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bq24071 and NiMh battery

Roberto Aceiton
Prodigy 75 points
Other Parts Discussed in Thread: BQ24071, BQ2002

Is it possible to use a bq24071 to charge a 3 cell NiMh battery (3.6V) ???? The charge profile looks like could work at the expense of never detecting charge termination....

any ideas?

 

 

  • 0
    TI__Guru**** 150750 points

    This is not recommended.  The danger with never being able to detect termination is continuing to charge the cells at the full C rate without being able to realize that the cells' temperature is rising due to overcharge (Nickel cells' temperature rises as the cell is fully charged and continues to rise if they are overcharged).

     

    The BQ2002 is a Nickel linear charger that is recommended.

  • 0 in reply to Chris Glaser
    Prodigy 75 points

    Thanks for the information.

    What I am really trying to do is to take advantage of the DPPM feature of the BQ24071, however Li-ion batteries can't be used in my application. Is there anyway to still use this IC (or a similar one with DPPM) while using the BAT output as a current limited voltage source?

     

    thanks in advance,

    Roberto.

  • 0 in reply to Roberto Aceiton
    TI__Guru**** 150750 points

    DPPM is only designed to be used on Lithium cells.  If you use a Nickel chemistry, the problem still comes down to reliably detecting termination to keep the packs within a safe temperature range.  Constantly varying the charge current during a fast charge will cause significant changes in the pack voltage and in the rate of change in pack temperature.  Pack voltage (-dV) and rate of change of the pack's temperature (dT/dt) are the 2 termination methods for Nickel cells and both require a fairly constant charge current to detect accurately.

    You may be able to use the BQ24071 with a thermistor if the high temperature fault point (typically 45 C) keeps your Nickel cells within a safe operating area.  You will need to verify with your pack manufacturer.