787 Batteries and Chargers - Part 1

[RR_NDB]

FlightPathOBN:


so much for RNP idle descent...

I knew it was a bad idea! :\ (http://www.pprune.org/tech-log/505695-787-batteries-chargers-13.html#post7662211)

:ok: :):)

[RR_NDB]

syseng68k:

It was only with the intervention of a very senior manager that we gained
access. (http://www.pprune.org/tech-log/505695-787-batteries-chargers-13.html#post7662170)

Lessons from the GURU (GE)

http://www.deansutton.com/wp-content/uploads/2012/01/jack-welch-300x200.jpg

Jack Welch (https://www.google.com.br/url?sa=t&rct=j&q=&esrc=s&source=web&cd=8&cad=rja&ved=0CHIQFjAH&url=http%3A%2F%2Fwww.focusadventure.com%2F25_lessons_jack_we lch_ten3_minicourse2.ppt&ei=siwHUdeML4uy9gS4rYGQDg&usg=AFQjCNEbFXS9Ks8w9fWtLzH4DUL3M-dv0g&sig2=PmXcc71tahyLOCIxE8RPiA&bvm=bv.41524429,d.eWU)

“Formality is the most silly thing in the world. Bunch of pompous bureaucrats! Formality slows a company down. Change is what excites people. If you’re stagnant, you’re dead. You’ve got to get people to embrace change, and not be paralyzed by it. People want CEO’s that care. Authenticity is enormous. Candor counts.”
(http://www.deansutton.com/jack-welch-formality-is-dead-change)

Question:

How to proceed with world wide outsourcing in a threatening scenario?

[RR_NDB]

Hi,

Li Ion cell operating window

http://www.mpoweruk.com/images/lithium_window.gif

Cycle life and temperature

http://www.mpoweruk.com/images/age_temperature.gif

"...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"
(http://www.mpoweruk.com/lithium_failures.htm)

Source (http://www.mpoweruk.com/lithium_failures.htm)

So, why they are wonderful for a new design? They "seduce". :) The performance is because they are "tuned".

If dangerous (critical) in airliners (air conditioned)...:} I prefer not think they working in GA. :{

[RR_NDB]

To be reviewed

Hi,

787 innovative design introduced Li Ion as main battery for the first time in (av) industry. We may think the battery will sit and wait most of their lifetime "waiting" for an emergency" in the DC bus. A very rare (very low probability) event.

If it happens how we can guarantee it will be able to supply the required power to the bus. (If it is not being used). Redundant elements (kept "offline") poses a Testability problem to the designers.

I don´t know how Boeing dealt with this issue. You may apply short duration pulses (discharge) to the cells to check it´s voltage "under "heavy" load.


The harness showed in battery pictures could be connections to the many cells and constituents of a BITE. We will be able to later verify that. The Built In Test Equipment could also be used to limit the cell voltages considering the series charging requires it due cells mismatch in the stack.

To be reviewed

[ross_M]

A Stuxnet equivalent that piggybacks on the charging circuitry software logic? ;)

[fuelevaporator]

temperature sensors are never sitting at hottest spot and in this case they are sitting far away of this hottest spot I would expect in the middle of the cell.

now provoke a rapid thermal runaway by eg provoking short circuit in the center of the cell.

compare real temperature in the center of the cell with temperature measured at now given location to find out difference of these temperatures.

if measured temperature at given position eg shows 80 degrees when real temperature runs through critical tmperature adjust charging soft- or hardware and figure out how much energy content the battery still has compared to minimum required.

fly if still sufficient or go for bigger batteries...

[RR_NDB]

ross_M:

A Stuxnet equivalent that piggybacks on the charging circuitry software logic?

:)

OTOH in an investigation EVERYTHING must be verified. (Trust but verify)

[RR_NDB]

fuelevaporator:

Certainly both batteries failed (thermal runaway) when "floating"

And thermal inertia (delays, sensor location, etc.) were not important.

:confused:

[saptzae]

Cells not found at fault, so far, so good.

From: Japan shifts Boeing 787 investigation from battery maker | HeraldNet.com - Work (http://www.heraldnet.com/article/20130128/BIZ/130129828)

Ministry officials said they will inspect Kanto Aircraft Instrument Co. on Monday as part of the ongoing investigation. It makes a system that monitors voltage, charging and temperature of the lithium-ion batteries.

I guess Kanto is responsible for the PCB's from the bat box.

[RR_NDB]

Hi,

Bjm bi @ (#246)

Welcome. Useful info on Securaplane features.

We may suspect important info was lost from BOS JAL APU battery due fire. Amazingly from the pictures the 2 connectors (PCB) didn´t melt.

We may strongly suspect the information was lost. IIRC NTSB chairman mentioned .PCB destruction.

[USMCProbe]

There are so many things that it could be. I doubt any aircraft has ever produced as much electricity. An airplane is a "floating ground". This many trons running through a machine provides huge opportunities for errors.

Everybody was a hoping for a simple smoking gun. They will find the answer, but when they do, it will probably be a single line of bad code, a single electronic component sourced from a dodgy supplier (China), or something poorly grounded, or grounded in a slightly different place than it should have been.

Almost all the world's lithium comes from China. Maybe somebody added a little "filler" to make a little more for little cost? Maybe a single grounding wire or ground plane has higher resistance than it should? Maybe a single component in the charging and monitoring system reacts poorly to temperature change?

Oh yeah, isn't carbon fiber a good conductor of electricity? Maybe a carbon panel is discharging static electricity into one part of the system, throwing off voltage readings?

Too many possibilities. Good luck to them.

[RR_NDB]

Hi,

USMCProbe:

"Too many possiblities"

We may think on EMI/EMC (groundind and shielding, etc.). I agree.

So far we know:

1) Both batteries went to thermal runaway WHEN FULLY CHARGED.
2) Cell overvoltage (IIRC > 4.025 V) may trigger the runaway to the cell.
3) A single cell runway promotes the runaway of the others.
4) The battery terminals didn´t exceed 32V
5) Recorded data (if) was not available after BOS case.
6) Batteries (main and APU) are rarely used (delivering power)
7) Bus spikes are not an issue. The batteries are not (most of time) "electricaly isolated from the bus"
8) The main battery DIODE MODULE failure could explain ANA case. We may expect the investigators checked it. Takes few seconds to test it.
9) Both incidents have in common the batteries.
10) The cells are serially charged. Evident from the pictures showing the connections to the cells.
(i would decide for a safer PARALLEL CHARGER)

So, we need more info.

[RR_NDB]

Hi

The battery System in both incidents didn´t exhibit the MANDATORY "Fault Tolerance and Graceful Degradation" characteristic.

FAA (and all) expected a much better behavior from TWO battery Systems.

In TAK the plane (due crew prompt action) showed the MANDATORY feature.

In BOS ABSOLUTELY NOT!

The grounding was a natural consequence.

[Lyman]

The landing in TAK (ANA) involved a warning on ECAM. Plus, smell.

SOPS in re: emergency landing would be an interesting discussion. It is a separate issue from the failure of the Battery....

It is in fact the most important issue. WHY? Because nothing about ANA should have caused the a/c to land, the system functioned within FAA RULES.

Likewise UAL, technically even JAL..... Says alot about the rulemaking, imo.

And, the 'legality' of the rules....It is a good foundation for Boeing's theory of defense regarding damages. If they demonstrate the rules were observed, the grounding becomes an unnecessary burden.....

[bjm_bi]

RR NDB,
Thanks for your welcome and reply.

The more I think about it, the more curious I am about the information provided by NTSB on the charger vs. the information provided for the battery (BOS). For the battery, everything -- photos, cat scans, physical access for reporters. For the charger, all I have heard is a general "no problem found".

And if the data collected by the charger has been lost, is that a design problem also?

Thanks to all the participants here. I've learned a lot.

bjm

[grebllaw123d]

I have read all the posts - in this thread and in the other 787 threads, but it has never been mentioned, which exact failure indications were present in the cockpits in the 2 cases.

In the ANA case it was reported that, "the crew received indications of battery problems, at the same time a burning smell developed on board."
OK, but which problems were displayed? Overheat? Fault? Or?
And which indications were there in the JAL case? Same as in the ANA case?
I suppose that this info is on the FDR tapes, but not published yet - but anybody knows?

Which warnings/cautions are there in the B787 cockpit regarding battery issues?
And what actions does the SOP call for?

(I have seen 3 different types of battery failure indication variations in my career: battery fault - meaning charging current outside limits (A340), battery discharge (B767) and battery overheat (F27).)

[RR_NDB]

Hi,

Grebllaw123d @ (#265)

There is a major difference in the 787 electric architeture in respect to the batteries.

In ANA case i would expect:

1) A battery fault warning indicating a failure.
2) A second one indicating battery temperature.
3) A third possible indicating smoke in EEbay

Interestingly to mention DC bus certainly NEVER SUFFERED any influence. (the battery is always OFFLINE if gennies (redundant) are working normally.

The approach to keep the battery "disconnected" brings advantages.

[Uncle Fred]

RR_NDB

Interestingly to mention DC bus certainly NEVER SUFFERED any influence. (the battery is always OFFLINE if gennies (redundant) are working normally.

Is this technically correct? Not having my flight manual at hand for the 777 but I thought the battery was online (so to speak) but just not carrying any load. I know the 777 is a different fish than the 787 but I am wondering why Boeing would have treated the basic battery logic any differently.

I know that offline might be defined as not carrying any load but I am speaking to the physical connection in this case e.g., the hot battery bus.

[Ian W]

Re http://www.pprune.org/tech-log/505695-787-batteries-chargers-13.html#post7662369

Just a simple question. How cold does it get in those battery bays? The diagram you show indicates that the cathode can break down and short circuit not a lot below zero.
The aircraft has flown a long way at high altitude and then parks at Logan in January (not the warmest spot). Could cold temperatures in the electronic bays cause a problem?

[hetfield]

Both E/E compartments on 787 are pressurized and air conditioned.

If the aircraft parks in Anchorage in the winter time for a prolonged period, well that's another story.

[RR_NDB]

Hi,

bjm_bi:

And if the data collected by the charger has been lost, is that a design problem also? (http://www.pprune.org/tech-log/505695-787-batteries-chargers-14.html#post7663350)

It ´s of great interest the tracking of new technologies during the teething period. Considering the low cost for data recording the designers could put the recording chips NOT IN THE SAME BATTERY CHAMBER. This could delay the analysis of WHAT and WHY.

The partition of building blocks should take into account all factors.

[RR_NDB]

Hi,

Uncle Fred:

Is this technically correct? Not having my flight manual at hand for the 777 but I thought the battery was online (so to speak) but just not carrying any load. I know the 777 is a different fish than the 787 but I am wondering why Boeing would have treated the basic battery logic any differently.
I know that offline might be defined as not carrying any load but I am speaking to the physical connection in this case e.g., the hot battery bus. (http://www.pprune.org/tech-log/505695-787-batteries-chargers-14.html#post7663491)

In an earlier post i commented on that. The scarce info we have so far points to a "switching" (automatic and immediate) of the battery (main) to the DC bus through a Diode. Doing that the designers could guarantee the bus will receive energy from the (charged) battery when this is required (when bus voltage starts to drop due any reason). As TURIN mentioned this happens automatically (when battery switch is ON).

I will comment further on that in few minutes.

[RR_NDB]

Hi,

Ian W and hetfield,

All this factors allow us to say we are dealing with critical parts. And they are not showing are "av. friendly". :mad: just the opposite.

When abused (electrically or environment) became furious. :E

[Uncle Fred]

RR_NDB

Good vector. I somehow missed Turin's post. Your and his points are well made--the battery is more or less isolated from providing power unless needed.

That is what I thought you said the first time but I just wanted to make sure that for some odd reason that the 787 did not depart from decades of precedence as to how the busses are powered and when.

I am still mulling over a point you raised on one of the threads (this one perhaps) regarding that unless the aircraft is completely unpowered (no external power for example) or else a serious in-flight degradation of the power supplies occurs, that the battery may never undergo a complete (or near complete) discharge and re-charge cycle. There simply would be no need for it.

There is something about that point that makes one wonder if it in any way relates to the matter at hand. I am afraid I cannot answer that but someone needs to...

[FlightPathOBN]

From what I remember, the system will ground it self automatically to cycle, it is supposed to ground on full charge as well, to never have a full charge...

Isnt the system run through the batteries on a constant flow? (even simply to provide a clean source?)

[glenbrook]

The landing in TAK (ANA) involved a warning on ECAM. Plus, smell.

SOPS in re: emergency landing would be an interesting discussion. It is a separate issue from the failure of the Battery....

It is in fact the most important issue. WHY? Because nothing about ANA should have caused the a/c to land, the system functioned within FAA RULES.

Likewise UAL, technically even JAL..... Says alot about the rulemaking, imo.

And, the 'legality' of the rules....It is a good foundation for Boeing's theory of defense regarding damages. If they demonstrate the rules were observed, the grounding becomes an unnecessary burden.....
Lyman.
I am not sure what you are saying here. That the ANA crew overreacted? That the grounding is unnecessary? Didn't you repost the FAA rules specifically excluding the leaking of elecrolyte and preventing thermal runaway? The crew had strong reasons to believe their battery was on fire, which it was.

[airman1900]

From Flight Global's web site an interesting article titled:

Elon Musk: Boeing 787 battery fundamentally unsafe
by Zach Rosenberg

Elon Musk: Boeing 787 battery fundamentally unsafe (http://www.flightglobal.com/news/articles/elon-musk-boeing-787-battery-fundamentally-unsafe-381627/)

[radken]

Maybe this is aleady mentioned in this thread.... but isn't one of the very real negatives about these LiI batts that they can simply, without any predictability, installed or uninstalled, new or old, suffer an internal short, and instantly dump huge current with resultant explosive arcing---- which will always ignite the flammables inside as well as adjacent cells? Isn't this how the cargo of Li batts brought down that Everglades DC9 about 20 years or so ago?

Isn't shaky batt technology, potential arcing, ignition, uncontained fire, et al, an unnecessarily nasty threat to colocate in the same area with flight critical electronics and thousands of wire pairs all ready to fuse together for the slightest of excuses? IMHO 'twas mostly the bean counters who have created this situation. Engineers would never have thought this up on their own unless forced to do so? Right?

[Machinbird]

Really agree with this statement by Elon Musk as linked in Airman1900's post.
"They believe they have this under control, although I think there is a fundamental safety issue with the architecture of a pack with large cells," writes Musk in an email. [B]"It is much harder to maintain an even temperature in a large cell, as the distance from the center of the cell to the edge is much greater, which increases the risk of thermal runaway."
The shorted cell in the NTSB briefing appears to show exactly this effect, short along the centerline of the battery plates. That is where the temperature sensing devices belong in each battery cell.

[Machinbird]

radken
I believe you have muddied up the details of the Everglades (Valujet) DC-9 crash.
There was a skid of loose oxygen generating canisters that was implicated in that onboard fire.

[USMCProbe]

RR NDB:

The cells are charged serially? I thought early on i read that the cells are charged, voltage and temp monitored, individually. i.e. in parallel.

Have a bunch of closely stacked cells being fast charged and discharged in series seems like it would be a really bad design. If for no other reason than hot or cold soaking overnight, then cranking the APU, then fast charging it again, would cause huge temperature variations from the center of the battery to the outside cells, unless there was active cooling, which there is not.

Just asking. Are the cells charged and monitored serially or in parallel?

I do think Lithium is the best battery for the job. It just needs to be done right.

[Lyman]

glenbrook, Hi

I could have been more clear; the post was meant to be somewhat tongue in cheek. It was (is?) Boeing's position that the rules were honored, that the grounding was a timid reaction to pressure from the political side.

They have a point, the fire was contained withn 20 inches of the case, no damage to nearby equipment, venting worked, etc.

But it is too late to unground... Boeing is keeping their screaming profanities behind closed hatches.

cheers

[radken]

Machinbird

Ahh, yes. I stand corrected. Thought about checking my facts but failed to follow up.

Some say these Li's are a mature product now. They should be, and I guess Boeing was counting on that being the exact case when the 78 elec design was finalized and flt testing later supported that conclusion. What a shame all this has now come up and spoiled the debut of this unique, and what will be one day, great aircraft.

[archae86]

The New York Times website currently shows as part of their January 30, 2013 content a story which leads with some details of (apparently for cause and unscheduled) removals of battery packs in the ANA fleet in the months before the recent unpleasantness.

This link is quite likely to a point behind their paywall, but even so may be useful to some of you who subscribe.

NYtimes battery removal article (http://www.nytimes.com/2013/01/30/business/boeing-aware-of-battery-ills-before-the-fires.html?pagewanted=1&_r=0)

It says that ten batteries were replaced. It mentions that in three cases the charger was replaced along with the battery. It quotes a GS Yuasa spokesman as stating that battery exchanges are part of normal aircraft operation, but gives no data from any source to provide context on whether this removal rate should be considered unusually high save for the GS Yuasa comment and a Boeing comment that the batteries were not lasting as long as intended.

