can perform the switching.

3) For APU battery it´s a different story. Much simpler issue.

We are needing more details in order to analyze better. Like schematic diagram. Not just block diagrams.

[TURIN]

Main bat is connected to the hot bat bus through a diode module to ensure the bat only gets charged through its charger. APU bat has no such protection as it is only connected to the APU start circuit (and nav lights when towing without APU.)


Posted from Pprune.org App for Android

[saptzae]

@TacomaSailor

Thank you for the great report. It analyzes pretty much all single cell failure scenarios.

Here is what I am using, covering multi cells:
http://focus.ti.com/download/trng/docs/seminar/Topic%202%20-%20Battery%20Cell%20Balancing%20-%20What%20to%20Balance%20and%20How.pdf

@RR_NDB
Did you see this approach used before? How many amps to be shunted? Voltage control loading a charging (or charged cell) through by pass?
Common practice with larger (Pb) batteries and also Li batteries. Not encountered it with NiCd due to negative cell voltage temperature coefficient.

See above application note by TI.

The ANA main batt. geometry mismatch was likely due what kind of abuse? During charging cycles?
Picture is post event, can't tell pre-event, but there are some clues.

The event:
Labeling cells left to right, top to bottom.



Cell #3 failed first, in a manner as outlined earlier, it shows "burned out" plates and also greater warping (thermal distress) around it
cells #2, #6 and #8 show substantial signs of thermal runaway
Cells #1, #5 and #7 show variations between plates and lesser thermal distress and over pressure. **
Cells #1, #5 and #4 closest to #3 show less damage than #2, #6 and #8 **
Conclude cell #3 has not thermally triggered thermal runaway of many/any?? other cells. **
Conclude cells except #3 failed by electrically induced thermal runaway, triggered by over voltage after failure (short) of #3 and remaining powered by the bus
Conclusion: Battery was kept at near 32V after #3 failed.

** But, it could be opposite, less bulging due to valves opening earlier.

Again, there are two independent failures, 1. and 7. Both have to be fixed.
7. seems to be the greater concern though, as it failed seven (7) very likely functional cells and multiplied the violence of the event.

Where is the source of information that the the battery is charged by the bus. I´ve heard of a diode.

The direct connection of a Li Ion stack of cells to a bus seems very dangerous. A much safer approach would be:
Battery is connected to and will be charged via the bus. There is no 60A charger on those PCB's. There is also no 150A+ diode handling APU starter. Thus, the bus voltage must vary with battery voltage.

And, bus voltage must listen to charger, how that works together with bus tying I don't know. On failure (of #3) the charger should disconnect the battery from bus.

How the battery is protected from bus is the golden question. It seems it was not. If it was not, pre-event cell deterioration may also be caused by it.

With these thin wires seems just impossible to control cell voltages during the charging. A likely scenario (during charging) JAL BOS fire.
No, that's just fine. The bypass current would cover only differences in leakage and possibly capacity and be up to only 1-5 % of charging current. Less than 3A. 10s of mA typical. Once leakage, or imbalance goes beyond a few %, cell has to be replaced.

@ Turin
Thanks for info. One main and one APU battery failed. If not caused by bus, it is must be the charger continuing to power the battery.

@ Turin
Any info on bus tying. Can APU bus connect to main bus?

Edit:I keep wondering about why the four cells on the left show a pattern different from the four cells on the right. It seems like that plates have slightly moved apart, or have changed their properties somehow.

Why only these four, and could this change be pre-event, and be related to the failure of #3?

Can this pattern be observed on other in-service batteries?

Edit2:
Wiring errors would be a very convenient explanation of 1.
Without being aware of bypass facility, I discounted wiring errors earlier. Now, wiring errors could lead to the wrong cells being bypassed and to over voltage on the others.

Wiring errors could explain the pattern (if it is deterioration) in the cells on the left and failure of #3. Did they swap left and right monitoring or bypass wiring?

Or, is there another problem managing half the cells?

But, it still would leave 7. to explain and fix. My analysis of 7. could be wrong like everything else. While I doubt it, and stick to electrically induced thermal runaway, all other cells could also have been destroyed by thermally induced thermal runaway.

[Machinbird]

The below is a screen grab from the NTSB briefing on the Boston battery failure:

http://home.comcast.net/~shademaker/BatteryShort.png

The circle marks the location of an electrical short that they discovered in one of the cells.

The only thing I can conclude from this picture is that this particular short probably resulted from cell over-temperature.

I make this statement because the short is located along the centerline of the electrode plates where the least heat dissipation occurs. It would also seem that any physical manufacturing defect would be found along the edges of the plates.

It should be pointed out that there may also be other shorts that were not pictured and if they exist, they may have a different characteristic than this one.

[saptzae]

On page 19 of http://www.ntsb.gov/investigations/2013/boeing_787/JAL_B-787_1-24-13.pdf is a CT scan of #3.

They call it 6 as their picture on page 20 is inverted from the one posted here. It is implied that this is the electrically shorted cell.

I eagerly await a CT scan of the ANA battery.

