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Original question:

BQ34Z100-G1: Why is QmaxPassedQ cleared at full charge?

BQ34Z100-G1: Why gauge indicate incorrect SoC after learning?

toshiyuki.umetsu
Prodigy 90 points
Part Number: BQ34Z100-G1
Other Parts Discussed in Thread: GPCCHEM

Hi them.

We used the BQ34Z100-G1 and completed the learning cycle. The gauge showed UpdateStatus=06, indicating that learning was complete.

Then, we charged and discharged and evaluated the remaining power returned by the gauge. The gauge is returning a likely correct SoC when charging. However, the SoC decreases sharply during discharge, and I believe this to be incorrect.

Is it because the CHEM ID is wrong? Also, are there any other possible causes?

Charge SoC

7041.Charge.csv

Discharge SoC

8272.Discharge.csv

Additional information

  • BQ34Z100-G1 (FW Ver.0.16)
  • CHEM ID = 0435h
  • 8S1P LiFePO4 Battery 40Ah (So using host scaling 2. Gauge's current and capacity is indicate 1/2 of actual value.)
  • FullChargeCapacity shows correct capacity. 
  • Discharge is performed at a constant current of 8000mA. Using scaling, the gauge is correctly showing 4000mA.
  • 0
    Prodigy 90 points

    Hi them.

    I noticed below. Gauge's UpdateStatus became to 06 but Max Error was 3%. According to datasheet, it indicate only learn Qmax.

    So I think that Ra table not updated.

    I will try to find out the cause of the failure.

  • 0 in reply to toshiyuki.umetsu
    Prodigy 90 points

    Hi them.

    I noticed below things.

    • Update Status = 06 (Learning cycle was finished)
    • Learned Status = 05 (Qmax updated. However, Ra Table not updated.)
    • Control Flag bit2 (RUP_DIS) was set during discharging.
      This indicate CHEM ID is wrong. (By TRM.)

    So I think the CHEM ID is wrong.

    Using CHEM ID 0435's deviation is 16.86% for using battery. is this deviation is large?

  • 0 in reply to toshiyuki.umetsu
    TI__Mastermind 37761 points

    Hi Toshiyuki,

    Yes, a deviation of 16.86% is too large. We want the deviation to be less than 3%.
    I would highly recommend you to use the GPCCHEM tool to find a more suitable ChemID.
    This tool uses a simple test of your battery to match it with batteries that have already been characterized.
    When you use this tool, a report will be sent to you that gives you the ChemID that closely matches
    your battery. Please reference this website: https://www.ti.com/tool/GPCCHEM

    Sincerely,

    Nick Richards

  • 0 in reply to Adrian
    Prodigy 90 points

    Hi Nick.

    Thanks for your answer.
    We detemined CHEM ID by using GPCCHEM already.
    However best deviation is its known value.

    Therefore, we think we need to reassess whether the gauge can be used with this battery.

    Please let me know if there is any way I can use this gauge with this battery.

  • 0 in reply to toshiyuki.umetsu
    TI__Mastermind 37761 points

    Hello Toshiyuki,

    You are able to use that gauge with the proper scaling.
    Do you still have the file that you submited to the GPCCHEM tool? If so, can
    you please send it, I want to verify that the process was completed successfully
    and that there is no other ChemID that can more closely match your battery.

    Sincerely,
    Nick Richards

  • 0 in reply to Adrian
    Prodigy 90 points

    Hi Nick.

    Here is our measurement data which was pass to GPCCHEM.

    40Ah_A.zip

    Then reported file is this.

    40Ah_A-report.zip

    Thank you.

  • 0 in reply to toshiyuki.umetsu
    TI__Mastermind 37761 points

    Hello Toshiyuki,

    I reviewed the files you sent me and I want to bring up two concerns. First, I see that there is
    a random period after the initial charge that another charge started, which should not happen. Second,
    I noticed that during the relaxation period that there is a small discharge current of about 42
    milliamps. It is recommended that during the relaxation period that the current through the battery
    is as close to 0 amps as possible.

    Also, it was brought to my attention that it is recommended that an LFP battery should have a relaxation period
    of at least 24 hours after charging for a more accurate characterization of the battery.

    So please run another test and make sure you are charging to the charging voltage and discharging to the terminal
    voltage as specified by the datasheet. I will outline the updated steps:

    1. Charge battery to full using a CC/CV charging method
    2. Relax for at least 24 hours
    3. Discharge at C/10 (4000 milliamps)
    4. Relax for at least 5 hours

    Hopefully, this time the gpcchem tool should return a more accurate ChemID.

    Sincerely,
    Nick Richards

  • 0 in reply to Adrian
    Prodigy 90 points

    Hi Nick

    Thanks to notice problems. We are going  to try to measurement again with specified methods.

  • 0 in reply to toshiyuki.umetsu
    TI__Mastermind 37761 points

    Hi Toshiyuki,

    Perfect, let me know if you run into anymore problems.

    Sincerely,
    Nick Richards