This is hardly proof, but to my eye is an additional suggestion that the actual operational environment on the aircraft is not compatible with the actual battery packs as delivered. A (rather distant) analogy might be the way certain socket locations on certain aircraft have been known to exact a severely reduced lifetime from incandescent bulbs because of excess vibration.

[Old Engineer]

This past day (Tues) the Wall Street Journal reported on its front page that an industry standards organization (unnamed on front page) had disagreed with Boeing on the choice of battery then being considered for the 787. WSJ reported Boeing as saying that the organization did not appreciate the high level of Boeing expertise in this area, or words to that effect.

OE

[hetfield]

The cells are charged serially? I thought early on i read that the cells are charged, voltage and temp monitored, individually. i.e. in parallel.

Have a bunch of closely stacked cells being fast charged and discharged in series seems like it would be a really bad design. If for no other reason than hot or cold soaking overnight, then cranking the APU, then fast charging it again, would cause huge temperature variations from the center of the battery to the outside cells, unless there was active cooling, which there is not.

Just asking. Are the cells charged and monitored serially or in parallel?@USMCProbe

Have a look to the pictures.
You will clearly see that the cells are put in serial. The thin wires at the joints come from the BMS which BALANCE charging current and monitor each cell.
So charged in serial, but adjusted individually.

Battery balancing - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Battery_balancing)


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

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

To put the BMS in the same case beside the cells, is not a good idea IMHO...

[Volume]

So charged in serial, but adjusted individually.Looking at the massive connector bars and the tiny wiring, by which percentage can individual charging be adjusted? And what is the "industry standard" with respect to individual charge adjustment, what does for example a Prius battery do?

[hetfield]

Looking at the massive connector bars and the tiny wiring, by which percentage can individual charging be adjusted?

Yep, good question.:ok:

I hope, it's not a design flaw....

[saptzae]

Ten batteries were replaced at ANA after failing, more at JAL. Any info on other carriers?

This is highly unusual, more so as charge end appears to be very conservative at 4V.

4.1V-4.2V charge end is common in consumer and industrial applications.

Every 100 mV above 4V induces four times the stress, it gets worse above 4.3V though.

At 4V, these cells should last a very long time, many years.

The failed batteries must have been examined. Mighty strange that nothing seems to have been done about it.

@Volume
Less than 5%/3A max, was discussed from:
http://www.pprune.org/tech-log/505695-787-batteries-chargers-8.html#post7656754
through:
http://www.pprune.org/tech-log/505695-787-batteries-chargers-10.html#post7658425
and the next 10 or so posts

[Chris Scott]

Quote from USMCProbe (my bold):
"Have a bunch of closely stacked cells being fast charged and discharged in series seems like it would be a really bad design."

Am currently pretty much out of my depth in this erudite, fascinating discussion. However, I cannot see how discharging the APU battery cells in parallel could provide enough "oomph", at about 4V, to start the APU.

As I understand it, the likes of RR_NDB are currently trying to work out how, in principle, the charging might be done in parallel?

[old dawg]

Looks like more data is coming to light.

http://www.nytimes.com/2013/01/30/business/boeing-aware-of-battery-ills-before-the-fires.html?pagewanted=all&_r=0

The various regulations on the design of aviation batteries, posted elsewhere, seem clear to me and what I would expect, so the problem seems to be something fundamental in the battery type and behaviour over the full temperature operating range; or the behaviour of the battery, charger, and various loads as a combined system over the full temperature operating range.

Earlier there was a mention of Testability which in simple terms is the designed means to test the full parameters of a system and simulate the operational environment in which the system will live.

I'd be interested to know the range of operating temperatures within the EE bay and APU battery location from 37,000 ft ASL to sitting on the ground, the external ambient temperatures, and anything that could influence those temperatures in the EE bay/APU battery locations.

I would then want to know when loads are placed on the battery and the timings of that in the knowledge of the changing temperatures from ground to flight levels and vice versa. The batteries that haven't failed yet might have some of that data.

Presumably there is a test rig for this system that does some of this.

I'm sure that professional organisations working on this problem are equally interested.

[syseng68k]

saptzae:


The failed batteries must have been examined. Mighty strange that nothing seems
to have been done about it.
The number replaced struck me as being rather odd as well. Why didn't this
raise concern ?. That level of replacement might suggest a problem in the
overall system design; pack temperature control in service, or perhaps vibration
related, though batteries failed in different locations.

The data sheet I have doesn't say how many charge / discharge cycles can be
expected. Perhaps you have some typical figures ?...

Regards,

Chris

[saptzae]

@Chris Scott

Quote from USMCProbe (my bold):
"Have a bunch of closely stacked cells being fast charged and discharged in series seems like it would be a really bad design."
All that works for the better part of 100 years, in every vehicle with an electrical system, including aircraft and submarines, as well as with big stationary 48V telco batteries and data center UPS installations. LiPo powered vehicles deserve special mention.

All those are serially charged and discharged. Balancing by bypass is used in all large installations, except NiCd perhaps, not sure there.

I think OP was referring really to the closely stacked cells, which probably is one of the weaker links in this system. Fortunately the box held up, although barely, but it did. Practical battery management is weaker still.

IMHO the weakest link so far is the response to those 10 batteries ANA had to replace. Alarm bells should have gone off no less than after having swapped 10 Engines.

I guess electrical systems must be harder to understand than turbines.

Shades of gray without black and white answers.

[syseng68k]

Chris Scott:


As I understand it, the likes of RR_NDB are currently trying to work out how, in
principle, the charging might be done in parallel ?.
It's debatable if there would be any advantage, since better methods exist to
ensure that groups of cells in series are charged and balanced correctly. The
disadvantage is that to do it, you would need high current multipole relays
to switch all the cells from series to parallel configuration. As far as I know,
it's never done that way, either in industry, aviation or anywhere else. The cost
and weight penalty would be prohibitive. It would also mean that the battery
would be offline when charging, since the voltage would then be 4v, not the 32v
required.

For the 787 battery, all the cells are hardwired in series, charged and discharged
in series. What we know thus far is:

1) Cells are organised in series, with cell to cell connections via flat metal straps
bolted to the cell terminals. This is standard practice.

2) Cells are charged in series and there's no evidence of a separate charge circuit
per cell. For 8 cells, it would require 9 high current cables from the charger
and there are only two on this battery.

3) It's almost certain that each cell voltage is monitored.

4) It's not clear if there is a temperature sensor per cell, or one sensor for the
complete enclosure.

5) It's also not clear if electronic cell balancing is being done, though there are
probably enough wires to and from the cells to the pcb's, to do this.

Perhaps someone else can add to the above list if there's anything missing ?...

Regards,

Chris

[saptzae]

@syseng68k

Along the lines of 4000 Cycles at 4V/80%, 1000 Cycles at 4.1V/90%, 250 Cycles at 4.2V/100%, 50 Cycles at 4.3V, 10 Cycles at 4.4V.

Li based cells keep almost all charge delivered. No gassing or heat. Cells age faster and faster above 90% charge (~4.1V). Above 4.2V cell deteriorates quickly. Heat develops by way of short or straight thermal runaway.

These batteries appear to be charged only 80% and not to see cycles like a phone, netbook or tesla roadster and will hardly be discharged below 60% capacity.

(Percentages and voltages may vary with technology and design)

All these batteries should last several years.

10 out of 30 bat's in a year? Ridiculous.

[saptzae]

@syseng68k

5) It's also not clear if electronic cell balancing is being done, though there are
probably enough wires to and from the cells to the pcb's, to do this.

Clear to me, two PCB's for exactly that purpose in the box. The upper for control and monitoring. The lower for balancing.

Does not seem to work as needed though, if it does, I would start looking for a hidden bypass somewhere powering the batteries.

Still, the monitoring should see and log all abnormal conditions and fire off warnings before batteries fail.

[hetfield]

IMHO not a good place to put a BMS.

[saptzae]

IMHO not a good place to put a BMS.

777 and others do the same. Even got a cooling fan.

Considering the number of connections, it is the best place to put it. Logs go to the charger and failsafe battery disconnection is also managed there, I hope.

When cells fail the PCB's (failed to) serve their purpose and are irrelevant after a few minutes of logging.

There will be a really interesting report one day.

[saptzae]

GS Yuasa Li-ion battery cells selected to power International Space Station -- ROSWELL, Ga., Nov.*29, 2012 /PRNewswire/ -- (http://www.prnewswire.com/news-releases/gs-yuasa-li-ion-battery-cells-selected-to-power-international-space-station-181349711.html)

Edit:
10 year design life. 16 cycles per day (50%* discharge): 58440

Guess they tune cells and charge just to 3.8V - 3.9V.

*90 min cycle with 35min eclipse, varies with load.

[syseng68k]

saptzae:


Clear to me, two PCB's for exactly that purpose in the box. The upper
for control and monitoring. The lower for balancing.
Not convinced :-). Normally, in projects where there is a mix of digital
and measurement quality analog electronics, the analog and digital
sections are separated onto separate pcbs, or the analog sections are
enclosed in screening cans to reduce digital noise. That would suggest
that the board nearest the cells is for the analog and the lower board
handles the digital. The fact thet there are several larger pin count
devices on the lower board suggests digital logic, possibly memory or
microprocessor class devices.

The other point is w/regard to the bypass, where worst case of 10w per
cell needs to provided for. Even using switch mode tech, you still
have to dissipate that power somewhere and there's little evidence of
parts to do this on the boards.


Still, the monitoring should see and log all abnormal conditions and
fire off warnings before batteries fail.
Agreed - the data log for the battery would be logically the first place
to look for the events that led to the failure, but where is it and
why wasn't this escalated back up the chain to Boeing ?. Such a
battery replacement rate should have been noticed at some level...

Regards,

Chris

[saptzae]

Not convinced
That's alright. :)

To me it does not seem possible to do LiPo without, as the compounding imbalance will destroy the cells. http://focus.ti.com/download/trng/do...0and%20How.pdf (http://focus.ti.com/download/trng/docs/seminar/Topic%202%20-%20Battery%20Cell%20Balancing%20-%20What%20to%20Balance%20and%20How.pdf)

Edit: And there is an example with switch mode to pump power between cells.

[syseng68k]

saptzae:


That's alright.:)

To me it does not seem possible to do LiPo without, as the compounding
imbalance will destroy the cells.
http://focus.ti.com/download/trng/do...0and%20How.pdf
Clever. I was assuming resistive cell balancing, but switched capacitors
would get the job done in a much smaller volume. So they are probably
doing cell balancing on one of those boards...

Regards,

Chris

[RR_NDB]

Hi,

I will post ASAP the block diagram of a PARALLEL CHARGING WITH BITE designed during the last days.

All considerations like cost, reliability, MANDATORY K.I.S.S. approach, etc. was taken into account.

The use of SERIES CHARGING (evident from the pictures) to a battery with adjacent cells (thermally speaking) is imho a recipe for problems.

The location of the batteries in close vicinity to electronic modules and THE PLACEMENT OF TWO DENSE PCB´S in the same chamber of the cells SUGGEST the DECISION MAKING ON USE OF Li Ion was based on:

CELLS WIL NOT FAIL, WILL NOT go to THERMAL RUNAWAY AND BATTERIES WILL BETTER THAN PREVIOUS "STANDARDS" (Ni Cd).

This imho an ERROR, was partly made in "high rocks" of Boeing as we can imagine.

Sad and concerning.

PS

Parallel charging can be done with the cells connected in series. Additionally you may be able to "help" a less capable cell to deliver when battery is being used (as we know, rarely). Imagine 8 (identical) circuits (5 Amps avg, 20 Amps max) connected (floating, obviously) directly to ea. cell).
You can balance easily, manage and incorporate a very capable BITE to track cell performance)

[syseng68k]

saptzae:

10 year design life. 16 cycles per day (50%* discharge): 58440


Even my own limited experience with li suggests 100's of charge discharge
cycles and that's in consumer product. I know the lead acid gel batteries
that the telcos use have a 10 year design life and the earlier wet cells 20-30
years, even if that is under float conditions...

Regards,

Chris

[archae86]

Such a battery replacement rate should have been noticed at some levelThat story is evolving this morning. A Seattle Times article quoted a Boeing source at more than 100 replacements. However, many of those are for reasons other than observed premature discrepant behavior in service.

Somewhere on those PCBs lives a function that "locks out" usage of the battery if it is excessively discharged, which then must be removed and returned to GS Yuasa. Apparently there are inadvertent operational errors somewhat akin to you or I leaving the dome light on in an older car which can trigger this removal reason. They also lock themselves out if "improperly disconnected", whatever that means. Another cause is going past the allowed age limit (remember that a lot of these hulls must have had their first batteries installed years ago).

While that may well bargain the hundred down to a much lower number of genuine interest to us, it obfuscates the question of how many genuine in-service discrepancies were seen. And the Boeing excuse list would not seem to cover those three reported cases in which the charger was changed along with the battery. Mis-diagnosis? Real problem?

I harbor a suspicion that somewhere in the removals is the signature of a genuine problem related to the major incidents, but that is just a mildly informed guess. I hope Boeing engineering is mining that data source more energetically than Boeing PR is trying to make it look OK.

[Lyman]

Computing a component's suitability also depends on dependability.

Likewise cycles/time. If the suggestion from Boeing is that frequency of unsuitable performance issues were not somehow addressed ad nauseum in the certification process, they are smoking other than Lithium Cobalt Oxide.

There is no reasonable explanation for FAA not to know about the replacement rate in service. None. If it was logged, they know. If not, some one or other or many are in very deep doo doo.

[hetfield]

The location of the batteries in close vicinity to electronic modules and THE PLACEMENT OF TWO DENSE PCB´S in the same chamber of the cells SUGGEST the DECISION MAKING ON USE OF Li Ion was based on:

CELLS WIL NOT FAIL, WILL NOT go to THERMAL RUNAWAY AND BATTERIES WILL BETTER THAN PREVIOUS "STANDARDS" (Ni Cd).

This imho an ERROR, was partly made in "high rocks" of Boeing as we can imagine.


SPOT ON!

I fully agree.

[Lyman]

hetfield...

But that is not the case, the special language in the regs allow for fire, loss of electrolyte, and venting of toxic (hot) gases,

That means the materials encased were sacrificial, by definition. No consideration of isolation (engineering) was considered, if it was, it was rejected.
These are deliberate decisions, not blunders....

[hetfield]

"IMHO not a good place to put a BMS."

777 and others do the same. Even got a cooling fan.

Considering the number of connections, it is the best place to put it. Logs go to the charger and failsafe battery disconnection is also managed there, I hope.

When cells fail the PCB's (failed to) serve their purpose and are irrelevant after a few minutes of logging. Do T7 have Li-Ion batteries?

[cockney steve]

I think many people are losing the sight of an important fact.

The CELLS are Japanese
The Charge/discharge regulators are American.
The Assemblers are French..they make "the battery"!

the whole "box of tricks" "SHOULD" be an integrated "plug 'n'play" fitment , fully self-contained ,to hook straight onto the hookup wires and perform

Clearly it doesn't. the fault lies in the Thales -supplied "Electricity reservoir box"

WRT charge/discharge.....APU should be started off bus fed by 4 main gen's before shut-down....APU feeds all demands in conjunction with main Gen's until engines are shut down.
IF Apu is shut down for ANY reason, the aircraft is then dependent on an outside GPU for the next half-hour ,before the APU can be started again. As soon as the main engines are restarted (GPU?) the power is restored, but temperature/time limitation means that the APU will be inop, under these conditions, for takeoff.

Even if the APU is off, and all gen's fail, there's STILL the RAT to supplement the main battery (which only needs 5 minutes reserve)....under those circumstances, the F.D. cerw will have a lot more to worry about than wether the APU has cooled sufficiently for a restart :}

There is little doubt that there is adequate redundancy and capacity in the system,- even with a U/S APU battery,the APU has 2 alternative starting-modes....so the circle completes......
The components in the Thales-assembled Battery do not perform as a safe, integrated ,rechargeable source of stored electricity.

IMHO, individual cell charge/discharge is inadequately controlled/monitored.

The fact that a marginally -safe technology is used , certainly doesn't help! :eek:

[hetfield]

@cockney steve

What about the important BMS, built by "Kanto Aircraft Instrument"?

[syseng68k]

archae86:

Somewhere on those PCBs lives a function that "locks out" usage of the
battery if it is excessively discharged, which then must be removed and
returned to GS Yuasa.
Great info, thanks.

That's starting to give me feelings of dejavu, in that it's increasingly
common for equipment of all types to have no locally servicable parts.
The only recourse being to have the kit returned to the vendor, or their
designated agencies. Even where local servicing may be possible, service
information is often denied and it's designed to create an expensive
monopoly for the sole benefit of the vendor. In this case, why must the
battery go back to Yuasa and not the system integrator ?. At least, local
agencies should be able to interrogate the battery data log to determine
the detailed cause of the fault and thus eleminate spurious shutdowns due
to overzealous or faulty built in test.


Another cause is going past the allowed age limit.
Thats adds more weight to something discussed in a previous post, where I was
trying to work out why the data log for the burnt out battery appeared
to be unavailable. The suggestion was that the boards in the enclosure were
responsible for the data logging, (with good reason) and logged the whole life
of the battery. Because of board damage, the logged battery data would likely
be irrecoverable and make cause of failure very difficult to determine...

