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BQ79606A-Q1:Balancing by threshold.

Sebastian Mateos
Prodigy 90 points
Part Number: BQ79606A-Q1


Hi TI team:

When balancing the cells automatically by voltage threshold, in activation cycles the voltage of each cell drops, so that the balancing cuts before the cell actually reaches the programmed voltage. How can i fix this?

Thanks, Sebastian.-

  • 0
    TI__Genius 17370 points

    Hi Sebastian,

    Are you using a bq79606A EVM with the resistor ladder or is this a customer hardware board? If you are using the resistor ladder switches than you will see a huge drop in cell voltage and you will need to switch these off and use batteries through the battery terminal.

    Regards,

    Taylor

  • 0 in reply to Taylor Vogt
    Prodigy 90 points

    Hi Taylor,
    I am using the BQ79606A EVM connected to a 6Sx3 battery. The resistance ladder is off. The SOC of the battery is high (around 3.9v at 4.1v each cell). I will give you a graph of a 30-minute balancing session with a voltage threshold of 4v.


    You can see that cells with voltages greater than 4v are balancing. But measurements change when mosfets are activated.

    Thanks for your help.

    Sebastian.-

  • 0 in reply to Sebastian Mateos
    TI__Genius 17370 points

    Hi Sebastian,

    During cell balancing, there can be inherent inaccuracy based on the impedance of the cable and the battery cell itself due to the current pull. The best solution is to pause frequently during balancing in order to take a measurement and check the levels. This is all part of developing an algorithm that we leave in the customers hands to properly balance and check levels over time.

    Regards,

    Taylor 

  • 0 in reply to Taylor Vogt
    Prodigy 90 points

    Hi Taylor,
    The problem with this is that i can't use the balancing threshold to automate the balancing. 

    Thanks for your help!

  • 0 in reply to Sebastian Mateos
    TI__Genius 17370 points

    Hi Sebastian,

    This is not to say that you cannot use the balancing threshold to meet your needs. It just means that you need to perform some characterization to determine a better threshold to use to meet your goals (perhaps offset a little bit). As the datasheet suggests there can be up to +-55mV of error for the CBDONE threshold comparator at this battery range so your algorithm should take this into account.

    Regards,

    Taylor