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bq2050h capacity dropping

Douglas Deeds
Prodigy 60 points
Other Parts Discussed in Thread: BQ2050H

I am working with a system that has a bq2050H designed into a lithium battery pack. The system charges the battery pack using a MAX1758 Li battery charger IC. For most users, the system runs from a DC supply and rarely runs from the battery pack. We are seeing a rapid decrease in the reported RCAC value without the system going on battery or off DC. For example, one unit is reporting around 80% capacity after one month without having been run on battery and always plugged in. The charger is working as expected and battery voltage is around 8.4 V. I have noticed that the CI flag is set, but discharging the battery completely and recharging does not clear the flag. Let me know if you need any further information.

 

  • 0
    TI__Guru 73830 points
    The Self Discharge feature could downgrade the Remaining Capacity. Is your pack operating at a high temperature?
  • 0 in reply to ThomasCosby
    Prodigy 60 points

    Thanks for your response.

    The pack is split and is opposite sides of a metal block that is kept at 37 deg C.   The other parts of the battery would be at ambient temperature so the pack temperature would be somewhere in between.  Usually it's reporting 20-30 C since the unit is rarely used on battery so it's always on the charger.

    This is an old design and I had to find the schematics to find the setting for PROG5.  It is connected to ground through a 100K resistor so this would put the compensation at somewhere between NAC/512 and NAC/256.   To get 20% capacity loss in a month it would have to be nearer to 40 C.

    For this application where we are mostly likely always charging, is the self discharge compensation still active?

    Should we disable the compensation?

  • 0 in reply to Douglas Deeds
    Prodigy 60 points

    Since my last post, I've confirmed that the bq2050h is physically on the end of the battery that is not adjacent to the metal block at 37 deg C.

    And only half of the battery pack is next to the metal block at 37 C so it's unlikely to change the sensed temperature.

  • 0 in reply to Douglas Deeds
    TI__Guru 73830 points
    I would try disabling the self discharge to see if that helps. I think that is the only feature that would cause the capacity to decrease while idle.