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BQ40Z80: RSOC not reflect capacity

Kunny
Prodigy 240 points
Part Number: BQ40Z80
Other Parts Discussed in Thread: BQSTUDIO, GPCRB, GPCRA0

TI support,

RSOC has not reflected the battery capacity at real time.

I have finished until learning cycle(LStatus 0x0e). I believe it's ready to use.

But prior to mass production, I did the test of discharge characteristic using logging by bqStudio at different temperature as shown below:

(I need wide range of temperature in my application.)

1. Charge the Li-po battery(6S 1P) to full at 25degC of temperature.

2. Discharge to empty(rate 0.3C) at 25degC. I got the graph of discharge on Voltage and RSOC at 25degC.

3. Charge to full at 25degC.

4. Left the battery at -10degC well-relaxed over 4 hours.

5. Discharge to empty(rate 0.3C) at -10degC. I took the graph of discharge on Voltage and RSOC at -10degC.

Results are:

25degC: RSOC=2% at 3V/cell

-10degC: RSOC=7% at 3V/cell

Continuing discharge at -10degC almost reached at less than 2.5V/cell(dsg stopped), RSOC still kept 7%, though.

Why RSOC does not decrease by following the ambient temperature?

Please let me know any concerns or suggestions you may have.

Regards,

Kunny

  • 0
    TI__Expert 3030 points

    Hi Kunny,

    It seems your low temperature resistor value needs some correction, you can use GPCRB tool to correct for low temp resistance, which might be helpful to your question.

    Best Regards,

    Abraham

  • 0 in reply to Abraham Rashid
    Prodigy 240 points

    Hi Abraham,

    Thank your for your inputs.

    I have two questions about GPCRB.

    1. Do I need GPCRA0 test to be done prior to GPCRB low temperature optimization?

    2. According to 2.2.2 Test Procedure in sluubd0 saying "6. Discharge the battery at system typical high rate...", though,

        can GPCRB test also accept lower current rate like C/5 in spite of discharge rate of 10C typically in my application?

    Or is there any possibility that setting:IT Gauging Ext(AMB_PRED=1)  will improve to some extent?

    (Present setting of AMB_PRED=0)

    Regards,

    Kunny

  • 0 in reply to Kunny
    TI__Expert 3030 points

    Hi Kunny,

    1.GPCRA0 optimizes the room temperature resistance value, you can skip that since you already did learning cycle.

    2.GPCRB supports lower current but optimized parameters work best under lower current, typical application current should be used to get the best accuracy in real application. IT Gauging Ext(AMB_PRED=1) may not make much difference since it's not directly related to RSOC calculation.

    Best reagrds,

    Abraham

  • 0 in reply to Abraham Rashid
    Prodigy 240 points

    Hi Abraham,

    Thank you for your clear and simple answer. I'll try GPCRB test to get better result.

    I have a additional question concerned about this issue.

    I set IT Gauging Configuration[CELL_TERM]=1 that means using cell-based termination, not stack-based.

    RSOC doesn't turn 0% compulsory after one of cells crossed Term Min Cell V threshold which are set to 3000mV(Term V Hold Time=180s).


    Where else do I have to check?

    Regards,

    Kunny

  • 0 in reply to Kunny
    TI__Expert 3030 points

    Hi Kunny,

    Could you provide .gg file you used as well as your log file?

    Best Regards,

    Abraham

  • 0 in reply to Abraham Rashid
    Prodigy 240 points

    Hi Abraham,

    Here are gg and log file.

    Hope this will help.

    6837.DF.gg.ziplog_20210205_dc-rx_at-10deg_with-gg.log.zip

    Regards,

    Kunny 

  • 0 in reply to Kunny
    TI__Expert 3030 points

    Hi Kunny,

    It seems cell voltage is not lower than 3000mV long enough,  it's 112 s in the log file but 180 s in your configuration. You can change Term V Hold Time to a value shorter than 112 s for cell-based termination to take effect.

    Best Regards,

    Abraham