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Lithium Iron Phosphate BMS

Amish Bhandari
Prodigy 70 points
Other Parts Discussed in Thread: BQ76PL536, BQ76PL536A

I am looking to design a BMS for LiFePO4 batteries. I will be using 24 cells in series.

Is there an IC I could use that would allow to monitor the SoC and also balance the batteries?

Also, I am looking to design a modular system with one master or a master slave module with one master and multiple identical modules.

Thanks

  • 0
    TI__Genius 13700 points

    Hello Amish,

    Have you looked through The BMS solutions guide?

    http://www.ti.com/lit/sg/slyt420/slyt420.pdf

    Does the diagram on  using the bq76PL536 cover what you are talking about?

    Ryan May

  • 0 in reply to Ryan May
    Prodigy 70 points

    It does answer my question...to an extent.

    But I'm not clear on the resistance values needed...or how to calculate them, if I want to build it from scratch, and not use the EVM.

    Also, if I use the EVM, can it balance the cells as well, or do I need to design that myself?

    Amish

  • 0 in reply to Amish Bhandari
    TI__Genius 13700 points

    Hello Amish,

     

    I am looking through the datasheet and EVM guide for the BQ76PL536A to see if we can find the answer to your question.

    http://www.ti.com/lit/ug/sluu437b/sluu437b.pdf

    The resistors are are most consistently discussed in the EVM (Pg. 2) and the datasheet (Pg. 19) is a 1k precision resistor for measusring the cell voltages. These resistors are coupled with 100nF capacitors.

     

    The datasheet on Pgs. 48-51 provides some extensive shcematic examples for stacking multiple chips and a look at the sensing resistors and the cell balancing that is accomplished by external power resistors and NFETs seen on Pgs. 49-51. The balancing resistors in the datasheet example are 47 ohms.

    I will look through this example and see if there is any explanation for the value that is selected in the example schematic.

     

    Ryan May