[TURIN]

Saptzae.
The APU AC BUS can be tied to the L and R AC busses.
From what I can see the only connection from the APU Battery is through the Start Power Unit (SPU) this converts 28vDC to 115vAC this then goes to the ATRU which converts to +/-130vDC which via the CMSC (Common Motor/Start Controller) is routed to the APU starters (VFSG). The APU hot bat bus doesn't connect to anything else from what I can see except if the Towing Switch is selected 'on'. In which case it powers the Position lights.
The APU charger receives it's power from the FO's Instrument Bus.


Posted from Pprune.org App for Android

[RR_NDB]

Hi,

Machinbird (#183):

"Temperature as trigger of cell short circuit."

This matches the model of the battery being "abused" by a fast charging (operating near or within it´s temp. limits)

The charging regime (APU batt.) could be the main BOS JAL factor. With cells probably degraded before? How many hours operated before?

Likely it was being recharged when started to fail. Or
(imo, less probable) started to runaway during or just after delivering high current to APU starter.

[syseng68k]

Over in rumours and news, #273, re-checked posted a link to the ntsb
press briefing video:

Chairman Deborah A.P. Hersman briefs the media on the JAL Boeing 787 battery fire investigation. - YouTube (http://www.youtube.com/watch?v=wVMkt3sFwh0&feature=youtu.be)

How to say very little over a long period, is the first thing that strikes
me and looks like the event is being carefully stage managed.

More interesting are the areas discussed, where the battery analysis takes
centre stage. Seems a bit odd to me, since any battery that suffered such
catastrophic failure would be expected to have cell deformation and evidence
of internal short circuits, yet the images are presented as though something
profound.

Possibly more important and not being discussed as yet is the intelligent
charger. A charger of that would be expected to have internal non volatile
storage and software to log both normal and abnormal conditions. For example,
the number of charge cycles and the voltage, currents and timescales involved.
There should be a log of the events and conditions that led up to the failure
which would be downloadable for analysis. Perhaps they are doing this already,
but no reports as yet...

Regards,

Chris

[RR_NDB]

TURIN (# 181)

A failure in the diode module (typical is short circuit) may explain the smoke ATC saw.

APU circuitry doesn´t require the diode as you understand (APU batt. never is directly connected to a supply. Just to loads: APU starter, through the modules you mentioned or to the lights when towing with APU ON). The charging of APU battery is not normally made during her only two above mentioned uses as we can imagine.

[RR_NDB]

TURIN,

With a diode module between the battery and the DC bus you have an automatic switching that inserts the main battery in the bus WHEN THE BUS VOLTAGE IS BELOW BATTERY MINUS DIODE VOLTAGE DROP. To keep the 32 V battery "disconnected" the bus voltage must be operating above 33,5 V or so.

What is the typical Voltage in the bus?

Mac

[Lyman]

Short circuit would degrade the poly over time, due heat, so I am interested in the end cap integrity. Also, wouldn't Li metal tend to aggregate at the 'top'' of the cell, across the plate(s)? Are these cells three wound plates, or one continuous? The NTSB lab table appeared to have several 'unrolled' plates on it.

The NTSB briefing definitely looked scripted, the questions most definitely so. Nothing asked that wasn't covered in PPRuNe by the third day of grounding, imo.

This is a once in a lifetime opportunity to see how things work at this level of government, commerce....Boeing finally figured out the advisability of staying quiet. They may be minus a few people, those who spewed like electolyte...

I am annoyed at the unprofessional use of the language. Not even Hersman seems to know the difference between "How" and "Why"....

It is what it is....

[RR_NDB]

Bear,

I will love to see politicians being short circuited.

The best would see being grilled by the bouncing of what they say.

A lot of electricity in the air (augmented by comments not backed by good technicians)

Indeed, a lifetime oportunity.

[syseng68k]

RR_NDB


Question: How many amps the thin white wires could carry without being transformed in fuses? 1 amp? By pass?
From the image, it looks like those cables are 2-5A rated, but difficult to say
for sure.

There's no sign of power semiconductors and heatsinks on the pcb's though, which
mitigates against the idea of cell balancing electronically. Power dissapation is related
to voltage and current. Consider the following:

Fast charge rate: 65Ah / 1.5hours = 43 Amps + say 10% for losses = 47 Amps,
Say 50Amps absolute max.

Balance current 5% of charge current worst case (from saptzae) = 2.5Amps

Cell voltage = 4.2V max

So, worst case power dissapation in the bypass circuitry would be: 4.2 x 2.5 = 10.5W, per cell.

You would need 8 power semiconductors for the whole battery, together with associated heat sinks and there's no evidence of this on the pcb's...

Just to complete the loop on voltage sensing, you would need 2 sensing wires
per cell, or 16 wires total for 8 cells...

Regards,

Chris

[Lyman]

FAA made a mistake with Lithium, and they know it. It is such a seductive technology, who wouldn't want it integrated with such a groundbreaking airplane (787)....

In reading the considerations, the motive for allowing the LiIon battery is clear, Economics, not airworthiness, or safety.

It reads like a waiver without a safe foundation, written to ennable an experiment in commercial carriage

That is not the FAA's purpose. The purpose of the FAA is to say NO....until safety is satisfied...

How do we know? Because the AD makes it plain that their mission was avoided.

They were not satisfied with Lithium safety from the beginning, all the considerations are written to prevent fire.....or to mitigate one that starts

Which makes perfectly obvious they are allowing the possibility of fire for a system that is not critical to safety, to flight, or to their mission, only to money

Now that the horses have bolted the corral, they command Boeing to "demonstrate the safety of the system" while allowing, in their initial approval, for unsafe conditions they now say are insufficient?

