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Damaged cell, safe or not?

BlueSmoke

New Member
Joined
Feb 4, 2021
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16
I'm working through this pallet of cells and I found one with a decent dent in it. All the other cells were high quality, very clean, very limited scratching or very slight denting.

This cell has a dent that is approximately 4.5mm deep with an impacted area 2cm by 1cm. Should I be concerned about this? I don't care how it looks, I only care about how much more likely this one is to catch fire or take out my BMS or other cells.

Are there any tests I can do on it other than put it in a pack and try it out? It is the same voltage as all the other cells and there's nothing leaking.

IMG_20211028_000820.jpgIMG_20211028_000805.jpg
 
I did some studying on how these cells are built and the corner like this is a good place to have damage. If it had been on the long side I wouldn't have tried to use it. I put this cell in a 16s pack with 3 thermal sensors on the cell and tested it out. The whole pack charged and discharged full capacity. A little more actually. This cell was not the limiting cell in the pack either. The temperature of the cell was normal during the full run. It did not bloat more than any other cell. I did not use compression. I'm still a bit wary of compressing it in the final installation, but based on how these cells are constructed, it should be fine.
 
I did some studying on how these cells are built and the corner like this is a good place to have damage. If it had been on the long side I wouldn't have tried to use it. I put this cell in a 16s pack with 3 thermal sensors on the cell and tested it out. The whole pack charged and discharged full capacity. A little more actually. This cell was not the limiting cell in the pack either. The temperature of the cell was normal during the full run. It did not bloat more than any other cell. I did not use compression. I'm still a bit wary of compressing it in the final installation, but based on how these cells are constructed, it should be fine.
I've tried to find details on how they were constructed, where did you find information on how they were built?

Thanks,
Gil
 
I never found anything absolutely definitive. I found a bit of technical discussion of it though on a message board somewhere. Unfortunately I didn't save the link. An engineer was discussing that these type of cells typically contain pouch cells inside that are welded together. So the vulnerable areas are the 2 large flat sides. There would be a fully exposed pouch on the inside of the thin aluminum case. The narrower sides are still vulnerable but not as much. The corners are the least vulnerable places, but it depends on the pouch construction. If they are constructed like solid rectangles they are more vulnerable than if they are constructed like MRE pouches. I believe based on some EV cells I've seen deconstructed that the pouches are more likely to be similar to MREs than solid rectangles.
 
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