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BQ34Z100-G1: Number of cells in series for a 2S4P battery

Martin Lastrup Hviid
Prodigy 20 points
Part Number: BQ34Z100-G1

Tool/software:

I am debugging a design where we have a 2S4P LION polymer battery pack.

Nominal V: 7,4
Nominal capacity 24Ah@2A load

I can see that the engineer (who is no longer in the company) configured the battery as 1 cell: Configuration,"Registers","Number of series cell","1","num"
Is that because the "number of series cell" refers to battery packs in series or is it a mistake?

The issue we see is incorrect display of LEDs. Our system has four LEDs, but at:
100% capacity 4 LEDs = ON
96% capacity 3 LEDs = ON (only few minutes)
96% capacity 2 LEDs = ON (only few minutes)
96% capacity 1 LEDs = ON (until discharged)

This relates to this previous thread:
https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/539017/bq34z100evm-no-display-of-state-of-charge

I hope you can guide.

Best regards,
Martin

  • 0
    TI__Mastermind 25855 points

    Hello Martin,

    This question has been assigned and will be reviewed when possible.

    Thank you,
    Alan

  • 0 in reply to Alan Frias
    TI__Mastermind 25915 points

    Hi Martin,

    The number of cells in series refers to the total number of cells in series from the top of the battery back to the negative terminal of the battery pack. Having the number of cells in series set to 1 is most likely a mistake. 

    Regards,

    Diego

  • 0 in reply to Diego
    Prodigy 20 points

    When all parameters are set correctly (to the best of our knowledge) for our LiPo battery pack with one 1 cell we get this overview:series, the


    If I change to 2 cells in series the 8093 mV doubles to 16V.
    Based on this, the correct setting seems to be 1 cell in series, but it conflicts with having a 2S4P battery pack?

    Please advise.

    Thanks,
    Martin

  • 0 in reply to Martin Lastrup Hviid
    TI__Mastermind 25915 points

    Hi Martin, 

    Ah understood, I have encountered this problem before, I believe it is related to calibration. 

    Please read through this thread: (+) BQ34Z100-R2: Voltage and temperature calibration issues - Power management forum - Power management - TI E2E support forums

    It is important that both the number of cells in series is accurate, and the voltage reading is accurate for the impedance track gauging algorithm so accurately estimate SOC.

    Regards,

    Diego

  • 0 in reply to Diego
    Prodigy 20 points

    Hi Diego,

    Thanks for sharing the link to the other thread. According to that thread, the voltage divider doesn't take the number of cells in series into account during voltage calibration. This explains why it shows a 2x value after configuration with the setting at 2 cells and the correct value when the number of cells in series is 1 (which is incorrect for a 2S4P battery pack).

    Voltage divider value with 1 cell in series after calibration:

    Configuration,"Registers","Number of series cell","1","num"
    Calibration,"Data","Voltage Divider","9539","mVolt"

    Voltage divider value with 2 cells in series after calibration:

    Configuration,"Registers","Number of series cell","2","num"
    Calibration,"Data","Voltage Divider","9540","mVolt"


    What is your recommendation to best trick this?

    A
    1 Perform calibration using the 1 cell in series setting
    2 After calibration, manually reduce the voltage divider to: value/2
    3 Change cells in series to 2

    B
    Perform the calibration using the 2 cells in series setting
    During calibration I only enter 50% of the voltage reading to achieve a voltage divider value for one cell

    Best regards,
    Martin

  • 0 in reply to Martin Lastrup Hviid
    TI__Mastermind 25915 points

    Hi Martin, 

    I recommend method A, this is how I typically calibrate my EVM.

    Method B may achieve the same results. However, I have never tested this method before.

    Regards,

    Diego

  • 0 in reply to Diego
    Prodigy 20 points

    Hi Diego,

    Thanks for the quick response.
    I will test method A. Once I have confirmed this works with proper LED status indicators, is the correct path then to follow the guide: SLUA903–July 2018, Achieving The Successful Learning Cycle to perform a golden image?
    If so, can I then upload the golden image to flash in my production without having to perform learning cycles on new battery assemblies? (I will be running a verification for each though).

    Thanks,
    Martin

  • 0 in reply to Martin Lastrup Hviid
    TI__Mastermind 25915 points

    Hi Martin,

    Here are the high-level steps to creating a golden image.

    1 calibrate the device

    2 identify the correct chemid

    3 configure basic parameters listed in learning cycle document and complete learning cycle

    4 set additional parameters for use case

    5 test to verify performance

    Regards,

    Diego

  • 0 in reply to Diego
    Prodigy 20 points

    Thanks Diego,

    @4: What additional parameters can be set for use cases?

    (Don't worry - if you can answer this, you have resolved my issue;-)

    Best regards,

    Martin

  • +1 in reply to Martin Lastrup Hviid
    TI__Mastermind 25915 points

    Hi Martin,

    It's difficult to list everything but here are some things that come to mind.

    Load mode 

    Load select

    for LFP cells : LPFrelax DODwt

    For NiMH: NiMDT/NiDV

    Smoothing: if needed

    Current taper window

    Charging voltage

    Charging taper voltage

    I recommend reading through Pack configuration A-C to see if any bits would benefit your application. 

    Regards,

    Diego