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bq78pl114 balancing stopping prematurely

Steve14663
Prodigy 170 points
Other Parts Discussed in Thread: BQ78PL114, BQWIZARD

If anyone has had experience with this chip and could explain a couple of problems we have been having it would be much appreciated.

1. The chip stops pumping charge whenever the cell voltage differential is greater than about 200mV, which is naturally when it is most required.

2. The AtoD converter for banks 1 and 3 seem to affect the AtoD for banks 2 and 4 respectively. We noticed during calibration that if the cell 1 voltage dropped below about 2400mV the value read from cell 2 was always 2000mV, regardless of its actual voltage. This problem is also seen in cell 4 when the voltage of cell 3 drops below 2400mV.

  • 0
    TI__Intellectual 1940 points

    1.  Check document SLUU330A page 25 Section 3.6 Cell Imbalance.  There is a safety rule that disables balancing based on the conditions of the cells.  Within this rule are settable parameters which control how it operates.

    2.  Power to the bq78PL114 comes from the cell voltages at V1, V2, V3, V4.  Seeing 2000mV is an indication that the device is not communicating to the bqWizard.  This is likely due to a low cell voltage.  There is a parameter called EUV Threshold.  The default value is 2500mV.  Below this point the device shuts down.  The bqWizard will still poll however.  This is why you may see 2000mV and likely a communication error message in the Status Bar.

  • 0 in reply to Jim M15252
    Prodigy 170 points

    Thanks Jim, i had looked at the cell imbalance rule, but this parameter will open all the FET's as a result, stopping either charge or discharge and fusing the pack. This is not the case as charging and discharging still continue, just with no balancing.

  • 0 in reply to Steve14663
    TI__Intellectual 1940 points

    1.  Which cell balancing algorithm are you using?

    2.  The bqWizard allows data logging.  If you would like, send us data that shows what you are experiencing and a .ppcsv file that captures your register settings.  Cycle data is usually best to see a pattern of performance.  Configure your logging to include at least Net Pumps, Pack Voltage,  Current, Cell voltages, cell OCV, cell SOC.

  • 0 in reply to Jim M15252
    Prodigy 170 points

    Thanks Jim i tried changing this cell imbalance fail parameter, and despite its description this seems to have fixed the problem.

  • 0 in reply to Jim M15252
    Prodigy 200 points

    Actually i've seen the problem internal to the 114 chip.  Cell 1 and 2.  But I heard that internally is is the same as a series of 102 chips.

    But there is still a big problem.  If I have an undervoltage problem of a cell and a "102" unit shuts down, not communicating, isn't this the same as a "cross talk" mux problem with a multiplexed A/D problem we had in the past were an out of range channel in a mux causes faulty readings in neighbor channels .

    Isn't this a big problem if is "Over-ranged" reading and causeing fuses to blow, FET's to shut down and can only right itself with a software reset?