battery charger problem ... help please

Discussion in 'Electrical Forum discussion & Blog' started by randomwalk101, Jul 16, 2007.

  1. randomwalk101

    randomwalk101 New Member

    Hi all. I have a 12V Craftman's cordless drill. It's not too old, however it was discontinued. I used it very sparingly. The drill/battery is working great. But recently, the charger is not working to charge the battery anymore.

    The charger is basically a 120 ac volts -> 14.5 dc volts @ 200 mA transformer or whatever that little black thing is....with a wire connects to the adapter that attaches to the cordless (removable) battery. I'm pretty sure the transformer (charger) is dead..I tested with the multimeter and instead of giving 14.5v it gave like 0.01volt.....(yes, the drill said 12V but its orginal charger said 14.5v...don't know why).

    Question is, instead of through the whole thing away (drill and all), can I just cut up that bad transformer (charger) and attach another 12 volt charger (or 14.5v if I can find one) to it..does that amperage (200mA) matter?
    Can I use something like 12v (or 14v) with higher amp like 2amp???

    The closest charger unit I found is input 110v -> output 12v dc @ 1A
    Will this do? What will that higher Amp rating do? Will it blow up if I leave it charging or something? I get real nervous when it comes to electricity. Please give me your advice. Thank you.
  2. leejosepho

    leejosepho DIY scratch-pad engineer

    Yes, you can replace that AC adapter as long as you get it connected correctly, meaning DC + to + and - to -.

    A twelve volt battery is considered fully charged when it contains 12.8 volts, and it takes a higher voltage to actually get it there. Charging systems in automobiles usually charge batteries at 13.8 ... and 14.5 can do that a little more quickly.

    Something has to either stop or slow the charger once the battery is up to voltage, and my guess here is that the 200mA of the original adapter was serving as that limit. So yes, it is probably a bad idea to use a 2A adapter in its place.
  3. speedbump

    speedbump Previous member

    Riverview, Fl.
    If you start pumping more amperage to the battery than the 200 ma, you may be overheating the battery, not a good idea. They probably had the smaller transformer in that charger for a reason. Try to find a smaller one if you can and the battery will last longer.

  4. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    New England
    Batteries can only handle a certain level of trickle charging or you will destroy them. Now, it might handle a faster charge, but then it would need some way to throttle that charge down to a trickle once it decided it was fully charged. The smarter chargers do that. Don't mess with that unless you know what you are doing as some batteries will not only overheat, they can explode if not treated right. Also, deep discharging and overheating decreases their life.
  5. Mikey

    Mikey Aspiring Old Fart, EE, computer & networking geek

    Central Florida
    4 suggestions:

    1) See if Sears Parts can sell you a new charger;
    2) See if someone on the auction site has the whole outfit for sale (right now there are two Craftsman 12V drill kits for sale, current bid is $9.99, 6 days left in the auction;
    3) Tear the charger thingy apart, see what's failed, and fix it;
    4) Cut the cord off the charger, attach two spring clips to it, and run the drill off a 12V battery.
  6. Bob NH

    Bob NH In the Trades

    New Hampshire
    I have two Craftsman Universal Chargers that cover the range of 7.2 V to 24 V. If your battery fits that kind you could find one in a Sears store.

    You must be careful with chargers. I blew one working at a remote site when I used it with an inverter system. When I got a new on it had a tag on the cord that said operation on an inverter source will cause them to fail. There was no such tag on the original one.
  7. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    New England
    All the inexpensive invertors, and many of the mid-range ones basically make square waves, which can drive some circuits crazy. The better ones make stepped sign waves, and the best ones make a decent sine wave, but you'll pay a fair amount for it.
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