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BQ34Z100-G1: SoH CALCULATION

unai sanchez
Prodigy 220 points
Part Number: BQ34Z100-G1
Other Parts Discussed in Thread: BQ34110, BQSTUDIO

Dear all,

I have developed a new product with LiFePO4 batteries and I am using the bq34z100-g1 to estimate SoC and SoH of the battery.

I would like to know at which points is bq34z100-g1 updating SoH.

- Are there any conditions that mus be fullfiled to do a SoH calculation? Or can it be calculated at any time?

- Which parameters are taken into account to calculate SoH?

 

Best regards, 

  • 0
    TI__Guru** 105760 points

    Hello Unai,

    Depending on your application, I may also consider the bq34110 for applications with LiFePO4 if you are using it in a rarely discharged application or battery backup.

    The SOH will only change when there's a Qmax update or Ra update. We use the design capacity and calculated FCC using a set current (SOH load 1) at room temp. The only parameters that would change to affect SOH is the Ra and Qmax.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 220 points

    Ok, understood Wyatt.

    One question about Qmax update:

    - Once the battery has been fully charged and FC flag is active, is it necessary to wait until bq34z100-g1 gets valid DoD measurement for Qmax update or is 100% SoC assume as one valid point?

     

    Best regards, 

  • 0 in reply to unai sanchez
    TI__Guru** 105760 points

    Hello Unai,

    It needs to take a DOD measurement, when FC is set the cell voltages would not be relaxed so they would not correlate with the OCV.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 220 points

    Thanks Wyatt.

    It needs to take a DOD measurement, when FC is set the cell voltages would not be relaxed so they would not correlate with the OCV.

    However, the purpose of take a DoD measurement is to relation the OCV with the SoC (via the selected chemistry file). When FC active, you know the SoC is real (you know is 100%) although cells are not relaxed. 

    I have logged with bqStudio and I have seen that in the moment FC is set the following parameters become 0: DOD Passed Q, DOD Time, DOD0,QmaxDOD0, QmaxPassedQ and Qmax Time.

    That is why I thought that no relax time were necessary after FC set. What do you think?

     

    Best regards,

  • 0 in reply to unai sanchez
    TI__Guru** 105760 points

    Hello Unai,

    SOC and the DOD do not correlate directly because DOD is based on the chemistry ID. 0% to 100% can be smaller for SOC than the scale for DOD because DOD is based on the full spectrum of the battery.

    Can you share the logs of this occurring? The gauge should only update DOD0 when an OCV is taken.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 220 points

    Thanks Wyatt for the explanation.

    Attached you can find the .xlsx file where you can see how these parameters (DOD Passed Q, DOD Time, DOD0,QmaxDOD0, QmaxPassedQ and Qmax Time) become 0 when full charge is met. (row 1136 in file)bq34z100_SoH_calc.xlsx 

    How can you explain it?

    Best regards,

  • 0 in reply to unai sanchez
    TI__Guru** 105760 points

    Hello Unai,

    Can you also share your .gg file of the configurations?

    I believe what is happening since you are using LiFePO4 batteries, the LFPrelax function is enabled, this algorithm forces an OCV to be taken at FC because the voltage for this battery chemistry can relax back down to a flat region voltage, making it hard for OCV correlation the normal way Impedance Track works for other chemistries.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 220 points

    Hello Wyatt,

    You are rigth, LFPrelax in enabled as we are using LiFEPO4 batteries.

    Here you can find the.gg fileLiFEPO4_BAT_RELAX.gg.csv

    So, with this data, can we take the FC point as a valid point for Qmax update?

    Regards, 

  • 0 in reply to unai sanchez
    TI__Guru** 105760 points

    Hello Unai,

    Yes if the LFPrelax function is running then you will be getting an Qmax update when the FC is set.

    Sincerely,

    Wyatt Keller