NTSB chairman Deborah Hersman said last week that investigators have concluded that a short circuit occurred in cell number six of the pack's eight cells. (Source: NTSB)
Another story came out yesterday, saying that Boeing intends to provide more space between cells. It's worth mentioning, however, that Boeing's spokespeople are not commenting, so we don't know for sure.
"The gaps between the cells will be increased." as immediate solution will allow a breathing space for further improvements. SAFT mentions in their battery manual:
"Un espace de 30 à 50mm doit être laissé libre sous les modules pour permettre la désoperculation des éléments en cas de problème."
Google translation - I love this tool
A space of 30 to 50 mm must be left in the modules to allow uncapping elements in case of problems.
The problem still exist but this short solution will reduce the cascade effect in case of a cell failure and will improve the local cooling - trough enhanced sufrace contact with the air environment.
I saw a graphic that Boeing was going to stick a vented containment around the existing battery box. I doubt that will satisfy the FAA and NTSB. Aside of the whole qualification time lag, why wouldn't they swap the Lion battery units with NiMH-based assemblies? Since they seem to have the space to put a box around the existing box, they could definitely go to a lower energy density battery technology.
this link shows some of the aviation incidents involving smoke, fire, extreme heat or explosion - and we continue to fly. 787 battery issue is a marketing issue, I hope the Dreamliner wil not change the name to Incubusliner.
@g_ost: It's hard to tell whether Airbus's decision to switch to NiCd for the A350 is more about public relations or safety. They've been flying A350s with lithium-ion batteries successfully so far. But being able to say that they don't have the "bad" battery chemistry that Boeing has may give Airbus an advantage with customers and regulators.
Due to 787 battery problems Airbus dispensed for A350 to the installation of lithium batteries. The first aircraft will be delivered with cadmium batteries, not lithium batteries. But the first test flights will attend Airbus with lithium batteries.
For large capacity multi cell series/parallel batteries each series stack typically will have its own controller. If thermal runaway begins in one cell, the consensus seems to be removing the charging current will NOT stop the runaway. See the nfpa link:
Other links regarding marine applications of lithium-ion batteries indicate that monitoring the individual cells (series stacks) is absolutely critical to prevent runaway. If this degree of protection is reasonable for a boat, I can't imagine it isn't practiced on an aircraft.
Yes, isolating each cell physically and electrically is doable, at a cost - but, if due to manufacturing defect or degradation over time, a cell develops an internal short, is it sufficient to just stop the charging current? Or will the stored energy through the short circuit lead to thermal runaway anyway? Does anybody here know?
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