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BQ40Z80: SOC estimation problem.

Kamil Leskiewicz
Prodigy 30 points

Part Number: BQ40Z80
Other Parts Discussed in Thread: BQSTUDIO, GPCCHEM

Hello Texas Instruments INC.,

I have a small problem with the SoC estimation in BQz80 on my 6S1P BMS design with BAK N18650CP cells. In charging mode the SoC (RSOC) estimation looks in my opinion very good. The value of this parameter is calculated from 0% to 100% within all time range. But in the discharge mode this parameter is discontinuous at level about 30%. The BQ40z80 reported that RSOC is 0% but discharging process is continued without any problems. Please see pictures below. I do not know what is the reason of this behavior. Can you check this? In attachment, you can find bqstudio logs from measurements. Generally my question is why the BQ40z80 was stop linear RSOC calculation at 30% in continuous discharge process with 2.5 A load?

I will be grateful for your support. 

Regars,

Kamil Leśkiewicz

//----------------------------------------------------------------------------------//

BQ40z80_6S1P_BAKN18650CP_CHG_DCHG_profile.xlsxBQ40z80_6S1P_CHG_raw_data.xlsxBQ40z80_6S1P_DCHG_raw_data.xlsx

  • 0
    TI__Guru** 106795 points

    Hello Kamil,

    Can you share your .gg file with your configuration information?

    Also were you able to complete a learning cycle and use the GPCCHEM tool to find the best matching chem ID? That is a requirement for impedance track gauging to accurate report RSOC.

    If you have configured everything and completed a learning cycle some reason for RSOC drop are the load select setting used, incorrect resistance table, bad chem ID match. The .gg file will help clarify the settings used.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 30 points

    Hello Wyatt,

    We did some charging/discharging cycles with our battery. And now I see that everything is OK. The RSOC is estimated in all time without any jumps. Please see the pictures below. After first charge/discharge we had jump from level about 25% to 0% RSOC. After second charge/discharge we had jump from level about 15% to 0% RSOC. And after third cycle we have linear estimation up to 0% and this is very good news. So I think that BQ40z80 needs some cycles of charging and discharging to estimate RSOC in correctly way. What do you think about this?

    I sent to you our .gg file in private massage. Did you see this file? I am waiting for your feedback.

    Regards,
    Kamil Leśkiewicz

  • 0 in reply to Kamil Leskiewicz
    TI__Guru** 106795 points

    Hello Kamil,

    I see in the log you have the LStatus at 14 so that means you have completed learning. The gauge will perform better the more cycles as it optimizes the Ra and Qmax data. Another big factor is making sure Valid Charge Termination (VCT) happens right at full charge. Your data looks good.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 30 points

    Hello Wyatt,


    In my application BQ40z80 has a sleep current set at 10 mA. So when discharge current drops below 10 mA then BQ40z80 goes to sleep after 4 minutes delay. And in next step BQ40z80 goes to shutdown state after 1 minute. And similar situation is at end of discharge. The battery will be discharged to 0%, FETs will be switched off and BQ40z80 will go to shutdown state after 5 minutes. So my question is about moment of correctly reading of Valid Charge Termination. The read of VCT is done immediately after end of discharge or this may occur later when BQ is in shutdown mode?
    I am asking about this because in my application BQ40z80 is most of the time in shutdown mode to have low current consumption. When user want to use battery then he has to press waku-up button.

    Regards,

    Kamil Leśkiewicz

  • 0 in reply to Kamil Leskiewicz
    TI__Guru** 106795 points

    Hello Kamil,

    Generally I would not recommend keeping the gauge in shutdown mode during normal usage, only when it's going to storage for long periods since waking up from shutdown the gauge has to recalculate since everything in RAM is lost.

    VCT is done during the charge period (Valid Charge Termination) you should be able to find more details in the TRM when exactly it occurs.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 30 points

    Hello Wyatt,

    Thanks for your support. I think that we can close this thread.

    Regarding to shutdown mode. I think that I will open a new question in the future.

    Regards,
    Kamil Leśkiewicz