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12 Volt cordless drill

Discussion in 'Electrical Engineering' started by John, Oct 27, 2003.

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  1. John

    John Guest

    I was given a drill with 3 extra plug in batterys but did not receive
    the charger.Is there any reason why I cant rig a connection and use a
    auto type trickel charger ? A replacement charger costs $60.
  2. pkh

    pkh Guest

    I'd bet that a trickle charge current for a car battery is probably way
    too much to trickle charge some C or sub-C cells! Look on the internet
    for charge rates for cells of the same type and size as yours, and
    compare that to the trickle charge current rating on your car battery


  3. Rusty

    Rusty Guest

    With a car battery charger you will never know when the cordless
    drill battery is fully charged and will risk overcharging it and
    destroying it. The $60 charger has a built in circuit to stop
    charging when the battery voltage rises to the correct voltage for a
    full charge. This is very different from that for a lead-acid car
  4. Louis Bybee

    Louis Bybee Guest

    MAHA sells a unit that will charge Nickel Cadmium, and Nickel Metal Hydride,
    batteries. It has charging pins that will adapt to almost any pack. I find
    it very useful as it will charge almost any pack, in any configuration, from
    I believe three to twelve volts. It has a corded temp sensor that will
    disconnect the charger if the pack gets too hot.

    It also includes an adapter that will allow operation from a cigarette
    lighter receptacle.

    The feature I really like is the ability to discharge then charge the pack.
    I find that this will bring back many NiCad packs.

    It's not as convenient as the OEM charger, but it makes up for it by
    adapting to many packs.

    I believe this same model is also sold at Radio Shack for $29 to $39.

    Remove the two fish in address to respond
  5. Guest

    The auto type charger is not good for this. You can build
    a simple charger for less than $10.00. The trick is to
    figure a way to conveniently connect the charger to the

    The simple charger consists of a DC supply providing at
    least 2 volts more than the battery voltage, an LM317 chip
    configured as a current regulator, and a 22 ohm resistor
    to set the current to ~56 mA for trickle charging. The DC
    supply can be a wall wart rated to provide ~200 mA or more.

    Generally speaking, if you set the charge rate for between
    50 and 60 mA you'll be ok for recharging drill batteries at
    a trickle rate. If you want to be more exact, you'll need
    to determine the capacity, C of your batteries in order to
    determine charging rate. It will take about 30 hours of
    charge at this rate (~56 mA) to fully recharge a completely
    discharged drill battery. If you go to a C/10 rate (about
    100 mA), you can recharge in about 14 - 16 hours. The
    downside of that is a greater probability that you will harm
    the battery by overcharge - say by leaving it on the charger
    too long, or perhaps by having the circuit operate at
    something lower than C/10. The ~C/20 rate (56 mA) gives you
    a much better margin for error.

    A more sophisticated charger can be built or bought, but
    if you want to keep it cheap and simple, it's hard to
    beat three components.
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