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diy solar

Oddity when balancing 4S LFP pack connected to BMS…

I am now thinking I didn't let the cells fill enough and the self discharge dropped them into the 3.36 range... I will fill them all the way to under .5a at 3.6V this time.
If you do that, they should hold above 3.5v for a couple of days.

Or at least long enough for you to get them all there.
 
Like I said, I am ONLY charging a single cell at a time.
I connected #1 now. Once it is full I will post the page showing it and 4 full, then I will move to 3 fill it, and then 2... maybe it'll normalize...
You have 4 cells connected in series with the BMS hooked up and you are attempting to balance each cell with a 5 amp power supply. The behavior you are seeing is wierd and I don't understand why it's happening.

It could be the BMS is causing the self discharge but the BMS doesn't draw much current. Anyways ignore the voltages of the other cells. Charge each cell to 3.65 volts and you should be fine. Disconnect the BMS and then check for self discharge. My EVE cells also were above 3.50 volts after sitting for a couple of days....with nothing connected to them.
 
I am now thinking I didn't let the cells fill enough and the self discharge dropped them into the 3.36 range... I will fill them all the way to under .5a at 3.6V this time.
Yes, if they didn't get saturated they drop quite a bit in the first hour.
 
You have 4 cells connected in series with the BMS hooked up and you are attempting to balance each cell with a 5 amp power supply. The behavior you are seeing is wierd and I don't understand why it's happening.

It could be the BMS is causing the self discharge but the BMS doesn't draw much current. Anyways ignore the voltages of the other cells. Charge each cell to 3.65 volts and you should be fine. Disconnect the BMS and then check for self discharge. My EVE cells also were above 3.50 volts after sitting for a couple of days....with nothing connected to them.
These are used 32650 cells, and I nicklestrip spot welded them into 160Ah packs. Pack 4 always reached coputoff first, that’s why I’m trying to top balance. I don’t want them all the way to 3.65, I don’t want to stress the used cells. All to 3.60 should balance them well into the knee…
If this behavior repeats, I will try to 3.65… but I’m leery of that.
 
These are used 32650 cells, and I nicklestrip spot welded them into 160Ah packs. Pack 4 always reached coputoff first, that’s why I’m trying to top balance. I don’t want them all the way to 3.65, I don’t want to stress the used cells. All to 3.60 should balance them well into the knee…
If this behavior repeats, I will try to 3.65… but I’m leery of that.
Yeah you don't need to go all the way. 3.60 volts is fine. Since you have made packs with used cells that changes things as far as self discharge. But 32650 used cells in good condition self discharge should still be low.
 
Yeah you don't need to go all the way. 3.60 volts is fine. Since you have made packs with used cells that changes things as far as self discharge. But 32650 used cells in good condition self discharge should still be low.
Yeah, the pack has sat at 3.5 on 4 for weeks, the other 3 packs hovered around 3.34ish, which led me to bring them all above 3.4, when the mess happened I was confused, why charging one would discharge others… even the high one.
 
very confusing symptoms! i literally have no idea ?‍♂️ what would cause this set of effects

following thread to learn
 
Getting close on 1, and 4 is slowly drifting down.
 

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Cell 1 is taking WAAAY longer to hit 3.6v...
My guess is the cells i used have huge variances and there must be some weak cells in pack 4, and some high drain cells in pack 1... ugh this is frustrating.
 
Ew, sounds like a (potentially very time-consuming and annoying) teardown and individual cell capacity test is in order. I don't envy you.
 
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