help with a battery charger....

Discussion in 'The Projects Forum' started by dthx, Nov 14, 2013.

  1. dthx

    Thread Starter Member

    May 2, 2013
    194
    14
    I have a discontinued handheld vhf radio and Ive lost the charger.
    The radio works great....the manufacturer has discontinued the radio and all of it's parts...
    On the rechargeable battery tucked into the radio it says.....
    STANDARD (the manufacturer of the radio)
    Model CNB350 (the model number of the battery pack)
    7.2v 1100mah
    ni-cad
    Can any of you help me design a circuit that will charge the battery?
    Being the Neanderthal I am...I just dont want to throw the thing away...it works great...!
    D.
     
  2. wayneh

    Expert

    Sep 9, 2010
    12,123
    3,047
    Do you already have any wall warts or chargers that you want to use for this?

    Their are many approaches. Would you plan to leave it on the charger all the time, or just during a charge cycle?
     
  3. Dr.killjoy

    Well-Known Member

    Apr 28, 2013
    1,190
    156
    What about using a charger for the R/C cars? ??? I think they use 7.2v batteries..
     
  4. t06afre

    AAC Fanatic!

    May 11, 2009
    5,939
    1,222
    Is the battery pack charged inside or outside the radio. If it is charged inside the radio. It may have charger electronics built into the radio. And the charger is probably just a DC source.
     
  5. inwo

    Well-Known Member

    Nov 7, 2013
    2,433
    315
    Simple answer.
    Charge it at any voltage over the battery voltage.
    Limit current to a few hundred ma.

    When battery is warm it's done.
    Further charging=bad.

    Nicads won't have a predictable knee voltage to limit charge time.

    Look for wall warts. Let us know vdc and ma.
    Need a ma meter to know if it will even accept charge.
     
  6. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    Dumb NiCad chargers are typically constant-current (not constant voltage). It is up to the user to disconnect the battery from the charger when the battery is full. Left connected to the battery, the charger will heat the battery, and dry out the electrolyte. The rule-of-thumb for charging a 1100mAh NiCad is charge it for 14hours at 110mA. If you know that only half the capacity is likely gone, then charge for half the time, i.e. 7h.

    Back when I carried a NiCad powered handy-talkie radio, I had multiple battery packs for it. The game plan was always run the radio until the pack went dead, swap packs, and put the dead back on charge for 14 hours.
    I used an electro-mechanical wall-outlet-clock-timer set for one hour to turn off the charger.

    This is the kind of timer that has the slide-out switches that give one hour per slider. I would turn the timer on manually, and then rotate the wheel on the timer so that it shuts off 14hours hence. Then it would automatically turn on for one hour every 24 hours until I needed the battery pack, keeping it topped up for instant use without cooking it...

    This way, I got several years of utilization out of a NiCad pack; much longer than you get if you use 10% of the battery capacity, and throw it on charge for 14hours, or worse, throw it into the charger and forget it for several days...:(
     
    Last edited: Nov 14, 2013
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