Regards,

Chris

[saptzae]

Where components are made does not really matter (to me).

That several distributed suppliers must be integrated does not help. However, this is just "normal".

The components in the Thales-assembled Battery do not perform as a safe, integrated, rechargeable source of stored electricity.
Concur, at the system level.


IMHO, individual cell charge/discharge is inadequately controlled/monitored.
Concur


The fact that a marginally -safe technology is used, certainly doesn't help! http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/eek.gif
Right, but are ladders more than marginally -safe?, after all, one can fall down :confused:

What matters is management. That known deficiencies (10 bat's out of 30 replaced at ANA ) were not addressed in time is "not uncommon" mismanagement. Would they have been proactive, they could have started what the NTSB does now after the first three failures, and the fleet would not have been grounded.

That's what I am here for, to learn.

[saptzae]

Do T7 have Li-Ion batteries?

No, but they have corrosive alkaline and alu eating electrolyte, can overheat and short and boil, spilling the electrolyte all over.

My point is that the basic architecture is the same, implementation is common practice in aerospace.

[hetfield]

No, but they have corrosive alkaline and alu eating electrolyte, can overheat and short and boil, spilling the electrolyte all over.

My point is that the basic architecture is the same, implementation is common practice in aerospace. And my point is, do not put a BMS into a case where a "thermal runaway" (Li-Ion) may happen...

[saptzae]

@RR_NDB

I will post ASAP the block diagram of a PARALLEL CHARGING WITH BITE designed during the last days.
Looking forward, I provide a free review.

@archae86

That story is evolving this morning. A Seattle Times article quoted a Boeing source at more than 100 replacements. However, many of those are for reasons other than observed premature discrepant behavior in service.

Sorry, 10 out of 30 at ANA is plenty to wake up to,with plenty of time. :=

[syseng68k]

saptzae:

No, but they have corrosive alkaline and alu eating electrolyte, can overheat and short and boil, spilling the electrolyte all over.
Agreed. Anyone who's lifted the lid of a nicad after brisk charging will see
evidence of electrolyte and the fumes to go with it.

In this case, I wonder if the so called fan in that enclosure is there for cooling, or primarily to exhaust the corrosive gases ?.


My point is that the basic architecture is the same, implementation is common practice in aerospace.
Electronics and cells of any type don't mix and just because it's common practice,
doesn't mean that it's correct, nor that it isn't just wrong by design :ugh:. Everyone
else does it, so it must be ok, right ?.

Designers must question everything, especially their own assumptions and those of
the people they most respect...

Regards,

Chris

[saptzae]

@syseng68k
In this case, I wonder if the so called fan in that enclosure is there for cooling, or primarily to exhaust the corrosive gases ?. Cooling, one would not want to exhaust alkaline gases into an alu fuselage.

As to the gases, like with Pb, it's primarily hydrogen/oxygen, which this poster learned in his early teens, when a car battery blew up in his night desk after being _accidentally_ shorted. (head light makes a good reading lamp).

Electronics and cells of any type don't mix and just because it's common practice, doesn't mean that it's correct, nor that it isn't just wrong by design :ugh:. Everyone else does it, so it must be ok, right ?.
Engineering practice generally has a sound basis. For example, practically every modern LiPo battery has electronics for balancing integrated.


Designers must question everything, especially their own assumptions and those of the people they most respect...
Right, against convenience, one should not make assumptions at all, because assumption is the mother of _all_ failure.

See, think, validate goes both ways. We have still not seen all the facts and can not make assumptions on changes before understanding the cause.

[rottenray]

And my point is, do not put a BMS into a case where a "thermal runaway" (Li-Ion) may happen...First, according to the securaplane website, battery history is recorded by the chargers - not the BMS co-located with the battery cells.

(We've been dispelling this myth every other day as someone who hasn't done due reading brings it up again and others in the same state accept it as fact.)


Next, once a cell enters thermal runaway, the job of the BMS has officially ended once it orders the final disconnect of the pack - there is nothing more it can do as the pack is headed for failure at that point.

(It's worth noting that this, too, apparently worked as advertised as there was a "drop to near zero" recorded on the batt of the ANA aircraft.)


Putting the BMS inside the battery case makes it easier to calibrate and more reliable. You are dealing with DC levels into the millivolts, and at these low voltages even the best connectors can add undesired and unpredictable resistance.

Since the BMS isn't recording history, nothing is really lost if it gets badly degraded when a battery does a thermal runaway.

[saptzae]

@rottenray

Fully concur, thank you :ok:

[Chris Scott]

Some time ago I argued that, if special restrictions were put on the discharge and charge of the APU battery in advance of a complete fix, ETOPS flights requiring the APU would still be possible if the APU was started - perhaps in flight - prior to the beginning of the ETOPS leg, using the main electrical system, as a pre-emptive measure. I pointed out, however, that starting it in flight would be a hostage to fortune, in that cold-soak MIGHT (though should not) inhibit APU start. A more reliable tactic would be to start it before departure, as an idling APU uses little fuel, particularly at cruise altitude.

Quote from cockney steve:
"WRT charge/discharge.....APU should be started off bus fed by 4 main gen's before shut-down....APU feeds all demands in conjunction with main Gen's until engines are shut down.
IF Apu is shut down for ANY reason, the aircraft is then dependent on an outside GPU for the next half-hour ,before the APU can be started again. As soon as the main engines are restarted (GPU?) the power is restored, but temperature/time limitation means that the APU will be inop, under these conditions, for takeoff."

What are these temperature/time limitations? Not something I've ever found a problem on other types, and a typical long-haul turnround time is about 90 minutes or more.

[mm43]

@rottenray

You're on the right track.:ok:
#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.My point all along. Logging is separate issue, and that I agree can be done in a separate E/E rack, with each battery pack logged in with its own IP type address, i.e. a Plug 'n Play arrangement, to avoid loss of valuable data.

[hetfield]

Sorry,

it's not about logging.

It's about controlling/charging.

[syseng68k]

rottenray:


First, according to the securaplane website, battery history is recorded
by the chargers - not the BMS co-located with the battery cells.
I had a look at the securaplane website few days ago and couldn't find
any detailed info re: where the logging is done. This may depend on
particular system requirements. Can you post a link to the relevant page
for the actual 787 charger system ?.

To summarise the discussion re: battery data logging:

1) In the charger, which I originally suggested, but that leaves the
problem of what happened to that data ?. It should provide an audit
trail of the events leading up to the failure and would expect it to
be the first thing examined. Yet, no word about this.

Also, it makes the exchange of either battery or charger more inconvenient
since the logged data no longer matches that for the battery. That is,
there needs to be a process to download, store the data from the charger
and ensure that it's tagged to the battery that's been removed. Hence,
the suggestion that the data may be stored in the enclosure. There's
a lot of electronics there and while they may just have made a meal of
it, it does suggest further functionality.

2) Internal to the battery enclosure, which makes more sense from a
maintenance pov, but such data would be unlikely to survive a fire
using the present layout.


It's worth noting that this, too, apparently worked as advertised as there
was a "drop to near zero" recorded on the batt of the ANA aircraft.
Sorry, but a drop where ?. The associated dc bus, in the fdr, or what ?.


Putting the BMS inside the battery case makes it easier to calibrate and
more reliable. You are dealing with DC levels into the millivolts, and
at these low voltages even the best connectors can add undesired and
unpredictable resistance.
What was being discussed in context was the data logging: where it takes
place, what parameters are stored (timeline ?) and where that data is
now ?...

Regards,

Chris

[syseng68k]

mm43:


My point all along. Logging is separate issue, and that I agree can be done in a separate E/E rack, with each battery pack logged in with its own IP type address, i.e. a Plug 'n Play arrangement, to avoid loss of valuable data.
That is another option and had heard that Boeing were using ethernet transport for
non critical data to reduce cost, but for critical subsystems such as this ?.

If they did, let's hope they made a better job of it than Windows. Actually not that
bad these days, but it usually takes until SP3 before they thrash out *most* of the bugs...

Regards,

Chris

[rottenray]

Quote:
First, according to the securaplane website, battery history is recorded by the chargers - not the BMS co-located with the battery cells.I had a look at the securaplane website few days ago and couldn't find any detailed info re: where the logging is done. This may depend on particular system requirements. Can you post a link to the relevant page for the actual 787 charger system ?.The 3rd paragraph, just above the images, on this page: Innovative Inverter Technologies and Main Ship Battery Chargers for Power Conversion (http://www.securaplane.com/products/power-conversion)

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.It also mentions it in their product brochures.


Quote:
It's worth noting that this, too, apparently worked as advertised as there
was a "drop to near zero" recorded on the batt of the ANA aircraft.
Sorry, but a drop where ?. The associated dc bus, in the fdr, or what ?.Neither article was that specific, but both IIRC mentioned the battery dropping to "near zero voltage."


Sorry,

it's not about logging.

It's about controlling/charging. What? The circuits in the battery box? Finding the problem?

[syseng68k]

rottenray:


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.
Thanks for that and clears up one mystery. Obviously didn't look hard
enough.:=.

From the above, it seems like there should be a complete timeline of the
events that lead up to the failure. Will be interesting to see what it says,
but still curious as to why this wasn't the first thing examined...

Regards,

Chris

[TURIN]

Chris Scott.
Temp/Time limits on the APU are due to a rotor bow problem caused by excess heat soak after shutdown.. The quick fix is to leave the APU inlet door open to allow sufficient ventilation of the APU powerplant. Long term fix will be hardware/software changes.


Posted from Pprune.org App for Android

[saptzae]

@TURIN
Long term fix will be hardware/software changes.
Cute, a software patch to de-bow the rotor.

Seriously, it should be possible to use the inverter powered starter, reprogrammed to support it after shutdown, at very low speed (5-10%), to ventilate for a few minutes. Would not pull much power really, 32V/10-20A on battery for 10 minutes would be minor.

[cwatters]

I'm sure it's fine but looking at the photo posted a few pages back..

What's the clearance between the two output bus bars and the metal brace that runs under them? Look where the black sleeving ends. This clearly isn't the cause of the current problem or the brace would be melted.

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

[saptzae]

@cwatters
What's the clearance
Hard to judge. I'd say 5mm+

I was thinking, assembling and wiring these boxes, with all cells at least at minimum charge, must be really interesting.

[hetfield]

It's amazing how proper balancing is done with these tiny wires.

[TURIN]

Saptzae.
Re: Motoring the apu after shutdown.
Unfortunately, the APU starter motor controllers are liquid cooled and would need the PECS (Power Equipment Cooling System) to function after shutdown. Which is fine if you are on ground power but not if you are shutting the a/c down.


Posted from Pprune.org App for Android

[USMCProbe]

Sorry I misspoke. I did mean I was surprised that the batteries were not charged in parallel, individually. Including monitoring individual current. I did not mean I was surprised they were discharged in series.

I don't design or work on airplanes but fly them. I have done a lot of automotive electrical stuff, professionally. I was shocked at the pictures of the BMS wiring.

A bunch of little wires with crimped (and probably soldered as well) eyes being held in place by little screws seems archaic. I am sure the wire and terminals are the best money can buy, but you just don't see that anymore in higher volume production stuff. Maybe Jaguar (Lucas) still does it that way? Did Thales buy Lucas?

[USMCProbe]

Sorry I wrote it wrong again. I thought lithium batteries were charged individually in an application like this. Discharged in series is a given.


When I read the NYT article about the ANA battery fire, they said the crew noted a normal voltage, then zero voltage. I believe they referred to the zero voltage as a short circuit, not that the battery charger had stopped charging "as designed". If the battery charger had stopped charging, the voltage would have dropped slightly to actual open cell voltage, assuming no load on the battery. Airbus puts a little connecting line on the EICAS to show that the battery charger is connected, but you still look at the voltage across the terminals. It has been 8 years since I have flown a Boeing, I believe they all just show battery voltage. Above 28 volts the charger is working.

[syseng68k]

saptzae:

Seriously, it should be possible to use the inverter powered starter,
reprogrammed to support it after shutdown, at very low speed (5-10%),
to ventilate for a few minutes.
Good idea, the starter / generator is inverter driven, so may only need a software
change to implement that.

Not a new idea either: 1994 and maybe earlier Audis had a small run on water pump to keep coolant
circulating around the turbo to prevent heat soak damage...

Regards,

Chris

[fizz57]

A couple of thoughts....

Boeing's insistence on retaining the lithium batteries make me think that they weren't chosen just for their size and weight, but that some electrical characteristic (such a low internal resistance) make them central to the design of the electrical system. It's been said here that the diode essentially isolates the battery from the bus in normal operation, but this isn't strictly true: any undervoltage, even for a time measured in milliseconds, will cause the diode to conduct and the battery to attempt to prop up the bus. The 787 electrical system is huge by aircraft standards and may be subject to many transient effects as the various loads start and stop, within a time frame that the main generating system may not be able to compensate for. So the battery may have a more active function in the system than just a backup supply.

Secondly, I find the present focus on the batteries and chargers as isolated systems to be pretty naive. The engineers at the various plants involved can be assumed to be reasonably competent and that they would have picked up on any design fault that results in an MTBF of only a few months (or one that will be identified by outside, non-expert inspectors). Rather, the problem is likely to be a result of battery operation within the complete aircraft system, whereby electrical or environmental loads are being placed on the battery that were not envisaged in the specification or tested for during construction.

Edited: fixed typo

[RR_NDB]

Hi,

fizz57 @ (#337)

Indeed, high current transients due (negative) voltage spikes in DC busses may "stress" the battery (due it´s low internal resistance).

Questions:

1) This condition was not analyzed and tested by Yuasa?
2) This spykes (voltage and current) were recorded? (FDR has resolution to "see"?, battery charger recorded it?)
3) Failure modes are correlated to this "non thermal" stimuli?

You introduced a good point. I commented earlier on batteries normaly working as "capacitors" when directly connected to a DC bus. With a diode (you never apply positive spykes to the battery) but you make the battery "go to the bus" immediately if the bus voltage falls below, ~ 30 V as i put in an earlier post.

[RR_NDB]

Hi,

Questions:

Typically in the 787 commercial operation the APU and MAIN batteries how long probably operated supplying current? I.e. :
1) APU battery started occurred frequently? Certainly not. Towing? Yes, but at low amps and few minutes. Low discharge.
2) MAIN battery (probably only on ground (tarmac, towing and hangar) operated (estimated) how many hours ? (each plane)

I suppose in both uses (APU and MAIN) the use (time) was low. (compared to their capacity).

So we could expect they were most of time being charged (most time being "trickle charged" or charged with high nominal charge current during few minutes)

I think we may say say these batteries exhibited a low MTBF despite a light use. (MAIN battery is "out of the bus" if BUS voltage is "normal" (gennies ok).

Exceptions: Possible spikes as suggested by fizz57 @ (#337) (probably much larger than 1C (65 Amps)

This "electrical environment" aspect is perhaps the last one we may imagine (characteristic of the 787) if chargers, BMS algorithms or defective components are to be discarded as causing the low MTBF.

I aasume the designers put a way to not allow discharge of ANY cell below a "safe" voltage. Remember you CAN´T depend on these batteries too long at ground. GPU, APU or engine gennies are essential for (prolonged) prolonged use. And a "automatic" disconnection shoul be adopted. (due a limitation of cells).

This may explain part of the low battery MTBF of the fleet.

[Lyman]

Square peg, round hole. Except in this case, a round battery into a square case.

I think the reality of the technology is catching up to Boeing, and it is sad.

"Innovation" is like "sophistication"....

If you can't pull it off, you look silly.

[RR_NDB]

Hi,

Thinking on how different is the application of these (suposed) "proven" cells on the new design of 787 and:
1) The low MTTR
2) The "diode scheme"
3) The DC generation from redundant sources
4) The higher electric energy use for more functions
5) The ripple naturally present in busses
6) The Boeing selection of this battery
7) The offering of just une option: Li Ion

How is done the filtering of the busses? There are capacitors banks along the busses? Or any "sudden drop" of voltage makes the battery supply the energy (through the hi speed switch - the diode). If there are spikes (sudden negative going voltage levels) in the busses the battery is not as "offline" as previously thought.

OTOH we may imagine most high power loads (that required the 1.45 MW generation capability) are AC driven.

[syseng68k]

fizz57:


A couple of thoughts....

Boeing's insistence on retaining the lithium batteries make me think
that they weren't chosen just for their size and weight, but that some
electrical characteristic (such a low internal resistance) make them
central to the design of the electrical system.
From info we have, the ability to fast charge LI might have been
attractive for some operational reason. Of course, they are much
lighter, but the reason may also have been that it is a much more
modern technology, with many benefits over either lead acid or
nicad. Well proven, so why not use it ?.


Secondly, I find the present focus and the batteries and chargers as
isolated systems to be pretty naive.
Perhaps, but that's where the fault originated and in fact, the
NTSB focus has been in that area since the problem surfaced, right or
wrong. The battery data log is in the charger and it seems strange
to me that they spent a week tearing batteries, down, subjecting
them to minute examination, when the event timeline to failure may be
elsewhere. Nasrudin's Lost Key, or what ?.


