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bq40z50 RSOC determination at low temperature

Dietmar Fischer
Intellectual 275 points
Other Parts Discussed in Thread: BQ20Z65, BQ40Z50

Hi

Currently we have the problem with the bq20z65 BMS-Solution that the cell-pack voltage drops at the begin of discharge at low temperature(about -10°C) below the Term-Voltage threshold.

This leads to a drop from e.g. 100% state of charge to 0%. We know that this Term-Voltage threshold is, let say, the zero-point for the gas gauge determination.

So as soon as the pack-voltage falls below this threshold the state of charge will reset to 0%. But during discharging the voltage rises over this threshold again caused of cell self heating during discharge.

My question is now, is this behaviour also be expected  with the newer IC bq40z50?

Thanks and best regards

Dietmar

  • 0
    TI__Guru 73830 points
    Dietmar,
    The bq40z50 does have some low temperature accuracy improvements to the Impedance Track algorithm. In addition, the device offers more parameters and tools to help analyze gauging issues and help you to compensate for them.
    Tom
  • 0 in reply to ThomasCosby
    Intellectual 275 points

    Hi Tom

    Thanks for your prompt reply.
    Especially regarding the Term-Voltage, bq40z50 will have same behaviour as the bq20z65, right?
    That means, as soon as the cell pack voltage falls below this voltage, the gas gauge will report RSOC = 0%.
    Is that the case, then we can't solve our problem with the bq40z50.
    Or will the bq40z50 reports RSOC >0% as soon as the voltage rises again above the Term-Voltage Threshold during discharge by self heating.

    Thanks

    Dietmar

  • 0 in reply to Dietmar Fischer
    TI__Guru 73830 points
    Dietmar,
    The RM and SOC will be forced to 0 when the voltage drops below the Term Voltage with either device. Both devices will run simulations during rest and RM can increase.
    Tom