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Resistor value for battery charger

Discussion in 'Electronic Basics' started by R Farris, Nov 19, 2004.

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  1. R Farris

    R Farris Guest

    Okay, I think this is a basic question...

    Bought an rechargable drill at a garage sale. Of course it doesn't work -
    because both batteries are discharged. Turns out the problem is with the
    battery charger. It is composed of a transformer that plugs into the wall
    and a base unit that holds the 12VDC battery.

    The wall unit works okay and produces 17VDC @ 400mA. The problem is with
    the base unit. When I took it apart I found a single ceramic resistor that
    was wired in series - but it was burned beyond recognition.

    Okay, my question: what value of resistor do I need to buy to replace the
    burned one?

    rf78801x.att.net
     
  2. john jardine

    john jardine Guest

    Mine has a 4.7ohm 1Watt. (there's a IN4001 rectifier diode in there as
    well).
     
  3. R Farris

    R Farris Guest

    Great, thanks much!
     
  4. Mike

    Mike Guest

    Sometimes you can get lucky by finding a parts diagram. Who makes the drill
    and what model?

    Are there any readable numbers/symbols on the old part?

    Mike
     
  5. a

    a Guest

    Well, its a Ryobi HP1201 drill and the charger is part 1400674 but I could
    find no schematics for it (the charger). I did find a parts diagram for
    the drill but not a breakout for the charger.

    Ron
     
  6. Kent Regal

    Kent Regal Guest

    Some of the charges are smart-chargers, in that they have a third wire
    connected inside the batterypack that senses the pack voltage as it is
    charging.

    You can tell if yours has this because there will be a third contact on the
    pack and in the charger connection well.

    It sounds like yours may be a simple constant voltage charger with a current
    limit resistor.

    I suspect the reason the resistor is damaged is your battery pack's nicad
    batteries has one or more shorted cells. This causes the pack to draw more
    current than it would normally.

    If this is the case, it's time to get another batterypack. You could open the
    pack and measure which of the cells have a voltage and which are at zero
    volts. You will likely find some are dead. Replacements are available, but, the
    other cells are likely to fail soon as well.

    I've tried the capacitor "shock" method to revive some nicads, but with limited
    reliability. The "shock" is a current surge from a capacitor that removes some
    of the internal crystaline structures that develop in a dead battery which push
    through the battery separator material.
     
  7. Mike

    Mike Guest

    I was also unsuccessful locating a parts diagram for the charger. Although,
    I did find many results of people having the same problem..

    Perhaps someone that reads this group has the same drill and can give you
    specs by disassembling theirs..

    Mike
     
  8. a

    a Guest

    Only two contacts and the series resistor.

    Thanks to all.

    Ron

    PS There are some smart folks out there!
     
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