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Original question:

BQ40Z80: The BMS is not charging or discharging the battery

BQ40Z80: Battery balancing and charging Issue

Rajavarman s
Prodigy 50 points
Part Number: BQ40Z80
Other Parts Discussed in Thread: BQ25792, BQSTUDIO, EV2400, GPCCHEM

I have designed a BMS system with 4 cells in the series configuration using BQ40Z80RSMT IC. I have verified the schematic and footprints and the connections to the IC. The BMS is connected to a battery charger IC BQ25792 for charging and discharging. Charging and discharging is happening, but there is no balancing in cell during discharge. Even though all four cells are fully charged, one battery get drained faster than other batteries. BAL_EN bit is enabled in  Gauging status register (0x0056). Is there anything I need to check to enable the Cell balancing.?

Battery charging also happening till 4V only, but the full capacity of the battery is 4.2V , is there anything I need to change to change the battery charging capacity?

I do not have EV2400 also for checking using BQstudio and I am using 18650 Li - ion battery .I have read the chemical ID (0x0006) and the value I am getting is 0x1210.

Please use the attached schematics for reference.

  • 0
    TI__Genius 11535 points

    Hi Rajavarman, 

    Is your gauge configured for 4 cells? The default is 6 cells so it could be triggering some kind of protection or PF. In order for cell balancing to occur, the gauge is required to be in relax mode so please check that the gauge has relaxed long enough.

    You will need to select the proper chemID for your batteries in order for the gauge to properly calculate full charge capacity and other parameters.

    Best,

    Jessica

  • 0 in reply to Jessica H.
    Prodigy 50 points

    Hi Jessica,

    I have configured the gauge for 4 cells only. How to select the proper chemID?
    If I have found out the chemID using GPCCHEM tool , then how to set that chemID in the gauge?

  • 0 in reply to Rajavarman s
    TI__Genius 11535 points

    Hi Rajavarman,

    You will need to get an EV2400 to program the chemID. 

    Best.

    Jessica

  • 0 in reply to Jessica H.
    Prodigy 50 points

    Hi Jessica,

    Actually, I do not have EV2400 to program the chemID. Also, it is difficult for me to use the EV2400 in my board.Is there any way to program the chemID without using EV2400?
    Is programming the chemID necessary to read the battery capacity as I will use different batteries during the production it will be difficult to calculate chemID for different batteries and program that using EV2400.

  • 0 in reply to Rajavarman s
    TI__Guru** 102415 points

    Hello Rajavarman,

    The gauge must have the correct chem ID uploaded and learning cycle completed before it can start gauging and balancing batteries. The gauge uses capacity calculations for each cell to determine the balance time it needs. You will need to use the EV2400 to upload a chemID because the chemistry ID information is proprietary.

    If you are planning to use multiple different batteries in the system you will have to upload a new golden image into the gauge to match the battery inserted.

    You can use the GPCCHEM tool and SLUA903 for the process to get the gauge working correctly, but you will need the EV2400 to continue.

    Sincerely,

    Wyatt Keller