Hersman is correct, fire is not expected. She must not have got the memo from FAA....

[RR_NDB]

Bear,

I was also in love with her, until my son started to use the dangerous units in his RC models. He was not allowed to recharge it inside our home.

(These batteries reminds the joke on why hurricanes were named with female names.)

Chris,

FAA authorizes, Thales offers the "seductive" batteries to Boeing, Securaplane design solutions, Yuasa offers the cells, PCB´s are manufacture (OEM) and the mix is integrated in 787 with algorithms, protections, etc.

The mess starts. The politicians go to the stage (visibility)

Who is the ultimate responsible for the losses?

No problem...you can socialize (the losses). This was made since 2009 crisis.

Irony: A backup part (main battery) and the other to start an AUXILIARY power unit.

In a highly redundant (seems truly a dream in this respect)
(innovative electric plane-even bleed air app., windmill gennies in engines, etc.)

Batteries power is just 2/1000 of A/C power)

Sad

[Lyman]

My issue is with the regulation, not the technology. The ironic part is the steps needed to mitigate risk in a system that is required to provide safety in an emergency. Once (re)Airborne, the fleet could fly fifty years without primary power system fault that requires interruption with a system that has grounded the fleet due its own failures. In its first year of service.

Short sighted, sloppy, weak, ignorant.

It is patently clear the original rules were woefully lacking, even permissive instead of restrictive....

There is a warning label in Commerce: "Cannot be made SAFE".... By the time Boeing demonstrates a hefty ceramic battery vault with poured in place conductors, pressure sensing exhaust that dumps into the airstream, and cooling systems that have to work nonstop, with controllers and motors that are shielded from electrolyte, ad nausea, small nuclear reactors will power us about the heavens.

[RR_NDB]

Bear,

Remembering the "wise" words on 999% or similar. (Boeing could need US Treasury funding). Better to "fire" Li Ion and revert to Ni Cd´s...

I am curious to learn on the conditions of the other 94 batteries in the other (47) planes. This may solve more easily the puzzle. Just CT can show a lot. And the surviving ones could be used again. For APU.

Technical point:

Why not have a mix of Li Ion and Ni Cd´s:

If a EFFECTIVELY PROTECTED Li Ion fails a smaller Ni Cd enters in the circuit. This can be easily made in the A/C main battery section.

For APU it could be adequate the Li Ion (after the review)

[Machinbird]

Hersman is correct, fire is not expected. She must not have got the memo from FAA....
Lyman
If you will recall, NTSB is independent of FAA, and makes recommendations as they see fit on incidents that are within their purview. These also include rail, highway and pipeline incidents.

FAA is the agency that is responsible for safety of flight. Sometimes those areas of responsibility conflict.

Hersman's statements were a careful summary of what they actually knew to date (which is not all that much), and how they intended to proceed.

[Lyman]

I am interested in the point you are making. What is it?

Hersman is being exceedingly kind to the FAA and their huge problem.

Hersman cannot say: "Fire is not allowed". Yet in a piece of non critical kit that has a history of spontaneous combustion FAA are allowing an expectation of fire. In their poorly worded 'release to service' of this problematic technology, my favorite is that any combustion/damage may not exceed a sphere of 56 inches. Not "Contained" but exceed

As if a fire is somehow self limiting to a certain volume, excluding flame from other, more critical, systems'.

This is a BACKUP BATTERY, not a generator (of which there are six), or a brake system, or......

Boeing demonstrated no need for the Lithium Battery, none, not even an honest statement that it would be light, energetic, and sexy in a brochure.....

The goat in my post is FAA....not Hersman. :ok:

[cwatters]

With a diode module between the battery and the DC bus you have an automatic switching that inserts the main battery in the bus WHEN THE BUS VOLTAGE IS BELOW BATTERY MINUS DIODE VOLTAGE DROP. To keep the 32 V battery "disconnected" the bus voltage must be operating above 33,5 V or so.

Interesting point. Is is just a diode? Lithium cells can be damaged by over discharging. I would hope there was something that protected the battery from feeding the bus via the diode if the bus voltage was too low for some reason. eg I would hope it's not a simple diode but a diode and an electronic switch with under voltage detection.

You have to be quite careful about recharging a lithium battery that has been allowed to go too flat.

[Lyman]

It is a backup system, please tell me it must be selected, and is not "inadvertent" or "automatic"?

Also, Why only two Batteries? If both are "back up" what starts the show?

Back up batteries are used casually in line-service? Come on......

The reason we know? FAA requires a minimum charge for dispatch.

That is a sign that this battery needs to maintain a minimum energy for definition of its role. I don't think they are saying "Charge it before Launch".

"EMERGENCY USE ONLY" comes to mind....

[Machinbird]

After looking at the picture of the exemplar battery in the NTSB report, one thing puzzles me about the smaller monitoring wires. There appear to be 3 wires that are attached to electrically potential-equivalent points on each inter-cell junction.:confused:

One on a cell connector on one side of a battery cell, one on the interconnector that connects to the next cell, and one on the cell connector on the other side of of the interconector. (Hope that is clear)

I cannot believe that these wires are all measuring potential. Some of them are either shunt wires or serving some other function such as temperature monitoring (although how that might happen is not obvious)

[syseng68k]

Lyman


Boeing demonstrated no need for the Lithium Battery
I'm not sure about that. I read somewhere else that there is system / operating
requirement that the APU battery be fast charged over a time scale and at a rate
that would not be possible using lead acid or nicad.

