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Electronics & Test

NTSB: Short Circuit Caused 787 Battery Fire

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Battar
User Rank
Platinum
Airlift
Battar   2/13/2013 9:22:42 AM
When I wore a military uniform (never mind which color) I remember we had some communicaion equipment which had lithium batteries installed. The equipment was labeled "Do not airlift" because no one trusted the batteries to behave themselves in the air. Nevertheless, I don't remember ever seeing one of these boxes damaged by battery failure. Maybe the correct fix is to switch to a safer battery technology (LiFePO, fof example). Less energy density, but the airlines can make up for it by charging obese passengers a surcharge (they are a prime example of low energy density). Sorry for not being politically correct.

baxterl
User Rank
Iron
Re: Cause or Effect
baxterl   2/13/2013 9:33:08 AM
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Of course, a short circuit can't cause overheating, it should actually make the cell heat up less.  Perhaps they mean a "somewhat short" circuit.

AREV
User Rank
Gold
Battery for Boeing
AREV   2/13/2013 9:54:05 AM
The best thing is this - We will create a battery technolgical leap with this issue. If the analysis is correct the solution has already solved itself -fix the initial or isolate the components of the battery so a small section at 500 degress will not ignite more of the battery or surrounding componets and the issue cannot migrate to the rest of the battery.  I commend Boeing for using this technology. If every issue they ran into was solved by adding a cooling system (weight) and revering to the tried and true the plane would be a 707 with lipstick on it - just like a typical marketing department requested. Engineering is not for the faint of heart. In ten years we'll look back at the 787 as a relic that pushed us forward. It will create battery powered cars that actually make sense and cents.

Chris PE
User Rank
Gold
Problems with batteries
Chris PE   2/13/2013 9:57:03 AM
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We all know that lithium batteries are not the state of the art.Funny is that I have an old Samsung 225 with ORIGINAL battery for 10 years. Lithium batteries are bit strange.They should not be discharged completely like SOME others can.I found out that NiMH are also praclically trash if you discharge them fully.So, some kind of trickle charge is a good idea.I am onot a chemist, but I suspect that once the chemistry of a battery goes to extreme ,be it under , or over limits , that battery is unuseable.As far as temperature goes lithium batteries have been used on ships for many years with a great success.Cooling(or in case of airplane ,sometimes heating) and stable pressure is a key here.Unfortunately planes have no natural constant cooling and experience huge changes in an air pressure.

plasticmaster
User Rank
Silver
Re: Battery for Boeing
plasticmaster   2/13/2013 10:00:51 AM
Now you're talking! Excellent observation AREV. At the very least, this incident/challenge is keeping Boeing foreward moving down the innovative and technological path.

Pedro111
User Rank
Iron
smart batteries?
Pedro111   2/13/2013 10:06:36 AM
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Wouldn't be possible to put some intelligence into these batteries? 

I can see having a simple monitor for voltage and temperature of each cell. If one cell got hot or reduced it's voltage a redundant cell could be switched in.  Of course the monitor would also report status upstream to the aircraft electronics.

Surely this has been considered in the past. Does anyone know why it is not practical?

plasticmaster
User Rank
Silver
Re: Problems with batteries
plasticmaster   2/13/2013 10:08:47 AM
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I'm confused. Cooling can be achieved using liquid, gas, or air. VW did it with the Beetle (using air) to cool the engine. A transatlantic flight will see outside temperatures of -65°F. Couldn't this air be harnessed in some way to act as a cooling agent on these batteries? (providing that's the real problem)

Charles Murray
User Rank
Blogger
Re: Cause or Effect
Charles Murray   2/13/2013 10:21:35 AM
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Great point, plasticmaster. Adding an active cooling system would indeed add weight. Depending on the type of cooling system used, the weight of the battery pack could jump from 63 pounds to a little over 100 pounds. As you point out, an additional 40 pounds tends to make aircraft engineers unhappy.

bdcst
User Rank
Platinum
Re: Cause or Effect
bdcst   2/13/2013 10:40:26 AM
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Like I've said before, if the battery is prone to runaway thermal failure, it really needs to be designed to be jettisoned like a fuel tank when it gets into trouble, or insulated and isolated in such away that it can burn itself out without smoking up the aircraft or risking further damage.  Additional thermal sensors alone are not going to fix this problem!  I'm also concerned that charging is not done on a cell by cell basis as is the case with all of the consumer Lithium Ion battery packs I'm familiar with.  This is the only reliable way to catch faulty cells before they fail catastrophically or to insure proper charging.

Charging the cells in series configuration requires perfect matching of each cell.  And if they don't track with age, serious overcharging of some cells could result!  One of the benefits of individual cell charging is being able to measure cell temperature and control the charge cutoff accordingly.  In a series strung pack, the weakest cell, the one that attains end of charge temperature first, would have to force charge termination for the entire pack.  There is no way to use the voltage curve to safely terminate the pack's charge if one cell starts to go bad.  In fact, if a cell's voltage gets depressed due to a partial internal short it might result in a prolonged charging cycle which would further damage the bad cell.

With Boeing indicating they want to add more temperature sensors to the battery, I wonder if they presently only monitor the entire packs temperature and not individual cells.

Amclaussen
User Rank
Platinum
Re: Airlift
Amclaussen   2/13/2013 10:41:00 AM
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As any model aircraft amateur who has been into electric powered models can attest, Lithum batteries are a peculiar animal.  They need dedicated chargers, a lot of Tender Loving Care and some luck too.  They can go crazy from time to time.  A heavy walled ceramic pot is not out of place when charging them.  (May I suggest you to take a look at some photos of completely burned down cars when someone left a small battery pack charging inside).

I'm surprised that some overly 'creative' engineers at Boeing went on using this technology on a plane, when everyone that has some real-life experience with Lithium cells has developed a lot of respect and a healthy dose of distrust too.  Subcontracting/Outsourcing this set of components is another reason for failure, as responsibility is thrown around and diluted all too easily.  It will not be easy to precisely know what happened, as bad reputation is going to be "managed" in order to perform a crisis handling that will pretend that the original battery chemistry selection was either very "advanced", or "bold" or a "breakthrough"...

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