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BQ76952: Host Controlled Balancing

Mike Stallone
Prodigy 50 points

Part Number: BQ76952
Other Parts Discussed in Thread: BQSTUDIO, EV2400

Hello,

 

I'm trying to run host-controlled balancing and having some issues. Passive balancing (where the BQ76952 runs its own balancing algo) works, however. I need host-controlled balancing to work, and cannot figure out what is going wrong. My setup:

 

Custom board with a BQ76952, attached to a 16-cell cap bank that is being used to simulate a battery cell-pack. Balancing is to be done with the internal resistors in the BQ76952. 

The pack is at rest (no discharge/charge current), and I'm attempting to level out the pack using the internal resistors using host-controlled commands

I have attempted to send both of these cell-balancing commands, if either works that would be acceptable for my application, but neither works (ie. cell voltages do not change, reading "active_cells" does not show any balancers active, etc.)

image.png

 

I am sending host-controlled balancing commands using a custom-board over I2C; the I2C has been tested for several hundred hours and works. I have also attempted to send these commands using the EV2400 using BQstudio, and had the same results; the pack is not balancing

 

Here are my balancing settings:

image.png

I have changed cell balance interval to many different settings 1->60s to no effect

 

It doesn't make sense to me that "passive" balancing would work, but "host-controlled" balancing wouldn't. Do you have any suggestions for things I could be missing? The datasheet seems to suggest that "host-controlled" balancing only happens when the system is charging; can host-controlled balancing not be done at rest?

  • 0
    TI__Expert 4490 points

    Hi Mike,

    To avoid the conflict of autonomous cell balancing and host-controlled cell balancing, could you clear Settings:Cell Balancing Config:Balancing Configuration[CB_CHG] and Settings:Cell Balancing Config:Balancing Configuration[CB_RLX] to disable autonomous cell balancing?

    You should set cell balance interval to a big value for test purpose, like 60s. Also, you should take care that make sure you don't accidentally turned on the adjacent cell balancing when you write 0x0083 subcommand.

    BRs

    Kian

  • 0 in reply to Kian Lin
    Prodigy 50 points

    Hello Kian,

    My question is - why is host-controlled balancing not working for me, but the autonomous balancing is working for me?

    ---

    ---

    Answers to your other questions below:

    Why shouldn't I turn on adjacent cell-balancing? The reference manual does not clarify

    I have CB_CHG and CB_RLX disabled, already. There should be no conflict with autonomous balancing

    I have Cell Balance Interval set very low, here, because I am balancing with a cap-bank which has low capacity; 60s recalculation on the balancing time is too long, the caps will be discharged under my CUV in that time, and I can send the balancing command every 200ms pretty easily. Is there an issue with setting it to 1s balancing time?

  • 0 in reply to Mike Stallone
    TI__Expert 4490 points

    Hi Mike,

    Here is a note explains more details on cell balancing. Cell Balancing With BQ769x2 Battery Monitors (Rev. A)

    The host-controlled cell balancing subcommand takes up to 1 second to take effect. So, it is recommended to use longer interval. Are you using resistor + capacitor ladder to test the balancing? Typically, I don't recommend to test like this because you could trigger protection and stop balancing immediately. Do you have a cell simulator? Or, may be you can use DC source to simulate cell. 

    For host-controlled balancing, adjacent as well as non-adjacent cells can be balanced. But i don't know if you configure the hardware properly. So i suggested you not using it for test purpose.

    BRs

    Kian