Engineering of this type has nothing to do with emotion, seduction etc, other
than the usual designer's passion to do the job right :-).

Who knows what we will be told though. With so many $ at stake, some of the
vendors could be bankrupted if found to be at fault...

Regards,

Chris

[saptzae]

@Turin

The APU AC BUS can be tied to the L and R AC busses.
Thank you. That eliminates the bus as the culprit at BOS. Cause of other cells destruction is down to the charger, continuing to power the battery after failure of #3, or purely thermal.

[saptzae]

@Machinbird

After looking at the picture of the exemplar battery in the NTSB report, one thing puzzles me about the smaller monitoring wires. There appear to be 3 wires that are attached to electrically potential-equivalent points on each inter-cell junction

Redundancy of sensing and balancing?

Edit: Upper PCB looks like for control and sensing. Lower PCB for balancing. Seems to be a lot of electronics for this functionality.

[RR_NDB]

Hi, cwatters (#199)

I yet expressed my concern on the max current the main battery is alowed to supply the DC bus. In an earlier post we discussed the issue.

Points to mention:

1) As confirmed by TURIN there is a diode module easily understood as the switch that put the (charged) battery in the bus. I agree with your concern that a limiter is important. I consider ESSENTIAL when using these dangerous batteries, let´s say, DANGEROUS CELLS. Even with superb circuitry they will remain DANGEROUS.
2) A limiter to be safe must be integrated to the System Software (unless you put a FE in the cockpit). Which are the priorities when the bus needs the help from the (main) battery?
3) As i understand the Battery charger is connected BETWEEN the battery and the diode module. The management of the best configs in a degrading scenario is not so simple.
4) And you must always respect the weakness and criticality of the dangerous cells. Who in the project made the algorithms ? (required and certainly existent). Boeing or a partner?

Integration teething pains? Or nightmare?

[syseng68k]

Machinbird


After looking at the picture of the exemplar battery in the NTSB report, one thing puzzles me about the smaller monitoring wires. There appear to be 3 wires that are attached to electrically potential-equivalent points on each inter-cell junction.
There was a brief explanation in post, #177 but put more simply, the use of
two wires to each cell isolates that cell measurement from any interaction with
the other cell voltages and currents.

Also, wires may be dualled in some places to provide redundancy against a
single wire break. This would also allow diagnostics to detect a broken wire.
Such dualling is not uncommon...

Regards,

Chris

[RR_NDB]

Hi,

Machinbird (#201)

Redundant wiring...

What the designers made is still beyond my imagination.

The thin wires, over the cells, the connectors used and TWO PCB´s all inside the chamber where the hot cells are is UNBELIEVABLE.

[Lyman]

syseng68k

Quote:
Boeing demonstrated no need for the Lithium Battery? (sorry, my quote)

You reply...I'm not sure about that. I read somewhere else that there is system / operating requirement that the APU battery be fast charged over a time scale and at a rate that would not be possible using lead acid or nicad.

And, they would not have. If FAA requires a performance level that cannot be met with current technology, then they have gone into the design business. And Boeing would not design an aircraft that could not be built under current regs. Would they build a bird that was dependent on concurrent rule change? No, the rule predated the design...

If that is the case, the Dreamliner is dead. It is at least cemented in concrete to Lithium....because without back up electric, no current a/c can be airworthy. And if 787 won't certify with anything but Lithium.....

Maybe the bridge back to NickelMH burned in the EEbay?

[syseng68k]

What the designers made is still beyond my imagination.

The thin wires, over the cells, the connectors used and TWO PCB´s all inside the chamber where the hot cells are is UNBELIEVABLE.
...yes and if the battery data logging is on those boards as well, then the audit trail
for the death of the battery is lost forever :eek:

How that ever got past systems engineering beats me...

Regards,

Chris

[saptzae]

@RR_NDB

The thin wires, over the cells, the connectors used and TWO PCB´s all inside the chamber where the hot cells are is UNBELIEVABLE

As to electronics in the same box, I prefer this over adding another box. The wiring to it could not practically be protected.

I am still trying to understand the failures.

Could one make the thing simpler and thereby safer? Perhaps.

[RR_NDB]

Hi,

On the 6 wires attached to ea. one battery terminals (strips) we may comment:

1) They measured the voltage in the best circuit points. Inside the battery and directly at cells
2) Redundancy may explain half of the wires (triple) with a voting scheme.
3) Other 2 (1 in ea. strip) could be to simplify the measurement of the adjacent cells voltage (near to minus and plus battery terminals)
4) The remaining two could be the mentioned bypass.

IMHO the matching using bypass is not the best way as emphasized when comment on much safer parallel charging.

[syseng68k]

saptzae:


As to electronics in the same box, I prefer this over adding another box.
The wiring to it could not practically be protected.
In fact, you don't need another box. There's already a multipin connector
back to the charger and one would expect the battery sensing and management
electronics to be in the charger enclosure, not at the battery, where it's
vulnerable to cell leakage.

