First cell in 4S config always overcharging.

[electric]

Ya, the BMS is stopping the current at 3.5v for that cell while the other 3 are around 3.37 - 3.4. I guess I am wondering why that cell gets to 3.5v so quickly and the others come up more slowly.

Because you bottom balanced originally, which means no balance at the top, which is exactly what you are seeing.

 

[wntrhwk]

Electric, since I bottom balanced I cannot now try a top balance? This is what I am trying and the voltage is not changing.

 

[Ampster]

Does this process take days/weeks?

Yes it can depending on the Amps that your charger can put out. I also never understood the issue with cell # 4 either. Did you get them to 3.65 volts? Unless you did there is now way to determine which of the two possibilities that I and others were saying.

@electric makes a good point, the bottom balance in the first place maybe why you were seeing one cell high. That cell may be slightly less capacity but it is not worth worrying until you know how much or test the other 3 cells. At this point, as I suggested earlier, put them in the pack and log the results. Also, just so everyone is on the same page, let us know if you charged them in parallel to 3.65 volts or if you quit before then.

 

[electric]

Electric, since I bottom balanced I cannot now try a top balance? This is what I am trying and the voltage is not changing.

It may take many hours, depending on how much current is flowing.
Also, your BMS is working correctly, so you don’t really have to do anything. You won’t get more usable capacity from your battery as it’s always limited by smallest cell.

 

[Ampster]

Electric, since I bottom balanced I cannot now try a top balance? This is what I am trying and the voltage is not changing.

Okay, you answered the question. There is no reason except your own patience and time that you cannot top balance. Yes it will take time for the voltage to get to 3.65 volts. Do you have a ways to measure Amps. What was the setting on your power supply before you connected the cells? You need to double check that. One step at a time and it will become much clearer.

 

[MisterSandals]

Just realize that with your 100ah cells, 4 cells connected in parallel become a 400ah cell. So if you are charging (from dead empty) at 4 amps, it will take 100 hours.

 

[Ampster]

Just realize that with your 100ah cells, 4 cells connected in parallel become a 400ah cell. So if you are charging (from dead empty) at 4 amps, it will take 100 hours.

That can seem like for ever in ordinary times.
It may be forever if the OP does not have his voltaage settings correct.

 

[wntrhwk]

Yes it can depending on the Amps that your charger can put out. I also never understood the issue with cell # 4 either. Did you get them to 3.65 volts? Unless you did there is now way to determine which of the two possibilities that I and others were saying.

@electric makes a good point, the bottom balance in the first place maybe why you were seeing one cell high. That cell may be slightly less capacity but it is not worth worrying until you know how much or test the other 3 cells. At this point, as I suggested earlier, put them in the pack and log the results. Also, just so everyone is on the same page, let us know if you charged them in parallel to 3.65 volts or if you quit before then.

I apologize a lot and will do it again. It is difficult to follow thoughts through because of my issue, I will try better. First off, I did manage to get the pack that was in parallel to 3.6v per cell and let them rest (Bench PS set at 3 amps/3.6v). I then put them back in series, put a 2amp load on it until the voltage dropped to 13. I then hooked up my panels and charged back to the 13.85v. after 20 minutes at Absorption the one cell started creeping up, making it to 3.52v while the other cells were in the 3.4 range. Where I went on a tangent here is that I have another 50amph pack that I was trying to top balance. I setup that pack the same as the one I have been working on. The first pack took only a few hours to reach 3.6v, my second pack, even after several hours barely increased in voltage. One thing with the first pack, after charging completely, and in the float stage, I again put a 2 amps load on it and it went from around 13.7v to 13.15v in 15 minutes. It did stay at 13.15 for over 4 hours.
If this is all confusing please let me know and I wont waste all of your time. I tend to dabble in things a bit over my head at times hoping the process will "sink in". I do appreciate all of your comments and help.

Mike

 

[Ampster]

No worries. This will be instructive to others. Take the time to include details and that will be helpful. Because we only have 60 minutes to edit, I sometimes sleep on a draft of a complicated post to see if I have better clarity in the morning.

 

[wntrhwk]

Yup, two options either one Cel has less capacity, or one cell has a higher stat of charge than the rest.
Either way, it cannot take as much charge as the rest, so it reaches top voltage first...
you could drain that cell below 3.4v, and then hook it back into the pack and see if it holds better.

Hello Supervstech, thx for the reply, that sounds like the way I will go. Another question, not to beat a dead horse here, can I hook up a single cell of my pack, set it to 3.6v/2 amps, and try to top balance it? If all my cells start out at similar voltages would not a cell having issues take a charge differently than a good cell? Thx for your help.

 

[Turd Furguson]

remember that voltage means absolutely nothing. I have 85-90%ish depleted cells sitting here that read 3.2+ volts at rest but were 2.8ish during discharge. They'll quickly drop back after applying a load.

you need to decide whether to top or bottom balance; the stonger/weaker cell determines the charge/discharge limit accordingly.

based on your comments I'd suggest a top balance to guarantee a known starting point, and bottom balancing is a process in itself. Set charger to 3.65v and walk away. There's currently another active thread on this.