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I have two lithium battery packs with separate BMS, Can I connect the packs in parallel, will the BMS get damaged or will something happen?

12v 10ah battery pack, I have three in total and each has it's own bms and for now I want to connect two packs in parallel, I'm confused whether the bms will get damaged or what will happen? will it work?

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  • \$\begingroup\$ It depends entirely on the tech details of the BMS. \$\endgroup\$
    – Andy aka
    Commented Mar 9, 2021 at 16:54
  • \$\begingroup\$ BMS: 12v 20Amp capacity \$\endgroup\$
    – Minx
    Commented Mar 9, 2021 at 17:10
  • \$\begingroup\$ That is not enough information. Make, model? Do you have a manual? \$\endgroup\$
    – Justme
    Commented Mar 9, 2021 at 17:22
  • \$\begingroup\$ I don't have those, what will happen if I connect two battery packs in parallel and they both have separate bms inbuilt...? \$\endgroup\$
    – Minx
    Commented Mar 11, 2021 at 16:38
  • \$\begingroup\$ Be carefull, if the batteries have different SOCs a high current will flow from the higher to lower SOC battery. This current will destroy the fuse in best case. In worst case the cable can meld or the overcurrent can destroy (fire!!) the battery cells. \$\endgroup\$
    – A.R.C.
    Commented Mar 12, 2021 at 13:26

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I would only attempt this if both battery packs were at the exact same voltage and both packs were constructed out of the same chemistry cells(Lithium ion to Lithium ion, or LifePo to LifePo.). I would not mix chemistries as a lithium ion and LifePo max out at different voltages. My educated guess is that you are just making a 1S2P pack out of the individual packs. If they are at the same state of charge (voltage), the BMSs should not fight each other unless one of your packs is internally self discharging at a faster rate than the other one. And on that self discharge note, I would also only attempt this if both packs are of a similar level of wear and tear. It may be successful with an old and new pack but I personally would only join them if the cells had lived similar lives together. Otherwise one pack will just be dumping energy into the other pack to keep them both at the same voltage level.

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