Used 12s4p Packs Combined For 12s16p

Braddudya

100 W
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Jan 30, 2022
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I have some 36v LiFePO4 packs that are 12s4p. I am trying to combine them for a solar adventure van project (the van will still be gas).

I could add a BMS to each pack and then wire them in parallel with each other. Or I could wire each parallel set together to make one battery with one BMS. Is there a rational for or against either case? These are used batteries so they are not matched cells between packs but does that make for big problems? I see mixed cell packs regularly in builds.

I do already have an Ant BMS good for 400amps or so which would be more than enough to run the 3000W 36V inverter
 
They are unmatched cells only because they have different levels of use but they are a123 LiFePO4 cells packed in super high quality packs for hospital machine backup power (I believe) so they aren't used and abused old cells.

Someone has to do something with all these partially used cells. If there is truly a stigma against upcycling relatively safe brand name LiFePO4 cells that would be quite sad. I suspect that is not the case though.

Thank you for the information. I would like to do individual BMS but it may be needlessly expensive.
 
If you parallel them just at the mains, one BMS won't work, unless you run balance wires across everything, which starts to be lot of wires.
I ran a lot of mismatched packs, so would sometimes just have one BMS that I would plug in to the different packs periodically.
I wasn't worried about having it controlling the discharging, but whichever way you go, just don't get complacent about checking things with a meter pretty often.
 
Voltron said:
If you parallel them just at the mains, one BMS won't work, unless you run balance wires across everything, which starts to be lot of wires.
I ran a lot of mismatched packs, so would sometimes just have one BMS that I would plug in to the different packs periodically.
I wasn't worried about having it controlling the discharging, but whichever way you go, just don't get complacent about checking things with a meter pretty often.

I would only parallel the mains if each pack had its own BMS. What I would like to do it just run heavy jumper wires between each pack to connect each parallel group. This would make it one big single battery. I just don't know how big of an issue it is that one pack might have been used more than another. I am guessing that it will be just fine. I want to run a 3000W inverter which is like 100a at most so that's 6.25 amps per a123 26650 cell. It's a tiny draw for these cells.
 
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