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Dreamliner batteries - 1/21/2013 3:03 PM   
jquid



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Status: offline 		Ok,

So NTSB says battery failures not due to overcharging. So I figured why not see what the hobby/sport has to say about it. I think we have more experience with using these batteries and what not to do with them. So lets post our gueses as to what caused them to do this:

Batteries looklike they have been under water for a year! My guess is this: "Pure lithium is very reactive. It reacts vigorously with water to form lithium hydroxide and hydrogen gas." (Wiki).

So my assumption is somehow moisture is getting in or being released from the battery packs. Maybe something to do with the assembly environment. Say we assemble them at room temperature, and no controlled humidity, then bring them up to 30Kft, and we let water vapor come out of them, forming hydrogen gas, small amounts possibly, and that could be enought to create the smoke/fire reported. Also the water coming out is causing the graphite in the electrolyte to come out as well, I think that is the grey stuff all over, electrolyte.

Ok that is my shoot from the hip thought- anyone else?
have fun.

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RE: Dreamliner batteries - 1/22/2013 5:31 AM   
chuckk2


 

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Status: offline 		Interesting picture. I wish that it had higher resolution.
I wonder what happened to the top of the case (that was removed)

http://www.gsyuasa-lp.com/aviation-lithium-batteries
This web site shows the Li Aircraft Data sheets for the Li cells.



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RE: Dreamliner batteries - 1/22/2013 2:01 PM   
dirtybird


 

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Status: offline 		Are the batteries stored in a non pressurized area?

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RE: Dreamliner batteries - 1/22/2013 2:35 PM   
1320Fastback



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Status: offline 		How could they not be in a pressurized area.
As ours can puff I would imagine at altitude they would explode.

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RE: Dreamliner batteries - 1/22/2013 2:50 PM   
pilotpete2



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Status: offline 		No, the location is pressurized, but each electronics bay has an outside vent that is part of the cabin air exchange system. The plane has multiple outlet vents for the pressurization system to bleed out the stale cabin air. By locating one of these outlets in each of the battery locations, the electronics bay will be at a slightly lower pressure, and smoke will be inclined to be drawn out the vent. I saw a photo on the http://www.pprune.org/ site. In the photo, you could see the smoke stain on the exterior of the plane coming from the vent. While they apparently could smell some smoke in the plane, there was no visible smoke in the cabin AFAIK. I certainly hope they get to the bottom of the issue quickly, but when you consider that in in flight incident the battery appears to have burned up completely, there was no spreading of the fire, and smoke was vented out of the plane very effectively.
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RE: Dreamliner batteries - 1/22/2013 5:50 PM   
dirtybird


 

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quote:

ORIGINAL: 1320Fastback

How could they not be in a pressurized area.
As ours can puff I would imagine at altitude they would explode.


They are not lipolys.
My daughter is a Boeing auditor. She fears there are some layoffs coming. I hope not, I have a son working A/C #87.

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RE: Dreamliner batteries - 1/24/2013 3:57 AM   
chuckk2


 

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Status: offline 		This is starting to get interesting!
The company that makes the charger/battery management system may not have designed it specifically for the Yuasa cells that are used.
As far as I know, the different chemistry can be a player, due to slight voltage differences. If I were to compare things to our RC Lipos, I'd also wonder about how accurate the voltage measurements are, due to temperature ranges, and component tolerances.
(We used to see problems over the full mil temp range, even with full mil qualified electronic components. )
I shudder to think about the potential problems created when industrial grade components are involved.
(Mil qual components, in general, are a thing of the past.)

Lets say that the charge voltage limit for a LiPo is 4.20VDC. 4.1 VDC is not a real problem, other than not fully charging the cell.
What is the "real" voltage limit? 4.2V, 4.25V, 4.3V, etc. When does it become a problem? 
The discharge charts for the Yuasa 65A aircraft cell show a lower voltage than the 4.2V we use for LiPo's.

When you get down to hundredths of a volt, temperature and even dis-similar metals can be factors in measurement accuracy.

Think about a situation that was a concern decades ago.  SAC bombers were on alert, with a short time requirement to be operational and airborne before a "first strike" incoming missile might take things out. Not a few SAC bases were located in the "Northern Tier", which means that very low outside temperatures can exist. Think North Dakota, as an example.  Then, at high altitude things are much colder.
While the 787 battery compartment conditions are tempered by exhaust cabin air, there are still extremes of temperature and possibly pressure to deal with. Then, consider what happens when the aircraft is on the ground, with systems shutdown, no heating or cooling, and higher pressure, temperature, and possibly humidity than in the air.  Are there really effective filters in  the  battery vent systems? (and so on)
What if any alarm systems are still active? Are there any fire suppression systems that might activate?
If the danger is great enough, how about an in flight ejection system?  I'd also favor a spit it out on the ground system, but there are as many drawbacks as an in flight ejection system.  (A battery just came through my roof, and it's on fire?)  


