upgrading a DYI battery pack

[Secular]

Last year I made a 15s5p battery pack of sanyo ncr18650ga. Currently sitting at 110 cycles. I want to expand the pack (15s8p) without having another BMS (My current BMS is the Aliexpress Bluetooth bms, 15s, 60a). I would add another 3 ncr18650ga in parallel to each series branch.


I know this isn't ideal but I don't see this being a safety issue. The new batteries will end up discharging a bit into the old ones on the same branch but the BMS monitors each series branch.

From searching it seems as long as I add them in parallel everything should be fine. In series can get you in trouble.

Thoughts?
Thanks

 

[dustNbone]

Should be fine, as long as the existing cells haven't been severely abused in their short life they should still be fairly close in spec to new ones.

Make sure the existing cells are at the same voltage (+- .01V maximum variance) as the new ones, to avoid an uncontrolled current current rush from the higher ones to the lower ones when you connect them initially.

 

[john61ct]

I might consider doing a separate 3P pack in parallel, if the available space allows.

That way if it does turn out the older one fails much earlier, you still have a healthy pack to get by on, no need to scrap the whole thing

Yes means a new BMS

 

[Secular]

Yeah I really don't want another BMS. I can't connect and monitor two to my phone which I have up every ride. A valid point though

 

[john61ct]

Maybe replace with one master BMS wired externally, but still keep the sub-pack modules physically separate.