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BQ20Z655: Issues with Battery Learning

Carolus Andrews
Mastermind 22630 points

Part Number: BQ20Z655

Team,

I have a customer who is running into issues with learning on BQ20z655. They are using a 3S, 1P battery. They areonly charging it to 12.3V instead of 12.6V. After waiting over 5hrs on the charge, they would expect a QMAX update as the data sheet states if they don’t meet the dV/dt before then, and they aren't seeing this. To their knowledge, all the requirements are being met to get an update, but nothing is happening. Could you provide any feedback here as to what might be going on?

I’ve attached Dataflash and SBS log files. 

Dataflash.zip

goldenfiletest3.log

  • 0
    TI__Mastermind 42535 points
    Hi Carolus,

    You need a minimum passed charge for 1st qmax to be above 91%. I'm not sure that at 12.3V, you cross that threshold. Therefore you won't have a qmax update. Please charge it higher. Further updates will not need this threshold.
  • 0 in reply to Batt
    TI__Mastermind 22630 points

    Batt,

    Thanks for the reply. Just to clarify though, is the 91% capacity based off of the programmed Design Capacity? If it is, then it should have worked because they programmed the Design Capacity to 2300 mAhr. If not, can you comment a bit more on how the 91% is configured in the device?

  • 0 in reply to Carolus Andrews
    TI__Mastermind 42535 points

    Hi Carolus,

    No, while it superficially may appear that it's the design capacity, it's actually the DoD or the depth of discharge. What's more is that this is reliant on the chem ID of the cell that you're using. While you may be able to modify the RSOC by changing design capacity, the DoD from the chem ID finally determines the actual RSOC. My suggestion is for you to try to charge it to full at least for the first time. That way you can absolutely be certain of the actual Qmax of the battery. From that point onwards deducing 91% should be easy in case you were to reflash the gauge and attempt a similar cycle on a similar pack.

  • 0 in reply to Batt
    TI__Mastermind 22630 points

    Batt,

    even going to full DoD and charging to 12.6V, they failed to get an update. Upon further thought 2300Ahr is greater than 91% of 2500Ahr and should have also worked. Something else is going on here.

    Can you further explain this:

    Offset Error — If offset error accumulated during time passed from previous OCV reading exceeds 1% of

    Design Capacity, update is disqualified. Offset error current is calculated as CC Deadband / sense

    resistor value.

    It could be they are getting some error that we are not seeing.

  • 0 in reply to Carolus Andrews
    TI__Mastermind 42535 points

    Carolus,

    Please upload the logs here.

  • 0 in reply to Batt
    TI__Mastermind 42535 points
    I will also need their srec or senc file.
  • 0 in reply to Batt
    TI__Mastermind 22630 points

    Batt,

    I uploaded DF logs and the golden file in the original message. Could you share a little more detail on the other files you need?

  • 0 in reply to Carolus Andrews
    TI__Mastermind 42535 points
    Hi Carolus,

    I looked into your log. You are simply not reaching charge termination. Without primary charge termination, your passed chg will not quality for a qmax update especially if you are learning for the first time. Also, please send me the srec, I need to check some chem ID related information as well.

    In the meanwhile, I would suggest that they charge it up to 12.6V and then run the test. That way you are sure to qualify for a qmax update on chg termination.