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BQ78350-R1: EDV Gauging : "Better Calculation" Compensation of temperature

Adam Botka
Intellectual 455 points
Part Number: BQ78350-R1
Other Parts Discussed in Thread: BQ78350, BQ76930, BQSTUDIO,

Hello again,

Thank you for the lot of help in the past. We have a battery pack 10s6p BQ78350 BQ76930. I would like to have a question regarding to the calibration and EDV/CEDV settings.

We use EDV mode (EDV_CMP=0) temperature and load will not be compensated. If the pack temperature will be ~40-45°C the AFE detects more then ~40mA discharge current without load. Battery voltage is higher with ~20mV.It is normal in EDV mode?

It will be compensated in CEDV mode ? Can we compensate it in EDV mode? It is optimizable by the rate of temperature coefficients of the key components? 

Best regards,

Adam

  • 0
    TI__Prodigy 590 points

    Hello Adam,

    My understanding for your questions is when the temperature is running at 40~45C, the current report by the BQ76930 is 40mA when no load and the report the voltage is 20mV higher ? Could you show us the register that report this value ? what's the value of the sense resistor resistance you used ? 

    For the CEDV algorithm, it make compensation for the battery pack capacity when in high/low temperature and cell aging, but didn't for the measurement result. 

  • 0 in reply to Jessica LI
    Intellectual 455 points

    Hi Jessica,

    Your understanding is right. It was reported by the bqStudio with current measurement unit (RPM box on the left side).

    We use two 2mOhm resistors (LRMAT2512-R002FT4) parallel.

    Best regards,

    Adam

  • 0 in reply to Adam Botka
    TI__Guru 54715 points

    Hi Adam,

    The experts on the BQ78350-R1 are out of the office this week.  The BQ76930 will have temperature characteristics. 

    CC gain has a specified temperature coefficient, offset is small but is a best fit specification.  With 1 mOhm 40 mA would be 40 uV or about 4.7 counts.

    Cell voltage measurement can vary across temperature, it does not have a specific temperature coefficient. Cell voltages will increase with temperature, I do not know their temperature coefficient, but commonly to see the voltage rise as the cells heat.

    The CEDV algorithm does not adjust the reported voltage or current.  It will adjust the point where the battery is considered to be at certain states of charge.

    If this does not answer the question please clarify and the experts can look at it on their return.  A gg file and logs are typically helpful in understanding behaviors.