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BQ40Z50: Cell Balancing Permanent Failure

JeremyG
Intellectual 631 points
Part Number: BQ40Z50

Hi,

I'm after some guidance on using the Cell Balancing Permanent Failure function.  I've just had a CB PF and can't quite understand why.

The 2S1P pack I'm working on uses 5Ah LiFePO4 cells and I'm relying on the gauge's internal bypass FETs for balancing - which should provide around 10mA of bypass current.

I have used default values for Max Threshold (240h), Delta Threshold (40h) and Delay (2c).

I have seen some large Cell Balance Timer values during testing (near word limit of 65535s), but this is equivalent to only 18 hours, safely below the 40h Alert threshold.

To advance from Alert to Trip (SLUUBU5A, p.28) requires that the Delta Threshold is exceeded for two cycles, or Max Threshold.

Can you provide some clarity please on how this function works?  I noticed that the PF trip coincided with a QMAX update.

Thank you,

Jeremy.

  • 0
    TI__Genius 12215 points

    Hi, Jeremy

        The CB Time time Cellx, stored in lifetime dataflash is used to compare against the time the gauge has been used for balancing, not the Cellx Balance time in the SBS Registers.

        Please check the time in the log file with CB, see if this time has surpassed the threshold