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BQ79612-Q1: Balancing 18S modules

May
Genius 9880 points
Part Number: BQ79612-Q1

Hi Team,

Customer is interested using the BQ7961x in their application and they want to know if this is the best device to meet their requirements, please see details below.

The way our pack is setup is in 4 segments of 18 series cells, using 2 daisy chained 12S balancing chips per segment each balancing 9 cells. We were looking at the BQ7961X series of chips to accomplish this; however, after reading through the documentation I did not see any methods to have multiple chips balancing the same segment (Ex. one chip balancing cells 1-9, one chip balancing cells 10-18).

Is this possible with the BQ7961X series of chips? or are there any other options from TI we could explore for balancing our pack?

Thanks.

Regards,
May

  • 0
    TI__Intellectual 1760 points

    Hi May,

    Can you tell me a little bit more about more about your setup? Is the plan to have a single '612 device per 9S or is the plan to use all 12 channels and to mix segments across devices? For the case of 9S per device you should be able to just cell balance as normal. For the 12S case you will need to handle the busbar case which is covered in the datasheet in section "9.3.7.1.3 Cell Balancing Handling"

    The other option is that we are currently working on the BQ79718 device which is an 18 cell device.

    Thanks,

    Geoff

  • 0 in reply to Geoffrey Grimmer
    TI__Genius 9880 points

    Hi Geoff,

    Just received response from customer, please see details below.

    We were attempting to balance a 72S pack that is in 4 18S isolated segments. The original plan was to use two ‘612 devices daisy chained together with 9 cells per chip to balance one 18S segment. In the BQ7961x reference designs the pack is always grounded out at the bottom of the balance chip (after the last cell); however, I don’t believe this would be possible with how we need to set-up our pack. I couldn’t see any workarounds for using multiple ‘612 chips to balance a single segment, and have realized that a fully distributed BMS design with one balancing/monitoring chip per cell may have been the better solution.
    The BQ79718 chip sounds like it would be the perfect fit for what we wanted to design. Unfortunately, as we are a formula team, we are under tight time restrictions and I don’t think we will be able to use it for this year’s project.

    Thank you.

    Regards,
    May

  • +1 in reply to May
    TI__Intellectual 1760 points

    Hi May,

    To clarify the gnd of the '61x does not need to be pack gnd. The ground reference for the IC would be the bottom side of the lowest cell that is connected to that IC.

    Thanks,

    Geoff

  • 0 in reply to Geoffrey Grimmer
    TI__Intellectual 1760 points

    Here is a quick diagram of what I am meaning.