I recently finished up my build of 2x 6s8P 18650 30Q packs. Well mostly finished… Having issues charging one of these packs in particular. I built these to replace my blown up Turnigy 6s 20000mah lipo bricks, hence the identical form factor. This is my first battery build and I will be running these two packs in series as 12S8P.
Here is a pic of one of them finished and the other under construction.
Here is a pic of one of them before kapton tape and heat shrink. I used 0.2x8mm pure nickel strip double thick across all series connections and triple thick across the 2 main +/- busses on each battery. Then paralleled the two 4p busses together to 8P using 8awg wire. Should be pretty solid from a current carrying standpoint.
No BMS on these and just balance charging. You can see the balance lead configuration in the pics.
So here’s the problem:
The second battery (the naked one in the pics above) has a series cell that won’t charge. The very first time I put this pack on the charger I think I cell 3 got up to like 3.8-3.9V. The other 5 cells went up to 4.2 as they should. I decided to test these batteries out on my board in my pool (my efoil dyno) anyway and run one almost complete discharge cycle. They worked awesome (compared to my turnigy batteries). They barely got warm and had lots of run time. I ran the packs down to about 3.2V per cell (cell 3 might have been at 3.0). I up them back on the charger.
Battery #1 charged up just fine with every cell charging evenly and finishing off at 4.2V per cell.
Battery #2… not so much. Cell 3 never got much above 3.6-3.7v. Cell 6 stopped at like 4.1V. All other cells were at 4.2.
Here is a picture of the charge progress an hour and a half in:
Here is a picture of charge progress 2 and a half hours in:
I also tried charging this battery on ch2 of my dual battery charger to see if it was something wrong with the charger. Same results.
Cell 3 just really doesn’t seem to be taking a charge too well.
Disclaimer: i did have a couple sketchy spot welds that may have gotten fairly hot. Maybe these damaged the cell somehow?
Has anyone run into something like this before? What might cause a cell (or a set of 8 parallel cells in this case) to not get up above a certain voltage?
Thanks for the help!