The engineers at the various plants involved can be assumed to be
reasonably competent...
More than just competent. Imho, the 787 is a revolutionary design,
in the same way that the A340 was when it was introduced. Technology
moves on and with any step change, there are far more risk than with
an incremental metoo design...

Regards,

Chris

[RR_NDB]

Hi,

The (negative going) voltage spikes in the bus is similar to:

Imagine a large piston engine (mechanically) connected by a rod to a flyweel. The stress to the connection could destroy the rod. The diode could be viewed as "part of the rod". And the series connected cells must be capable to supply the large current spikes. The spikes could concentrate in some (area) concentrated points during the transient? And all these current spikes could even create oscillatory voltage transients increasing momentarily cell voltages above nominal levels?

The low MTTR reported probably was on MAIN batteries for other reasons. (supposing very rare use of APU battery discharging high current. And during towing the load is light. )

[syseng68k]

How is done the filtering of the busses? There are capacitors banks
along the busses? Or any "sudden drop" of voltage makes the battery
supply the energy (through the hi speed switch - the diode). If there
are spikes (sudden negative going voltage levels) in the busses the
battery is not as "offline" as previously thought.
I think your'e chasing a red herring here, or something, as there
have been similar failures in functionally different areas: Standby
power and APU start.

This would suggest that the problem is with the battery / charger
subsystem, as it's the only thing in common, afaik...

Regards,

Chris

[FlightPathOBN]

so many threads on this...

here is an interesting piece by Elon Musk...

An aerospace-capable version of Tesla's battery has been developed for use in SpaceX's Falcon 9 space launch vehicle. SpaceX, also owned by Musk, competes with Boeing/Lockheed Martin joint venture United Launch Alliance for customers. Boeing has thus far declined offers of assistance from Tesla and SpaceX, says Musk.

"They [Boeing] believe they have this under control, although I think there is a fundamental safety issue with the architecture of a pack with large cells," writes Musk in an email. "It is much harder to maintain an even temperature in a large cell, as the distance from the center of the cell to the edge is much greater, which increases the risk of thermal runaway."

"He's engineered [Tesla's battery] to prevent the domino effect, while Boeing evidently doesn't have that engineering," adds Sadoway.

Elon Musk: Boeing 787 battery fundamentally unsafe (http://www.flightglobal.com/news/articles/elon-musk-boeing-787-battery-fundamentally-unsafe-381627/)

[fizz57]

@syseng68k (if I had a name like yours it would end with 6502)

I'm referring to Boeing's latest statements on the batteries. There's no quibble with the design choice of Li-ion, despite all the scaremongers there aren't any insoluble technical problems and in a few years we'll be wondering what all the fuss was about. My point was just that if the batteries were simply reserve power banks then an interim replacement with Ni-Cds to get the planes flying again should have been the first option. This seems to indicate a more fundamental reason for the choice (probably on the A350 as well).

My second comment was based on the expected result that nothing was found wrong with either the batteries or the chargers. Expected because given the quality of the engineers (a bit of irony in my post there, as a sop to those wo think anything not Boeing shouldn't be in the air) I'm sure that both the batteries and the electronics are top-notch. So the reason for the failures, catastrophic or otherwise, must be elsewhere.

Given the novelty of the design, there are bound to be unknowns in the entire system even if the individual components are well understood. What margins were taken by the system integrators? Did Boeing construct a full-scale replica of the electrical system (as the Concorde engineers did with their fuel system) or was it all simulated? What were the inputs to the simulations? I think that these are the sort of questions that should be asked.

[RR_NDB]

Hi,

Chris,

I learned many years ago we must look to every possible detail. It could explain the fact(s).

Let´s wait to learn on % of failed batteries (MAIN or APU). One battery (BOS) is not an argument against the model.

The Decision Making on Li Ion usage as main certainly was more complex. (vs APU) The diode (if not used in other A/C) "protects" the (critical) battery in just one direction.

What is common:
1) Both batteries failed (APU and MAIN)
2) Battery of same type
3) Circuitry around (BC, BMs)

The higher electric power in 787 and the adoption of these higher capacity batteries must be viewed as something decided by fundamented reasons. The decision certainly was not trivial.

[FlightPathOBN]

RR,

It appears hundreds of batteries have cycled down...with only a few of these birds in ops...

seems more like a fundamental failure of the assumptions...(supported by Musk, but perhaps biased)

obfuscation of the issue will not only lead to an extended process of this system,

but perhaps is the foundation of the unusual regulatory response to all processes...

[RR_NDB]

Hi,

Elon Musk email touches in a VERY IMPORTANT point. He has concerns on the cell size and (seems) the temperature gradient inside. He would not emphasize in this "high rock style" message the correlation between cell size to the thermal runaway threat wirthout strong reasons backe by what he learned, know and consider a flaw.

PS

Fizz57 and syseng68:
My nickname could be 4004. Slower and less capable (just 4 bits) vs 6502 and 68000 but "the first one, years ahead"....

[FlightPathOBN]

nice RR..

dont forget..

pioneers get slaughtered..

settlers prosper.

[RR_NDB]

Hi,

FPO @ (#348)

Yes, FAA, NTSB and a lot of people around the world are concerned and working diligently to answer WHAT and WHY. Deborah Hersman expressed this very well in the briefing.

Boeing is in a defensive mode and i agree with your feeling.

[archae86]

The Seattle area TV station King5 has posted a story simply attributed to "sources" (http://www.king5.com/news/aerospace/Could-Boeing-have-a-fix-for-the-787-battery-problems-189115821.html) asserting that Boeing is considering an approach to continuing to use the existing battery system with upgrades to containment and venting. As I doubt that even a profound understanding of just what happened in the JAL and ANA incidents will lead to a change which will have all stakeholders believing there will never be another one, I personally believe that continued use of these batteries requires improvement in precisely these two areas.

The idea here is that thermal runaway lithium cell failures should be rare, but that if one should happen anyway the design should safely contain damage to the battery itself, by adequate thermal and mechanical shielding to adjacent structures and equipment, and safer (which has to mean more constrained) venting of the unavoidable hot byproducts overboard.

I think this is on a correct track--though I certainly hope that improvements driven by real understanding make the cell failures far less common than they seem to be now. A complete redesign using a different chemistry is doubtless entirely possible, but the timeline when one includes all stakeholder approvals, testing, and regulatory hurdles would probably be very long even were the 777 solution "dropped in", and yet longer on a more original design.

[RR_NDB]

Hi,

Archae86,

I liked it. Fault tolerance and Graceful Degradation will be improved with this approach.

This afternoon i was imagining special compartments with each battery, near plane outer surface with safety mechanisms. A bigger battery case with separated cells (ea one in a chamber), cell conections in the top, manifold with 8 bifurcations (metallic) and means to promote escape of cell leaks (even fire), etc.

All with improved battery management for charge and discharge. WRT to electrical circuitry:

Individual cell management, adaptive voltage (charge) CONTROL (not just monitoring).

Temp sensors PER CELL and other details like battery case geometry, parallel cell charger with extra features are being studied.

The opportunity was being motivating for me in an electric (actually hibrid) vehicle design, being R&D´d. Safety first.

[Ian W]

From WSJ Dreamliner Batteries Needed Replacement Before Incident - WSJ.com (http://online.wsj.com/article/SB10001424127887323701904578273283088672060.html)

In the U.S., investigators have collected world-wide data for the 787 fleet indicating that as many as 160 batteries may have been replaced, including before and after delivery, according to people familiar with the details. The primary reason 787 batteries have been swapped out, these people said, are that they were improperly disconnected. They were left to discharge without any other power sources on the aircraft, causing a deep discharge; or they expired, people familiar with the matter said.

Sounds like a fair amount of mishandling rather than unexpected battery failures.

[RR_NDB]

Hi,

Ian W,

A battery or a System with them could (should) have means to warn when going below a given threshold. The circuit to perform it cost less than USD16.
Not just mishandling...

[FlightPathOBN]

Exactly..it seems much better to shut down the use of the battery power, than to permanently take down a cell...

this doesnt solve the thermal run away issue..

seems like the system is far too complicated, answering stop gap, (if/then) rather than solve the issues.

I think perhaps that Musk's opinions have some very good value...after all, look how many vehicles they roasted up...

[Ian W]

RR_NDB
A battery or a System with them could (should) have means to warn when going below a given threshold. The circuit to perform it cost less than USD16.
Not just mishandling...

If someone wants to disconnect a battery incorrectly then it will still cause problems the quote actually goes on to say

In many cases, according to these people, internal battery safety systems kicked in as designed, preventing maintenance officials from recharging the affected batteries.

I was just pointing out that the large number of battery failures seemed to be due to mishandling. Perhaps there needs to be more protection against that as well but its not an airborne occurrence - its a line maintenance issue.

[RR_NDB]

Hi,

FPO,

Simple:

Smaller cells (iirc the popular "18650") separated and liquid cooled. Ea. About the volume of a stretched C type flashlight cell. (est. 10 ~ 20 % more volume)

The idea to use an "av. standard case" (we may comprehend the reasons) WITHOUT cell spacing and without "any" cooling certainly was an important factor to the outcome.

[RR_NDB]

Hi,

Ian W

Your second point agree.

What you mean by "incorrect disconnection"?

[USMCProbe]

APU battery usage depends on how diligent an airline is about not using the APU. Some airlines try to not use it at all costs. Some use it every flight, maybe twice (before engine start and before shutdown). Only one of those times will the APU battery be cycled. The other time it will probably started off the main buses. I don't work for ANA so I don't know what they do. A medium/long haul aircraft might start its APU 2-10 times per day.

The APU takes about a minute to start. So 30-40% of the battery capacity is used very quickly, and the battery will probably heat up a bit. If it is then recharged very quickly (10 minutes?), it will heat up even more.

The backup battery should not get much use. Starting up a "cold" airplane, the battery might be used just to get essential power up to do a APU start. Also cleaners might need a little light, so a mechanic might turn the batteries on. Opening and closing cargo doors. etc. Not high draw stuff, and not for very long.

I only saw a "dead" backup battery once. Someone left the battery switch on overnight, or maybe someone outside disconnected external power with the BATT switch on.

[Ian W]

RR_NDB
What you mean by "incorrect disconnection"?

That was the quote in the WSJ story. I presume that there must be a procedure for disconnecting the battery that was not followed. It may be an area to be investigated.

[inetdog]

One of the descriptions stated that, among other things, opening a fuel fill door turns on the whole fuel monitoring, transfer pump, etc. system (on battery if no other power is connected) and leaves it on until the door is closed.
They felt that was one of the major causes of battery flattening.

[mm43]

What comes first? The Batt~DC Buss blocking diode then the Batt CB, or is the sequence reversed?

Am I right to assume that both the above are outside the battery pack?

[Old Engineer]

It's amazing how proper balancing is done with these tiny wires.

Comments about this have appeared several times. Perhaps I can describe a way in which this could be done.

We want to pass a slightly different charging current through each cell. Instead of 8 chargers each running at 40 amps, say, let's have one charger running at 40 amps, and perhaps one master control on this so that it can taper off at 20 or 10 amps. This will make the math of the example easy to follow.

Let's overlay a current loop thru each battery (two small wires to the two terminals of a cell, common and +/- DC). Let's use an overlay current that may be as great as +2A DC, or 0, or even -2A DC. We'll take +2A DC to mean the 2 amperes is added so as to flow in the same direction as the 40A chargilng current from the main source. Now that means that an overlay of -2A would flow in the opposite direction to the main charging current of 40 amps.

Now you say current cannot flow in two directions in the same wire. That is certainly true. However a guy name Kirchoff proved that you could do your calculations as if it did, in loops of your choosing. So even tho such calculations are in some ways not literal, they do give correct and quick answers. In fact, you can build circuits based on the imaginary math, and they will actually give real currents.

Let's say the target voltage on full charge is exactly 4 VDC per cell, and 40 amps for say an hour will bring a 65 Ah battery of 8 cells back to 32 terminal volts on the battery. This means it was discharged down by some number of ampere hours less than 40, but not exactly known.

Let's say we do know that on average, when the cells are new and uniform, and the same discharge has been made) a 41 A charge will bring the cells back to 4.1 V per cell; or of 38 A, back to 3.8 V, and so on. To know this we have attached a 3rd small wire to the output of each cell to measure cell voltage (between cell common - above - and the 3rd wire).

Let's say we have a cell that is only showing 2.9 V when six have all reached 3.0; and another that is in the hot center of the stack, and being warm, it charges more and shows 3.1 V. Because our electrical trim tab is so small, we must begin correction of the current on these two cells once a difference appears. So we apply +1 A overlay to the first problem cell through the small wires, and -1A to the second problem cell. So the 1st problem cell gets 41 A, and the 2d 39 A, net effective charging current.

By the way, the necessary wires to carry these currents can be related to the usual household wiring, where a #14 AWG in Cu carries 15 amps, a #12 20 amps, a #10 30 amps, a #8 40 amps. The plug in power harness from the GPU may need #8 cables for the main charging current and return.

In smaller wires, it is 10 amps for a #16 wire, 7 for a #18, and from that (ie, less 8 numbers) a #26 for two amps. The relations (in US, logarithmic among wires) are 3 numbers to double the copper area, 6 numbers to double the diameter; because of the surface area effect, 4 numbers to double the ampacity. A #10 is one-tenth inch in diameter. For Al wire, add 2 in size; altho I'd think Cu was more likely at a battery. Insulation, I'd think between 15 and 30 mils here.

Now, from all that, with the ruler scale on the battery pix, a pretty good idea of the battery wiring can be obtained, with a little help from CBrd considerations, as follows.

On a circuit board, a half amp can be handled with a top-hat power transitor; 1 or 2 amps with one mounted on a metal slug; but above that (say 5 amps) something with fins (not seen) is going to be needed; there may be some slugged devices. So it's possible eight 2-amp lines of the "trim" current supply are provided from the ground charger. My guess is yes and that the charger controls the current trim in accordance with the cell voltage telemetry transmitted digitally. All this may be in the "data" cable.

IIRC, an incident of operation with only the power cable attached was reported. The questions then are:

1. Is the ground charger multipurpose, whereby the data cable is not used for other battery types? What disconnect sequence? What is the effect of not connecting the data cable?

2. Is capabilty to vary the charging current by cell by 2 amps either way enough? Is it that or more?

3. Is this cell balancing done only on charging, or also discharging? It is obviously impractical in the scheme outlined during APU cranking.

4. Plus all the usual-- algorithims, floating discharge on bus, etc.

OE

[ross_M]

In fact, you can build circuits based on the imaginary math, and they will actually give real currents.


:D

Loved that!

[TURIN]

What comes first? The Batt~DC Buss blocking diode then the Batt CB, or is the sequence reversed?


From memory, no schematic available at the moment.

APU BAT
FO's Instrument Bus-CB-Bat Charger-Batttery-APU Hot Bat Bus-SPUC-SPU-ATRU-CMSC-APU VSMG.


MAIN BAT
CAPT's Instrument Bus-CB-Bat Charger-Battery-Diode Module-Hot Bat Bus-Bat Bus Contactor-DC Bus (Can't remember which one).

As you can see the diode module is there to ensure no backfeed from the Hot Bat Bus to the battery in the event the Bat Bus Contactor stays closed when normal power is supplying the DC Busses.


One of the descriptions stated that, among other things, opening a fuel fill door turns on the whole fuel monitoring, transfer pump, etc. system (on battery if no other power is connected) and leaves it on until the door is closed.
They felt that was one of the major causes of battery flattening.

Yup. The "battery only" refuelling option is there to get just enough fuel into the left main tank to allow the APU to be started. (Approx 15 mins).

The backup battery should not get much use. Starting up a "cold" airplane, the battery might be used just to get essential power up to do a APU start. Also cleaners might need a little light, so a mechanic might turn the batteries on. Opening and closing cargo doors. etc. Not high draw stuff, and not for very long.


The first bit is about right but lighting will come from the Virtual ground Handling Bus which will only be powered from External Power or Normal Busses.
Cargo doors are hydraulically operated from stand alone electrically powered hydraulic pump packs. Again power is from the Virtual Ground Handling Bus which will only be powered from External Power or Normal Busses.

I only saw a "dead" backup battery once. Someone left the battery switch on overnight, or maybe someone outside disconnected external power with the BATT switch on.

Me too.:O
However at least the old style battery could be recharged in situ. Not this beast.

One of the peculiar 'gotchas' at the moment is the workaround to ensure APU rotor bowing does not occur. It essentially means selecting the APU start switch to 'on' after the APU has shut down to re-open the APU inlet door for ventilation and then switching the Main and APU batteries off. It is possible I suppose that some of these flat battery problems could have been caused by this. Catch all phrase of mishandling? :suspect:

[keesje]

If this batteries has an excellent measuring and control system, why didn't it cut off / send low warnings when it approached it critical low level? Or did it.

