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BQ78350-R1: Wrong Remaining Capacity / RSOC during charging

Georg Hoffmann
Prodigy 40 points
Part Number: BQ78350-R1
Other Parts Discussed in Thread: BQ78350, BQSTUDIO

Hello!

I have a problem with the bq78350 2.02
The connected cells are 15S6P LiFePO4 cells with in total 22.8 Ah

The current scaling factor is 10. In Charging and discharging in the following diagram, a current of 10 A is used which is correctly reported as -1000 and 1000 in bqStudio.
During discharge, the calculation of Remaining Capacity and RSOC works perfectly. Also the sync point for EDV2 (diagram at x = ~3500) with 7% RSOC creates nearly no deviation. So, calibration and calculation of the CEDV parameters is done properly.

I've worked with many different batteries built with the bq78350 and never had problems like the one i have now:
During charging, the Remaining Capacity rises much lower then it should. I calculated a nearly perfectly and constant factor of 20 compared to the actual charged capacity. As said before, the current is reported correctly and the change of the capacity should just be a sum of the current over time, so I can't think of a mistake that causes this, nether in hardware, nor software configuration.

I also checked the calibration, CC Gain is fine. And all problems with calibration or other things should affect charge and discharge in the same way, so I can't understand how this is possible.
It's configured in the way, that RSOC is synced to 100% at Valid Charge Termination.

Please help me solving this problem.

Best Regards
Georg

  • 0
    TI__Guru** 105760 points

    Hello Georg,

    Please share the .gg file of your configuration and the BQStudio log of the tests you are performing so we can verify the behavior.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 40 points

    Hello Wyatt,

    here is the export and two different log files:

    export.csv

    2072.log1.log

    2500.log2.log

    Thank you for helping me!

  • 0 in reply to Georg Hoffmann
    TI__Guru** 105760 points

    Hello Georg,

    I didn't seem anything very obvious in your configuration that would cause an issue. If you have any of the smoothing bits turned on, I would recommend disabling them for a test since this can cause the gauge to coulomb count at different rates, this is how the gauge smooths SOC by injecting charge to the CC. I believe this may be what is occurring.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 40 points

    Hello Wyatt,

    I tried different settings and deactivated smoothing, but I still have the same problem. But I found an additional problem now, which you can find in the attached log.

    The Charge Term Taper Current is set to 150 (=1500 mA because of scaling)
    In the log you can see that the VCT occured in line 46. The voltage for the charge termination is okay, but the current is much higher than the limit of 1500 mA (it was nearly 18 A)
    So, the wrong current (as it seems by factor 20) is not only here at the coulomb counter while charging, but also at the measurement for the charge termination.

    It is still the case that everything else is reported correctly during charging and discharging: Current and AverageCurrent report the true values in all cases. The calculation of the coloumb counter during discharge is always right, but not during charging.

    Sincerely,
    Georg Hoffmann

    08b_charge.log08b_charge.log

  • 0 in reply to Georg Hoffmann
    TI__Guru** 105760 points

    Hello George,

    I took a look through the firmware, I see there are a few areas which could cause differences between the discharge and charge. If you re-upload a default SREC file to the gauge does this issue go away? I am suspecting there may be some data corruption, is it possible at some point the gauge was not auto-detected and a BQZ file was manually selected? This could cause memory corruption if flash was written with the wrong BQZ.

    Sincerely,

    Wyatt Keller