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Original question:

BQ27426: Reserve Capacity

BQ27426: Reserve Capacity

user4369354
Expert 1220 points
Part Number: BQ27426

Dear Onyx san,

I tested the following items to confirm Reserve Capacity.
【Setting】
・ Terminate Voltage = 3300mV
【Condition】
(1) Enable Reserve Cap: Load Select / Mode = 81, Reserve Cap: 100 mAh
(2) Disable Reserve Cap: Load Select / Mode = 00, Reserve Cap: 0 mAh190610_Reserve_Cap.xlsx

In the above (1), SOC was not 0% at a voltage higher than the termination voltage which you said “The gauge ought to report 0% at a higher voltage and not at your terminate voltage”before. However, True SOC was 0% at a voltage higher than the termination voltage 3300mV. Whcih should we use SOC or True SOC for fuel gauging? (I thought we would use SOC normally).

Previous your comment
https://e2e.ti.com/support/power-management/f/196/t/774603?tisearch=e2e-sitesearch&keymatch=%20user:395463

Best regards,

Chiaki Endo

  • 0
    Expert 1220 points

    Dear Onyx san,

    There was an error in Condition and the attached file.
    (1) Enable Reserve Cap: Load Select / Mode = 00, Reserve Cap: 100 mAh
    (2) Disable Reserve Cap: Load Select / Mode = 81, Reserve Cap: 0 mAh

    190610_Reserve_Cap2.xlsx

    Best regards,
    Chiaki Endo

  • 0 in reply to user4369354
    TI__Guru* 76230 points

    hi Chiaki

    You will have to  use the true soc in this case.

    thanks

    Onyx

  • 0 in reply to Onyx Ahiakwo
    Expert 1220 points

    Dear Onyx san,

    Thank you for your reply.
    What is the difference between SOC and True SOC?
    Is there a problem using True SOC for fuel gauge instead of SOC?
    In particular, the "may jump" described in TRM P27 5.18 is concerned.

    Best regards,
    Chiaki Endo

  • 0 in reply to user4369354
    TI__Guru* 76230 points

    Chiaki

    The true SOC is the actual SOC of the battery. The filtered is mathematically adjusted to ensure the user has a good experience in the event  that there is a temperature change that causes SOC to jump.

    Depending on your needs the true or filtered can be used. you can see from your log files that the filtered soc stayed at 1% till terminate voltage was reached. to prevent this from occurring, clear the sochold1 flag. This will allow the filtered SOC to terminate at a higher voltage like the true soc.

    thanks

    Onyx

  • 0 in reply to Onyx Ahiakwo
    Expert 1220 points

    Dear Onyx san,

    Thank you for your reply.

    When sochold is set to 0, SOC is 0% at a voltage (3485mV) higher than the Terminate Voltage (3300mV) (see attached sheet "(3) Enable_SOCHold0").

    190612_Reserve_Cap.xlsx
    At this point (SOC = 0%, V = 3485mV), which parameter indicates that 100mAh of Reserve Capacity remains?
    Any parameter difference between voltages 3485mV and 3297mV are not equal 100 mAh (see line 170).

    Best regards,
    Chiaki Endo

  • 0 in reply to user4369354
    Expert 1220 points

    Dear Onyx san,

    Sorry, colud you answer this question as soon as possible?

    Best regards,
    Chiaki Endo

  • 0 in reply to user4369354
    TI__Guru* 76230 points

    HI Chiaki

    From the gauge's estimates, there is 100mAh capacity between when terminate is reached and the terminate voltage. The gauge ended charge at a higher voltage than terminate. I am not sure i understand what the compaint is. Can you clarify.

    thanks

    Onyx

  • 0 in reply to Onyx Ahiakwo
    Expert 1220 points

    Dear Onyx san,

    My understanding is that the capacity between the voltage of the following (1) and (2) are 100mAh as Resereve Capacity.
    Is this correct?
    The problem is that the True RemCap between (1) and (2) is not 100 mAh.

    【Configuration】
        Termination voltage: 3300mV
        Reserve Capacity: 100 mAh
    【Discharge data of Sheet "(3) Enable_SOCHold0" in Excel】
        (1) Voltage that SOC changes from 1% to 0% : 3485mV
        (2) Termination voltage : 3297mV
    【True RemCap】
        (a) 0 mAh: at 3485 mV
        (b) -68 mAh: at 3297 mV
        (c) Difference of True RemCap between (a) and (b): 0-(-68) = 68 mAh

    The problem is that the value of (c) is 68mAh not 100mAh.
    In this case, (a) should be higher than 3485mV.

    The capacity of this battery is 800mAh (min), so the Design Capacity is set to 800mA, but the capacity of the battery used for measurement is about 850mAh.

    Is this affecting above problem?

    Best regards,
    Chiaki Endo

  • 0 in reply to user4369354
    TI__Guru* 76230 points

    Hi Chiaki,

    The 100mAh reserve capacity will be accurately reflected post-factum, if the gauge has learned the chemical capacity and the cell impedance *and* if the load prediction is close to the actual load.

    Your log file shows that Qmax is 800mAh. This number looks suspicious (equals design capacity) that the gauge hasn’t learned Qmax yet (and likely neither has it learned cell impedance), hence capacity simulations will be more or less off from reality.

     

    The coulomb count between 3485mV and 3300mV is 67mAh. So while this is significantly less than 100mAh, it’s not unusual when the gauge hasn’t learned the properties of the actual cell yet.

    The conversation will be taken offline and handled during the concall.

    thanks

    Onyx