12S8P Battery pack with 96 Panasonic CGR18650CG

[Raexon88]

Hi, I have a 12S8P 50.3V battery pack for my underwater scooter. One of my cell strings is worn out and needs to be replaced. So I’m about to order 96 Panasonic CGR18650CG cells to replace the whole pack as the old cells that are glued together.

These are my measurements on the batterypack BMS after a dive and the scooter shutdown:

Pin 1: 4.17V
Pin 2: 4.19V
Pin 3: 4.17V
Pin 4: 4.19V
Pin 5: 4.18V
Pin 6: 4.18V
Pin 7: 4.18V
Pin 8: 4.17V
Pin 9: 4.02V
Pin 10: 4.19V
Pin 11: 4.19V
Pin: 12: 4.17V

Here you can see that the cells on string 9 are 0.15V lower than the rest of the cells. And I suspect that when I use the scooter the BMS cuts the power to the scooter because of these cells reaching a voltage below the cut-off setting of the BMS.

So if anyone has done this before any or have seen this problem before on pack any tips for fixing it would be much appreciated.

I am thinking about using the Samsung INR18650-35E instead of the Panasonic as they have the same capacity.

Bjørn-Kristian Lampe Johannesen

 

[john61ct]

You are on track.

Note that "string" refers to units in series.

"Group" seems to be the common term for paralleled cells.

After you replace the cells, a capacity test may show that some can continue to be used for another purpose at slower discharge currents.

70-80% SoH is the usual go/no-go threshold for EoL.