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BQ40Z60: Imbalanced cells in production

user4788380
Prodigy 50 points
Part Number: BQ40Z60

I am using a bq40z60 gas gauge in 4S configuration. Batteries are Li-Ion NCR18650B (Chemistry ID 2012). 

Now I run a learning cycle on one board and after that set  Update Status to 02 and Cycle Count to 0. If I use this Golden file on another board in production that has imbalanced cells (e.g 3800mV, 3800mV, 3800mV and 4300mV), will the bq40z60 on the second board balance the cells without generating Safety Alerts/Statuses during charge/discharge?

Thanks!

  • 0
    TI__Guru* 76230 points
    no it will not until the qmax of that pack has been updated then it will try balancing the sales. If any of the safety thresholds is exceeded, it will start set the flag and the corresponding fet action will the gauge has been configured for will occur.
    thanks
    Onyx
  • 0 in reply to Onyx Ahiakwo
    Prodigy 50 points

    Is the only option therefore to assemble battery packs out of cells that have similar voltage?

    How to estimate, what is the allowed voltage deviation between the cells that would not cause single cell Safety Statuses (e.g CUV, COV)?

    Is the only way to ship products with balancing enabled by the following procedure?

    Fully discharge, wait 5 hrs (Update Status 0x04)

    Fully charge, wait 5 hrs (Update Status 0x05)

    Fully discharge, wait 5 hrs (Update Status 0x06)

    Fully charge, wait 5 hrs

    Fully discharge, wait 5 hrs (Update Status 0x0E)

    Charge to desired level.

    What would happen if the learning cycle will not be performed on shipped products and the user never fully discharges the battery pack? Is it possible that the cells become so imbalanced that bq40z60 will not allow the pack to be fully charged/discharged due to Safety Statuses (e.g CUV, COV)? What would be the recommended procedure to ensure that balancing is working properly?

    Thank You for assistance!

  • 0 in reply to user4788380
    TI__Guru* 76230 points
    Yes, it is absolutely necessary to assemble batteries that have similar voltage. That is typically how it is done. The gauge prevents imbalance from occurring. You are the one that gets to set the CUV and COV thresholds based on your battery specs.

    The procedure you typed out is the learning cycle procedure so yes that is what you need. If learning is not performed you will not have accurate gauging. You are not to carry out learning on each pack. You are to perform just one learning and then extract a golden file which will be programmed on multiple devices. if you want balancing to occur, update status has to be kept as 0E. Otherwise if update status is 06 on your golden file, when you cycle and have one more qmax update it will go from 06 to 0E and balancing will be active.
    thanks
    Onyx