I've done discharge tests and the curve looks normal. But it seems at least for the very first one or two charges the cells voltage raises a lot more than one would expect. (DC and AC IR are both good)
For example. My cells(MB31) were delivered at 3.33V. By any SOC/voltage table this is about 80% full. But the very first discharge test (from "as delivered") resulted in about 130ah (I have the curve elsewhere, I'll post it later if people are interested). I then charged it fully and a full discharge test showed 330AH and the curve is by the book.
Then I assembled a 16s pack. I charged it till 3.42 per cell on average (half of my cells at 3.45 half at 3.38 - there were two batches). I though surely they must be at 99% full by now.
So I set them up in parallel and I started charging with 40A. Many hours have passed and ~530AH later cells that were on 3.45 are on 3.53V cells that were on 3.38 are at 3.48. Almost no current flows to higher voltage cells (0.2A per cell) so this 530AH must have gone into 8 cells with lower SOC. So 66AH per cell above 3.38V !
Isn't that quite unusual for LFP? I never had EVE cells before and this post is not a complaint, the capacity and power delivery is fine. I'm just puzzled by these cells seemingly defying usual SOC/V tables during charging. Both my higee cells, old crappy CALB , as well as few types of pouch cells I had were almost fully charged at around 3.4V.
Perhaps this is only for the first few charges?
For example. My cells(MB31) were delivered at 3.33V. By any SOC/voltage table this is about 80% full. But the very first discharge test (from "as delivered") resulted in about 130ah (I have the curve elsewhere, I'll post it later if people are interested). I then charged it fully and a full discharge test showed 330AH and the curve is by the book.
Then I assembled a 16s pack. I charged it till 3.42 per cell on average (half of my cells at 3.45 half at 3.38 - there were two batches). I though surely they must be at 99% full by now.
So I set them up in parallel and I started charging with 40A. Many hours have passed and ~530AH later cells that were on 3.45 are on 3.53V cells that were on 3.38 are at 3.48. Almost no current flows to higher voltage cells (0.2A per cell) so this 530AH must have gone into 8 cells with lower SOC. So 66AH per cell above 3.38V !
Isn't that quite unusual for LFP? I never had EVE cells before and this post is not a complaint, the capacity and power delivery is fine. I'm just puzzled by these cells seemingly defying usual SOC/V tables during charging. Both my higee cells, old crappy CALB , as well as few types of pouch cells I had were almost fully charged at around 3.4V.
Perhaps this is only for the first few charges?