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Original question:

BQ78350-R1: Fixed_EDV SOC Calculation Method in bq78350

BQ78350-R1: EDV_CMP and Self Discharge of BMS

Kevin Knicker
Expert 1091 points
Part Number: BQ78350-R1
Other Parts Discussed in Thread: BQ78350

Tool/software:

Dear TI Team,

I am wondering if setting EDV_CMP to 1 takes into account self-discharge and electrical load settings to adjust the State of Charge.
Specifically, if a pack is going be sitting idle for some time, I would expect the voltage to decrease due to self discharge from the cells and the BMS electronics.

Will the state of charge adjust (decrease) accordingly to account for this?  For example, if a pack is at 50V and 90%, and self discharges to 48V, will the fuel gauge still read 90% or will is decrease accordingly?

I also see there is a Self Discharge Rate parameter.  Is this used to account for loads that aren't going to be seen by the sense resistor? Mainly, the load of the BMS electronics on the cells?

Thanks,


Kevin K

  • 0
    TI__Mastermind 37761 points

    Hello Kevin,

    Please allow me some time to look into your questions.

    Regards,

    Adrian

  • 0 in reply to Adrian
    TI__Mastermind 37761 points

    Hello Kevin,

    Unfortunately, BQ78350 is one of our CEDV algorithm gauges and this algorithm is not able to adjust SOC based on a drop in open circuit voltage unless the voltage reaches one of the EDV thresholds. So, if the voltage drops from 50V to 48V then the gauge will still read 90% SOC. Now, for this you should utilize the self-discharge parameter register, as this will updated remaining capacity and should update SOC. Yes, this will take into account the load not seen by the sense resistor.

    Regards,

    Adrian

  • 0 in reply to Adrian
    Expert 1091 points

    Thank you, Adrian.

    That helps.  I will adjust the self discharge register accordingly.

    Best Regards,
    Kevin