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Cell balancing for Ni-MH battery in series

S.Satoshi
Guru 21685 points
Other Parts Discussed in Thread: BQ2000, BQ25887

Hi,

I understand that the charger IC for Ni-MH can charge multi-cell Ni-MH battery but don't have cell balancing feature. Then do you have any idea or example circuit to add cell balancing feature externally?

Best Regards,

Satoshi

  • 0
    Guru 21685 points

    Let me add part number, bq2000 as example charger IC for Ni-MH.

  • 0 in reply to S.Satoshi
    TI__Mastermind 24075 points

    Hi Satoshi,

       Sorry for the delayed response, for some reason the BQ2000 tag did not appear. For other posts if you mention part number when creating the post we will have a much faster response time!

       You are correct that most charger IC does not have integrated cell balancing feature, apart from our new BQ25887 I2C Controlled, 2-cell, 2-A boost-mode battery charger with cell balancing. This does not do Ni-MH charging however.

       Generally for Ni-MH batteries, cell balancing feature is not as important for multiple cell configuration as Li-ion as this battery chemistry is a little more forgiving with being overcharged as compared to Li-ion. NiMH can respond to increased voltage by internal shuttle reactions that are equivalent to a chemical short-circuit inside the cell. Essentially slightly excess charging of NiMH is converted to heat and dissipated which is why deltaT/deltat (termperature change) is a valid NiMH termination condition. If you are charging at a low C, this gives the other cell/s a little more time to balance out, while the slightly overcharged cell dissipates heat.

        With that being said, you can take a look at out battery monitors and balancer portfolio for cell balancing IC. Once you find a suitable part for your system, you can create a new post with the part number as the title and the expert regarding those parts can answer your questions.