BMS related ?

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BMS related ?

Postby expresso » 12 Sep 2021, 16:28

Quickie 636 - 230ah LifePo4
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Re: BMS related ?

Postby Gnomatic » 12 Sep 2021, 17:02

I don't claim to know exactly how EV's are made. But on something like a Tesla, the charger is actually built into the car. So imagine your chair with a built in PL8. I have to think, given that Tesla is a Silicon Valley company and designs their own circuit boards and software etc themselves, that they are not using some generic off the shelf BMS to control and charge the thousands of cells in their cars.

LG builds the batteries and assembles the packs for GM to use in those cars. GM has very publicly put the blame on LG. Most recently, GM seems to think they've figured out the problem. They've recalled every bolt every made because of this.

"The automaker initially discovered the problem in batteries from one of LG’s Korean plants, and it recalled cars with those cells last November. But then more Bolts caught fire, and other LG plants were ensnared in the investigation, spurring two expansions of the recall. The problem, GM said, has been traced to a torn anode tab and a folded separator."

“What we’re looking at is a perfect storm,” Less said. The Bolt’s battery packs are made up of pouch-type cells, which are essentially layers of cathodes, anodes, and separators that are flooded with liquid electrolyte and encased in a flexible polymer pouch. The torn anode tab, he said, would create a projection in what should be an otherwise flat battery. The projection brings the anode closer to the cathode. “And that would probably be OK if the separator was where it was supposed to be,” he said.

But in problematic Bolt batteries, the separator wasn’t where it was supposed to be. Separators are placed between the anode and cathode to prevent the two electrodes from touching. A torn tab wouldn’t necessarily be an issue on its own because the separator would prevent any projection from bridging the anode-cathode gap. In cells with a folded separator, though, the gap would be missing from at least part of the battery. If the anode bridges the gap, Less said, “you have a short, and it’s all downhill from there.”

“It wouldn’t surprise me if both defects are caused by the same thing,” he added. “I would imagine that the separator must be folded at the edge near where the anode tab is at. What I’m guessing is that at some point during the handling of the cell, before it’s fully packaged, some part of the robot machine is catching. The tab is catching, the separator is catching—something is catching very infrequently so that it hasn’t been noticed, and it’s causing this damage.”

https://arstechnica.com/cars/2021/08/mi ... ery-fires/
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Re: BMS related ?

Postby Burgerman » 12 Sep 2021, 21:19

Yes. Its a cell construction issue. Lithium ion doesent like internal shorts as they turn into fireworks.

Which is why we use Lifepo4 instead. I have had a hobby packs go off like a firework too. Fortunatly at the airfield. Not even touching it. So just burned some grass. Very exciting though!
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