Imho, the only things that should be in the enclosure are the cells and
perhaps a small pcb supported by the connector, carrying inline fuses to
protect critical wiring.

We just might have to agree to differ on this one, but it all helps the
enquiry :-)...

Regards,

Chris

[RR_NDB]

Hi saptzae,

They could use separated chambers. The sensing AND the preprocessing of the voltages and temperature as you know is highly CRITICAL. The connectors used inside the same enviroment is a weak point. The harness (testability) another issue.

The failure of both batteries perhaps can be explained by the only thing common in both incidents. The battery itself. Heat and electrolyte leakage conpromising this circuitry not adequately located.

[RR_NDB]

Hi,

Chris @ #209

Indeed. We can strongly suspect we lost the information. Why?

If the measurement is conpromised (as happens in Pitot icing) the recorded parameters are useless.

We will need better ways to monitor these Dangerous Cells in order to allow the to be used in airliners.

Still LOL´ng on the "999% required"

[mm43]

Imho, the only things that should be in the enclosure are the cells and perhaps a small pcb supported by the connector, carrying inline fuses to protect critical wiring.I suspect the reason for the present arrangement is to keep the battery management system intrinsic with the cells that it controls. Additional and unquantifiable ohmic losses could present a significant problem for remote monitoring.

[RR_NDB]

mm43, (# 215)

With the "guarding" config (Kelvin bridge) and other alternatives you can do it precisely and reliably very far.

Regards,

[RR_NDB]

Bear @ #208

The retrofit to Ni Cd is (technically speaking) ABSOLUTELY POSSIBLE.

Problem is problems are mounting and the technical aspect is one among other.

The Review is IMO the major issue.

A virtual stalemate was created with the threat to make everybody loose.

And the chances to precisely identify what led to BOS fire and TAK smoke are not 100%

[hetfield]

I'm afraid, no RC jockey would buy a LiPo battery with this architecture for a 100 USD modell plane.

[HazelNuts39]

There appear to be 3 wires that are attached to electrically potential-equivalent points on each inter-cell junction.Yes, and there are 7 such inter-cell junctions. There are also 7 wires at each of the two remaining battery terminals. That seem to be all 35 wires of the visible battery harness in that picture. So where are the temperature sensors?

[Lyman]

RR_NDB

Possible in every way but one? If Boeing utilizes the Licell pursuant to the "waiver" (the 'restrictions') because their design cannot accomodate NiMH, then they cannot even propose it.

They then sink or swim with LiPolymer. To do that, they must redesign the entire technology. They then have to show, against existing prejudice and accident history, that LiPolymer is safe, to a degree established by the authority that put them on the ground.

Why are the cells wrapped rectangularly? From a geometric standpoint, why not cylindrical? Flattening a two phase material roll creates build at the edges, and ooze at the ends. Why conductors at the top, not the side? Why stacked chock a block in a cube, instead of nested in a "honeycomb, horizontally? Why then a conductor for a case, and not a cast ceramic vault?

A thin layer of plastic to isolate the looms from solid metal conductors, so the insulation fails, and the sensing and control looms all short together?

A lash up, suitable for Mickey Rooney's soap box racer?

[Machaca]

That seem to be all 35 wires of the visible battery harness in that picture. So where are the temperature sensors?

37 on the upper harness.

The lower harness (narrower connector on lower left) likely runs to a temp sensor under each cell.

[syseng68k]

MM43, #215


I suspect the reason for the present arrangement is to keep the battery
management system intrinsic with the cells that it controls. Additional
and unquantifiable ohmic losses could present a significant problem for
remote monitoring.
The remote monitoring isn't a problem, but it may be that the reason why
the electronics and (?) data logging are in the enclosure is that system is
designed with enough storage capacity to log the whole life of the battery.
If it's in the charger, there has to be a process to ensure continuity and
accuracy of existing data. If either the battery or charger are replaced in
service, the logged data will no longer match that for the battery. It's
issues like that that can make system design so complex, trying to resolve
all the conflicting requirements.

Still doesn't excuse the unprotected boards though and they should have at
least used a separate sealed compartment, as RR_NDB suggested a couple of
posts prior to yours...

Regards,

Chris

[Lyman]

I think first off it is cheaper to build as a compact unit, secondly, it is easier (cheaper) to R/R as a unit and third, it conforms cleanly with the spirit of the FAA rule to isolate the pack (all of it) away from other EE equipment, in case of fire, expansive failure (explosion), electrolyte spatter, and draining thereof.

Y'all have done a great job of describing how better to build it. Know this, Boeing knows this as well. But they built it the way they built it.

The reason? Also an interesting discussion. For one thing, LRU....

[archae86]

Not that there is much meat there, but in case of interest there is a Sunday press release (http://www.ntsb.gov/news/2013/130127.html) which is being reported in some press as exonerating the charger. It reads to me more like they ran through tests of electronics removed from the incident JAL aircraft at the manufacturers' sites without finding a detectable fault.

This does go some way to saying the units were not faulty compared to intention. It does nothing to allay concern that the design as intended might place eventually intolerable conditions upon the battery--at least that is my view.

[RR_NDB]

archae86:

...at least that is my view. (http://www.pprune.org/tech-log/505695-787-batteries-chargers-12.html#post7659941)

Just abuse. That is my feeling too.