Anyway it seems Airbus better Indentified the risk of the use of these batteries at the start of the program, warned everybody, seperated the cells for cooling, took smaller ones and... developped a plan B in parallel just in case off..

Airbus says it has a Plan B for A350 jet batteries | Reuters (http://www.reuters.com/article/2013/02/01/us-airbus-a350-batteries-idUSBRE91006F20130201)

[cockney steve]

interesting comments in the last 2 posts. A former life saw me as a service-engineer for Medical equipment. (mainly Prem. baby incubators)

We recognised the capacity for abuse and misuse and as far as possible , designs were developed to circumvent "unplanned" "usage"

The saying was, " design to be idiot-proof and it'll be almost nurse-proof :ooh:

Now Turin talks of an unorthodox procedure to overcome a major inherent design fault (distortion of Rotor due inadequate provision to dissipate soaked-heat.

(incidentally.SYSENG 68K , the BMW Mini-Cooper also uses a "run-on coolant pump and it was these devices causing unexplained spontaneous combustion of the cars,,,caused a major recall...Deja-vu!)

@ KEESJE. AIUI, the connection/balancing/discharging/monitoring ai all internal in the "battery" , it being a self-contained sub-system.
One therefore makes the assumption that all charge/discharge functions must go via the "charger"which is then a glorified power-supply/filter as seen by the battery. One also assumes the safest way to transfer the data from inside the Battery, to the data-storage within the charger, is simply to superimpose the digital(AC) info on the main cables and filter it off at the charger (destination)

That way, It's impossible to charge/discharge the battery cells without the controller talking to it's interface. any other "secondary-plug" system is, IMO, wide-open to human error as well as adding another load of wires/connectors into the "potential fault" chain.

No doubt these cells can be used safely in this particular application, but they need to be conservatively used with a much larger safety-margin than they already demonstrate.

Charge/discharge monitoring is, IMO, critical....in the "fuel-door" instance, the batt. should self-disconnect long before it reaches a critical level, just like your cell-phone battery does,- OK, you then have to get a ground-power connection to continue refuelling, but you can then safely restart the APU or a main engine to restore power to the battery-charger (assuming the GPU doesn,t perform this function.)

It needs to be understood that only the "middle" part of the stored energy is actually available for safe use.

Over-discharging effectively destroys the cell. charging to the limit brings a possibility of spontaneous combustion. therefore, like the pilots keep clear of "Coffin Corner" and" Stall" these batteries demand usage in the "safe" part of their envelope.

A design that allows cells to routinely fall below "lockout" level, is ,IMO incompetently and poorly engineered. (Unless it's a deliberate and cynical ploy to sell more batteries :hmm:) but no firm would put profit before dependability,would they?

[saptzae]

@mm43

Am I right to assume that both the above are outside the battery pack?
Diode module is external, for main battery only as TURIN explained above. Shorting this battery's connection without protection would lead to a firework. Looking at the picture, near the lower end of the right bus bar is a device, which may be a breaker.

@Old Engineer
Here it is how balancing is done in practice.
http://focus.ti.com/download/trng/docs/seminar/Topic%202%20-%20Battery%20Cell%20Balancing%20-%20What%20to%20Balance%20and%20How.pdf


IIRC, an incident of operation with only the power cable attached was reported. if you are referring to the securaplane incident, the technician had not connected the management connector, which, according to one scenario, may have caused the conflagration. The report is linked in one of my earlier posts.


1. Is the ground charger multipurpose, whereby the data cable is not used for other battery types? What disconnect sequence? What is the effect of not connecting the data cable?
All Li based batteries have management electronics built close by, and are charged by a dedicated charger. 787 powers charger from an instrument bus as above.


2. Is capabilty to vary the charging current by cell by 2 amps either way enough? Is it that or more?
2A is plenty, 10s to 100s of mA typical.


3. Is this cell balancing done only on charging, or also discharging? It is obviously impractical in the scheme outlined during APU cranking.
Only on charging. Discharge must be stopped when the weakest cell is empty to prevent reverting it (below).

The critical reason for active balancing is to prevent cell over voltage.


4. Plus all the usual-- algorithims, floating discharge on bus, etc.
Undervoltage, monitoring/logging, emergency cutoff.

Li cells cannot be deep discharged below about 2.7V and must be replaced.

Pb cells can be deep discharged, as long as cells do not revert. And _must_ be charged without delay to prevent capacity loss by sulphate formation.

NiCd cells can be deep discharged and left without fail, as long as cells do not revert.

Reverting cells
With all batteries, reverse charge occurs when the weaker cell(s), after being totally discharged, get charged by the stronger cells in reverse polarity.

To understand, imagine an AA cell and an AAA cell in series on a load, what happens when AAA cell is discharged, while the AA cell still has not completely discharged. The voltage accross AAA cell will revert, destroying it.

[keesje]

A design that allows cells to routinely fall below "lockout" level, is ,IMO incompetently and poorly engineered. (Unless it's a deliberate and cynical ploy to sell more batteries ) but no firm would put profit before dependability,would they?

Steve, thnx. Exactly what I'm wondering about. Next to the battery uncontrolled heating problems.

[EEngr]

A design that allows cells to routinely fall below "lockout" level, is ,IMO incompetently and poorly engineered. (Unless it's a deliberate and cynical ploy to sell more batteries ) but no firm would put profit before dependability,would they?Routinely, yes. But one of the functions of the battery systems is to provide power in an abnormal (emergency) situation. In this case, its better to kill the battery by running it dead than to lose the aircraft.

The problem now becomes: How do you differentiate between an abnormal condition and some maintenance person leaving a switch on at the end of shift? Without incorporating a bunch of air-ground and other logic with its failure modes?

[Pub User]

The problem now becomes: How do you differentiate between an abnormal condition and some maintenance person leaving a switch on at the end of shift? Without incorporating a bunch of air-ground and other logic with its failure modes?

Is that really such a problem for a machine with a core computer system? I would have thought it would just be a matter of a software tweak.

[Lyman]

Imaginary math can also cause a disastrous result.... One that may need some real math. Or engineering.

Hubris....

[saptzae]

@Pub User

Is that really such a problem for a machine with a core computer system? I would have thought it would just be a matter of a software tweak.

Practically all technical details were discussed already, at least twice. Time for a little philosophy.


Assumption is the mother of all failure
Fix one problem, create two anew
Shades of gray, no black and white
When to and when not to, that is the "to be or not to be" question
I like to read much more than to write

[inetdog]

Over-discharging effectively destroys the cell. charging to the limit brings a possibility of spontaneous combustion. therefore, like the pilots keep clear of "Coffin Corner" and" Stall" these batteries demand usage in the "safe" part of their envelope.

A design that allows cells to routinely fall below "lockout" level, is ,IMO incompetently and poorly engineered. (Unless it's a deliberate and cynical ploy to sell more batteries ) but no firm would put profit before dependability,would they?

One of the potential advantage of Lithium batteries is that they have about 20% of their energy storage capacity below the point of no return state of charge (SOC). This means that in a true emergency, you still have 1/5 of the nominal battery energy available as long as you are willing to replace the battery after the incident.
But this raises the problem of how to make use of this reserve. You have to either set the Low Voltage Cut Off (LVCO) inside the battery pack to allow discharge into the reserve if nothing outside the battery itself stops the current flow at a higher voltage, or you have to allow for some sort of signal to override the LVCO in the case of a true emergency.
I have no idea which approach the system designers took, if indeed they planned for the use of the reserve capacity.
But even if they set the LVCO above the point of no return, I can see that they would want to latch this condition in case the discharge to that point may have actually taken one or more cells into the danger zone. Possibly after the battery is returned to the factory, it can in fact be recharged after testing. But in terms of certification, etc. it would probably make more sense just to do a quick forensic analysis and then discard it.
That strategy relies on over-discharge being an infrequent event, and that does not seem to be the case here.

One therefore makes the assumption that all charge/discharge functions must go via the "charger"which is then a glorified power-supply/filter as seen by the battery.

But, as described, the charging algorithm, specifically the fast charge without overcharge part, was designed by the charger manufacturer, and would require some significant exchange of data between the charger and the battery's internal management system. Did Yuasa design part of the overall charge control (not just balancing) into the battery pack based on instructions from the integrator? Or does the charger receive full data from the battery and decide what voltage to apply to the pack as a whole? Is the information flow one-way or bidirectional?

[saptzae]

I mentioned it before, the batteries are rated at 4V, so about 80% of LiCo limit charge at 4.2V

@inetdog
Concur with your 20% spare margin at the expense of destroying batteries.

But, I don't buy this, inline what we have seen and documented in this thread, and according to the NYT report, ANA clearly found several operational failures which had nothing todo with "operational misuse".
http://www.nytimes.com/2013/01/30/business/boeing-aware-of-battery-ills-before-the-fires.html?pagewanted=all&_r=0

After all, what is the foundation of this business? Following procedures.

[Lyman]

But that is the frustrating thing. Thus far, no one is privy to Boeing's "intentions" with the new technology.

It strikes me that is the basis of discussion at this point. Muddying "Emergency" (back up) duty with normal ops is the challenge, one apparently not met.

The mitigating conditions speak of pretty aggressive outcomes, fire, smoke, collateral damage to other systems, etc. For an Authority, FAA, JTSB, to allow for such outcomes in an emergency is one thing, but an expectation of such dangerous behavior becoming a "normal" expectation, (non emergency, non "back-up"), cannot possibly be the purpose of what essentially could be interpreted as a "waiver" for other than "abnormal" ops.

Could it?

So, here is the predicted outcome: Airworthiness is the call of the FAA, so if not met, the responsibility can be laid at the Feet of FAA, letting Boeing off the hook from some pretty severe sanctions. But, the FAA has no Money, so Boeing will pick up the tab for "Continued Airworthiness".

That is the way it is set up, grousing about it is useless. I hope it happens quickly and safely.

[hetfield]

@Old Engineer

Thx for the explanation:ok:

[Uncle Fred]

Just have to say Gents (or Gentesses as the case might be) that this is PPrune at its best.

I fly airplanes, not build them, and thus have to march quickly to try to keep pace with the more detailed engineering explanations. Yet there seems to have gathered a good group who aspire to make the unknown, known and it benefits us all. Many thanks for the reasoned and searching dialogue. Good work.

Never would have thought that a discussion of batteries would be so interesting. Maybe next it will be tyres or fan blades...

[RR_NDB]

Hi,

Uncle Fred (http://www.pprune.org/members/270275-uncle-fred):

Never would have thought that a discussion of batteries would be so interesting.
(http://www.pprune.org/tech-log/505695-787-batteries-chargers-19.html#post7669864)

A long time ago i started to respect these devices that many people consider not so important. In one opportunity in winter time i kept a Ld acid battery being night long charging (~ 2 Amps) and before leaving with my VW beetle when disconnecting the leads a loud hydrogen explosion (inside the car) made me respect the issue a litle more. :)

...group who aspire to make the unknown, known and it benefits us all.


Precisely, this is the motivation behind our diligent work. These devices are not simple, Boeing, NTSB and many professionals in the industry are learning (technically speaking) and trying to do the best for Aviation Safety.

The message to the high rocks of the entities involved including FAA is clear. The issue deserves kind attention.

Thanks for your incentive.

[Chris Scott]

Quote from TURIN:
"Chris Scott.
Temp/Time limits on the APU are due to a rotor bow problem caused by excess heat soak after shutdown.. The quick fix is to leave the APU inlet door open to allow sufficient ventilation of the APU powerplant. Long term fix will be hardware/software changes."

So let's get this right. We have an APU that has to be treated with kid gloves, including 30-minute rest breaks, and currently no on-board battery available to start it. I remember flying a long-haul airplane about forty years ago that was still dependent on a GPU for meaningful electrics on a turnround. It was called a Seven-Oh-Seven.

Right now, its great-great grandchild is looking to be a bit of a dog. Shame.

End of rant... :)

[Uncle Fred]

Quote from TURIN:
"Chris Scott.
Temp/Time limits on the APU are due to a rotor bow problem caused by excess heat soak after shutdown.. The quick fix is to leave the APU inlet door open to allow sufficient ventilation of the APU powerplant. Long term fix will be hardware/software changes."

So let's get this right. We have an APU that has to be treated with kid gloves, including 30-minute rest breaks, and currently no on-board battery available to start it. I remember flying a long-haul airplane about forty years ago that was still dependent on a GPU for meaningful electrics on a turnround. It was called a Seven-Oh-Seven.

Right now, its great-great grandchild is looking to be a bit of a dog. Shame.

End of rant...

Your not alone on shaking your head on this one Chris. Of the Boeings that I have flown I have only had a problem once and that was on the 777 when it auto-shutdown due to an internal limit.

Kid gloves is correct--among the systems on an aircraft that should report fit for duty when called upon the APU is certainly in that august group. Having to wet-nurse this thing as Turin describes is not instilling much confidence at the moment...

[bsieker]

Now my information may be about 2 years out of date, but what I have seen says that after APU shutdown "there is no cooldown period", several times. To me that indicates it can be started again immediately after shutdown.

The only cooling period during which no restart should be attempted is after two consecutive failed start attempts from the APU battery alone. And that is presumably a battery limitation, and not an APU limitation.

Also,

[After shutdown] (t)he APU continues running in a two minute cooldown cycle. [...] At any time during the cooldown period, the APU may be returned to its running condition by placing the APU selector back to ON.

[Chris Scott]

Bernd,

Yes. The limitations you describe from two-years-old information are in line with normal practice for conventional APUs back to the 1960s. Unfortunately, as I've commented before, I was never clear whether the delay before a third start attempt was to avoid overheating the starter motor, or the battery, or to give unbernd fuel a chance to drain into the drains tank (from which it is subsequently ejected!).

However, this APU, unlike others, is not required to provide the vast amounts of bleed air needed for air conditioning and (pneumatic) engine starting. So it is a very different beast, I guess. Presumably, the "rotor-bow" problem described by TURIN only came to light on service entry.

[TURIN]

Correct. As I said, this quick fix is to ensure continued operations of the APU, albeit with awkward ramifications for the operator.
All a/c have these type of issues throughout their service life. It just so happens that the spotlight is shining ever so brightly on this one and we are seeing them.

[USMCProbe]

It might not provide massive bleed air for AC and engine start, but it is going to have to provide massive amounts of electricity to accomplish the same things.

The starter for the engines on the 78 is electric, not pneumatic?

Lots of new stuff.

[hetfield]

The starter for the engines on the 78 is electric, not pneumatic?Yes..

"Another fundamental architectural change on the 787 is the use of variable frequency electrical power and the integration of the engine generator and starter functions into a single unit. This change enables elimination of the constant speed drive (also known as the integrated drive generator, IDG), greatly reducing the complexity of the generator. In addition, by using the engine generator as the starter motor (an approach used with great success on the Next-G eneration 737 APU), the 787 has been able to eliminate the pneumatic starter from the engine."
AERO - Boeing 787 from the Ground Up (http://www.boeing.com/commercial/aeromagazine/articles/qtr_4_06/article_04_3.html)

[mm43]

@ TURIN, saptzae;

Thanks for your responses to my query at #363 (http://www.pprune.org/tech-log/505695-787-batteries-chargers-19.html#post7668532).

The blocking "diode" will most likely consist of parallel high power MosFets to reduce voltage drop and hence power dissipation.

My overall impression is that a Li-Ion battery consisting of multiple cells in series must have stringent manufacturing requirements for matching the impedance of each cell over the max/min operating cell temperatures. Only by selecting matching cells will charge/discharge cell balancing have a reasonable chance of keeping the battery as a whole in a stable state.

[RR_NDB]

Hi,

1)

Why Boeing 787 can´t be equipped with another battery?

We can list the reasons? And quantify the implications?

Weight, Volume, etc. (for 787 required currents and Amperes x hour)

2)

An alternate battery (or a set of alternate batteries) could be used to shorten the "grounding time"?

3)

What about the implications (of a change) WRT "integration" to 787 circuitry, chargers, circuitry (Diode modules, etc.)

4)

There is (are) other(s) reason(s) for the grounding?


:confused::confused::confused::confused:

[Romulus]

Are any of the alternatives certified for use though?

[saptzae]

@mm43
Either schottky diodes or power mosfets with reverse current cutoff circuitry.

Yes, cells must match closely.

Charging includes cell voltage balancing by current bypass. Discharge is not balanced.

Questions on my mind (Picture: CT scan of JAL APU bat at BOS)
http://i337.photobucket.com/albums/n385/motidog/GSYuasa7872.jpg
Cells top left #1, top right #2 to bottom left #7, bottom right #8. #3 was identified by NTSB as shorted (#6 in their rotated picture).



Why all and only the left cells #1, #3, #5, #7 show similar horizontal "streaks"
What are physical/chemical differences between left and right cells after strip down
What is the (expected) effect of these streaks on cell characteristics, such as leakage, capacity, charge current vs cell voltage
Were similar streaks found in other batteries
Can streaks be recreated in new cells by electrical or thermal means
Why cells #2, #6, #8 show more bulging than others
Was #3 the first cell to fail
Did failure of #3 induce over charge of other cells
Did failure of #3 thermally conduct to nearby cells (#1, #4, #5) and cause thermal runaway in any of them
Which cell valves were found ruptured

[USMCProbe]

I would say #1 and #3 are the closest to normal, and the streaks are normal. When the rest of the cells were overcharged they all bulged and the spaces between the individual "plates" (not sure that is the right term), and the batteries, disappeared.

