I apologize if this has been asked and answered, but I have a lot of Atlas O track bumpers and I would like to wire an LED to each of them, powered through the track. I'm confused about all this talk about resistors and diodes to allow the LED's to work with AC track power. Can you make it simple for me? Thanks!
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On my 2 rail, power from one rail through a 270 ohm resistor to the red led leg out(either one) the other led leg to the other rail. My rails have 18 volts ac. I did not install a protection diode. Led bumper 3 years and going strong.
I'd still use a diode and probably a 470 ohm resistor, you're livin' on the edge. 
Thanks willygee. I'll give that a shot.
John, what do you mean "living on the edge?"
Pushing the specs of the LED's. Maximum reverse voltage for most LED's is in the 5V range, with an 18V transformer, you have negative peaks of 12.6 volts.
Thanks John.
gunrunnerjohn posted:I'd still use a diode and probably a 470 ohm resistor, you're livin' on the edge.
Now that i think of it it was probably a 470ohm...still no diode..i would follow GRG suggestions though.
All the advice is spot on, however, be sure to check the rating on the diode. The replies so far are assuming the diode is rated for a forward voltage of about 2 volts. Radio Shack sells a red diode with a forward voltage rating of 12v -- adding a resister will make this diode too dim for most model RR applications. Using it without a resister is okay but a standard 2v LED with a 400-500 ohm resister will be brighter. Here is a link to a video on how to make your own bumpers using spare RR ties.
The diode that RS sells has more than just the LED, it already includes the resistor. 
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