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787 Batteries and Chargers - Part 1

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787 Batteries and Chargers - Part 1

Old 24th Jan 2013, 06:36
  #121 (permalink)  
 
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Looking at the Thales/Boeing design and the FAA special considerations, it appears that the approach was to assure cell failure would never occur--as it seems self-evident that no serious measures to avert propagation to adjacent cells were employed, nor were serious measures to contain damage to nearby systems.
Imho, they did not bother to mitigate cell failure spreading to other cells as this would be weight and size prohibitive (likely worse then NiCd and not near certain to work either).

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

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

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

What is unexpected and not reasonable is that 2 out of 100 or so batteries in service fatally fail within about year. Two points really do not add up to a curve, but the fact still is of great concern
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Old 24th Jan 2013, 09:29
  #122 (permalink)  
 
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Do you mean rather than the NTSB or FAA?
@YRP

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

BTW, just found this:
Securaplane said it makes two battery charging units used on the 787, one for the APU battery in an aft bay, and one for the main ship battery used in a forward bay, which provides backup power for flight critical controls.
U.S. NTSB reviewing whistleblower claims in 787 case - chicagotribune.com

So, the chargers are not identical.

Last edited by hetfield; 24th Jan 2013 at 11:58.
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Old 24th Jan 2013, 09:53
  #123 (permalink)  
 
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For those who never heard about Lithium batteries, and if the RC guys are taking it seriously..........

Complete Guide to Lithium Polymer Batteries and LiPo Failure Reports - RC Groups

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Old 24th Jan 2013, 13:40
  #124 (permalink)  
 
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Li Batteries & Vibration

The Yuasa battery being used in the 787 and what appears to be its prismatic cells are unfamiliar to me but our experience with all Li batteries is that there is a threshold vibration level that will cause rapid cell damage and lead to shorting behavior. In our aerospace application we've tested pretty much every cell type and none of them are particularly tough. Our application has a considerably higher vibration level than most transport aircraft however. I am sure that the battery in question was qualification vibration tested before it ever flew but I wonder if the actual in-service vibration level of that battery installation is what was expected. Our experience is that if the vibration threshold is exceeded the failure is prompt. The operating temperature of these cells is a issue as well. Just how hot does that compartment get when the aircraft is on the ground?
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Old 24th Jan 2013, 14:02
  #125 (permalink)  
 
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@Hetfield,

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

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

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

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

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

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

Overcharge of individual cells seems a more likely scenario to me than the cells itself. But it does not have to be the charger, it could also be the bus.
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Old 24th Jan 2013, 14:56
  #126 (permalink)  
 
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saptzae,

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

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



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

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

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

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

Regards,
Chris
[With apologies to John Tullamarine for the thread-drift.]
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Old 24th Jan 2013, 15:00
  #127 (permalink)  
 
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Ironic

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

- IATA Dangerous Goods
- Transport not allowed on passenger aircraft
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Old 24th Jan 2013, 15:04
  #128 (permalink)  
 
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@A33Zab


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

One (747F) was a hull loss, both pilots died.
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Old 24th Jan 2013, 16:45
  #129 (permalink)  
 
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Chris Scott

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

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

I have no idea of the current draw when starting the APU.
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Old 24th Jan 2013, 23:04
  #130 (permalink)  
 
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Different Threads.

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

For those trying to learn from all this very valuable info, surely it makes it harder to follow?
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Old 24th Jan 2013, 23:26
  #131 (permalink)  
 
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For my dough, this thread carries the weight. Here are pilots, engineers, and experience. This thread is Platinum, R+N, Copper.

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

Here be the real deal.
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Old 24th Jan 2013, 23:59
  #132 (permalink)  
 
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The real deal

Salute!

Thank you, Lyman.

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

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

We have had many spirited exchanges here, but I have yet to see a lack of respect for the posters' thoughts and theories and explanations of how things work in the real world.
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Old 25th Jan 2013, 00:02
  #133 (permalink)  
 
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The JAL incident seemed a lot more potent than 'a fart out of the tailpipe'.
An equipment fire that takes the Logan Airport fire dept 40 minutes to put out is a safety of flight issue, imho.
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Old 25th Jan 2013, 00:14
  #134 (permalink)  
 
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Originally Posted by hetfield View Post
One (747F) was a hull loss, both pilots died.
As yet there has been no confirmation or denial that the LI cargo was responsible for the fire. Any recommendations have been precautionary only.
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Old 25th Jan 2013, 00:36
  #135 (permalink)  
 
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etudiant ....... The JAL incident seemed a lot more potent than 'a fart out of the tailpipe'.
An equipment fire that takes the Logan Airport fire dept 40 minutes to put out is a safety of flight issue, imho.


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

Eighty Six Minutes.

etudiant? mois aussi....
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Old 25th Jan 2013, 02:28
  #136 (permalink)  
 
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As yet there has been no confirmation or denial that the LI cargo was responsible for the fire. Any recommendations have been precautionary only.
True!

Why?

Revenue?
Money?

Who got the balls to exlude Li-Ion on airplanes?
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Old 25th Jan 2013, 05:50
  #137 (permalink)  
 
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Briefing contents

Hi,

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

This means:

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

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

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

There are other points to comment. Im further analysing.

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

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

An immediate decision to revert to Ni Cds appears urgent and inevitable.

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

Very serious issue. Painful teething! And a "virtual stalemate" (If Li Ion usage insisted).
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Old 25th Jan 2013, 13:37
  #138 (permalink)  
 
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RR NDB writes:
My comment is because considering certainly there is no discharge control (perhaps will be required for Li Ion in aviation) the analysis is concentrating in:
I'm pretty sure there is, it would be inconceivable to connect an uncontrolled load (ie DC starter motor, etc) directly to any Li battery. All of the "big" loads on the 787 are AC or driven from the +/- 270V DC bus and have no direct connection to the battery buses. The APU starter is a starter/generator which has its own (load-limiting) controller when using the APU battery for start power.

The simplified graphic in this post shows high-power distribution.

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

Story with pix here.
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Old 25th Jan 2013, 16:15
  #139 (permalink)  
 
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They don't know if the short was the chicken or the egg(cause or effect).

They have the results. They don't know what the triggering event was or the sequence of events.
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Old 25th Jan 2013, 16:24
  #140 (permalink)  
 
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rottenray:

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

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

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

Regards,

Chris
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