It looks like 7 of the cells were damaged.

Nice picture. Which battery is this? Different aircraft?

[saptzae]

@USMCProbe

Picture is of CT scan of JAL APU bat at BOS

Thank you for your interpretation.

[USMCProbe]

#3 looks the least damaged. To me that means the BMS did a good job balancing the charging, and the whole thing was overcharged. IMHO that means there was not a single defective cell. 7 defective cells? Possible but I think #3 just got lucky.

7 bad cells is possible. If they are, at least Yuasa is consistent.

I think Boeing has their work cut out for them. I think the problem is systemic, and the only way to recreate the problem is to..........fly them and instrument the heck out the charging/BMS/batteries.

[Machaca]

NTSB stated Feb 1:
The auxiliary power unit battery, manufactured by GS Yuasa, was the original battery delivered with the airplane on December 20, 2012. It is comprised of eight individual cells. All eight cells came from the same manufacturing lot in July 2012. The battery was assembled in September 2012 and installed on the aircraft on October 15, 2012. It was first charged on October 19, 2012.

Examination and testing of an exemplar battery got underway earlier this week at the Carderock Division of the Naval Surface Warfare Center laboratories in West Bethesda, MD. The tests consisted of electrical measurements, mass measurements, and infrared thermal imaging of each cell, with no anomalies noted. The cells are currently undergoing CT scanning to examine their internal condition. In addition, on Thursday, a battery expert from the Department of Energy joined the investigative team to lend his expertise to the ongoing testing and validation work.

An investigative group continued to interpret data from the two digital flight data recorders on the aircraft, and is examining recorded signals to determine if they might yield additional information about the performance of the battery and the operation of the charging system.

Next week, the NTSB battery testing team will initiate a non-invasive "soft short" test of all cells of the exemplar battery. This test will reveal the presence of any high resistance, small or "soft" shorts within a cell. Also, an NTSB investigator will travel to France with the battery contactor from the JAL event battery, for examination at the manufacturer. The battery contactor connects a wiring bundle from the airplane to the battery.

[bill good]

Looking at the CT scans it appears the metal cases are touching & the internals are pushed out of shape which results in shorts everywhere!! Nothing would protect the pak if that occured & the charge circuit continued to provide a nice stable 30 V into this mess. It would not be a good thing to continue with this type of cell if could short out to the case & the metal box containing the cells !!. There is some idea not to float charge Li Ion but to charge then disconnect until needed. Could this get the aircraft back flying if the battery was isolated for flight? After all this is not reliant on the battery for systems in flight. It is still available for the energency case if required. I would be pleased to help Boeing further all they have to do is call me.

[USMCProbe]

Saptzae;
Can you post a CT scan of a perfect, undamaged battery?

[saptzae]

@USMCProbe

If I could, I would have.

Scan was published by the NTSB.

[USMCProbe]

I can't see any pattern. If it was a single bad cell going off, I would expect to see a "damage gradient", no matter how the heat was generated.

I would also guess this was a single event. Had it happened numerous times I would think all the cells would have bulged. Each time it would have happened, heat would be generated, and then the whole pack would get heat soaked, and slowly cool down over time. Single event, stopped by the fire crew, and cooled down.

They have lots of smart folks working on this. I am sure they are going down a hundred different paths at the same time.

[USMCProbe]

Question for the BMS/electrical gurus:

For some reason they put the main battery terminals extremely close together on the outside of the case. 30V is not a lot, but the higher the voltage, the more it can jump. Lets say a little dirt/condensation/grease is allowing a very very small amount of current to flow on the outside of the battery case between terminals. How would this affect the sensing function of the BMS? I would think it would be a slow draw, always pulling the battery voltage down slightly, requiring - more charging?

I am not an aircraft mechanic. Do normal 28V aircraft batteries put their main terminals an inch or two apart?

[RR_NDB]

Hi,

The battery (high current) is the aviation standard.

This is PERFECT.

Question:

Why Thales decided (together Yuasa) use THE SAME GEOMETRY for the battery?

They had time during 787 R&D to think in other sizes or geometries for the battery.

[kilomikedelta]

From the photos in post #1 of this thread, the battery terminals (J3) seem to be about 2 inches apart and about 1/4 inch in diameter. The CT (computerized tomography) scan is an X-ray horizontal 'slice' at about the level of J3. The GSYuasa data sheet http://www.s399157097.onlinehome.us/SpecSheets/LVP10-65.pdf for the LVP65 battery seems to suggest that each cell comprises six sub-cells (connected in parallel at top and bottom?) which appear as 'streaks'. The cell anodes and cathodes, I'm sure, are not connected to the cell case.

[RR_NDB]

Hi,

In addiction to the 4 "simple questions" in my post #389 and the one concerning battery geometry i have another:

The recharging time of both batteries is critical in 787? Why? The highly redundant electric power generation is noth enough?

[TURIN]

The recharging time of both batteries is critical in 787? Why? The highly redundant electric power generation is noth enough?


Who said it was critical? I can't find a reference for that.

AFAIK The recharging requirement for the 787 battery is no different to any other.

Except perhaps for emergency brakes in the event of a total electrical failure on takeoff before V1.

[RR_NDB]

Hi,

TURIN,

The most important question (until now UNANSWERED) was posted some days ago by Sandy...(i didn´t find post #):

"Why the insistence on this battery?"

The prolonged grounding of this Dream Craft is to be caused by lack of a DC supply (rechargeable "on the fly") with the electrical specs of the WRONG SELECTED BATTERY?

PS

I am not blaming the cells: The battery CLEARLY was not designed with the reliability and dependability required by the Dreamliner. IMO the problem is: a "nightmarebattery"

The Dreamliner, a technological dream, deserves a Battery. Not a poorly designed one.

URGENTLY.

PS2

A DC SUPPLY IS A VERY BASIC "THING". What is happening is surreal for me.

[Lyman]

So NTSB have begun looking beyond the battery, to other possible failure modes.

Boeing replaced as many as one hundred fifty batteries prior to grounding.

Almost enough to upgrade the entire fleet in service.

Until two old batteries lit up.

There has not been a "mystery" from the outset.

"it is inconceivable Boeing would not know what the problem was, since before evidence of it became known".

QED

Occam is being rudely abused, here and elsewhere....

[RR_NDB]

Hi,

Probably we are watching one of the best examples of:

Keep It Complex Stupid.

It´s very easy to go to complex situations. You just need to be incompetent. It´s not simple to maintain situations "under control". You need to be competent in Technical and mainly in the "organizational aspects".

[TopBunk]

I understand that they have replaced 165 batteries. Quite a few of those were lifed items - remember that a lot of 787's have been standing around for a long time.

I also understand that Boeing are hoping to fully instrument an airframe with a view to conducting a series of test flights within the week, with plans in place to regain airworthiness within the month, albeit with certain modifications including measures such as venting to atmosphere and possible enclosing the battery in a welded steel container.

[Lyman]

Yes, enough replacements to refit the in-service fleet. They would not have done that without banking on its acceptance by the authority.

Which means an ongoing violation of the letter and spirit of the Certificate.

With people on board, in "commercial carriage"......

(should I have bolded that?) "with people on board".....

Flight test in commercial carriage?

That is an ad hoc and illegal "Airworthiness Directive"

If the "new battery" is different in any way from the OEM, the violation is cut and dried. If it is merely a "fresh OEM" there is still a violation, one a bit more arguable, imo....Plus, how did they "ferry" the "replacement" batteries? A question I posed three werks ago?

Did FAA issue a "Notice of proposed rulemaking"? Seems public comment should have been solicited in allowing "highly dangerous cargo" to fly?

[RetiredF4]

Grant me one (maybe silly) question.

Could the problem be related to the amount of composite materials of the aircraft structure with regards to static charging when in flight or due to insufficient grounding of the cell when on ground after flight? When i get a static discharge in my house, it´s most time asociated with some non metallic material.

As it looks now, a fault in the batteries or in the charging system should have been found some days ago, therefore there could be a greater problem maybe typical for this special built aircraft, which was not considered in testing.

[sb_sfo]

"Until two old batteries lit up"

Drawing your attention to post 395:

The auxiliary power unit battery, manufactured by GS Yuasa, was the original battery delivered with the airplane on December 20, 2012. It is comprised of eight individual cells. All eight cells came from the same manufacturing lot in July 2012. The battery was assembled in September 2012 and installed on the aircraft on October 15, 2012. It was first charged on October 19, 2012.

6 months after build and less than 3 weeks in revenue service is not an "old" battery.

[Lyman]

I very much respect your writing sb_sfo.

Consider what I wrote, in all its possibilities, and look for where it might be correct, not wrong.

Sorry if this is rude, and I do not think you need an explanation, but if you do, you might not "get" it.

Hint: from the BEACH BOYS, "She's Real Fine, My (#)409"

A general comment. NTSB have "moved on" to look at additional systems.

Where does it say, "The Battery Performs to SPEC". I hope it's there, but I could not find it.

In reading anything, anything issued by the governmental agencies, there is virtually always more in what "is not written".

[RR_NDB]

Hi,

RetiredF4 (http://www.pprune.org/members/302846-retiredf4):

Could the problem be related to the amount of composite materials of the aircraft structure with regards to static charging when in flight or due to insufficient grounding of the cell when on ground after flight? (http://www.pprune.org/tech-log/505695-787-batteries-chargers-21.html#post7673140)

When you put electric power Systems managed by sensitive electronic circuitry you must look carefully to Electromagnetic Interference and Compatibility. (EMI/EMC).

Grounding and Shielding is another issue in the innovative 787 design. The issue of fuel storage in the plane deserved special attention like "inerting" and carefull structures bonding, etc. The ANA 747 hit by a bolt just after takeoff (http://www.pprune.org/www.youtube.com/watch?v=6J9Cc1bMZOs) is an example of what we are subject and the Concorde yaw damper being interfered by HF transmitter keying (as mentioned by Cj in AF447 threads) are to be remembered.

Normally LOW IMPEDANCE circuitry are less prone to be interfered. But:

1) High current and possibly Spikes could interfere in analog and even in digital circuitry.
2) We have inside the battery case more than 500 (estimating) devices and it seems also a high current switch. The two PCB certainly has a "safety role".

I would not consider EMI/EMC in this cases (batteries) as priorities to be looked.

But when investigating, specially when you are in the dark WRT to WHAT and WHY as put by NTSB chief you must look to everything. Even after you find a smoking gun. You may have more than one design problem. The FAA review has this merit. Will spot in other possible issues.

Your comment is pertinent to a new design using "less metal".

[RR_NDB]

Hi,

TopBunk (http://www.pprune.org/members/24800-topbunk):

I understand that they have replaced 165 batteries. (http://www.pprune.org/tech-log/505695-787-batteries-chargers-21.html#post7673063)

I heard this important fact was not considered a safety issue.

I hope Thales, Yuasa and, last but not least, Boeing started to look to WHAT and WHY since the facts started to mount.

[glad rag]

thinking out of the box here....

I know of 3 airframes [mil and civ over 30 years onthejob] that had circulating current issues along with their associated bond/earth configurations once in service..

2 of them were FBW as well, both with fair % composites construction.....the one left was the F4 in it's final years of service....

....corrosion, intergrannular and especially the less than obvious galvanic, leading to bonds and earthing paths going "high" resistance.....currents finding their "own" way through ex areas...

...just saying...

ref..Corrosion of Aluminum and Aluminum Alloys - Google Books (http://books.google.co.uk/books?id=iEeiQEeLOmYC&printsec=frontcover#v=onepage&q&f=false) chap 5

Which, Lyman, :) brings us neatly round to our original opening gambits, electrical installation "quality" from that photograph....:hmm:

[Lyman]

My patience was wearing thin, waiting for additional support.

:ok:

I am still awaiting some outside interest in "itinerant Polarity reversals"

slippers, pipe, Super Bowl......

[glad rag]

slippers (http://www.pprune.org/newreply.php?do=newreply&noquote=1&p=7673381#), pipe, rounders When you've seen it, done it, eaten it [and probably shagged it] sometime in your past [and have the T shirts to prove it] you develop that "don't need the sh1t" second sense that gives you that little 10% extra margin that stops issues becoming PROBLEMS.

Nobody wants to employ [or listen to] the old guys anymore. :ugh:

See where it gets you?:}

[TURIN]

I class myself as a simple individual working in a complex industry.

However, this thread and the one running in R & N seems to have been hijacked by philosophers typing in riddles.

No offence but could we please speak plainly for the sake of us simple folk.

Thanks. :\

[mm43]

A cropped image from one recently published by NTSB, showing internal arrangement within a cell.

http://i47.tinypic.com/29fxnip.jpg

[hetfield]

Thx mm43

That's very interesting.

Looks like 6 sub-cells are put in parallel to a "master" cell of (1/8) 65 Ah.

Who/what is doing the internal balancing?

[mm43]

A very good question.

All the talk has been around balancing each of the 8 cells within the battery, but we seem to have within each of those 8 cells another 6 sub cells, but they are in parallel and provide the low impedance required for high current discharge.

There doesn't seem to be a practical way of balancing the sub cells - a crowbar comes to mind.;)

[hetfield]

To put it simple...

There are 48 cells in a 787 battery, right?

Eight "master cells" are balanced/monitored, right?

The sub cells are NOT BALANCED / NOT MONITORED, right?

[mm43]

The sub cells are NOT BALANCED / NOT MONITORED, right?
The CT scans show nothing to indicate monitoring of the sub cells, so in that respect it would appear that your assumption is correct.

[kilomikedelta]

I think you're catching on. Most modern electronics run off a 3.3V supply.

[glad rag]

No offence but could we please speak plainly for the sake of us simple folk. Easy, push the limits without the skills or competence to do so and it WILL come back on you.

Discount hard won experience at your peril.

etc,etc, as explained earlier in the thread re-hiring new "grads" and bumming out the older, expensive guys.

thought it was pretty straightforward really.

OOOO the rounders bit.

Sorry.

:}

AND. Whilst the detective work in following posts is to be highly commended, :D , the point isn't in the detail, it's WHY and HOW.

keep at it guys.:ok:

[Speed of Sound]

The sub cells are NOT BALANCED / NOT MONITORED, right?

They are not monitored, no.

If you look at the multi-pin connectors on the edge of the PCBs they look to be carrying 16-18 connections each, therefore no more than 36 'data' lines to the monitoring system.

Also if you look at the actual connections to each cell, the only connections are to +ve, -ve and the shunts between cells.

[hetfield]

@SoS

So, no balancing of each of the 48 cells, right?

[Lyman]

I am not trying to be funny. Depending on the random (chaotic) transient (and functional) isolation of the cells, to include metallic dendrites, the actual number of 'cells', depends on characteristics that were not designed. That includes fluctuating polarities, in stress.

64? 137? xxx?

[kilomikedelta]

One monitoring connection to the + and - of each cell. One connection to each intercell strap and six connections to each of the + and - buss bars.

[sb_sfo]

My concern is that someone who, unlike you, I, and others, may not have read the entire thread stumbling in here, sees your post, and believes that at least the battery in the JAL incident was not essentially brand-new.

Anybody remember the post some 300 ago about the article in Flight Global that mentioned that Boeing had changed the architecture of the battery, and was going trying to get the new version in the first delivered aircraft? Is that where they decided to go with the 6x8 configuration? Has this thing had ANY flight test?

[Lyman]

sb sfo

I had not considered that. We are on exactly the same page, except for one thing.

I do not think the "proposed change" was architectural, but chemical.

They reported they were switching to Manganese Oxides prior to delivery of the first 787 to ANA, its debut client.....as I recall.

So you got my point re "new". Yep.

A "fresh" unit of an "old" technology, etc. :ok:

[syseng68k]

A few days away and there's pages of it to catch up with :eek:

I don't know where the "subcells" is coming from, but there are 8 cells only. If it looks
like more, that's just the manufacturing process, or a trick of the light ?..

From what we know, all 8 cells are individually monitored and each cell has current balancing during charging...

[hetfield]

I don't know where the "subcells" is coming from, but there are 8 cells only. No!

Eight packs a 65Ah, each consistent of 6 parallel connected cells.

To make clear, one single cell can't hold 65 Ah!

[syseng68k]

NTSB playing with high tech kit to find out what many suspected
anyway and still no info as to the cause of the problem, in public
at least.

My premise is still that there's basically nothing wrong with the
batteries, despite ntsb playing with them for many, many days, almost
obsessively. Makes one wonder what the real agenda is there.

Assuming that the batteries are ok, this leaves only a few possibilities.

1) Operational conditions far outside those expected, which may have
prompted software bugs in the charger or management boards to become
exposed during fast charging.

2) Again, software bugs or insufficient monitoring of individual cells
under heavy load, say apu starting, which caused one or more cells
to be discharge beyond safe limits.

