Charger vs Battery

Discussion in 'General Electronics Chat' started by Gadwood74, Mar 30, 2012.

  1. Gadwood74

    Thread Starter New Member

    Mar 30, 2012
    Hi - might be a very easy question, but I really can't understand anything in electricity (voltage vs mAh, ...).

    I have this battery

    The wall charger turned very hot and does not work anymore.

    I have this one I could use:

    Are the battery and the new charger compatible?

    It is for a RC truck.

    Thanks. If anyone can try to tell me why it is OK or not with not too technical wording, I would appreciate.
  2. ajm113


    Feb 19, 2011
    As long as the adapter fits and has the same voltage. (Voltage MUST equal) Amps/miliamps MUST be equal or more then the original. The charging circuit will only use the current it needs. Anything else, the circuit will not work properly or the battery will take a very long time to charge.

    Electricity is a very easy concept, just think of it as water. Voltage is the amount and amps is the current. (How fast the water is moving.)
  3. Gadwood74

    Thread Starter New Member

    Mar 30, 2012
    Thanks. In fact, the original was a 9V / 250mAh output. According to your comment, I wonder why the battery is 7.2V and the related original charger has a 9V output. Is this why it is not functionnal anymore?

    Here's the original one

  4. bountyhunter

    Well-Known Member

    Sep 7, 2009
    A "7.2V" (nominal voltage) battery has to rise up to about 8.4V to fully charge. The wall cubes in the picture are usually not regulated: they put out the specified voltage at the listed current draw, but the voltage is a lot higher at lighter currents. Measure the voltage with no load and see what it is.

    The NI-MH batteries do not like sustained overcharge at levels higher than about 1/20 - 1/30 C rate (about 70 mA for your battery) so you should measure the charger's current output when loaded enough to hold it's voltage at 8.4V. If it's higher than 70 mA, don't let it run more than about 12 hours.
  5. Audioguru

    New Member

    Dec 20, 2007
    It is not a wall charger. It is a cheap power supply used as a charger but it is missing the current-limiting parts that are in a real charger.

    Probably it tried to charge a battery that was discharged much lower that ever before and since it has nothing to limit the current then it was severely overloaded and died.

    Your 7.5V power supply is also just a simple power supply, not a charger.
    Its voltage is too low to fully charge the battewry.
    It will also get too hot if it tried to charge a dead battery.

    I can't see the polarity of the output plug on the 7.5V power supply. It might have its pins reversed from what is needed. The original had a positive center pin.