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RE: Dreamliner batteries - 1/24/2013 4:56 AM   
dirtybird


 

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Status: offline 		Again they are not lipos. They are lithium ions.
Modelers are the only people nutty enough to use lipo's.
You would be in trouble if you charged them to 4.2 volts.
In the picture above it appears to me the wiring burned out due to overload.
The FAA is currently in AZ checking out the charger,made in Tucson, and the APU made by Pratt and Whitney in Phoenix.

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RE: Dreamliner batteries - 1/24/2013 7:34 AM   
chuckk2


 

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"The following factual information has been developed about the battery: It consists of eight cells of 3.7 volts each. All eight cells had varying degrees of thermal damage. Six of eight cells have been CT scanned and have been disassembled to expose their electrodes. All electrode windings in the battery are in the process of being photo-documented and are undergoing microscopic examination. In the coming days, the remaining two cells will undergo the same examination. Additional information will be provided tomorrow." (24 Jan)

The cell terminals are connected together by metal straps. The burnt up wiring seems to serve the same sort of functions as the balance plug wires on our LiPos.
I never said that the Yuasa battery was a LiPo.  But, comparisons can be made, much as you might compare an Pb AGM battery to a "standard" Pb Battery.
The NTSB calls the battery a 3.7V per cell battery, which is interesting, because that's the same nominal voltage printed on my RC LiPo batteries.


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RE: Dreamliner batteries - 1/24/2013 9:42 AM   
4*60


 

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RE: Dreamliner batteries - 1/24/2013 3:21 PM   
dirtybird


 

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http://online.wsj.com/article/SB10001424127887323968304578247830800960840.html

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RE: Dreamliner batteries - 1/24/2013 10:44 PM   
chuckk2


 

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Status: offline 		So the battery pack overheated, and went up in the way common to Li batteries.
What little I saw of the cell interconnecting straps looked like excessive output current
was not the problem.

I'd guess (without any adequate basis) that the temperature changes incurred in flight and then on the ground,
coupled with "stuffing" as large a cell as possible into a case are involved. It may also be that the electrolyte was not exactly as designed,
due to such things as contamination.  The pictures I have seen so far don't tell much that is useful.
Was this a progressive thermal runaway, where one cell failed, and started the whole thing, or was it a failure in multiple cells?

Should the cells be farther apart, with more cooling? Should they be placed such that thermal runaway has less of a chance to "cookoff" adjacent cells? Or should the weight penalty be accepted, and convert to NCADs?  (At least double the weight, with new battery management/charging equipment?)

Given that the 787 is intended for long international flights over water, I'd suggest that if  Li batteries continue to be used, there should be a way to easily get rid of the battery before it causes significant damage.

I really am surprised at the 787 Li battery voltage.  Reference "standard" voltages for large aircraft were both higher and lower than the Li battery
used in the 787.  (~12,24,48 V DC for "low" voltages, and 400hz AC single or three phase at ~120/240, with special cases as high as ~600.
 
Apropos of nothing. In the 1970s and 80s, I worked for a large aviation company that specialized in military aircraft and special purpose electronics. When I was in engineering design/development, one of our in house designed and built power supplies was originally designed and rated to at or above 50k feet. Getting a megawatt of power at 15kv, and keeping things from shorting out over the mil temp range, as well as fitting in a fairly small package was quite a challenge. Li batteries were not even considered/available/used at the time. We looked at NICAD and Pb batteries, combine with such things as "ultra" capacitors.  (low voltage, low leakage,multi Farad  storage capacity)


 


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RE: Dreamliner batteries - 1/25/2013 11:31 PM   
Flypaper 2



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Status: offline 		Todays li-ion batts are rated at 4.2 volts per cell. On the other website at said that a short was the cause of the fire.

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RE: Dreamliner batteries - 1/25/2013 11:43 PM   
thailazer



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quote:

ORIGINAL: 1320Fastback

How could they not be in a pressurized area.
As ours can puff I would imagine at altitude they would explode.

The cabin pressure on an airliner at altitude is usually between 4000 and 6000 feet MSL, so those batteries do get some pressure cycling as the aircraft climbs. I am sure the engineering team would be looking at that. Lipos have such tight geometries to get the power density that they have that it seems to be they would not be very robust with pressure changes and any physical pressures.

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RE: Dreamliner batteries - 1/26/2013 1:44 AM   
chuckk2


 

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quote:

ORIGINAL: Flypaper 2

Todays li-ion batts are rated at 4.2 volts per cell. On the other website at said that a short was the cause of the fire.


