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Design Capacity in the parameter setup of the BQ20z80V110

Frank Burmeister
Prodigy 40 points
Other Parts Discussed in Thread: BQ20Z80

Hello,

i have a question concerning the BQ20z80.

We use LiION cells with 1950mAH and an reserve capacity of 187mA.

Can I change the design capacity to 11763mAh to get a higher state of health.?

What will be happen?

Are there any consequences?

Best regads

Frank

 

Ich hätte nochmals eine Frage bezüglich dem BQ20Z80:

Momentan haben wir bei unseren Batteriemodulen eine Reverve-Capacity von 187 mAh im Parametersatz eingetragen.

Als Design-capacity tragen wir momentan einen Wert  von 1950mAh ein.

Nun haben wir festgestellt, dass sich bei dieser Konfiguration auch der State of Health verändert, weil ja der BQ20z80 die Reserve-Capacity von der Fullcharge-capacity abzieht.

Das ist in unserem Fall aber schlecht, weil wir ein Gut /Schlecht-Kriterien bei unseren Packs einsetzten und bei diesem niedrigen State of Health-Wert Batterien aussondern müßten.

 Könnte man nicht „einfach“ die Design-capacity von 1950 mAh auf 1763mAh ändern?

Was hätte das für Konsequenzen?

Vielen Dank für die Mühe.

 


  • 0
    TI__Genius 14015 points

    Frank,

    You can just set Reserve Cap-mAh to be 187mAh. This will cause the gauge to report 0 capacity when there is still 187mAh of reserve left. More information about this can be found on page 169 of the Technical Reference (sluu276).

    Regards,

    Jason

  • 0 in reply to Jason Blackman
    Prodigy 40 points

    Jason,

    the Reserve-Capacity is already set to 187mA. My question is: What happens, if  I change the design capacity?

  • 0 in reply to Frank Burmeister
    TI__Genius 14015 points

    Frank,

    Changing the design capacity will affect the State of Health of the battery, which is equal to Full Charge Capacity / Design Capacity. It will also affect the Absolute State of Charge (ASOC), which is equal to Remaining Capacity / Design Capacity. The ASOC will report 100% earlier than expected, since the Design Capacity will be lower than Full Charge Capacity (which is what Relative State of Charge is calculated with). 

    Just to be clear, I was saying that you don't have to change Design Capacity in order to have that reserve capacity of 187mAh.

    Regards,

    Jason

  • 0 in reply to Jason Blackman
    Prodigy 40 points

    Is the Qmax-update not affected?

  • 0 in reply to Frank Burmeister
    TI__Genius 14015 points

    No, Qmax will still be directly related to the actual capacity of the battery, regardless of the application. The initial Qmax and the Design Capacity are typically the same, taken from the battery datasheet, but in your case they will be different.

    Regards,

    Jason

  • 0 in reply to Jason Blackman
    Prodigy 40 points

    I found this in the BQ20z80 userguide:

     

    PassedCharge has to be more than 37% of DF:Design Capacity for an update to occur. For the first cycle

    (with DF:Update Status = 4), 90% of DF:Design Capacity is required because this cycle takes place in the

    factory settings and Qmax is learned for the first time.

    In order to prevent Qmax fluctuations, a first-order smoothing filter is applied to all Qmax readings except

    in the first cycle. Readings with lower PassedCharge are assigned lower weights in the smoothing.

     

     

    ??????

  • 0 in reply to Frank Burmeister
    TI__Genius 14015 points

    Frank, I apologize -- you are correct. With the changed Design Capacity, a Qmax update could happen if you charged/discharged at least 632.3mAh (37% of 1763) instead of 721.5mAh (37% of 1950). I believe the Qmax update formula will still be accurate, it could just happen more often. 

    Again, I apologize for the oversight.

    Regards,

    Jason