headlight & resistor

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

  1. jaijef

    jaijef New Member

    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.

    Any help is appreciated.
  2. woodone

    woodone Member

    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

    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

    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.

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