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Replace battery charger for a kid's toy

Discussion in 'Electronic Design' started by DaveO, May 21, 2007.

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  1. DaveO

    DaveO Guest

    The wall-wart battery charger for one of the kid's toys gave out, and
    I'm looking for ideas to replace it. The toy is powered by two 6VDC
    batteries; the wall-wart charger says "output 12VDC 1.2 amps".

    Continuity tester says there is no circuit between the charger and the
    blade connectors at the end of the wires.

    I thought I re-purpose a computer power supply for the task, but
    output of the power supply is 12VDC 12 amps. So I'm trying to apply
    the reading I've done on this: can I simply put a potentiometer inline
    and dial current down to 1.2 amps? Does the potentiometer or a
    resistor change the amperage but not the voltage? (The reading hasn't
    been too clear on this point.)

    I'd appreciate any knowledge imparted, or links to a good source of
    info. Thanks!
  2. D from BC

    D from BC Guest


    D from BC
  3. Chris Jones

    Chris Jones Guest

    What exactly do you mean here? This could be normal....

    No you don't want to put a potentiometer in series, that will lower the
    voltage. You do want a fuse in series, however.

    The toy will (or at least should) draw only the current that it needs, when
    supplied with the correct voltage. If the toy develops a fault, then it
    may draw much too much current, which the PC power supply will easily
    supply, and then the wires will get hot, melt, and possibly set fire to
    your house. If you put a fuse rated at perhaps 1.5A connected in series
    with the positive wire between the PC power supply and the toy then you may
    be able to prevent such a fire. Insulate all connections thoroughly and
    securely to prevent them from shorting to the case of the power supply or
    other grounded objects.

    In order to make the PC power supply work, it is sometimes (but not always)
    necessary to put a load on the 5V output of the power supply. You may find
    that a small automotive bulb works, or you can buy a power resistor. For
    example, a 10 Ohm power resistor rated for 10 Watts should make it work.
    (It is not called upon to dissipate 10 Watts in this case, but the ratings
    of many power resistors are rather optimistic so it pays to specify a
    somewhat larger size than is theoretically needed.)

    Unless you are able to get a knowledgeable friend to check over your
    installation for safety, I would advise not leaving the thing plugged in
    unless under direct supervision.

  4. Ralph in NH

    Ralph in NH Guest

    Wall warts can be susceptible to impact damage. Typically the transformer
    is soldered to a cheap single-sided PCB. When the unit falls and bounces
    off the floor, one or more transformer terminals can be ripped from the
    solder joint, or the foil can be cracked. If you can get the case open, you
    may want to check for such damage. As another post suggested, get someone
    knowledgeable to check your handiwork!

    Best regards,
    Ralph in NH
  5. DaveO

    DaveO Guest

    Hi, Chris and Ralph, and thanks for your replies. I realized too late
    that I posted to the "design" electronics group rather than the
    "basic" group and was hoping not to incur the wrath of the regular
    users- and I appreciate the time it took to develop cogent responses.

    The fuse inline is a great safety idea that hadn't occurred to me-
    thanks. I'm planning to watch over this thing very closely when the
    time comes.

    Thanks again!
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