I have some out-of-sight staging on my DCC layout. I have installed a DTDP micro switch on the end of each track. When the train reaches the end of the track it opens the circuit to the track and stops the train. This part works fine. But I also wanted to use the Normally open contact on the switch to turn on an indicator light to tell the operator that he is in the limit.
My initial attempt was to have the switch operate a 14V bulb off of the DCC current. I found that this pulls the voltage too low and faults out the controller. An LED uses very little current but usually operates on DC. Can an LED (with the proper resistance) operate off of an AC current? (It still has current in the right direction for half the time). Will this unbalanced power consumption screw up my controller? I'm a little afraid to try it without knowing what it might do to my system.
Any other ideas for operating an indicator light off of my DCC current. I don't currently have a second voltage source. Eventually I will have a 12 VDC for my building lighting but that is a few years away.
Thanks ahead of time.
Jim in Costa Rica
Modeling freelance Northern California late 1930s
Jim:
You can use an LED as long as you hook a resistor (1K OHMS or so) in series with one leg of the led. Although this will work, the LED won't last too long since it is exposed to the reverse current and it doesn't like that very much. The better solution is to use a bicolor led or two regular LEDs back to back or a standard led back to back with a regular diode. In each case a suitable resistor must be used. The best solution for power really would be to power your led(s) with either a DC or AC supply.
Joe
Using an LED to indicate DCC track power on.
You will need a voltage-dropping resistor in series with the LED. You will also need a reverse polarity protection diode.
VPS = 14.4V VL = 2.6V VD = 0.7V IL = 20mA = 0.02A R = 555 ohms. You can use 560 ohms from Radio Shack. Using a 560 from Radio Shack, W computes to be 0.224. Use a 1/4W resistor or larger. Radio Shack has 560 available in ½W size. Use that.
I got this from Allen Gartner's website. For lower current, about 10 ma, use a 1k resistor.
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Rich
If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.
Thanks Joe and Rich. That worked!!
Regards,