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BQ40Z50 - Full charge capacity drops immediately to 0 on discharge

Karl Schwabe
Prodigy 90 points

Other Parts Discussed in Thread: BQ40Z50, BQSTUDIO

My BQ40Z50 instantly drops its estimate for the Full Charge Capacity to 0 on discharge.Here is a graph from bqStudio that I plotted showing the error.

I am using the battery as a "backup battery" where power is provided from the battery (at 14A), if the main power supply drops out. Under testing the Full charge capacity suddenly drops to 0, hence the Remaining SOC also drops to 0. I was hoping to use the Remaining SOC to indicate that I need my application to shut down.

I have performed a learning cycle on the battery. The CF1 bit in LStatus is set and the Update Status is 06. The max error it is reporting is 1%.

Does anyone have any ideas as to why the Full Charge Capacity drops instantly to 0? I suspect it has something to do with some of my Data Memory setting being incorrectly set up for the Gas Gauging, but I don't know where to start looking.

  • 0
    Prodigy 90 points
    I have found what partially caused the problem. My term voltage set in Gas Gauging was set too high, and as soon as the load switched over to drawing from the battery, the voltage dropped a bit below the term voltage value, and I think the Gas Gauging algorithm then didn't know what to do, so it set the Full charge capacity to 0.

    I still have the problem that the Remaining SOC drops off suddenly when it hit +/-25%.
  • 0 in reply to Karl Schwabe
    Prodigy 90 points

    I have performed a few more tests with the LiPo. This is one of the discharge curves that I have been getting. The RSOC (Relative State of Charge) suddenly drops off to 0%. This leads me to think that I can't trust the RSOC values that I am getting, and I don't know which config parameters could be the cause of this incorrect RSOC estimate. Anyone have any ideas?