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Battery problems on Dreamliner

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Conundrum

Mon Jan 21 2013, 09:02AM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061

This is of relevance to me as I am also using Li-Ion cells for my electric bike build.
As there are significant safety issues even with the controllers I have, does anyone else have any
ideas for adding safety features?

So far it appears that the failed cell(s) did not overcharge, which leaves cell defect at manufacture or some other
anomaly.
I would theorise that the problem may in fact be with the safety vents on the cells as they are very large format (Liquid) with more in common with a lead acid.
If this opened up during flight due to a combination of pressure changes and temperature then didn't reseal, the cell thus affected could have been contaminated with moisture leading to a runaway condition at full charge.

Steve Conner

Mon Jan 21 2013, 10:38AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Lithium ion batteries will 'splode now and again for no apparent reason. Airlines don't allow them in checked baggage, they keep them in the cabin where the crew can put them out in flight.

Of course the plane's own batteries are magical aerospace grade units that can never catch fire

Josh Campbell

Tue Jan 22 2013, 04:48PM

Registered Member #5258 Joined: Sun Jun 10 2012, 10:15PM
Location: Missouri - USA
Posts: 119

I would not want to be one of the engineers that had any part of that idiocy even if it was just a manufacturing defect.

Andre, If I were using large Li-ion cells on anything I would at minimum monitor temperature of the vents or upper most portion of the cell. And initiate a shutdown/sound an alarm in the event of a high temp alarm. There are other preventive measures that should definitely go into place such as power in/out monitoring, environmental monitoring, etc since the temp alarm might only notify you once irreversible thermal runaway has begun.

We need new batteries!

Sulaiman

Tue Jan 22 2013, 09:16PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

I suspect that the problems may be related to amp.hour capacity vs. temperature,
a lithium ion battery can store more energy at room temperature than when cold,
so if a battery is fully charged at room temperature,
where do the amp.hours go to when the battery is cold?

I have been charging current-limited to 4.2 V for c85% capacity for this reason
could charge until charging current drops to x 1/20th of C for full charge
but the extra 15% isn't worth the risk, for my applications.

Ash Small

Tue Jan 22 2013, 09:48PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Sulaiman wrote ...

I suspect that the problems may be related to amp.hour capacity vs. temperature,
a lithium ion battery can store more energy at room temperature than when cold,
so if a battery is fully charged at room temperature,
where do the amp.hours go to when the battery is cold?

I have been charging current-limited to 4.2 V for c85% capacity for this reason
could charge until charging current drops to x 1/20th of C for full charge
but the extra 15% isn't worth the risk, for my applications.

Severe cold could also have caused the problem with the cracked window, and possibly the leaky pipework as well.

teravolt

Wed Jan 23 2013, 03:59AM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

At work we had a li-ion project and and the cells were packed prety tight. during the testing they ignited in there steal chamber and melted the inside. they evacuated the building and the fire department wouldn't tuch it

Steve Conner

Wed Jan 23 2013, 03:36PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Hence, Murphy's law of energy storage systems: The higher the energy density, the bigger the bang when (not if) it goes wrong.

Conundrum

Wed Jan 23 2013, 07:12PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061

Lol.. Corollary to Murphy's law of Conservation of Flammability. Expense is proportional to the resulting KABLAMMO when it does finally vent with flame.

BigBad

Wed Jan 23 2013, 07:16PM

Registered Member #2529 Joined: Thu Dec 10 2009, 02:43AM
Location:
Posts: 600

Still, compared to fuel tanks, not a lot of energy and much lower energy density, and the aircraft involved landed without any deaths or injuries.

OTOH aeroplanes' fuel tanks have completely exploded (deflagrated) in mid-flight without warning before leading to the loss of all onboard.

radiotech

Thu Jan 24 2013, 03:05AM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546

Just looking at the image of the damaged battery module, it is hard to tell what
is the fire extinguisher compound and what is the overheated parts. However the
battery buss work looks intact as do the terminals. I wonder if that white plastic
guard (against some fool dropping a wrench across the terminals) had melted.

The wiring kinda looks like an electric forklift harness I shorted out once .B-)

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