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Original question:

bq40z50 - how to start

BQ40Z50: BQ40Z50 gauge for multi capacity battery

Zheng Tao
Prodigy 125 points
Part Number: BQ40Z50
Other Parts Discussed in Thread: GPCCHEM

Hi,

I've a product design to support multi capacity battery. In detail, Milwaukee 3 cells M12 3AH, 4AH, 5AH. All are 12V voltage battery, increasing there capacity by add cells in parallel.

As I know, when do the gauge learning, we need to set the design voltage and design capacity. The voltage is not a problem, the capacity is a problem. How should I set the design capacity to support all the 3AH, 4AH, 5AH.

If BQ40Z50 can't support this requirement, any other suggestions?

Many Thanks!

  • 0
    TI__Mastermind 28450 points

    HI Zheng,

    For clarification, are the 3AH, 4AH, and 5AH cells being added together in parallel, or are they in series and other cells are being added to them in parallel?

    Regards,

    Anthony Baldino

  • 0 in reply to Anthony
    Prodigy 125 points

    Hi Anthony,

    M12 3AH,4AH,5AH will not be used in the same time. There is only one battery slot, user will insert M12 3AH battery in default. But sometimes user will insert 4AH replace the 3AH battery. Or replaced with 5AH battery.

  • 0 in reply to Zheng Tao
    TI__Mastermind 28450 points

    Hi Zheng,

    We would not recommend changing the inserted battery with another battery of different capacity. The Impedance Track algorithm relies heavily on the Design Capacity and the parameters learned over time for accurate gauging, with changing the cell capacity greatly altering the performance of the gauge.

    Regards,

    Anthony Baldino

  • 0 in reply to Anthony
    Prodigy 125 points

    Hi Anthony,

    Thanks for the reply. But it will happen on this project of changing battery capacity. 

    Can it be expected:

    After changed the battery capacity, the gauge learning it by itself. After several times full charge and full discharge cycle, the battery level will be accurate. Even 5% deviation of bettery level is accepted on this case.

  • 0 in reply to Zheng Tao
    TI__Mastermind 28450 points

    Hi Zheng,

    Each time the cell is changed for another cell of differing capacity, there are static parameters such as design capacity, design voltage, etc. that will need to be manually changed to match the new cell, along with changing the ChemID that is being used by the gauge. When these values are changed, another successful learning cycle will need to be completed for the gauge to learn the new values of the new cell. If these steps are not completed each time a cell of differing capacity is entered to the gauge, then I believe the accuracy error will greater then 5%.

    Regards,

    Anthony Baldino

  • 0 in reply to Anthony
    Prodigy 125 points

    HI Anthony,

    In this case, when change battery, the votlage and ChemID are not changed. Only the capacity changed.

    I did a simple test with EVM and M12 3AH battery. The gauge learned the capacity after one full charge and discharge cycle. I'll change the battery to 5AH and see what will happen.

    Thanks!

  • 0 in reply to Zheng Tao
    TI__Mastermind 28450 points

    Hi Zheng,

    Another option is to use the GPCCHEM tool attached below on each to see if the ChemID is different for each of the cells. I do believe that the values programmed by the chemID does take the capacity of the cell into account

    Regards,

    Anthony Baldino