yeloglo white led's

[Anonymous]

I have installed the Yeloglo white LED in my locomotives. As I run them I realize when you switch directions on the locomotive the light goes out, (LED directional current). My question is do I have to install a regular diode to prevent damage to the LED when you reverse, thus reversing current direction?

[tstage]

David,

An LED is a diode and diodes only pass current in one direction.  You are not harming your LED in any way by running your locomotive in reverse.  You should, however, have at least a 1K resistor soldered inline to keep the LED was going poof.

If you are running your LED via a decoder, your blue (common) and white wires are connected to your front headlight.  To run the rear headlight, you would need to hook up your blue and yellow wires.

Tom

[Anonymous]

That is very interesting, because I am having trouble with the LED burning out, and I am using the supplied 470 OHM resistor for 10-16 volt operation but that seemed really low to me. It is a 3-4 volt LED.

[river_eagle]

white leds {and their dyed brothers, golden/sunny whites} are a bit more finicky then the standard red/yellow/green versions, and you should have either a plain diode to stop reverse power spikes from the motor, or if you have leds for both foreward and reverse lights they protect each other for DC operation.
in DCC the decoder provides reverse protection for the led
reverse voltage spikes can damage white leds.
I generaly use 3 volt leds with 470 ohm 1/4 watt resistors, but sometimes sub a 560 if I want dimmer lights for numberboards and such.

[tstage]

David,

I knew I should of asked you before.  Are you running DC then?

Tom

[Anonymous]

Yes, I am running straight dc right now, I took the advice of both gentlemen, I put a 1k resistor inline, and a diode to protect it from reverse current. As soon as the LED went out when I changed directions I realized a few things about electronics I have forgotten from years ago. We will see now if any of them burn out. Thank you guys for your responses.

[rrinker]

 DEFINITELY protect the diode from reverse voltage. The white varieties are especially unable to handle large reverse voltages, especially over the long term.
 Yes, a diode only allows current to flow in one direction. However, when that same current flows the opposite way, think of it as a dam. The water piles up behind the dam. If too much piles up, the dam bursts (LED is damaged).
 When there are two diodes connected anti-parallel, so that one is one when the current flows one way, and the other is on when the current is reversed - all is fine, nothing extra needed. So in a DC loco, if you have something connected like this:
           
              |----<resistor>---<led>----|
left rail---|                                         |---right rail                                       
              |----<resistor>---<led>----|
 

You don't have to worry about it - current will always flow through the path of least resistence and the LED that is off (reverse-biased is the technical term) will not be in any danger as the second LED will be conducting.

                                                     --Randy

[tstage]

Randy,

It's always good to have you around to further explain electronic stuff.  I always learn somethin' new...

Tom