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BQ34Z100 & BQ29200 Cell Balancinge Effect on SOH and SOC

Morgan Smith
Prodigy 160 points
Other Parts Discussed in Thread: BQ34Z100, BQ29200

Hello


We have a design using the BQ34Z100 and a BQ29200 overvoltage protector with in built cell balancing.

The cells are arranged as 2 in series.

As I understand it the balancing circuit shunts the cell with the highest voltage via some resistors untill the cells are balanced, this current will not be seen by the BQ34Z100. I assume that the voltage will adjust though, which will be seen by the gauge.

This balancing technique seems to be common, how will it effect the IT algorithms estimation of SOC and SOH?

Is it not a big issue?

I assume if the cells need serious ammounts of balancing the SOH is pretty low anyway.

Thanks

Morgan

  • 0
    TI__Guru 73830 points

    Morgan,

    Cell balancing does remove capacity from the cells. This is not normally an issue, because capacity is removed from cells with higher stored capacity as they are charging. Capacities should be balanced at charge complete. The gauge go on to monitor the voltages during rest and update Qmax based on the capacity in the pack. The bq34z100 and bq29200 configuration will balance the cells and initialize Qmax during rest. One difference is that the bq29200 can remove capacity while the pack is not charging and the bq34z100 does not know about it. This can contribute to some the error, but the Remaining Capacity and FCC can adjust during rest based on the OCV. If you have a 2S configuration, then you could also consider using one of our other devices that provide integrated cell balancing and gauging.

    Tom