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First time top balancing - Doing it Right?

Famtraveler24

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Jul 22, 2020
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Hi all. First adventure into battery building. I attempted to pre-charge my 8s 280ah pack, wired in series and connected to an Overkill Solar 8s BMS set to stop current when a cell hit 3.65. All cells but 3 were matched at the factory st 3.3. The other 3 were 3.4, 3.26 and 3.28.

After charging about 24 hrs, I woke this morning to see the power supply no longer charging and most cells at 3.35 or so. Seems maybe 1 cell hit 3.65 and shut off the power.

I went ahead and reconfigured the pack in parallel, removed the BMS, set my power supply to max current and 3.65v (see picture).

Should the power supply be showing low current like this?

Anything I could have done differently during the pre-charge?

Thx all.20211003_074428.jpg
 
Hi all. First adventure into battery building. I attempted to pre-charge my 8s 280ah pack, wired in series and connected to an Overkill Solar 8s BMS set to stop current when a cell hit 3.65. All cells but 3 were matched at the factory st 3.3. The other 3 were 3.4, 3.26 and 3.28.

After charging about 24 hrs, I woke this morning to see the power supply no longer charging and most cells at 3.35 or so. Seems maybe 1 cell hit 3.65 and shut off the power.

I went ahead and reconfigured the pack in parallel, removed the BMS, set my power supply to max current and 3.65v (see picture).

Should the power supply be showing low current like this?

Anything I could have done differently during the pre-charge?

Thx all.View attachment 67301

Replace those tiny wires with some 10 gauge wires. Use lugs for connections. You are inducing a lot of resistance: tiny wires, banana clips, and alligator clips. While waiting on wire to arrive I tried using some 16G wire with lugs I could get only 6-7 amps when the 10G arrived I got the full amps from my power supply.
 
Thx much. I have some 10 AWG. I assume the banana plugs stay? Or maybe use ferrules for the inputs to the charger?
 
Thx much. I have some 10 AWG. I assume the banana plugs stay? Or maybe use ferrules for the inputs to the charger?
Unscrew the outside plastic where your banana plugs go in, you can use lugs on them.
 
Nah dump the banana, get spade or ring connectors.

Also verify the voltage at the bus bar vs the output of the PS. Should be about the same but don’t touch the PS setting.
 
Unscrew the outside plastic where your banana plugs go in, you can use lugs on them.
That is the banana socket. they are made to use a lug if you unscrew the outside plastic pieces.
 
Last edited:
So it's okay for these 3.2v cells to reach 3.65v but no more than that?
 
I am no expert, but everything I've watched and read says that 3.65v is as high as a cell should be charged. Others feel free to weigh in.
 
So it's okay for these 3.2v cells to reach 3.65v but no more than that?
Yes, 3.65 is as high as you should go. Also make sure to verify voltage coming out of power supply with a volt meter. Check voltage where you hook up to battery. I have found that most power supply box off by .05.
 
I have not. Will now. BTW, is there a handy way to calculate how long it will take to charge my Batts from 3.35 up to 3.65, or to go from 10.30A down to 0?
 
Thx all. See attached. Current up to 10.3 A with 10AWG. I think that did the trick.View attachment 67304
Did your ps current fluctuate while charging? Mine would randomly vary in a range from, say, 5.15 to 5.70. I was expecting the current to be constant and trend down as charging progressed. I am wondering if the ps of faulty. Thank you.
 
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