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Voltage Question

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  • Rich Johnson
    I took the PCB out of my Bachmann Truck (G-scale 1:20.3). Very easy job. Installed my 2 7.2 B&D Batts. and an airwire decoder. The truck has LED head lights
    Message 1 of 2 , Oct 10, 2008
      I took the PCB out of my Bachmann Truck (G-scale 1:20.3). Very easy job.
      Installed my 2 7.2 B&D Batts. and an airwire decoder. The truck has
      LED head lights and a red led tail light. The wires to the leds are
      smaller than 30awg and fragil. They were wired for track power, and on
      all the time. I am very leary to just plug them into the decoder.

      Now for my Question: How can I figure out what resistor to use, or if
      I even need one to run the lights? It would be nice to plug them in
      and work FWD & BKW. Like page 13 shows. This is what I usually do for
      all my other locos. BUT at the bottom of the page it says lamp voltage
      is equal to the batts. I am using 2 7.2vdc batts == 14.4 worse case.
      They usually run about 13.5vdc.

      But I have no information on the voltage of the little leds in the
      truck. And they look almost impossable to replace if I guess the wrong
      resistor.

      Any Ideas??

      Rich, San jose Ca.

      Rich@...
    • Bill Swindell
      First of all, the headlights and tail lights should be on all the time, in my opinion. They are LED s and run on about 3.5 V. Subtract 3.5 from 14.4 and you
      Message 2 of 2 , Oct 10, 2008
        First of all, the headlights and tail lights should be on all the
        time, in my opinion. They are LED's and run on about 3.5 V. Subtract
        3.5 from 14.4 and you get 10.9V. At 20ma you need at 570 ohm, 1/4 watt
        resistor in series with each headlight and the taillight.

        I have the same truck and that is exactly what I am doing to mine.
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