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Voltage to charge NiMH batteries?

Discussion in 'Electronic Basics' started by Fred Furia, Jul 13, 2004.

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  1. Fred Furia

    Fred Furia Guest

    I recently noticed that my walkie talkies have a recharge port for an
    AC adapter. In each unit, I currently use 4 AAA batteries
    (rechargeable NiMH), which I currently place in my battery charger by
    hand. I am interested in using a universal AC adapter if I can, to
    avoid buying a costly adapter from the manufacturer.

    Here are two questions for the local experts:

    (1) If a universal AC adapter fits, what voltage should I use to
    properly charge the batteries? (Is it just 4 x 1.5 = 6?)

    (2) Since my universal adapter does not know what I am using it for,
    it will not stop powering when the batteries are charged. How will my
    batteries be affected if I forget to stop the charge at the right


    Fred (fred AT
  2. AC/DCdude17

    AC/DCdude17 Guest

    X-No-Archive: Yes

    They need to be current regulated, not voltage. If you're building a
    dumb charger, you'd want to use a configuration of resistor that gives
    approximately C/5 (if battery is 750mAh, charge current should be
    150mAh). Go for 6 hours of charge when fully discharged. If you
    overcharge too much, you'll cook the cells. Use a simple appliance
    timer with your universal adapter and problem is solved.
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