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Old 19th Jan 2013, 17:07   #1 (permalink)
 
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787 Batteries and Chargers - Part 1

The Washington Post reports:

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



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



Thales is the power system general contractor for the 787.

The chargers are made by Securaplane (a Meggitt company), who state:

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



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







Result of overcharge:

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Old 19th Jan 2013, 20:05   #2 (permalink)
 
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Thank you, Mach

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

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

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

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

In my mind, it ain't worth the extra battery capacity to require expensive charging systems and such. Then there's the requirement to have a good fire extinguishing system if one of the suckers goes into thermal runaway.
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Old 19th Jan 2013, 21:06   #3 (permalink)
 
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@gums

I agree with every word.

Nevertheless, the almighty FAA had a different opinion.....
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Old 19th Jan 2013, 21:22   #4 (permalink)
 
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The Thales Li-ion battery unit shown has a mass equivalent to 13.5 two litre bottles of cola. Perhaps restricting the drinks mixer selection and adding a few battery packs might moderate the transient draw of the 1 megawatt load of the aircraft. No doubt the marketing suits would be in high dudgeon regarding this suggestion. I suspect the electrical system weights and redundancy decisions were made by MBA's, which like papal pronouncements in catholicism, are infallible in the corporate religion.

Last edited by kilomikedelta; 19th Jan 2013 at 21:29.
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Old 19th Jan 2013, 21:46   #5 (permalink)
 
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Quote:
Originally Posted by gums
The whole battery thing reminds me of many software and iPhone/Droid folks that always want the latest and greatest apps.

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

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

...

In my mind, it ain't worth the extra battery capacity to require expensive charging systems and such. Then there's the requirement to have a good fire extinguishing system if one of the suckers goes into thermal runaway.
So who else do you give an extra weight allowance to so that you stick with older technology? Hindsight is a nice easy game to play but can you do it prior to the event? And how much extra weight allowance are you going to make for that "good fire extinguishing system"?

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

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

That's how progress works.
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Old 19th Jan 2013, 21:54   #6 (permalink)
 
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High tech gear

Mach,

Thanks for technical thread. Important issue.

The information you bring us shows there are software involved.

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


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

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

The days difference between similar incidents is just coincidence?

Battery subsystems now have their own FDR.

Could you comment something on the graph?
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Old 19th Jan 2013, 22:04   #7 (permalink)
 
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Testability

Romulus:

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

When designing innovative and complex machines the Testability issue is a big concern. And the plane testing phase may miss important details only detectable by time.
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Old 19th Jan 2013, 22:12   #8 (permalink)
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Romulus;
Quote:
Undoubtedly Boeing did their testing . . .
I expect that that question will be part of the investigation prior to re-certification of the B787. From the NYT this morning (Jan 19, 2013 10:54 EST:
Quote:
The government approved Boeing's use of lithium-ion batteries to power some of the plane's systems in 2007, but special conditions were imposed on the plane maker to ensure the batteries would not overheat or ignite. Government inspectors also approved Boeing's testing plans for the batteries and were present when they were performed.

Even so, after the episode in Boston, the federal agency said it would review the 787's design and manufacturing with a focus on the electrical systems and batteries. The agency also said it would review the certification process.
The FAA approval of Boeing's use of Li-Ion batteries is in the following document. One would expect that Boeing's testing and results will be examined against the FAA approval.
Special Conditions: Boeing Model 787–8 Airplane; Lithium Ion Battery Installation
AGENCY: Federal Aviation Administration (FAA), DOT.
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Old 19th Jan 2013, 22:23   #9 (permalink)
 
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gums:

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

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

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

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

On maintenance aspects and risks it´s clear Boeing heard the promises of the suppliers (Batt and chargers) installing it close to Electronic Equipment without elaborated safety schemes in case of major failures like the ones that occurred.
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Old 19th Jan 2013, 22:51   #10 (permalink)
 
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FAA attitude

Hi,

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

Quote:
...It will happen when all are confident they have a good solution that will contain a fire or a leak."
This opens a new front.

Quote:
Government inspectors also approved Boeing's testing plans for the batteries and were present when they were performed.
The Testability again must be remembered after the problems in BOS and TAK.
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Old 19th Jan 2013, 23:47   #11 (permalink)
 
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Lithium-cobalt, lithium-poly and lithium-ion batteries can be very unstable even under normal conditions; only the power management chip in your laptop battery stops it from bursting into flames when charging. Some have, even when not charging.
Enormous pressure on battery makers to increase energy density and decrease weight/volume, for phones / laptops / tablets etc. (and now for airplanes!) has resulted in increasingly daring & unstable designs being produced. In aerospace, this is all pretty new tech. The massive electric requirements of the 787 compared to other a/c only compound the problem.
Before the 787, I have never heard of any lithum-tech batteries being used for anything mission-critical in aerospace (please enlighten me if I am wrong).

