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BQ40Z50-R1: What determines the full charge Capacity Change,when FC or FD is set.

john xiao
Intellectual 470 points
Part Number: BQ40Z50-R1

Dear all:

I have design the 4S2P LiFePO battery pack,the designed capacity is 7800mAh.I choose the Chem ID is 0438.the gg file is 7800mah.gg.zip,I do charge-discharge cycles, when discharge the battery pack,after FD is set,I found the FCC jumped from 6898mAh to 7569mAh.after charge the battery pack,FC is set,I found the FCC jumped from 7569mAh to 6862mAh.the log file is discharge-charge log.zip.why the FCC jump is so big?What factors determine the  change?

  • 0
    TI__Expert 6575 points
    The primary reason for the large FCC jump is likely because the Qmax is not correct.
    From the gg file it shows that even though the "Update Status" = 06, the Qmax cycle count is 0 i.e. Qmax was never updated.
    If Qmax is not updated it will result in incorrect FCC value.
    Also, the SOC flags "SOC Flag Config A" and "SOC Flag Config B" shows that the condition for [TC] is set to both valid charge termination as well as RSOC, it will be better to select only one condition. The recommendation is to select valid charge termination. The condition for [FC] is set to both valid charge termination as well as Voltage threshold, again, it will be better to select only one condition. The recommendation is to select valid charge termination.
    From the log file, it looks like your discharge is stopping because Cell4 is hitting cell under voltage and during charging Cell2 is hitting cell over voltage. It will be better to use balanced cells when manufacturing the packs.
    Regards,
    Swami
  • 0 in reply to Swaminathan Ramanathan75031
    Intellectual 470 points

    Dear Swami:

    Thank for you reply.

    I have set Fast_QMAX_LRN=1,but the gg file show Qmax still not updated.this is gg file.7800mah-1#.gg.zip.why the Qmax not updated?

    I also found when the RSOC is 0%,Multiple discharge until CUV.FCC change more and more.this is discharge log file.1#_charge-discharge.zip.Why does this happen?