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I have 39 lithium cells, I want to make a 12 V battery pack with as much AH as possible. From what I've read, all BMS are only for cells connected in series. So for example, all 12 V battery packs are always 3S BMS and have three cells? Can I have multiple 3S BMS battery packs connected in parallel? Can I charge them from one charger? In short, how can I use all my batteries for a 12 V battery pack and is it at all possible?

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  • \$\begingroup\$ We don't know which BMS you have and can them be paralleled. We don't know what charger you have if it supports charging multiple packs in parallel. Using 13x3 cells would make make a 12V pack but we don't know if your BMS supports it, of your charger supports it, or if it is even a good idea to short 13 cells in parallel - if one shorts out the rest of the 12 will surely push some serious current into it. It does not seem very good idea. \$\endgroup\$
    – Justme
    Aug 29, 2023 at 22:17
  • \$\begingroup\$ @Danny In English, there is no space before question marks and punctuation. This may be helpful for you: lrdgcampus.com/blog/capitalization-rules \$\endgroup\$
    – JYelton
    Aug 29, 2023 at 22:36
  • \$\begingroup\$ This answer covers the topic in some detail Do I need BMS within parallel connections? \$\endgroup\$
    – colintd
    Aug 29, 2023 at 23:57

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Easy:

  1. Connect 13 cells directly in parallel to form a block
  2. Make 3 such blocks
  3. Connect them in series
  4. Connect the balance wires of the 3S BMS to the block of cells

The BMS doesn't know or care whether each block is a single large cell or 13 small cells in parallel. Electrically, they are identical.

(By the way, for 12 V, you don't want three LCO cells at 3.6 V each. You want four LFP cells at 3.2 V each. That's adds up to a nice and nearly-constant 12 V.)

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