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diy solar

Little problem top balance

Kokireg

New Member
Joined
Apr 30, 2022
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I just received my new cells to make a new battery for my motorhome.
I have already installed one that works very well.

But now I have a problem.
I have connected my 4 cells in parallel to make a top balance.
I put my charger at 3.61V and 20A charge.
I left it for about 48 hours. My charger was of course at 0A. so the cells were charged.

On the other hand I tested the cells with the multimeter and I have 3.726 V for each cell and thus 14.90 V when I mount it in series.
I think my charger has a problem (3.61V was not right).

Now I have to connect my BMS but I'm a little afraid to do it because of the 14.9V and 3.725V per cell.

any idea ???

thanks

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Now I have to connect my BMS but I'm a little afraid to do it because of the 14.9V and 3.725V per cell.
Connect up an incandescent light bulb or other light load to the paralleled battery and let it drain down to the 14.4-ish on your meter before connecting the BMS. If you can get it a little under where the BMS will start having over-volt issues then the BMS can re-balance and top off the cells when you have the pack complete. You've already done the bulk of the charging, let the BMS do the rest.
 
You should bleed their voltage down as soon as possible.

At this voltage there will be a slightly accelerated electrolyte degradation. Nothing to worry about if you reduce their voltage soon.

About 1 amp load should bleed them down in a minute or two. Do not be concerned if their open circuit rested voltage is not all exactly the same after bleeding as long as they are all above 3.45v which is fully charged cell. Any voltage above 3.45v is surface capacitance charge which has no significant capacity.

Once you get them below BMS overvoltage shutdown voltage you can connect them up with BMS.
 
Okay that's what I was thinking of doing.
I plugged in a small 12V led (I only had this on hand) before leaving for work.
It consumes 0.41A.
I'll leave it plugged in for a few hours like this until the voltage is lowered.
 
Did you adjust the charge voltage before or after you connected it to the cells?
 
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