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BQ40Z50-R1: First charge upon customer receipt of battery pack goes into Overcharge because initial FCC is much lower than actual.

Lon Schneider
Prodigy 200 points
Part Number: BQ40Z50-R1
Other Parts Discussed in Thread: BQSTUDIO,

Final Test records FCC at the end of test. Packs are then shipped in shutdown mode. When awakened, the FCC can be quite different.  Design Capacity is 2520 mAh.  Typically  FCC is close to this value when read in Final Test. But, when the pack is awakened, FCC can be 2000 mAh or less. FCC when first awakened (by bqStudio or by the companion charger) differs significantly between packs even though they were programmed with the same SREC, never run so no learning cycle would have occurred, and are at very similar OCV's. Charge is applied upon receipt and charge capacity delivered to termination can exceed FCC by 500 mAh or more. This results in an Overcharge Fault. Please explain how FCC is determined when a new pack is first awakened from Ship Mode.  

FCC can  change 15% or more from the first value read upon wakeup, if the pack is again shut down and awakened, but that does not happen consistently.

Thank you,

Lon SchneiderCOMPARE GGS FOR LOW FCC.xlsx

  • 0
    TI__Guru** 105590 points

    Hello Lon,

    When the gauge wakes up from shutdown or ship mode, or if it is reset, it will recalculate the RCC and RemCap values since they are stored in RAM. It will use the range from the DOD associated with your terminate voltage, and the DOD at EOC to determine the full range of SOC and FCC. If the gauge takes a voltage reading that is already loaded or being charged it will not calculate the right FCC/RemCap. Upon wakeup the voltage must be in OCV.

    You must complete a learning cycle and create the golden image that is downloaded in production, otherwise the gauging results will not be good. I also took a look at the xlsx file, what is the pack labeled as 341250-01107? The Qmax values between the two are completely different, I'm not sure if this is from the learning cycle being skipped, but if the Qmax as that far off from the real packs that is why the FCC is calculated so low:

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 200 points

    Hello Wyatt,

    I am familiar with how Impedance Track works, but I'm not clear on exactly how it calculates FCC upon first wakeup. . The packs are all programmed with the result of a golden file. The production GG and SREC are 341250-05114.  Columns being compared are different serial number packs, all programmed with SREC 341250-05114 which includes the gg content of 341250-05114 and CHEM_ID 2075 (Moli ICR18650M). 

    (File 341250-01107 is from a different product which also uses bq40z50-R1 but different cells. It was compared, only for the purpose of looking for clues. That is why its Qmax etc are different,  I should have deleted it..  Sorry for the confusion that it caused.)

    Due to the SOC of the cells, the packs are being awakened in the Vdisq region when new packs are first placed in the charger.   Mean Vcell is ~ 3767 mV, and the Vdisq region for this CHEM_ID is 3747 to 3792 mV..  (I noted an earlier CHEM_ID (0208) also associated with this cell and it had Vdisq well below this range. Perhaps a first step should be to check the accuracy of CHEM_ID 2075, at least for the range of Vdisq.

    When a pack that has not been cycled first wakes up in a Vdisq region, how does the initial value for FCC get determined?

    BTW, are you related to Keith Keller?   

  • 0 in reply to Lon Schneider
    TI__Guru** 105590 points

    Hello Lon,

    Upon wakeup they will use the OCV to initialize FCC, if it is in the flat region this can lead to considerable errors in the FCC estimation depending on the chemistries discharge curve.

    No problem, just thought it may be something related.

    I am not related (that I know of)

    Sincerely,

    Wyatt Keller