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BQ27426: Wrong SOC while discharging

Nicolas Venturo
Intellectual 810 points
Part Number: BQ27426

Hello,

I am testing a product using the BQ27426, and I encountered a strange issue. The product has a 10000mAh battery, and the terminate voltage is set to 3.2V. The BQ27426 reports a SoC of around 50% with the battery at 3.8V. However, when a large current (4A) is drawn from the battery, the voltage drops due to resistive losses in the wiring to around 3.4V. The BQ27426 measures both the voltage and the current correctly, but starts decrementing the estimated remaining capacity (and SoC) very rapidly, much faster than a coulomb counter should. I guess this is related to the voltage drop, but it causes serious issues, since the SoC because pretty much useless. Is there anything I can do about this?

Thanks

  • 0
    TI__Guru* 76230 points
    hello Nicolas,
    You will need to run a rel-dis-rel test to determine if this gauge will be suitable for your battery otherwise you will run into SOC accuracy issues. Pls follow the instructions in the link below to determine if the default chem id preprogrammed on the gauge would be a match..
    www.ti.com/.../GPCCHEM
    let me know if you have further questions.

    thanks
    Onyx
  • 0 in reply to Onyx Ahiakwo
    Intellectual 810 points

    Hello Onyx,

    Our battery is a 1-cell 4.4v Li-Po cell, why wouldn't it work with the pre-configured 4.4v chem ID (3142)? Besides, the guage works perfectly fine most of the time, the only issue we're running into is at low SoC (around 20%) and high currents (around 2A), where the SoC starts dropping very rapidly (much faster than should occur for a coulomb counter), and then suddenly jumps to 0%. I'm thinking maybe this is related to the system voltage dropping at high currents because of the series resistance from the battery, but I don't know if there's anything we could do to avoid this issue.

    Thanks

  • 0 in reply to Nicolas Venturo
    TI__Guru* 76230 points
    Nicolas,
    Even though your battery is a 4.4V, that doesn't mean the Open circuit voltage of the default chem id would be a match for your battery and that is why i said to run the test above. The issues you are seeing are typical symptoms of using a chem id that isn't closely matched.

    thanks
    Onyx