The analysis of the remaining (94) batteries could clarify very well.

Rgds,

[Machaca]

NTSB Update on JAL Boeing 787 Battery Fire Investigation (http://www.ntsb.gov/news/2013/130127.html)

January 27

WASHINGTON - The National Transportation Safety Board today released a fourth update on its investigation into the Jan. 7 fire aboard a Japan Airlines Boeing 787 at Logan International Airport in Boston. The fire occurred after the airplane had landed and no passengers or crew were onboard.

The event airplane, JA829J was delivered to JAL on December 20, 2012. At the time of the battery fire, the aircraft had logged 169 flight hours with 22 cycles. The auxiliary power unit battery was manufactured by GS Yuasa in September 2012.

NTSB investigators have continued disassembling the internal components of the APU battery in its Materials Laboratory in Washington, and disassembly of the last of eight cells has begun. Examinations of the cell elements with a scanning-electron microscope and energy-dispersive spectroscopy are ongoing.

A cursory comparative exam has been conducted on the undamaged main battery. No obvious anomalies were found. More detailed examination will be conducted as the main battery undergoes a thorough tear down and test sequence series of non-destructive examinations.

In addition to the activities at the NTSB lab, members of the investigative team continue working in Seattle and Japan and have completed work in Arizona. Their activities are detailed below.

ARIZONA

The airworthiness group completed testing of the APU start power unit at Securaplane in Tucson and the APU controller at UTC Aerospace Systems in Phoenix. Both units operated normally with no significant findings.

SEATTLE

Two additional NTSB investigators were sent to Seattle to take part in FAA's comprehensive review. One of the investigators will focus on testing efforts associated with Boeing's root cause corrective action efforts, which FAA is helping to lead. The other will take part in the FAA's ongoing review of the battery and battery system special conditions compliance documentation.

JAPAN

The NTSB-led team completed component examination of the JAL APU battery monitoring unit at Kanto Aircraft Instrument Company, Ltd., in Fujisawa, Kanagawa, Japan. The team cleaned and examined both battery monitoring unit circuit boards, which were housed in the APU battery case. The circuit boards were damaged, which limited the information that could be obtained from tests, however the team found no significant discoveries.

Additional information on the NTSB's investigation of the Japan Airlines B-787 battery fire in Boston can be found at Accident Investigations - Boeing 787 (http://go.usa.gov/4K4J).

The NTSB will provide another factual update on Tuesday, Jan. 29, or earlier if developments warrant. To be alerted to any updates or developments, follow the NTSB on Tw!tter at www.twitter.com/ntsb.

[Machaca]

Hopefully the ANA circuit boards are in better condition and yield clues as to why the protections failed.

[RR_NDB]

Lyman:

From a geometric standpoint, why not cylindrical? (http://www.pprune.org/tech-log/505695-787-batteries-chargers-11.html#post7659883)

Unfortunately we can raise a lot of questions. It´s a sad surprise the problems for the program. :{

[EEngr]

A cursory comparative exam has been conducted on the undamaged main battery. No obvious anomalies were found. More detailed examination will be conducted as the main battery undergoes a thorough tear down and test sequence series of non-destructive examinations.

Just the one battery? I'd want to see a statistically significant sample from the entire fleet. All would be even better, but there may not be lab time to do that many detailed teardowns.

[saptzae]

@EEngr
I'd want to see a statistically significant sample from the entire fleet

Yes, and of the ANA batteries. CT first, whether cells show bulging, a pattern (streaks) like the four cells on the left of the JAL APU battery at BOS. (pix linked #173), or other anomalies.

I sign off until more info is made public.

[Lyman]

If the cells are cylindrical, bulging is better tolerated, without impacting an adjacent cell. The spaces between cylindrical cells allow for containment of electrolyte if some spills. Also cooling air, if so equipped. Even liquid coolant could be used, under low pressure. "Density" has limits....

[RR_NDB]

Hi,

AD Requirements:

This AD requires modification of the battery system, or other actions, in accordance with a method approved by the Manager, Seattle Aircraft Certification Office (ACO), FAA. (http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgAD.nsf/0/8a1a8dc3135b60dd86257af60004cf4a/$FILE/2013-02-51_Emergency.pdf)

Blog of John Delisi (http://safetycompass.wordpress.com/)

[ross_M]

I'm placing my bet on "software bug".

[hetfield]

Whoever has to pay the bill...., no peanuts:\

[Lyman]

If Miss skinnybones had two other batteries, on line, the Back Up batteries could be saved for what they were intended for, abnormals.

Making up a complex system of charging and monitoring two emergency batteres to save the weight of two standard issue batteries has cost, so far, how much?

[mono]

Lyman. The batteries may also be required for (fairly) normal ops. You're forgetting a reasonably common scenario. Powering up a dead aircraft! While it may not happen that often there are certainly cases where the aircraft will be powered up using batteries alone. Allowing for a start sequence of perhaps 90 seconds and certainly massive current draw on the APU battery, it will be seriously depleted after an APU start. This is why it needs to be charged rapidly.

Your comments on this display a lack of knowledge of airline operations & battery construction techniques among other things.

