|Quoting kanban (Reply 1):|
posted this just before cut off
Yuasa makes these batteries for many land surface operations, trains, trucks, etc. and seem to have no problems. Possibly could the problem be related to the pressure differentials when flying... ie water boils at a lower temperature at elevation, so could the organic fluid in these batteries "boil" at altitude and leave the anodes/cathodes bare and in contact?
Remember what the B787 is great for... it has barely any pressure differentials, since it maintains a very low cabin altitude of 5000ft at cruise.
For the reference, I will put it on the board again for all airliners.net users.
I have said it before and I will say it again, Li-ion batteries may be the cause if the manufacturer doesn't meet the Boeing specs. Japanese companies are known for their integrity and have nothing to gain from fooling around with li-ion batteries on an aircraft. They charge enormous amounts of money for these, so I don't see the point of getting greedy just to save a few more bucks on a battery of a few tons of dollars.
-Li-ion batteries don't "self-combust" in normal operations. They can get hot during use, but they are unlikely to see temperatures as high as their kindling point.
-Li-ion typically explode or catch fire if the overcharge protection fails but that's very different to "self combustion", given that the overcharge is created by the elements that charge it.
-A li-ion battery can be unstable if charged beyond its capacity and stored in that condition. A shock could then cause the battery to catch fire or explode.
-The liquid solution is flammable. Flammable means that if lit on fire, it will burn.
This is why one needs to be careful when transporting li-ion batteries on an aircraft. If a battery gets damaged and the liquid flows into an electrical assembly, it could be lit on fire.
However, the ion solution will not catch fire by itself. Like any fuel, it needs a source of ignition.
Also, it's unlikely for a battery's protections to fail. These are normally fail-safe protections, unless they put an override to prevent the battery from going to fail-safe in an emergency. However, I don't think that Boeing would put an override on that overrides the fail-safe in a charging mode.
So there could be 3 ways for this issue to happen.
-too high temperatures in the e-bays, not enough air circulation, causing the li-ion solution to reach the flash point or the unlikely kindling point. I don't deem this very likely but LRU computers have been prone to overheating in the past.
-interface problems with the rest of the electric architecture. For instance, remember that the B787 runs on wild frequency generators without a CSU. This requires conversions and stabilisations to provide a clean source of DC power. Lack of stability could send the li-ion haywire, which I believe is a very possible cause. Any irregularities could make li-ions cook. As such, this is the most probable, in my opinion.
-batteries are not meeting design, test specs or the design itself is flawed. Li-ions have been on board of aircraft for several years now and never caused this kind of damage.
The battery containment is the least important feature and is the protection of last resort.
Has it worked? Difficult to say.
If I look at the video's from the evacuation of the NH787, I see thick smoke coming from the front starboard side around the aircraft and black lines running from the side of the fuselage, from something that looks like drain ports. I'm not part of the engineers who has been trained on the 787, so I don't know if that's supposed to be there but it doesn't look right. It is said that the hot liquid poured its way on a 12 feet stretch.
However the fire didn't destroy the entire aircraft or maybe it didn't get chance. So it's impossible to say if the containment saved the day, but judging by the smoke, it didn't do that good a job.
Anyway, Airbus CEO says on the A350-XWB usage of li-ions:
“There are some architectural differences and the suppliers are different,” Bregier said. “As Boeing said, the battery is not the issue, it’s the way you integrate it to the power system.”
[Edited 2013-01-17 13:30:46]