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BQ40Z50-R1: SOH/FCC error

Chen Jia
Intellectual 850 points
Part Number: BQ40Z50-R1

To whom it may concern:

We have a battery for power tools, which can discharge at high current, 15A to 25A. After several cycles, some of the batteries can't be used because the SOH was report below 60%.

After checking the fuel gauge, the FCC was only half of the design capacity, so the SOH was low.

A full charge/discharge cycle was applied with power supply and electronics load, and after this the battery recovered the FCC to over 95% of the design capacity, and SOH recovered as well.

2 batteries out of 150 had this problem so far. Could you help to do some diagnostic and find the solution?

Thanks a lot!

Chen

  • 0
    TI__Guru** 105760 points

    Hello Chen,

    Did all 150 tools have the same discharge cycle performed with high current? FCC will decrease with higher current due to IR losses, if the other 148 batteries did not experience the same load profiles they won't have an FCC drop.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Intellectual 850 points

    Hello Wyatt:

    Thanks for your reply. At least 50 out of 150 had the similar procedures, and others didn't have this issue. Even with the high current discharge, the FCC changed so much which was not ideal, from about 1900mAh to 1000mAh. Do you think this is normal? Or maybe we can add any compensation to mitigate this issue?

    Thank you!

    Chen

  • 0 in reply to Chen Jia
    TI__Guru** 105760 points

    Hello Chen,

    Can you share your the .gg files of before and after the test and log during the test? There may be some other factors that are affecting the FCC. Did your Ra or Qmax values change? SOH is based on a predefined load in data flash.

    FCC is calculated with the following formula: DataRAM.Full Charge Capacity( ) = Qstart+ PassedCharge + RM

    You can reference the impedance track app note: www.ti.com/.../slua455

    Sincerely,

    Wyatt Keller