Any out of band conditions should be logged by the charger, but there
appears to be no evidence of that from what we have been told, so a
hidden / intermittent software bug does start to look likely.

From info available, the chargers and monitoring have been used
elsewhere, but the software would be different and specific for each
application. Bugs can take years to become exposed in some cases and
only under certain sequences of events or timescales of operation. The
battery subsystem is still a very new product.

If the charger hasn't logged the real time sequence of events that led
up to the failures, then that is a deficiency in itself, imho...

[Lyman]

syseng68k


The trick is understanding the technique. Yuasa calls the electrodes "wound", yet they present as "folded".

So I repeat my question, syseng68k:

If the structure of each plate is continuous, only round (cylindrical) packing is acceptable.

"folding" a long thin structure concentrates mass under stress at each "return".

This also concentrates heat at the buildup, and traps heat at a center that could be geometrically oriented closer to the outer surface of each cell, if each cell was a cylinder, not a square (rectilinear) shape.

Seems like a major mistake, and Mr. Musk seems to agree.

[mm43]

@ hetfield;

Texas Instruments ...
A battery pack is constructed from a string of series and parallel cells. Each series cell, or group of parallel cells, requires protection from over-charge, over-discharge and short-circuit conditions.Overall, each group of parallel cells forms one of 8 series cells, and the only monitoring that is done is that of each parallel group as its contribution to the series. The very low impedance of the parallel grouped cells makes balancing of individual cells within the group extremely difficult.

Now, that's my interpretation, and I believe that is what the TI statement implies. I have been known to be wrong - on may occasions.:}

[kilomikedelta]

I don't see any folding in the photo in post #419 nor in the CT image.

[hetfield]

@mm43

Thx, I know....

The very low impedance of the parallel grouped cells makes balancing of individual cells within the group extremely difficult.

True, but irrelevant, negligible?

Don't think so.

[Lyman]

Frankly, folding is all I see.

The continuous "plate" can be seen on the Securaplane lab table...

NTSB photo

[syseng68k]

I really don't understand all the obsession with the batteries. Though
that is the part that failed, it's also the most low tech part of the
subsystem. Imho, those batteries were operated outside the data
sheet limits, otherwise they would not have failed. (Sticking neck far
out here)

The charger and monitoring systems probably have thousands of lines
of code and a vast array of electronics. Why have there been no questions
about that ?...

[syseng68k]

Lyman:

Mr Musk is free to have his opinion, but to use the phrase, his is
just one man's opinion of moonlight. For any design problem, there are
usually > 1 valid solutions and Mr Musk's application is very different
to that of the 787. His application involves high voltages, a much
greater number of cells and much higher power capability, so would
need a very different solution to that required for the 787. Sorry,
but sounds more like a self publicist at work, rather than serious
engineering. Yuasa have been building these batteries for decades,
they've been approved by NASA and the European Space Agency after
some of the most stringent testing. Are all those people and Boeing
really stupid ?.

Anyway, we all know what a certain gentleman said about "opinions"
all those years ago :}...

[Speed of Sound]

If the structure of each plate is continuous, only round (cylindrical) packing is acceptable.

Not if you want to pack more cells into the smallest volume! ;)

http://news.bbc.co.uk/olmedia/1390000/images/_1390088_watermelons300ap.jpg

[bill good]

Would the aircraft not automatically disconnect the battery if any of the cells went out of tolerance both high or low ? Could someone who knows the B787 aircraft respond please.

[kilomikedelta]

Bill, The flight deck crew responded to the SOP for a warning light and an anomalous odour. The information you request is proprietary and to which you are not privy. You may be hearing from the attorneys of Boeing or whatever subcontractor for even asking that.

[syseng68k]

kilomikedelta:

My take on that very funny post:

I have the gut feeling that we may be being led by the nose on this
enquiry. There's so much reputation and $ at stake that there may even
be people here who would conveniently steer the discussion off into
the boonies to mask serious analysis and possible discovery of the
truth. (Tinfoil hat aside) :confused:.

In fact, any battery of that type must be disconnected from load or charger if
cell voltages are outside high or low data sheet limits, otherwise, you are in
unknown territory. It's that simple...

[Lyman]

That is what makes non cylindrical unacceptable, trapped heat.

And no space between cells.....:ok:

Chris....I think the most powerful of any "scout" is Occam....:D

[bill good]

Two meltdowns different systems same battery. CRM extends to all sectors of aviation & attorneys are not part of the safety aspect BUT I am safe. (not worth much to any attorney these days & there are bigger fish to fry in this issue!!) & depending on what stage the warning would appear i.e. delayed temp warning requiring crew action V an automatic disconnect with warning is beyond my knowledge of this system hence my question. I would expect auto disconnect for any Li-Ion battery fault under all conditions but if it a problem to answer within this forum then email me. Aviation 25kHrs command & electronics made up all my life before time expired.
Regards

[kilomikedelta]

Bill, Your initial question was perfectly valid. My cynical response was only to point out that when management is questioned, they call out the legal rottweilers who advise that no further information be released (CoverYourAss). There does not appear to be any high current disconnect device within the Thales battery case and no apparent control signals to activate one. To me, breaking the circuit at a distance from the battery under high temperature/corrosive atmosphere circumstances would not be optimal engineering. Unfortunately CRM is a lucrative field for corporate lawyers to tap but they will ignore you when Boeing has deeper pockets. It's unlikely that anyone will give you a straight answer to your question when $$$$ are involved. Cheers, KMD

[saptzae]

@kilomikedelta

There is a contactor/breaker in the box, also referred to several times in this thread and visible on the CT scans here and in the NTSB report.

According to recent public info, a NTSB investigator is on the way to France with it.

:ok:

[Lyman]

Is it at all possible, that as fail safe, there is a fusible link?

[saptzae]

@syseng68k
... discussion off into the boonies to mask serious analysis ...
No need, we can do that better by ourselves :{

[USMCProbe]

I am sure if there was a short circuit, a fusible link would have worked. I think the APU battery is only used for a couple of things, so a short circuit would have been easy to identify as the problem. There would have been lots of heat damage in a small area. I think anything easy to identifyas the problem, would have already been identified.

I think they will only find it while the entire system is operating, probably in flight. The question is how to do that with a degree of safety that is acceptable.

I don't think disconnecting the battery in flight is enough. Lithium cells can be damaged, but not go nuclear for quite a while later.

[USMCProbe]

If we assume the two event aircraft were the only ones that fried their batteries, what was the condition of the two flights where it happened? In cruise flight, both batteries should get little to no use, and little charging.

There were no other system malfunctions.

787's use electric wing and engine anti-ice. Pilots on other aircraft use these sparingly, as they consume a lot of fuel (bleed air). Very occasionally, you have to leave the wing anti-ice on for a long time.

Electric engine and wing anti-ice would use massive amounts of electricity, all of which would have to be dumped into the aircrafts' grounding/bonding system.

[sb_sfo]

Minor point of correction--the 787 does use bleed air from the HPC for engine inlet anti-ice. It's the only bleed air consumer on the aircraft.

[USMCProbe]

And another. 777's engine anti-ice is "auto". Not on. You might not know it is turned on. But it was 12 years ago for my last flight on it. I think wing anti-ice was still on/off.

Is this correct on the 787?

[sb_sfo]

Switch positions are OFF, AUTO, ON for each engine

[TURIN]

Would the aircraft not automatically disconnect the battery if any of the cells went out of tolerance both high or low ? Could someone who knows the B787 aircraft respond please.


Is it at all possible, that as fail safe, there is a fusible link?

APU BAT.
Circuit Breakers between FO's Instrument Bus & Bat Charger and between Bat Charger & APU Hot Bat Bus/Battery.

MAIN BAT.
Circuit Breakers between Captain's Instrument Bus & Bat Charger and between Bat Charger & Hot Bat Bus/Battery.

[hetfield]

Would the aircraft not automatically disconnect the battery if any of the cells went out of tolerance both high or low ? Which cells? 1/8 or 1/48?

[saptzae]

@hetfield
Which cells? 1/8 or 1/48?
For purpose of management, "paralleled" cells count as one.

[USMCProbe]

I wonder why they can't just INOP the battery chargers during flight until they find the problem.

Something like this.

1. No APU starts off the battery, must use external power on ground to start the APU. No towing of aircraft without APU being run.

2. Specify a certain battery voltage for dispatch. There already is one, but make it higher, almost fully charged.

3. Before take-off, pull the battery charger CB's.

4. After landing start the APU off the mains, which is normal. Push the CB's back in.


Batteries should never get discharged more than a few percent. Batteries will charged a little bit on the ground, never in the air. Fully charged batteries are connected all the time for their primary purpose, backup.

[Old Engineer]

@saptzae (#369)

Thanks for commenting on my post (#364) about charging arrangements and balancing. The TI seminar talk on this was most interesting:


Here it is how balancing is done in practice.
http://focus.ti.com/download/trng/do...0and%20How.pdf


I was struck by how much remains unknown about how much and when to apply the balancing, with the resulting mention that balancing can do more harm than no balancing if done incorrectly.

Obviously, in those parts of the charging cycle where the correct action is unknown, there is the possibility of unsuspected harm from the balancing. Altho presumably small each time, it could accumulate. There is also mention that balancing of charge is more effective and more needed approaching fully charged; but that this part of the cycle is short, which limits the effectiveness. And similarly, balancing of discharge is recommended; but set up to drive a starter motor, this is not possible in the 787.

This 8-page talk has nine figures (9th didn't download for me), and is well worth reading. It is general to several battery types, but follows with some detail specific to lithium batteries. It is undated (unless I missed it). The examples seem to be small batteries (300-500mAh) in my impression, but some of the data can be extrapolated I think, altho not the experience.

One thing that concerned me was the MOSFET regulator chip idea-- if that is general and widely used, the concept would appear to vary the effective bypass by intermittently applying a fixed bybass. (Obviously a 787 battery regulator could not fit on a single chip.) During the no-bypass intervals, the effects to be avoided (e.g. lithium plating out at over-voltage on one cell) would still occur even if for reduced time. Another problem is that this circuit cannot be applied in discharge without consuming a portion of the charge capacity, if it were somehow applied except when cranking the APU.

Therefore, @USMCProbe (#460);

i agree that no charging should be done in the air, let the tow vehicles power the movement lights; and add that sufficient time and sensors should be provided to assure that the battery is cooling down after being charged.

Beyond all that, I wonder if these DC chargers are putting out currents with too much AC ripple on it (the smoothest filtering requiring heavy choke coils inconvenient to carry aloft)?

Again, I'm inclined to more effective system of very pure DC being supplied from the ground for balancing both up or down on charging, supplied as a regulated current output (not primarily voltage regulated) for each cell, based on a digital demand generated by voltage testing by the aircraft CBs. More elaborate and expensive (surely $16k would cover), but eliminates a couple more uncertainties. Of course, that may not do it, and this is not the time to be running tests (ie, in revenue service) as has been noted.

[clearblueskyy]

Well so I've been following news closely and I cannot seem to fathom how boeing missed out on such a minor glitch, how did they get the FAA's approval and by how much does this set Boeing back in terms of cost of replacement , spare parts , deliveries etc. IMO Boeing were counting on the 787 to do exceedingly well in the market ..?!

[alexd10]

I wonder why they can't just INOP the battery chargers during flight until
they find the problem.


We can of course made innumerable suggestions for workarounds (more or less fanciful), for the case they suffer of such shortage. As it seems that the most oblivious one (the change of the battery type) is inapplicable, let's try also:



Change the batteries after each flight with precharged and monitored/tested ones for at least ... days;
After any battery kicks in, monitor the electronic bay /and land asap;
Disable the charging circuit and install one.. /two..(as required) safe type batteries as stand by.... Eventually keep one on board and connect in really need only (If these bateries are indeed safe enough to be 'transported' in an aircraft and not to sensitive to fly (position, pressure variations, atmosphere, ..... not only temperature)
After all, the main battery is only for emergencies, and the APU usage can be temporarily limited through instructions

[TURIN]

I wonder why they can't just INOP the battery chargers during flight until they find the problem.


Do we know for certain that it is the charger that is causing the problem?

[saptzae]

The only component that "for now" seems less likely, is GS Yuasa cells.

Last weeks update and this weeks activities: Press Release February 1, 2013 (http://www.ntsb.gov/news/2013/130201b.html)

[hetfield]

I'm still concerned with the 6 sub-cells of each of the eight cells.

They are never equal/matched perfectly. Current oscillations may occur, but even a totally unmonitored thermal runaway...

Check this:

Serial and parallel battery configurations (http://www.buchmann.ca/article29-page1.asp)

A high resistance or open cell is less critical in a parallel circuit than the serial configuration but the parallel pack will have reduced load capability and a shorter runtime. It's like an engine running only on three cylinders. An electrical short would be more devastating because the faulty cell would drain the energy from the other cells, causing a fire hazard.http://www.buchmann.ca/article29_files/figure4.jpg

A weak cell will not affect the voltage but provide a low runtime. A shorted cell could cause excessive heat and create a fire hazard.

[RetiredF4]

Is the problem the charging of the cells?

Following the different threads the batteries are not used under normal ops, there schould be no charging cycle necessary. But nearly 150 batteries have been changed by the operators due to being in a critical low charging state. It can be assumed, that most of those low charging conditions were observed and most probably also took place on the ground, as otherwise we would have known about it earlier by some diversion reports. Both incidents happened on the ground or shortly after departure.

Something must have caused the unplanned discharging of those batteries, what we observe in the incidents is most probably the outcome of this prior failure.

Therefore forgive me when i dont think it is wise to look for the general problem in the battery or in the charging system. The battery should be protected against turning into some fireworks if for some reason a critical low charging state happens, but it shouldn´t drain either that low on a regular basis.

Therefore the problem has to be somewhere in the wiring and design of the whole instalation into the aircraft, an integration problem.

The questions being:
- What causes the draining of the batteries?
- When does the draining process start?
- Why are the built in provisions to prevent this low state ineffective?
- What systems have to be reengineered to prevent excessive discharging?
and at last
- How can the battery be protected against going fireworks.

[saptzae]

@hetfield

Appreciated, a sub cell consists of an anode-separator-cathode triplet. All but the smallest cells consist of many paralleled sub cells. It's like that for more than 100 years.

Sub cells shortens --> cell short + heat. Sub cell opens --> reduced cell capacity and increased inner resistance with potential for cell reversal.

Important here is that BMS+charger look after the cells, keeping them in their operating envelope and mitigate cell faults.

Mitigate: DISCONNECT charger on any cell fault. When in doubt, do not charge.

[cockney steve]

^^^^^ 466 the answer is, surely, a fusible link within the cell itself.

On more than one occasion I've seen a lead-acid automotive battery where the internal lead straps have melted inter-cell or individual plates have self-disconnected, simply by melting the internal connection

I made a couple of posts on the R&N thread....synopsis...charging unit and battery unit don't interface properly. boeing appear to have failed to ensure they did.....otherwise you wouldn't change out so many rechargeable batteries in such a short space of time..

[hetfield]

Appreciated, a sub cell consists of an anode-separator-cathode triplet. All but the smallest cells consist of many paralleled sub cells. It's like that for more than 100 years.Well, to my knowledge Li-Ion batteries aren't that old...

Important here is that BMS+charger look after the cells, keeping them in their operating envelope and mitigate cell faults.Yes, but how can a charger/BMS look after the sub-cells?

They have their own social life. The rich feed the poor until dead.

[TURIN]

The questions being:
- What causes the draining of the batteries?
- When does the draining process start?
- Why are the built in provisions to prevent this low state ineffective?
- What systems have to be reengineered to prevent excessive discharging?
and at last
- How can the battery be protected against going fireworks.



Leaving them switched on and ground power dropping off line.
Towing on Battery only for too long.
Fuelling on battery only for too long.
APU switch left in 'On' position (to vent APU core)

In short a lack of education by Boeing to it's students during training.
I for one have only learned about the major problem with this battery (IE don't let it drop below a certain charge state or it's u/s) on pprune. Not Boeing.

[RetiredF4]

@turin
That would be an explanation for some batteries, but not for 150. After the first unplanned changes normal people learn from mistakes. Is the true problem masked by some of these causes as you describe them?

And are you saying, that the battery changes have nothing to do with the known two incidents from ANA and JAL?

Boing and the 787 operators loose big money, and a lot of highly qualified people are looking into the problem. There are some possibilities imho:

1.) they know the cause already, but there is no quick solution at hand /approved by FAA and therefore there is no need to tell anybody, or

2.) they are looking in the wrong corner, are still looking at the symptoms and have´nt found the causes yet.

If an easy work around (like diconnecting from chargers) would be practicable, we would see it already. They checked the batteries, they checked the chargers, they are checking the PCB´s. They have hundreds of used and new batteries available for testing, and the grounded aircrafts as well. They came out with nothing until now.

Whatever we will see, it will be very interesting.

[saptzae]

@Old Engineer

Cell balancing is nothing new, used with large telco installations for the better part of 100 years.

In small batteries (up to starter battery size) Ni*, Pb* took care of itself well enough for practical use. However, cell imbalance is present there too. In a typical old car battery, one or two cells will typically cause the need for replacement. These cells were often impaired by imbalance.