As a general winge I'm also amazed at the rampant speculation and even conspiracy theories displayed in this thread. Let the NTSB do their job then perhaps we can speculate as to how Boeing will remedy the problem. :ugh:

[syseng68k]

As a general winge I'm also amazed at the rampant speculation and even conspiracy theories displayed in this thread. Let the NTSB do their job then perhaps we can speculate as to how Boeing will remedy the problem.
You always get a certain amount of noise in a public forum, but I think the
majority here are genuinely curious as to what went wrong. Also, possible
design flaws have already been exposed. Just as open source software is often
of better quality than the so called pro stuff, forums like these often have much
more of a clue as to what's what because of the wide range of skills and
experience of the contributors.

The spirit of enquiry, enquiring minds want to know etc :-).

If you think this is bad, you should try the newsgroups, where flame wars are an
everyday event...

Regards,

Chris

[syseng68k]

I posted this in rumours and news by mistake, but really a followon from the
previous post #222:

Just a few more thoughts:

If a $100 Terrabyte pc drive can have smartmon predictive failure and
usage logging, one would certainly expect it to be built into a
critical component such as the battery subsystem. Such diagnostics
are built into a wide variety of kit as standard practice these days.
On power up self test, the battery and logic can be tested before
allowing it to be brought online to charge or load. Such built in test
and monitoring should also be able to predict cell failure due to changes
in characteristics.

The fact that there's been no news about this suggests that either
a) It's not built into the design, or b) The function was on the internal
boards that were cooked in the fire. In either case, not very helpfull.

Otherwise, it would logically be the first place to look for the events
that led up to the failure. Mysterious indeed...

Regards,

Chris

[RR_NDB]

ross_M:

I'm placing my bet on "software bug". (http://www.pprune.org/tech-log/505695-787-batteries-chargers-12.html#post7661294)

Certainly there are algorithms "conditioning" the cells. :8 :}

The dangerous cells were pushed too far? During recharge?

[old dawg]

Read through all the various threads here with interest, and I am equally curious about the charging system.

I am an engineer although these days tend to manage others who build various systems. At one time in my career I was an EMC engineer and set up tests to try and break military comms systems using Conducted Susceptibility and Radiated Susceptibility test techniques. Doing this sort of work makes one think about systems and how they are influenced by various electrical signals, intended or otherwise. Any test of equipment or a system is only as good as the test parameters and the boundaries set.

I wonder, and this is maybe speculation, if there is a possibility of cumulative degradation of a component under some form of electrical stimulus. One example of something like that occurred in the shipping industry in 2010. Link to report enclosed.

Marine Accident Investigation: QM2 (http://www.maib.gov.uk/publications/investigation_reports/2011/qm2.cfm)

[RR_NDB]

Hi,

syseng68k:

The fact that there's been no news about this suggests that either
a) It's not built into the design, or b) The function was on the internal
boards that were cooked in the fire. In either case, not very helpfull.
Otherwise, it would logically be the first place to look for the events
that led up to the failure. (http://www.pprune.org/tech-log/505695-787-batteries-chargers-12.html#post7661457)

c) Or this will surface soon. I hope!

The alternate way will be "look" to the other 47 planes and related batteries.

As what was commented earlier by EEngr (http://www.pprune.org/tech-log/505695-787-batteries-chargers-12.html#post7660207)

Mysterious indeed...
Anxiety mounting...

[EEngr]

c) Or this will surface soon. I hope!There are two nations' regulatory agencies involved in the preliminary investigation. And some of us have multiple agencies with skin in the game (NTSB, FAA). And getting through the layers of subcontractors resembles peeling an onion (tears and all:{), I'm wondering how soon 'soon' will be.

Back when I worked at Boeing (and we still had some involvement in the design game), I could run down the hall and go talk to some engineer responsible for another subsystem. Maybe dash off a memo to record things. But once we adopted the outsource everything model (thanks, McDonnell Douglas), the equivalent communications had to go through 'proper channels' to ensure contractual compliance.

It would be interesting to see if the same is happening now. That is: Does the NTSB receive data from the actual responsible parties directly? Or does it have to work its way through both the contractual and international regulatory maze?

[TURIN]

RR_NDB.
The diode module is not "the switch that puts the bat on the bus" as you say. The diode module is between the bat and the hot bat bus. The hot bat bus is only connected to a main DC Bus when there is no other supply and the bat switch is on. The bat is not discharging unless there is a power failure of the main DC busses.
Hope this helps.



Posted from Pprune.org App for Android

[RR_NDB]

Hi,

old dawg and EEngr

Both comments makes me remember on Testability. I was concentrated on that issues on System, PCB and IC (LSI) level during many years. And i always had a great interest because worked before in Maintenance where i observed many difficult situations and even some unexplained facts "coming from design". Actually i designed for Testability, many items.

Both comments from you make me present the questions:

1) The batteries were subjected before to the same (routinely) conditions the 787 fleet experienced? Or even more demanding (routinely) concerning charging current, discharging current and temperature?
2) Are these batteries being exposed TODAY to this conditions in the Lab? (Yuasa or Thales) Or we would need to analyze the 94 remaining batteries.
3) In this case WHO would lead (and pay) the work?
4) The new battery (first use as main in an airliner) was equipped with enough data logging in order to analyze it´s performance after incidents or accidents?
5) Considering the current batteries are not just "cells in a package" how to manage the required work to explain WHY both cases happened?

Time is the only Testability "solution" really effective*. We never know how new components will perform in real life. Time proven parts are required in critical subsystems.

