OffGridInTheCity
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- Joined
- Dec 15, 2018
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I'm sure you have been following @hbpowerwall's series on powerwall/pack failure. The recent youtube today (THANK YOU!)
shows that 4'ish cell level fuses out of 40 blew during a short but 4 did not. This seems consistent with the fuse wire tests - e.g. the majority of fuse wires burned thru but a few didn't.
I wanted to discuss expectations about packs and cell level fusing. For me - I've always thought of cell level fuse / fuse wire as a way to protect the overall pack from a failed individual cell that shorted. And indeed, its pretty clear that if 1 cell out of 40 shorts, the other 39cells will produce A LOT of amps and likely cause that cell to disconnect from the busbar electrically.
I've never thought that fuses / fuse wire would *all* (100%) burn thru if a pack shorted. This is why I have battery level circuit breakers / fuses - so that if there's a battery level short it doesn't depend on cell level fusing to all 'blow'. As we see from @hbpowerwall's work - after a catastrophic event you could very well have a few cells (say 4 of 40) that are still electrically active. So I have some brain-fuzz and would like to discuss....
Its not clear to me that 4 (of 40) cells that are continuing to be electrically active after a catastrophic event is a failure. Because....
1) With battery level circuit breaker/fusing - we should have adequate protection from 'system shorts'.
2) If a cell or 2 (a minority of cells) in a pack shorts - the fuse wire will electrically disconnect it from the pack as the pack will have enough amps to blow a lot of the fuse / fuse wires.
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3) This case... an overheating cell started a cascading fire?. Not sure how cell level fusing is supposed to protect against this - what am I missing?
4) Side question - if the remaining 4 of 40 cells are so week they can't muster 2a or 20a to burn a 2a axial fuse or 30awg fuse wire... do we think they will catch fire? or will they just short out till they drain power? They may get hot but will they burst into flames - I'm not so sure from various you tubes I've seen.
Not sure I was all that clear - but I'm confused about the takeaways so far and would appreciate comments
I wanted to discuss expectations about packs and cell level fusing. For me - I've always thought of cell level fuse / fuse wire as a way to protect the overall pack from a failed individual cell that shorted. And indeed, its pretty clear that if 1 cell out of 40 shorts, the other 39cells will produce A LOT of amps and likely cause that cell to disconnect from the busbar electrically.
I've never thought that fuses / fuse wire would *all* (100%) burn thru if a pack shorted. This is why I have battery level circuit breakers / fuses - so that if there's a battery level short it doesn't depend on cell level fusing to all 'blow'. As we see from @hbpowerwall's work - after a catastrophic event you could very well have a few cells (say 4 of 40) that are still electrically active. So I have some brain-fuzz and would like to discuss....
Its not clear to me that 4 (of 40) cells that are continuing to be electrically active after a catastrophic event is a failure. Because....
1) With battery level circuit breaker/fusing - we should have adequate protection from 'system shorts'.
2) If a cell or 2 (a minority of cells) in a pack shorts - the fuse wire will electrically disconnect it from the pack as the pack will have enough amps to blow a lot of the fuse / fuse wires.
------
3) This case... an overheating cell started a cascading fire?. Not sure how cell level fusing is supposed to protect against this - what am I missing?
4) Side question - if the remaining 4 of 40 cells are so week they can't muster 2a or 20a to burn a 2a axial fuse or 30awg fuse wire... do we think they will catch fire? or will they just short out till they drain power? They may get hot but will they burst into flames - I'm not so sure from various you tubes I've seen.
Not sure I was all that clear - but I'm confused about the takeaways so far and would appreciate comments