Headlight switch

[SpaceMouse]

I broke the headlight in my Proto 2K S1 when I put the DCC in. But now I have a bunch 3mm white LEDs. I figure I can use one in the switcher with a 1K resistor. Sound about right?

Typically the LEDs would run on 3-4.5 volts.

[Seamonster]

1K would be too high a value for that voltage. An LED typically operates at 2 volts and 20 mA of current. To calculate the value of the resistor, subtract 2 from the applied voltage and divide that answer by 0.02. Use the next highest standard 1/4 watt resistor value. For 3 volts, that would be 56 ohms and for 4.5 volts, 150 ohms.

[howmus]

Hi SpaceMouse,

If it were me (which it isn't), I would use 14v, 45mA Grain of Wheat bulbs. They will not require a resistor in line. By the way, I did the same thing when I put the reciever for the HO Train Engineer (got rid of that unit in a hurry) into one of my Proto 2000 0-6-0s. The directions to replace the bulb or put a resistor in line was evidently for other people, Duh! Turned it on and Blink!!! No lights! Back to the subject, I think the grain of wheat bulbs will give you better lighting than the LED's. You can also get a resistor test unit at Loy's Toys that you can put in line to see which resistor will be right for the application. The URL to the page with Bulbs and LEDs at Loys is listed below. There are many other places that carry the bulbs also.

http://www.loystoys.com/loystoys/bulbs-and-leds.html

[rrinker]

I like LEDs - especially Golden White ones. They look right and never burn out (unless you goof on wiring).

1K is fine for DCC. I use 1K resistors in ALL mine. GW LEDs are about 3.5v. HO track voltage for most DCC systems is 14-15v. Thus, 1K is fine. Runs the LED on about 11ma, which is about half it's maximum, and it lights MORE than bright enough. Actually, the Zephyr I have now only puts 12v on the track, and GW LEDs with 1K resistors are SUPER bright.

--Randy

[howmus]

Hi again!

SpaceMouse, you might want to check out this article just for info on bulbs and their applications.
http://www.wiringfordcc.com/gorhlite.htm#a16

Have fun!