The Test Engineers responsible fort he new battery so important for a ~ US$40 Billion program indeed had a very complex and important task.

And the Decision Making (inside Boeing) was a critical, very critical one.

I hope someone is properly testing the Thales batteries right now.

(*)Yes, i know the JAL (main) battery was very young.

It would be interesting to see if the same is happening now. That is: Does the NTSB receive data from the actual responsible parties directly? Or does it have to work its way through both the contractual and international regulatory maze?

Could this be a cause for a virtual stalemate? And prolonged grounding?

TURIN, important detail. Will comment in few minutes! (http://www.pprune.org/tech-log/505695-787-batteries-chargers-13.html#post7661801)

[RR_NDB]

Hi,

TURIN:

The diode module is not "the switch that puts the bat on the bus" as you say. The diode module is between the bat and the hot bat bus. The hot bat bus is only connected to a main DC Bus when there is no other supply and the bat switch is on. The bat is not discharging unless there is a power failure of the main DC busses. (http://www.pprune.org/tech-log/505695-787-batteries-chargers-13.html#post7661801)

Exactly what i expected! And showing a VERY GOOD APPROACH used by the colleagues. :)

First a briefing on the DIODE (http://en.wikipedia.org/wiki/Diode) function. Actually it is a SWITCH. A fast switch. What flips the switch? The voltage between the 2 (only) terminals. They are used as switches since the beginning. (there are other uses).

As i can imagine in 787 main battery circuit the diode has the (Safety) function:

Make impossible the DC bus charge the main battery. This as i commented earlier would not be the safer way to charge the critical cells. Reasons: The bus voltage varies (due varying loads on it) and the current management (to charge the battery) would require a more complex and costly scheme. They designed very well, imho.

As i can imagine the designers put a redundancy (wisely) with 2 "means" to turn off the battery, as you made implicit. I probably would design exactly the same. :)

The switching function i mentioned in earlier post actually is the inherent diode function:

When the bus falls below (i estimate ~ 30 V) the battery power (kept at it´s top-nominal capacity by a charger certainly connected between the diode module and the battery) flows AUTOMATICALLY to the bus. As we may imagine, several important modules would die (reset) if the DC bus fails. The bus voltage would be not less than battery voltage level (decaying) minus the diode module voltage drop (less than ~2 Volts).

To be continued

In the meantime please comment on RAT and it´s relation to the important DC bus.

[bjm_bi]

I'm brand new here and am neither a pilot nor an engineer. But I have a strong interest in the 787 problem -- and in a solution -- and have found this board very informative.

This is from the Securaplane website:
"Securaplane battery chargers store every fault including battery over-temperature, cell unbalance, defective temperature sensors, defective charger/battery connection and GMT time/date of fault period. Our chargers possess extensive diagnostics such as charger microprocessor status and permanent memory of faults with readout to the integrated 8-character alphanumeric display."

My question: I haven't seen anything in the press or on this site (unless I've missed something) about whether the diagnostic information from the charger(s) is available and, if so, whether it has been helpful. Do any of you have knowledge or comments?

[RR_NDB]

Hi,

From the blog of John DeLisi, NTSB chairman:

During the 777 investigation, British Airways provided data on about 1,000 previous Beijing-Heathrow flights flown by 777s. The data showed that the accident flight flew at a slightly higher altitude during slightly colder-than-normal temperatures. But what really stuck out was that the accident flight descended largely with its engines in idle – unlike most of the other flights. (http://safetycompass.wordpress.com/2012/11/28/how-data-on-successful-flights-can-solve-accidents/)

787 case seems could require (and benefit from) the same approach.

How many months? :confused: :mad:

[FlightPathOBN]

I would call them a flow gate before calling them a switch! :}

[syseng68k]

EEngr:


Back when I worked at Boeing (and we still had some involvement in the
design game), I could run down the hall and go talk to some engineer
responsible for another subsystem. Maybe dash off a memo to record
things. But once we adopted the outsource everything model (thanks,
McDonnell Douglas), the equivalent communications had to go through
'proper channels' to ensure contractual compliance.
But would that stop you from calling the engineer to have an informal
chat, then formalise the results later to keep the paperwork straight ?
If not, how do you ever finish any complex multivendor project if even
a nut and bolt change has to go through formal channels ?.

Sounds familiar though. It can be bad enough within the same organisation.
I worked on a project with a large multinational computer company.
We were building a special system for a large customer. The computer
board had onboard firmware to allow bootstrap from a variety of hardware
devices and we needed to add some code to allow boot from an
unsupported device. The division that made the processor board were
in the US (we in UK) and flat refused to supply the source code. It
was only with the intervention of a very senior manager that we gained
access. Crazy, both working for the same company and assumed to be
working for the common good of the company.

Brookes wrote a book about big project management called "The Mythical
Man Month", iirc, in the 1970's, about software project management within
IBM. Well worth a read, software or not, even now...

Regards,

Chris

[FlightPathOBN]

Investigators starting focusing on how the engines behaved during long periods of idle in cold temperatures. And they found that an icy slush can build up on the fuel/oil heat exchanger, blocking fuel when the throttles are then increased. That finding led to new procedures and then a new design fix.

so much for RNP idle descent...

I knew it was a bad idea! :\