Atlas c40-8w ditchlight light replacement question

  • Thread starter TexasWestern70Mac
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since the dicthlight led's are not yet available as a replacement part, i thought of replacing the dicthlights with convetional incandescent mirobculbs.

looking at the wiring of the engine, the wires for the dicthlights and headlights get thier power directly from the electrical pickup on the wheelset. the LED's themselves then have the reisitors on the wires to reduce the LED's to the proper volatges. i have a few questions and this may help in the replacement of the dicthligh lights.

first off all the bulbs i am going to replace the dicthlights with are 1.5 volt; 15Milli amp; 1.2 mm dia. incandescent microbulbs. what would the proper resistor need to be, to reduce the voltage to the correct 1.5 volts/ 15Ma for the atlas engine?

if you do not know the type of resisitor for this types of bulb, what is the voltage and amerpage range of the atlas HO c40-8w so i can go to an electronics store to find the proper resistor and ask questions there? if i know the voltage and amperage range of the motor that would aide to find ask what resistor is needed.

however if you do know the type of resisitor for this type of bulb to work correctly on the HO c40-8w that would be the easiest way to install the new bulbs. an answer to either question would be ok, as long as one question was answered. if you know neither could you point in the right direction so i could find out what type of resisitor in needed?

this is basically the e-mail i sent to the tech guy at atlas, if anyone here can help me out since they may not deal with 3rd party lighting replacements, any suggestions or answers to the above questions would be appreciated, if you may happen to know the answer :)


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Hi Bill. Instead of resistors I would use diode rectifiers or a complete rectifier bridge circuit. The voltage across a rectifier diode will be about 0.75 volts and two in series or across the AC inputs to a rectifier bridge would give you 1.5 volts for your bulbs. The + and - leads would have to be connected together. If you put them in a motor lead wire the 1.5 volts will remain constant and brightness will be independant of motor speed as long as current is pasing through the diodes. A bridge circuit would be necessary if it was in a motor lead unless the loco would always be going in one direction, which is not very practical. To have the ditch lights directional , two steering diodes would have to be added to allow current to the correct set of lamps. Hope this helps.
Cheers :) Willis

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