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BQ40Z50-R1: BQ40Z50 max delta cell voltage

MJT
Prodigy 230 points
Part Number: BQ40Z50-R1

We tested 10 batteries using the same environmental conditions.

The Max delta cell voltage of 3 batteries is getting larger and larger. We don't know why only these 3 batteries had this kind of performance.

(1) how will the battery performance affected by this Max Delta Cell Voltage?

(2) In which situation, the Max delta cell voltage will be updated?

We just put these 10 batteries in a chamber and didn't perform any charge-discharge test. 

Thank you.

  • 0
    TI__Genius 12215 points

    Hi,

        Max Delta Cell Voltage is the voltage variation between the cells in the stack, the higher the value is, the more imbalanced are the cells in the same group. It is updated once the measured new value is greater than the old value.

       The imbalanced battery will has its capacity determined by the cell with minimum capacity or highest impedance. The battery will terminate charge before all cell reaches full charge condition and terminate discharge when the cell with lowest capacity reaches the terminate or UVP threshold.

       To avoid this condition, you will need to group the cells appropriately according to its voltage, impedance, as well as the capacity if condition allows, it had better to had the cells put into the same battery group with these parameters as close as possible. 

  • 0 in reply to Steven Yao
    Prodigy 230 points

    Hi, Steven,

    Thank you for your reply.

    I am attaching the test data for your reference.

    We do group the cells by measuring  the OCV and IR of each cell before the assembly.

    From the  test result, you could see that we could charge-discharge the batteries without kicking any protection.

    During the temperature cycle test, not every battery's Max Delta Cell Voltage is changed. 

    Will the Max Delta Cell Voltage be updated even the battery is just under the storage condition? 

    If the battery is imbalanced because of the increased Max Delta Cell Voltage, will the battery be charged-discharged properly?

    Thank you for you reply in advance.Max Delta Cell Voltage 2PCS 20191108.xlsx

  • 0 in reply to Steven Yao
    Prodigy 230 points

    Hi, Steven,

    Thank you for your reply.

    I am attaching the test data for your reference.

    We do group the cells by measuring  the OCV and IR of each cell before the assembly.

    From the  test result, you could see that we could charge-discharge the batteries without kicking any protection.

    During the temperature cycle test, not every battery's Max Delta Cell Voltage is changed. 

    Will the Max Delta Cell Voltage be updated even the battery is just under the storage condition? 

    If the battery is imbalanced because of the increased Max Delta Cell Voltage, will the battery be charged-discharged properly?

    Thank you for you reply in advance.5531.Max Delta Cell Voltage 2PCS 20191108.xlsx

  • 0 in reply to MJT
    TI__Genius 12215 points

    Hi,

        This value can be updated under sleep mode

        If the battery is imbalanced, the charge and discharge will be determined by the VIMA or VIMR bit in PF enable register

  • 0 in reply to Steven Yao
    Prodigy 230 points

    Hi, Steven, Thank you.

    Could we say that just because the Max Delta Cell Voltage increased doesn't mean the battery will be imbalanced during the charge/discharge stage?

    We experienced that the batteries worked just fine even the Max Delta Cell Voltage increased. 

    VIMR and VIMA PF function are enabled in these batteries, but PF didn't happen during the test.

    Thank you.



  • 0 in reply to MJT
    TI__Genius 12215 points

    Hi,

        There are other parameters to trigger Cell Imbalance fail, please refer to the detailed information in 3.12 in TRM

  • 0 in reply to Steven Yao
    Prodigy 230 points

    Hi, Steven,

    Thank you. We checked the setting of VIMR. I added in the previous excel file, please check it for us.

    During our tests, we didn't see that the batteries triggered VIMR or VIMA PF protection even the Max Delta Cell Voltage increased.

    The Max Delta Cell Voltage increased but the battery could be used without triggering any protection or terminating earlier.

    Is this possible?

    10 batteries have done the same tests, but only 3 of them has this issue. So we don't know how to explain this to our customer.

    Your explanation will be much appreciated.

    Thank you.5076.Max Delta Cell Voltage 2PCS 20191108.xlsx

  • 0 in reply to MJT
    Prodigy 230 points

    Hi, Steven,

    I am still waiting for your reply regarding my previous questions.

    During our tests, we didn't see that the batteries triggered VIMR or VIMA PF protection even the Max Delta Cell Voltage increased.

    The Max Delta Cell Voltage increased but the battery could be used without triggering any protection or terminating earlier.

    Is this possible?

    10 batteries have done the same tests, but only 3 of them has this issue. So we don't know how to explain this to our customer.

    Thank you.

  • 0 in reply to MJT
    TI__Genius 12215 points

    Hi, MJT

        The Max Delta Cell Voltage is relevant to balance status, but the Cell Balancing Fail is detected with other data, which is CB Time Cell1..4, the difference between these data is used to determine the CB bit in PF register, please refer to section 3.9 in TRM