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Battery stack generic question

I am building a BMS system with 8 LTC6811 + 16 LTC3300-1 (i.e.96S) using active balancing similar to the reference design.

I am using LTC3300 boost+ method to distribute charge to the lower half of the upper stack for all but the upmost stack.

Now I am questioning myself what will happen if the highest stack has the highest SOC - do i have to add passive balancing for the upmost stack or switch a load to the stack to get rid of the excessive charge ?

Maybe this question is stupid but any advise welcome ;-)

Best Regards, Tom

  • In short this is not necessary as LTC3300 can both supply and return charge from the secondary side of the transformer.

    In the suggested application circuit for this type of setup (figure 4), the LTC3300-1 output connects 6 cells above the cells which it balances.  This way, charge can be moved up or down the stack by the next LTC3300 IC as its cells are charged/discharged by the IC below it in the stack.

    In the case where highest SoC is on the top 6 cells, the LTC3300 below it will charge its cells by pulling current from the top 6 cells.  This can then be repeated by the LTC3300 below it to move charge down the stack as needed.  The reverse of this process can be used to move charge up the stack as you described above.

  • Oh thank you very much for clarification. Don't know why I assumed charge could not be transferred down as well (stupid me). I have only one board ready by now and will test with all 8 boards completed. Best Regards, Tom