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BQ40Z50-R2: OC register sets before cell reached 4.2V and Full Charge Capacity= Remaining Capacity

Moonmoon Pati
Intellectual 275 points
Part Number: BQ40Z50-R2
Other Parts Discussed in Thread: BQ40Z50

Hello TI,

The charging setup is connected with TI BMS with BQ40Z50 R2. The charging current has 55% ripple to test the lifetime. A single cell is connected 2500 mAh NCA chemistry with 18650 format. The charging current mean value is 2A so, time for full charge should be few minutes more than 1 hour. (from theory)

But the OC register in the BMS is triggered at 30 minutes aprroximately while charging after a full discharge and the CHG FET opens. The thing is remaining capacity and FCC becomes equal and SOC is counted as 100%. Hence, FET opens.

My setup can decrease current but still the time is not satisfactory (from theory). That is why the cell does not reach 4.2V actually, but BMS shows false OC register setting. When I checl with musltimeter it is never 4.2V at 100% SOC

Can anyone help me how to stop this ? Can I change the FCC myself so that the FET doesn't open earlier...?

as my cell have run only 58 cycles, the FCC of 1951 mAh (please see the picture below) is not satisfactory.

 

Regards,

Moonmoon

  • +1
    TI__Guru** 105770 points

    Hello,

    I think we have been helping with this project awhile and in previous threads it's been mentioned that the gauge is not really designed for charging with huge current ripple swings, the algorithm will behave strangely and it will be hard to debug.

    The OC is just indicating there's been charge after 100% SOC reported. This may be due to one of the low current swings from a previous cycle making the gauge think there was a full charge event and reducing DOD at EOC. That will lead to your FCC decreasing like you've seen.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Intellectual 275 points

    Thanks for the replies.