What's newer is the need for precise management of smaller Li* batteries. Every small battery has circuitry (these days often a single chip) built in.

For small cells up to a few Ah, balancing by resistive means is sufficient. The differences amongs cells are just a few percent, a balancing current in the 10s of mA is sufficient. Important is to prevent cell over/under voltage.

Discharge balancing is never done in high load applications. The available capacity is limited by the weakest cell.

Individual cells, which dropped capacity by a few percent are routinely replaced in large installations. Some, like stationary 48V Pb telco battery cells can be refurbished. I guess that it would be possible to replace individual cells of reduced capacity in the 787 battery.

[saptzae]

@hetfileld
Battery is an assembly of cells, connected in series, each cell consists of one or more sub cells in parallel. Whether the sub cells are in the same housing does not matter.

Yes, but how can a charger/BMS look after the sub-cells?It can't and it does not have to as the sub cells are all parallel.

They have their own social life. The rich feed the poor until dead.
Right, since life began, or energy that is.

[Lyman]

RetiredF4....

1.) they know the cause already, but there is no quick solution at hand/approved by FAA and therefore there is no need to tell anybody...

Almost certainly. And known cause is what caused the feverish replacement scheme. Buy time, hope for a fix.....with the blessing of the FAA.

Certainly "Flight Test" with people inside...

While Rolls R/Rs Intermediate shafts, the danger lurked..(QF32)

For all intents, a DENDRITE is an inadvertant "Fusible LINK"

[hetfield]

On Feb 5th 2013 the JTSB released a second progress report in Japanese (http://translate.googleusercontent.com/translate_c?depth=1&hl=en&ie=UTF8&rurl=translate.google.at&sl=ja&tl=en&twu=1&u=http://www.mlit.go.jp/jtsb/flash/JA804A_130116-130205.pdf&usg=ALkJrhgEl1x-8f5azoC283J9d9Q209G4lw) reporting that all 8 cells of the damaged battery, nominal voltage 29.6V, 75 Ah capacity at 28.5kg/63 lbs, showed thermal damage before the thermal runaway, particularly cells 3 and 6 are damaged. The positive electrode of cell 3 shows substantial damage and a hole, the internal wiring has melted down.Accident: ANA B788 near Takamatsu on Jan 16th 2013, battery problem and burning smell on board (http://avherald.com/h?article=45c377c5&opt=0)

http://avherald.com/img/ana_b788_ja804a_takamatsu_130116_3.jpg

8 cells?

48 I would say....

Sub cells not monitored/balanced/controlled at all!
check # 466

[RetiredF4]

frayed and broken earthing wire (http://www.csmonitor.com/Environment/Energy-Voices/2013/0205/Boeing-787-batteries-What-s-causing-their-thermal-runaways)

[hetfield]

"Large cells without enough space between them to isolate against the cell-to-cell thermal domino effect means it is simply a matter of time before there are more incidents of this nature," Elon Musk (http://www.csmonitor.com/tags/topic/Elon+Musk), CEO of electric car company Tesla Motors (http://www.csmonitor.com/tags/topic/Tesla+Motors+Inc.), wrote in an e-mail to Flight International (http://www.flightglobal.com/news/articles/elon-musk-boeing-787-battery-fundamentally-unsafe-381627/?cmpid=NLC%7CFGFG%7CFGFIN-2013-0205-GLOB%7Cnews) last week.

Boeing 787 batteries: What's causing their 'thermal runaways?' - CSMonitor.com (http://www.csmonitor.com/Environment/Energy-Voices/2013/0205/Boeing-787-batteries-What-s-causing-their-thermal-runaways)

Very funny, eight Yuasa cases, called cells, contain 6 sub-cells each.

[saptzae]

Damage seems worse than at BOS. Even a terminal was burned off.

Failure scenario seems similar to BOS though. A cell short, over voltage on the other cells and then thermal runaway.

@RetiredF4
Frayed and broken earthing wireCould be pre-existing, caused by intervention or a short to the case from a current source such as a cell shorting to its case. In case of short, I would expect more melting and burned insulation though.

If pre-existing, could cause floating battery case and (very remote) possibility of EMI disturbing BMU (the PCB's).

[Lyman]

The ANA battery failure has a different failure signal, imho. Although we see the BOS battery after complete combustion, in ANA, there is evidence of a high velocity, high temperature "jet" of gas from the top slicing through the connector. The energy is impressive. Does anyone think as I do, that may be evidence of a metallic dendrite cooking off?

[TURIN]

And are you saying, that the battery changes have nothing to do with the known two incidents from ANA and JAL?


No, but it's certainly a thought.

[bill good]

The whole installation has shown how the best of design can go wrong on so many levels. Internal shorts within the cells to case then via shielded cable to other components bypassing the disconnect circuits? One cell failure which lead to destroying other cells? I have never seen a more compelling case to remove the battery & replace with a super cap pac. (made in the USA)

[inetdog]

The only photo I have seen that shows what you describe is the one seen at this link. (http://blogs.crikey.com.au/planetalking/2013/02/06/dreamliner-runaway-battery-photo-on-ana-787-published/)
If I had to guess what happened, based on the nut being left behind while the connector is mostly missing, is that the connector melted rather than being explosively destroyed. But I suppose it might be possible for a jet of superheated gas to destroy the connector body and lug but leave the nut behind.
Another possibility is that internal elements of the battery were displaced enough that the connector plate formed a bridge between the plates themselves and got melted down or vaporized. With no kinetic energy involved, that could have left the nut behind.
I have seen pictures of wrenches and other tools that have accidentally shorted battery terminals, and what I see here is consistent with that too.

[USMCProbe]

The "frayed and broken earthing wire" looks like it was mechanically destroyed. I.e. somebody wanted to take the battery out in a hurry and didn't have the right tools. It is not burned/welded/melted. Somebody took a pair of pliers to it. The firemen did it.

I haven't seen any good pictures or scans of the ANA battery. I thought it was burned so bad that they couldn't really make a valid conclusion. The JAL battery was "lucky", in that they stopped the fire before complete destruction and they got a good look at the failure mode.

150 battery replacements does seem high at first, but 787's have flown thousandsof flights. Most of the CB's are "virtual" on the cockpit displays. It would not surprise me that unfamiliar ground crew would leave things powered by accident or lack of education. Especially during the day. At night you see the lights on. During the day, maybe not.

[cwatters]

Hetfield - the subcells appear to be in parallel with each other to make one cell. That makes balancing less essential and more difficult to do.

[Machaca]

USMCProbe: somebody wanted to take the battery out in a hurry and didn't have the right tools


The fire crew working the JAL 787 at Boston not only cut the wires, they ripped out some of the aluminum support and tore the battery box from its mounts:

http://i337.photobucket.com/albums/n385/motidog/JAL787battrack1_zpsf12cf31c.jpg

[vince_h]

I'll attempt to simplify things a bit wrt to series/parallel battery configurations.

It appears that the battery pack is made up of 8 individual batteries (NOT 8 cells!). Note this difference in terminology. Each of those 8 batteries appears to contains 6 individual cells in parallel. So 3.7V @ ~11 Ah per cell. All of the data (pictures, datasheets) I have seen points to each of the 8 batteries being monitored but not each cell in those batteries; the BMS "sees" qty 8 - 3.7 Volt batteries each with a current rating in the 65 Ah range.

Here is where it is possible for things to get interesting. Lets say a single cell (1/48 of the battery pack; 1/6 of an individual battery) goes bad. It is very difficult for the BMS to detect this because the other 5 cells are still putting out the correct voltage and accepting charge current. This can cause problems both during charging and discharging; however lets focus on charging. The BMS can be doing everything right and limiting charge current/voltage to the battery, however with 1 dead cell the other 5 are actually getting overcharged by 17%. That overcharging / discharging will heavily tax the remaining 5 cells which can induce further cell failures in the same battery. My **guess** (I haven't done math on this) is that 1 dead cell wouldn't cause thermal run-away / venting, however 2 or more dead cells within the same battery... :uhoh:

This scenario also fits with what has been said from the beginning. Several sources were pretty adamant that the batteries hadn't been overcharged. Based on the data they had from the electrical logs, that could well be correct. As a whole, the battery pack never received too much voltage / current. With a series-parallel design lacking individual cell monitoring, it is possible for individual cells to over charge/discharge while the pack as a whole looks fine.

I can see two possible "simple" solutions that wouldn't require much re-engineering beyond the battery itself (because their electrical interface to the aircraft could remain the same). Have a look at the LVP10 (same datasheets). There is a good chance that it is a single cell from the same mfg. Either monitor all 48 cells or monitor 6 strings of 8 series-connected cells. Either option would provide the BMS with a much better overview of individual cell problems and possibly the ability to remove a single string of cells from the circuit without taking the entire battery offline.

On a separate but related note: Unless we don't have the right datasheet (which is possible), how is it that the battery is only rated for -18C? Doesn't the certification process require for extreme cold start (at least -40 F/C) operations?

Vince (1st time poster; long time reader)

[saptzae]

@vince

Welcome!

Each cell contains several paralleled sub-cells in the same housing. Please lets use battery, as it is common practice, for an assembly of one or more cells.

From a BMS perspective, battery consists of 8 cells. How many sub-cells per cell is of no concern to BMS.

however with 1 dead cell the other 5 are actually getting overcharged by 17%Absolutely not! Charge is voltage limited, and _not_ volume limited, one dead sub-cell out of six would just reduce cell capacity (and thereby usable battery capacity) by 1/6th.

One can't really comment on what to change, prior to understanding what caused the failures.

Yes, these cells are rated to -18C only.

[hetfield]

@vince

Welcome:)

I really appreciate your support.

About overcharging a single cell (1/48 cells), I'm with saptzae, it's voltage limited.

About a bad single cell (short) I'm fully with you!

Let's say one cell out of six in one of the eight "cells" goes short.
The remaining 5 cells will deliver max current in that short until they are dead or the short cell is on fire. The BMS CAN'T stop this. It's an internal process out of reach for the BMS/Charger.

[TURIN]

Regarding low temp limit of -18c.

Both batteries are situated in pressurised/air conditioned areas.
The only time these batteries should be subject to extreme cold is if the aircraft is parked up, for long periods, with no power....er, during the winter.....oh!
Bugger!

[green granite]

As the electric car guy said, switch to round, true single-cell batteries, this would overcome the possibility of 'sub-cell' failure.

[vince_h]

saptzae / hetfield: Thanks for the warm welcome :)

I respectfully disagree regarding voltage based charging being a sufficient safeguard. For "old" technology (Pb / NiCad / Ni-Mh) cells, voltage based charging is a somewhat sufficient both as a charge strategy and as a detection method. Li-Ion is a totally different animal.

Have a look at a charge graph for Li-Ion / LiCO2 battery charging. Here is an example:

Charging Lithium-Ion Batteries (http://batteryuniversity.com/learn/article/charging_lithium_ion_batteries)

Charge is current limited (constant current) for a good portion of the charging cycle before transitioning to voltage-based charging. This information can be confirmed from various Li-Ion mfg spec sheets.

If a discharged Li-Ion cell is connected to a safe charge voltage (< 4 .2volts) without current limiting, it will overheat and may enter thermal run-away.

So I'll stand by my previous statement that the possibility exists to overcharge parallel cells in a Li-Ion battery without the BMS detecting it.

The only time these batteries should be subject to extreme cold is if the aircraft is parked up, for long periods, with no power....er, during the winter.....oh!
Bugger!That's what I'm talking about. I distinctly remember watching the A380 documentary and they covered the part where they flew to the arctic and the aircraft has to "overnight" in ~ -40. It then had to start without abnormal assistance.

Just something that caught my eye looking at that datasheet.

[inetdog]

USMCProbe stated:
I haven't seen any good pictures or scans of the ANA battery. I thought it was burned so bad that they couldn't really make a valid conclusion. The JAL battery was "lucky", in that they stopped the fire before complete destruction and they got a good look at the failure mode.
From the couple of pictures that I have seen (sitting on a wooden pallet), I would say that the ANA battery was actually in better shape than the JAL battery.
Pictures shown in some of the articles about the ANA battery were actually NTSB photos of the JAL battery (on a clean plastic pad with dimension calibration tags next to the battery.)

[saptzae]

@hetfield
Let's say one cell out of six in one of the eight "cells" goes short.
The remaining 5 cells will deliver max current in that short until they are dead or the short cell is on fire. The BMS CAN'T stop this. It's an internal process out of reach for the BMS/Charger. Fully concur, and I believe this is what actually happened to both ANA and JAL batteries.

I try to focus on what happened and want to stay away from what to change until failure is understood.

- There is no indication as of yet that the cells were bad ex GS Yuasa.
- To short, cell(s) must have deteriorated quickly
- What caused this deterioration
- Was deterioration during integration
- Was deterioration during operation (BMS)

- When a sub-cell@cell shorts, the BMS _must_ detect this and take the battery off-line. That did not work either. Clarify: The BMS must detect a cell short, which, at the initial event, will be a sub-cell short. How: By detecting cell voltage transients.

However, I can see merit in parallelizing 24 standard 3Ah cells via a (30A) fuse per cell. A single cell short would simply remove the shorted cell from the others, with much less energy dissipation and collateral damage.

Edit: A123 went broke after several batteries, consisting of small cells, went up in flames... A123 Replacing Batteries That Led to Fisker Karma Shutdown - Bloomberg (http://www.bloomberg.com/news/2012-03-26/a123-replacing-defective-batteries-that-led-to-fisker-shutdown.html)

[typhoid]

The Canadian regs require cert to -40c. The FAA do not.

Plus you can do the cert test and remove the battery during cold soak, only refitting just before you power up. But this should be SOP for all airlines if certified this way.

[guided]

As the electric car guy said, switch to round, true single-cell batteries, this would overcome the possibility of 'sub-cell' failure.

According to Tesla Roadster - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Tesla_Roadster) their battery pack has 53 kWh capacity at 375 V and weighs 450 kg. 787 battery has 2.2 kWh at 29.6 V and weighs 28.5 kg. So as soon as Tesla's battery gets downscaled 24-times while handling different voltage and the currents for starting APU and gets certified for aircraft it can be readily used. 2015, maybe?

[Swedish Steve]

Plus you can do the cert test and remove the battery during cold soak, only refitting just before you power up. But this should be SOP for all airlines if certified this way.

It is SOP on present day aircraft (A320/B737).
They all have procedures for parking in cold weather, and at Minus 20 or so that includes battery removal to a warm office.
It catches us out once in a while. We always put a hot air heater on the aircraft, and leave the batteries in and the outflow valves open. Then a pilot will read the FCOM and do something off his own bat.
It is amazing how much force there is with a heater hose connected, and the ditching button pressed on an A320, and you open the pax door. The FO caught the Capt as he flew across the jetty!

[RetiredF4]

USMCProbe
The "frayed and broken earthing wire" looks like it was mechanically destroyed. I.e. somebody wanted to take the battery out in a hurry and didn't have the right tools. It is not burned/welded/melted. Somebody took a pair of pliers to it. The firemen did it.

I haven't seen any good pictures or scans of the ANA battery. I thought it was burned so bad that they couldn't really make a valid conclusion. The JAL battery was "lucky", in that they stopped the fire before complete destruction and they got a good look at the failure mode.

out of this reference from today Japantoday (http://www.japantoday.com/category/national/view/japan-787-probe-finds-thermal-runaway-in-battery-2)

Photos distributed by the Japanese investigators show severe charring of six of the eight cells in the ANA 787’s battery and a frayed and broken earthing wire — meant to minimize the risk of electric shock.

There are some photos as well in the above reference.

[Lyman]

From Machaca' picture of the JAL accident....

The aluminum structure to the right of the photo shows evidence of being torn away from similar structure.

I don't think the firefighter could have accomplished that kind of damage, the Aluminum is torn. i think that could be evidence of an explosive force prior to arrival of the FF crew, an explosion.

Also there is damage in the adjacent bay to the right, fire damage, it looks like....Although early press was specific in claiming no damage to equipment "within twenty inches of the battary case", that seems to have been incorrect.

I think the twenty inch distance is a requirement of the 'special waiver' given to this LithiumIon chemistry...

[saptzae]

@hetfield

I though more about the practical side of detecting, in a timely manner, a short of a sub-cell. At that time, the BMS can't stop the cell failure, but it must protect the other cells by taking the battery off-line.

A short will not be static, it starts at a spot, current, temperature and pressure increase, it may even "burn out", but damage done will lead to further shorts nearby, propagate and short resistance will be transient with a reducing trend.

As you pointed out, a shorting sub-cell will "fight" five good sub-cells.

Thus, the the voltage variations seen by the BMS may be quite small and it may not respond in a timely manner.

What is timely? I am not sure, a few milliseconds at the most, below 100 microseconds would be better. Such short response time is difficult to accomplish.

Summing up, your concern about managing sub-cell shorting is valid, and i see your interpretation as a practical explanation for why a single cell short propagated to other cells.

What has to be done, is to make the BMS more sensitive to voltage transients on individual cells and shut charging down very quickly.