The RC LiPos are rated at usually 3.7 nominal, 4.2 full charge.

The NTSB cited 3.7 volts per cell for whatever reasons, and did not explain further.
I would not be suprised if they find that one cell shorted out internally, overheated, burst, and the ensuing events caused the whole battery to "cook off"
The pictures I've so far seen don't have enough detail to tell what the battery cells did under all the crud.



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RE: Dreamliner batteries - 1/26/2013 7:22 PM   
abelard


 

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Status: offline 		I think one factor is the problem of scaling to large size. Heat generation is a volume phenomenon, so it goes up with the cube of the battery dimensions. But heat rejection is a surface-area phenomenon, so it only goes up with the square of the dimensions. I don't know of any other application that uses Li-ions that big.

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RE: Dreamliner batteries - 1/26/2013 9:12 PM   
tailskid



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Status: offline 		I'm amazed that this wasn't discovered in the long testing period the plane went through....

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RE: Dreamliner batteries - 1/27/2013 2:26 AM   
dirtybird


 

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Status: offline 		I am sure Boeing ran all kinds of tests before the batteries were put in the aircraft.
Unfortunately you can never predict what the user will do.

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RE: Dreamliner batteries - 1/27/2013 4:37 AM   
chuckk2


 

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Status: offline 		There is a potential source of possible contaminants in the electrolyte, "small metallic particles". It seems that this is or can be a major issue for many LI cells.

Until more test results are made available,  Who knows what actually happened right before the "magic smoke" was released!

 


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RE: Dreamliner batteries - 1/27/2013 11:05 PM   
thailazer



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Status: offline 		The latest scoop here.....



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RE: Dreamliner batteries - 1/28/2013 1:10 AM   
1320Fastback



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Status: offline 		They seem to have puffed just like the LiPoly we use.

Sounds like a internal issue.

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RE: Dreamliner batteries - 1/28/2013 6:19 PM   
chuckk2


 

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Status: offline 		Monday morning news said no internal battery problems evident.

OK- What they have said so far
Voltage within limits.
Batteries went up in smoke and overheated.

This seems to say that either the charge current or discharge current caused failures.
One battery failed on the ground, with the plane parked.  Was an external power source in use?
One battery failed in the air (evidently), so it was likely being charged at some rate at the time.

While Li batteries have defined voltage and current charge/discharge limits, there is another consideration.
When charging a battery, you also have to consider the power (or watts).
Batteries can withstand short term high charge or discharge rates. Extending the time involved reduces the allowable rate.
Naturally, charging or discharging raises the internal temperature. 
The battery cell's internal temperature may not be monitored directly.

Wild guess - -
The battery cells internal temperature is higher than expected, and by the time  temperature increases reach the sensors,  it's too late!
What are possible solutions?  Reduce the time that the battery is allowed to charge or discharge at high rates? Find a way to better monitor battery cell internal temperature?

Can a switched (pulsed) charge rate be used to reduce the battery cell temperature rise, and still allow rapid charging?
When a charge voltage is indicated, how accurate must it be. Are there any margins or variables?

With our LiPo's full charge is supposedly 4.20VDC  What happens if the end charge voltage is say 4.18, 4,19, 4.21 or even 4.25 ?
Lower that 4.20 is rather obvious (slight undercharging)  To charge  to exactly 4.20, a slightly higher voltage must be applied, or no charge current will flow.
  
Boston Information (details) says that the APU was running while the cleaning crew was working on the A/C. Then it "cut out".
Perhaps they were using the APU for more than lighting?

The Japan battery failure is more interesting, since it occurred in flight, and the failed battery inside appearance is very similar to the one that failed at Boston. 


< Message edited by chuckk2 -- 2/7/2013 11:13 AM >

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RE: Dreamliner batteries - 1/28/2013 6:56 PM   
EloyM


 

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Status: offline 		Years ago, RCM's RC Electronics writer Jim Oddino, in one of his articles, stated: "When it comes to batteries, everyone is an expert".

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RE: Dreamliner batteries - 1/29/2013 2:10 AM   
1320Fastback



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Status: offline 		This is a reply to the video above on youtube itself, listed below it.

"27 Ah batteries which send the charge over 25 micron aluminum sheets. Is this not enough of a cause?"

< Message edited by 1320Fastback -- 1/29/2013 2:45 AM >

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RE: Dreamliner batteries - 1/29/2013 3:24 AM   
thailazer



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quote:

ORIGINAL: 1320Fastback

This is a reply to the video above on youtube itself, listed below it.

''27 Ah batteries which send the charge over 25 micron aluminum sheets. Is this not enough of a cause?''

Good point. Hopefully the current density in those incredibly thin sheets has been thoroughly characterized over peak loads, but it would not be the first time something quite basic was overlooked.

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