OK the power supply just switched to CV mode and the amps are decreasing slowly. Cell is now 3.43v. Going good.That is correct. Once the PS voltage reaches 3.65 volts, or very close to it, the PS should switch to CV mode and then the amps will begin to drop. Easy peasy. Still keep an eye on the cell voltages.
Top Balancing "How to"
- Thread starter snoobler
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Comparatively speaking, voltage will rise very fast now.
yea almost done.
Can the cells become unbalanced when the battery is not used often ?
Personally I wouldn't worry much about that. Keep your cells between the knees for extended life and your delta will also be low.
Once you put them all in a pack at 100%, no. One could have a high self discharge rate, but that is uncommon. If they have a reasonably close self discharge rate, then it would take quite a while for them to come unbalanced.
That's up to you.
I've done many to 3.65v and 0.1 amps in, and never had a problem. Some people gets nervous, but make sure 24 hours later it is above 3.45v where the real rise starts.
Do you mean that my cells have to be above 3.45v after 24 hours on resting ??
Only if you want it to work. I prefer above 3.5v.
After 6 hours resting, cells dropped from 3.58v to 3.37v
It wasn't saturated.
Yea.
I'm doing now a second pass, charging this time to 3.62v calibrated on the DMM.
My pack has a strange behavior even after top balancing. The first cell hit the bottom much faster than the others. It seems that i have a bad cell right ?
After it was "fully" charged to 3.62v each, i drained only 48Ah from the pack before the cell 1 hit 2.5v and triggered the BMS. So what can i do ? i could change the bad cell but is there an other way to keep it ?
Should i use an active cell balancer to transfert energy from the 3 others cells to the cell 1 on load and always keep them voltage balanced ?
After it was "fully" charged to 3.62v each, i drained only 48Ah from the pack before the cell 1 hit 2.5v and triggered the BMS. So what can i do ? i could change the bad cell but is there an other way to keep it ?
Should i use an active cell balancer to transfert energy from the 3 others cells to the cell 1 on load and always keep them voltage balanced ?
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Active balancer is not magic, the pack is only as good as the weakest cell. Depending on discharge rate and active balancer rate, might get an extra 5 amp hours out of it.
Hedges
I See Electromagnetic Fields!
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Although you don't have a picture to prove 3.62V each.
Presumably there was some divergence in voltages as shown down around 3.1V?
It seems like cell #1 has only 50% of expected capacity, but make sure cells really are top-balanced.
Sometimes after the act of parallel top balance people report settling to unequal voltage (happened due to poor contact), can't be sure at the voltages you show.
Some people report capacity a bit below spec on new cells, but nothing like 50%. It isn't badly bulged or some obvious difference, is it?
Oh, discharge rate: When cell hit 2.5V, how much current was being drawn? Contact resistance causes voltage drop below actual cell voltage. But that often shows up as elevated voltage on adjacent cell, so less likely.
Double check all cells with DMM.
Check all your connections. I had a funky bus bar connection on one cell terminal that threw off my top balance.
I agree with others it's most likely a connection problem. Disconnect the BMS and check your busbar connections. While possible, I would be surprised if the cell is bad. Did you check the resting voltages after you did your second pass? An active balancer will not help in this case.
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