headlight & resistor

Discussion in 'DCC & Electronics' started by jaijef, May 30, 2007.

  1. jaijef

    jaijef New Member

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    Hello all,
    I am installing a Digitrax decoder in my Athearn sd40-2.
    I was trying to wire in a new headlight set up using 2 12volt Microlamps from RadioShack. These have 60mA. So I am using a 22K Ohm resistor like the Digitrax book says to use w/any bulb over 50mA. The bulb will light w/o the resistor but it will not w/the resistor after the resistor has been soldered.
    Jaijef

    Any help is appreciated.
    sincerely
    jaijef
  2. woodone

    woodone Member

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    After the reister was soldered? Does this mean that at one time the lamps did light up? Then after you soldered them - no lights? Bad solder joint could be the problem.
    What voltage is being used?
    I am not sure, but with DCC, the voltage is a square wave pulsed voltage.
    That could make the resistor value wrong?
  3. Gary Pfeil

    Gary Pfeil Active Member

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    22k seems like an extremely high value. In fact, if the lamp lights with the output of the decoder without a resistor, a resistor along the lines of 180 ohm should work.
  4. jaijef

    jaijef New Member

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    fixed problem

    Thank you all for the replies.
    I ended up using a 22 Ohm resistor w/a 60mA 12V bulb. after the soldering was done, everything worked great.
    jaijef