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charging NIMH and NICAD batteries

Discussion in 'Electronic Design' started by Mark, Jul 18, 2003.

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  1. Mark

    Mark Guest

    say i want to charge a 2000mAH battery at 1C from a 4A current source. is it
    acceptable to do this with a 50% duty cycle or will this f*** the battery in
    the long run.??

    This seems to me like the eaasiest way to make a variable constant current
    charger and the battery voltage could be monitored during the off time.

  2. mike

    mike Guest

    With a little L and a diode, you can "average the current".

    I tried to measure the voltage during the off time with a processor.
    The voltage reading is VERY sensitive to how long you wait. The
    variation in interrupt latency of the processor caused the readings
    to change way more than the actual battery voltage changed. If you
    try this, use a hardware timer to precisely sample the voltage
    before feeding it to the A/D.

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  3. R.Legg

    R.Legg Guest

    It may be easier for you, unfortunately it wasn't for the guy's who
    have originally collected relevent data that allows you, now, to
    intelligently charge the cells.

    The open circuit cell voltage is not likely correlated to any
    published data, though the difference between voltages (off and on
    charge) can be an indicator of cell health and SOC - this information
    is not guaranteed to be available for the specific cells you are

    You would have to use blind time or temperature-terminated charging
    techniques, if the cells are capable of accepting the elevated charge

    You should consult the specific battery mfr's advice on this.

    When data is collected for a 1C charging rate, they are not fooling
    around, and do not expect you to be, either. 4A is 2C, regardless of
    duty, unless averaged externally before entering the battery
    terminals. The differences between charging efficiency at the two
    rates will depend on the battery.

    If you have the ability to control charging duty cycle, you no doubt
    have the ability also to to control the actual charging rate, and
    should do so, if you want predictable results. If you have the ability
    to monitor cell voltage, then monitor it under the conditions that
    correlate to the published data, to obtain predictable results

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