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BQ40Z50: Changes on FCC calculation for BQ40Z50-R5?

chee ming cheong
Prodigy 35 points
Part Number: BQ40Z50
Other Parts Discussed in Thread: BQSTUDIO

Good day,

I would like to know for BQ40Z50-R5 firmware, is there any changes related to FCC calculation?

I have encountered an issue where the FCC for the battery pack is dropped much lower compared to BQ40Z50-R4 firmware previously.

Before issued a ship mode command, the pack's FCC is 16.1Ah. Upon wake up, the pack's FCC dropped to 13.8Ah.

Please advise.

Thank you.

Regards,

CM

  • 0
    TI__Guru** 105590 points

    Hello CM,

    Both should have similar behavior when calculating FCC if the application is the same. There are many parameters which are used to estimate FCC and some of the parameters are stored in RAM which is lost when the gauge is shutdown, so it is expected to see some change in FCC.

    Can you share the two .gg files from -R4 and -R5 and some logs showing the behavior?

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 35 points

    Hi Wyatt Keller,

    Please refer to the attached .gg files for -R4 and -R5.

    I don't have the logs showing the behavior. The battery pack underwent full charge follow by full discharge and lastly follow by condition charge to 15% SOC. The BQ reported FCC is 16.1Ah after the condition charge. Lastly, the battery pack went into ship mode by command.

    After that the battery pack rested for 2 days before the final test. During the final test, the BQ reported FCC dropped to 13.8Ah which is out of the test limit.

    1) May I know the charging current during the condition charge will affect the BQ reported FCC as my Load Select is 7 and Load Mode is 0.

    2) May I know the FCC accuracy that the BQ chip can guarantee when comparing to the actual capacity (e.g. 16Ah). I would like to know if +-5% to the BQ reported FCC is reasonable.

    Thank you.

    Regards,

    CM

    R4.csvR5.csv

  • 0 in reply to chee ming cheong
    TI__Guru** 105590 points

    Hello CM,

    There is no expectation that FCC will stay the same before and after shutdown since this is not expected operation of the gauge, only during shipment or long term storage should shutdown be used.

    There is no spec related to how much FCC can change, as I mentioned with load select 7 you are using the previous discharge cycle max average current, if you shutdown this data is lost in RAM and will not be retained. You can try to test by selecting a fixed load select rate and see if the behavior changes.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 35 points

    Hi Wyatt Keller,

    Our production process will send the shutdown command to the gauge at the end of the test for shipment purpose. 

    However, referring to the BAT-A FCC at column T of 1st run- copy, we have seen a drastic drop in FCC from 19261 mAh to 12378 mAh upon exit discharge. Hence, the test has failed and sent a shutdown command to it.

    Next, we try to rerun the same test on the same unit, upon woke up, we can see that the FCC is back to acceptable value at the beginning of the test which is 18773 mAh at column T of 2nd run- copy. For the 2nd run, the FCC updated from 18773 mAh to 18440 mAh upon exit discharge which is acceptable.

    Could you explain this behavior/theory for this issue please, thank you.

    Regards,

    CM

    1st run- copy.xlsx2nd run- copy.csv

  • 0 in reply to chee ming cheong
    TI__Guru** 105590 points

    Hello CM,

    Is the discharge current in amps? It's not clear what the units are for all the logged values. Using BQStudio to log is the most helpful since we can see all the registers which give clues to the reason of the FCC jump.

    I did notice in your R5 configuration the Ra0 (the first grid point in the Ra table) is very high, please set this to 100mOhm or less, with such a high value it could impact SOC or FCC. Your R4 configuration does not have a large value for Ra0, if both of these are learned packs for the same battery they should have similar Ra tables.

    When you wakeup the battery pack, what voltage range do you do this in? For LFP chemistry it is important to wakeup at either low voltage or high voltage since the OCV is so flat.

    Sincerely,

    Wyatt Keller