Made a 3s12p pack, but something seems off.

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orbaxter

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Mar 11, 2018
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Hi, so I made a 3s12p pack out of recycled cells, everything was looking good until i realised that one of the parallel packs didnt seem to be discharging much. It's now been around 8 hours and it has discharged by a few mv to 4.06v while the other 2 packs are at 3.75v - there is a 20A fuse between that pack and the charge controller, could that have anything to do with it? I've also realised there's a 1v voltage drop between the fuse and the battery pack :/
 
1) Did you test each cell?, 2) did you capacity match each of the 3s parallel sets? 3) What is the load on the pack. 4) did you leave each cell charged and check for self discharge?
 
Yeah, I checked each cell - charged them all up then discharged with an imax b6 @ 1A, then used repackr.org (they all came out to around 20Ah per pack), 3 of those in series is 12v 20Ah. There were a few cells with little cell discharge, but I don't believe those are causing this much difference

Load on the pack is about 1A max atm
 
Pictures of your pack?
 
Also, the fact that 2 of 3 parallel packs are the same voltage doesn't seem to match up with the self-discharge theory, it's the most positive pack that has the higher voltage (3.75, 3.75, 4.08) - it's like the 3rd hasn't been discharged at all, which wouldn't make sense...

It's covered with electrical tape, and it'd be a hassle to get it all off (I was kinda paranoid about accidentally shorting it when drunk or something) - but all the cells have 5A fuses connected to copper bus bars, and then the bus bars are connected with 20A wire.
 
Some thing is weird. When I had an imbalance in my packs I tried discharging the Cell group as a whole and found that a cell by itself behaves one way and in a group totally different so I make smaller packs (of 8 cells in P) and test that set and label it with ti's capacity @ 8A discharge and my packs have been much closer. but looking at your problem a Picture of your setup would be helpful
 
Yeah, so I did some probing around and then one of the soldered wires fell off... It'd been riding on a bed of flux essentially which could've had high resistance. I'll resolder all of my wires tomorrow (and clean out the flux) and see if that fixes it - as for balancing what do you guys think would be the best option, attach my IMAX to the bus bars and hope it doesnt try to charge the other cells or charge them with the other 2 parallel packs disconnected?
 
For now I'd charge each cell seperatly to get them all at full charge then start from there. broken wires can cause that
 
It's gonna be extremely difficult to charge each cell individually, would charging the 3 parallel packs individually be a viable option?
 
Sorry Yes I mean charge the parallel sets of 12 cells as a group (1s in voltage)
 
if this is a li-ion battery pack, there might not be enough series connections. I encountered this before. Just add more nickel strip between the series connections.

To charge a battery pack that is seriously out of balance, I used a usb load tester(bleeds at 4 amps). You can connect that to the high cell and it will bleed that cell while the others charge. Without a way to bleed your high cell, a balance charger will take all day to charge at 1 amp, thats if it doesnt shutoff early.

usb load tester 4 amps

image_vyzexs.jpg


Heres a picture of my 3s30p 65ahbattery that had balance problems, you see not enough series connections. I rebuild by adding more nickel strips between the cells, now it stays in perfect balance.

image_tawqzi.jpg
 
jonyjoe505 said:
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Heres a picture of my 3s30p 65ahbattery that had balance problems, you see not enough series connections. I rebuild by adding more nickel strips between the cells, now it stays in perfect balance.

image_tawqzi.jpg
Click to expand...

It looks like one of those nickel strips is bypassing a fuse.
 
Alright, will do - thanks for your help and I'll give an update once the cells have charged.

Yeah, I'm keeping it balanced by using the same wire both sides - I don't think that would be too much of an issue as it is a small load
 
If you can break the connections that make the series connections, you could use alligator clips to put everything in parallel and let it all charge and self equalize.

It will at least do a better / faster job than the charger.
 
It looks like one of those nickel strips is bypassing a fuse.

Thanks never noticed that, looking closely its several places that are questionable.Now I have to rebuild again. The pin fuses I was using was not easy to work with.
 
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