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)
The classic question. Was it a manufacturing problem in the battery pack that caused the cell to short or did the pack overheat and then a cell failed, as so many people looking from the outside have suggested?
the cell presented is not the one from 787 but the technology should be similar.
The 787 battery pack has 8 cells serial hard connected. The cells can not be individual switched off in case of failure. The damaged cell still getting power from the good cells and aggravate the issue.
I understand that, but did the cell fail from being overheated, or did it become hot because it had failed? The folks at Tesla and others have said that this type of pack requires active cooling. If that's true will an overheated cell fail by shorting, or was the cell poorly constructed, shorted and then caused the thermal runaway?
tekochip, if I understand where you are going, is it the blame of the battery itself, or the electronics surrounding the pack. I'd be surprised if anyone takes "credit" for this mishap.
Yes, it does raise more questions. Because they've isolated the short circuit to cell number six, they should now be in a better position to track down the reason for the short. Hopefully, we'll be getting more news soon.
Yes, did it short due to poor construction, being deep cycled too often or being baked too long in that sealed box with no active cooling?
It's almost like having a murder case where the victim was poisoned, shot and stabbed by three different people and the coroner's report states that the victim died due to cardiac arrest.
If it's a manufacturing flaw, then Boeing is off the hook and they look good due to the limited damage caused. If it's an external problem, where the batteries are being utilized more than intended, then it indicates insufficient testing and/or new model growing pains and doesn't really indicate a significant problem at Boeing. If it's an overheat problem due to ignorance or post-testing/pre-production design changes, then it tends to reflect poorly on Boeing.
I guess we will only find out if Boeing volunteers the information.
Experts Sadoway and Elton Cairns "suggested that an active cooling system would provide an additional layer of safety for a cost that would be miniscule compared to other 787 sub-system costs. Sadoway again said last week that the Boeing batteries would be safer with active cooling. "That's what GM does in the Chevy Volt," he told us."
My first thought was weight. The Chevy Volt is a grounded vehicle that must generate enough electrical power to propel itself over pavement at a reasonable rate of speed...relatively slow compared to the 500+mph (ground speed) of a large commercial airline.
Like most other mechanical contraptions we've invented, turning electricity into power and power into motion is a big issue. The heavier the machine, the more power it takes to make it move. And thus more electricity. More batteries. More weight.
Wouldn't adding an active cooling system add considerable weight? And take up precious space?
It's been previously reported that the battery was not factory-original, that the battery that burned was replaced by the airline as part of maintenance.
The first 787 is barely one year old, and airlines are replacing batteries? Can you draw a parallel between 787 and a smart phone?
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