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BQ40Z50-R1: Remaining pack capacity suddenly drops from 10% to 0%

Martin Unsal
Prodigy 130 points
Part Number: BQ40Z50-R1
Other Parts Discussed in Thread: BQ40Z50, GPCRA0

Observed the following in a 4 cell BQ40Z50-R1 4S implementation with ChemID 0x1574. During an approx 4C discharge, the gauge's reported remaining capacity suddenly dropped from about 10% to 0. At the same time the full charge capacity also dropped by about 10%. The battery is now reporting a full charge capacity of 2084 mAh (after a full charge and several days idle time). So the sudden reduction in capacity seems to be anomalous.

 Voltage Temp DegC Capacity (mAh)
Time Current Pack Cell 1 Cell 2 Cell 3 Cell 4 Cell Full Charge Remaining
789.5 -7.969 14.134 3.531 3.539 3.538 3.526 56.45 2067 209
790.5 -8.236 14.125 3.53 3.537 3.534 3.525 56.55 2067 207
791.5 -8.082 14.128 3.529 3.535 3.537 3.527 56.55 2067 205
792.5 -8.064 14.128 3.529 3.536 3.536 3.527 56.65 2067 203
793.5 -8.085 14.12 3.527 3.533 3.534 3.526 56.75 1868 0
794.5 -7.896 14.123 3.524 3.535 3.536 3.528 56.85 1868 0
795.5 -8.553 14.071 3.514 3.521 3.523 3.513 56.85 1868 0
796.5 -8.315 14.11 3.524 3.533 3.532 3.522 56.85 1868 0

Is this expected behavior for BQ40Z50?

Is there a way to avoid this happening?

Thank you,

Martin

  • 0
    TI__Mastermind 25955 points
    Hi Martin,

    Just to confirm: You are discharging the battery fully in 15 minutes?

    Is this your common load profile?

    If so, please use your load profile with the GPCRA0 tool to create and utilize updated gauging parameters. The tool is found here: http://www.ti.com/tool/GPCRA0

    The user guide for the GPCRA0 tool may be found here.

    The above assumes that the ChemID is proper and device operation is at room temperature. If the updated gauging parameters don't result in a marked improvement, the next step will be to investigate the ChemID.

    Please let me know if the updated gauging parameters fix the issue.

    Sincerely,
    Bryan Kahler
  • 0 in reply to Bryan Kahler
    Prodigy 130 points
    Yes, full discharge in 15 minutes, at ambient room temperature (of course cells self heat as seen in above data). This is the typical load profile. I will look into GPCRA0, thank you.
  • 0 in reply to Bryan Kahler
    Prodigy 130 points
    Hi Bryan,
    Can you confirm that ChemID returned by ManufacturerAccess() command 0x06 is in binary coded decimal? In other words when it returns 0x1574, that is ChemID 1574, not ChemID 5492? Just double checking.
    Thanks, Martin
  • 0 in reply to Martin Unsal
    TI__Mastermind 25955 points

    Hi Martin,

    The ChemID is hex throughout.  We don't convert the value to decimal.

    Sincerely,

    Bryan Kahler

  • 0 in reply to Bryan Kahler
    Prodigy 130 points

    We have an inventory of fully assembled packs which demonstrate this problem. I would like to update them with gauging parameters generated by GPCRA0 tool. The pack has an MCU which can perform the following procedure:

    1. Unseal gauge
    2. Send ManufacturerAccess 0x0021 Gauging() command to battery to disable gauging
    3. Verify that Mfg Status Init[GAUGE_EN] == 0
    4. Write data flash values for changed Gas Gauging and Ra Table parameters only
    5. Send ManufacturerAccess 0x0041 DeviceReset() command
    6. Send ManufacturerAccess 0x0021 Gauging() command to battery to enable gauging
    7. Verify that Mfg Status Init[GAUGE_EN] == 1
    8. Seal gauge

    Is this the correct procedure to update Ra table and gauging parameters on an already-manufactured, fully assembled pack? If not, can you recommend a correct procedure?

    Thanks

    Martin

  • 0 in reply to Martin Unsal
    TI__Mastermind 25955 points
    Hi Martin,

    These steps should work.

    Sincerely,
    Bryan Kahler
  • 0 in reply to Bryan Kahler
    Prodigy 130 points

    Hi Bryan, just wanted to give a quick update - both the GPCRA0 procedure and the update procedure seem to be working pretty well. Thanks for the help!