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BQ20Z45-R1_BQEASY-SW: Fuel Gauge SOC Increase after Exiting Shutdown

jasonp
Prodigy 150 points
Part Number: BQ20Z45-R1
Other Parts Discussed in Thread: BQEVSW

Tool/software: bqevsw

I have created a golden file for a battery with 4s5p configuration using chem id 5895.

When I send the shutdown command (0x0010), the pack enters shutdown. When the battery exits shutdown, the SOC increases random amounts.

Example: SOC=22%

Before shutdown

SOC=22%

Full Charge Capacity = 15525

Remaining Capacity = 3344

Enter shutdown via command - OK

After exit shutdown:

SOC=34%

Full Charge Capacity = 16705

Remaining Capacity = 5530

I expect the capacity to remain the same, since a few minutes pass when exiting shutdown mode.

Why does this occur? 

  • 0
    TI__Mastermind 29865 points

    Hello, 

    This question has been assigned and will be reviewed when possible. In the meantime if you can attach the .gg and/or .log associated with the project.

    Thank you,
    Alan

  • 0
    TI__Guru 64266 points

    That's because the gauge must determine the depth of discharge of each cell, which is a function of OCV (Open Circuit Voltage). However, if the battery is being actively charged or discharged then it is not possible for the gauge to accurately determine depth of discharge as the measured voltage is not a true OCV. Some chemistries have a very flat OCV vs. depth of discharge curve hence depth of discharge can be quite off if you restart the gauging algorithm by turning on the gauge while the cells aren't truly relaxed.

    This will self-correct when the gauge detects a full charge or a full discharge or if you let the cells relax for a true OCV measurement.

  • 0 in reply to Alan Frias
    Prodigy 150 points

    batt_golden.zip|
    gg file attached

  • 0 in reply to jasonp
    TI__Guru 64266 points

    Please make sure that you only use shutdown mode if you either can accept an error in SOC on device wake-up or if you can control the current during gauge wake up so that the cells in the battery are relaxed and the gauge measures a true Open Circuit Voltage.