As a previous poster points out:
Quote:
Funny, but Toyota sticks with those nickel ones for their Prius.
Yep. Heavy and large by comparison, but well-known, predictable, proven tech.
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Old 20th Jan 2013, 00:02   #12 (permalink)
 
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TNX, boogle

Weight and form factor not a biggie.

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

I like the Li-ion batts for small stuff, but not big ones for mission-critical power supplies.
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Old 20th Jan 2013, 00:26   #13 (permalink)
 
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Might I suggest switching over to a Plutonium-238 battery, works by means of radioactive decay ,have a very long life, good energy density and at the end of the plane's life-cycle can be sold on the second hand black market for 'alternative' uses.

See, problem solved.
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Old 20th Jan 2013, 03:28   #14 (permalink)
 
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It woul be nuclear flying devices, not very ideal concept to accept...
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Old 20th Jan 2013, 08:29   #15 (permalink)
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Securaplane had a major fire back in 2006, there's a discussion about it here it has been suggested that it was due to a lithium battery catching fire while being charged or used. Unfortunately I can find no other contemporary accounts of the fire which destroyed a entire building apparently.
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Old 20th Jan 2013, 09:22   #16 (permalink)
 
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Quote:
Before the 787, I have never heard of any lithum-tech batteries being used for anything mission-critical in aerospace (please enlighten me if I am wrong).
Apparently the International Space Station, the F22 and F35 and the A380 all have LiIon batteries.

The same ones fitted to the 787 have "1.3 million hours of flight time" according the Boeing - so they are used in other places. I would suggest anything on the ISS is "mission critical" as its not easy to land if something goes wrong!
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Old 20th Jan 2013, 11:04   #17 (permalink)
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According to Leeham News and Comment:
The Airbus A380 uses lithium batteries to power its emergency lighting system. The US FAA set special conditions when certifying the aircraft. Airbus says “the batteries are small, limited, and are not in a frequently-active charging/discharging function.”

rest of article: A380 has, A350 will have lithium-ion batteries « Leeham News and Comment
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Old 20th Jan 2013, 11:24   #18 (permalink)
 
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Quote:
The battery that caught fire on the Japan Airlines 787 in Boston was the second main battery. This unit’s primary purpose is to electrically start the APU when neither of the engines is running and the aircraft is not connected to external ground power. In this case, the battery energizes the right hand of the two starter/generators connected to the APU. The aft battery also provides another minor role, namely power to the navigation lights during battery-only towing operations. The unit in the second incident, which forced an ANA 787 to make an emergency landing in Japan on Jan. 16, involved the main battery in the forward E/E bay. In this case, there was less damage, though spilled electrolytes, fumes and minor thermal damage indicated signs of overheating.
(Aviation Week)

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

Here a small example what to expect....


Last edited by hetfield; 20th Jan 2013 at 15:04.
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Old 20th Jan 2013, 17:19   #19 (permalink)
 
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Interesting charger design

The charger manufacturer got a patent Patent US5780994 - Detection of inflection point in secondary-battery charging process, which they claim as per Innovative Inverter Technologies and Main Ship Battery Chargers for Power Conversion to apply with the 787 charger. Last sentence from the abstract: Accordingly, the voltage response is no longer monitored and the time remaining to reach the inflection point is used to complete the fast-charge operation. _If_ they really charge like that, without the monitoring the cell voltage, the problems seen are to be expected, as even a minor mismatch (caused amongst others by aging) of the assumed inflection point to the actual cell would lead to overcharge. Lithium cells will degrade fast with minor (trickle) overcharge and absolutely will not not tolerate any overcharge at fast-charge current. NiCd and Pb cells would be much more tolerant.
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Old 20th Jan 2013, 21:33   #20 (permalink)
 
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words on that graph

Quote:
Originally Posted by Machaca
Here are some details and images of the 787 chargers and batteries:

Quote:
Originally Posted by rr_ndb
Could you comment something on the graph?
I happen to know the man who took the data, made the graph, and presented it to more than one conference--ballpark a decade ago. I discussed it with him extensively a few hours ago.

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

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

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

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

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

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

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

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