I bought some 3mm white LEDs to use as loco lights. Now, as I understand it, LEDs are only supposed to work if I put the positive on the LED's positive lead and the negative on the negative lead. But these are working regardless of whether the positive or negative are placed on either lead. So, do I misunderstand how LEDs work or are mine magic? Thanks.
Led's have an Anode + and a Cathode -. The shorter lead is the Anode. The led will light with Positive DC on the Anode and Negative on the Cathode. All the Led's I have work this way. If you are using DCC power to test the Led's they will light either way as the DCC power is AC. Are you using the correct resistors for the voltage you are using?
Yes, the series resistor is very important or your LED will be destroyed. I like to use about 1000 ohms. On DCC the LED will only be "on" half the time but it switches on and off so fast your eye can not detect it. I have noticed on the new LED Christmas light that they sell, that if you have a string bunched up in your hand, plug them in and wave them around in the dark, you can see the flashing. However that is 60 cycle and I believe DCC is much faster.
My LEDs won't work unless the Cathode/Anode rule is respected. I didn't know that the leads were different lengths, thanks for the tip retsignalmtr. I have been looking at the shape of the device in the bulb to get the polarity right. Only install experience has been some drop-ins and 4 hardwires Z2s in an N-scale engine. The drop-ins I can only guess that the LED is correctly installed and I have no idea how the juice is conditioned and fed to the LED. For the wire-ins I installed 1x480ohm resister in the blue common return wire for both head and tail lights. Another wire-up example from internet showed one resistor in the white and one resistor in the yellow and no blue wire resistor. Not knowing enough to figure out why one way or another. In short, cannot understand how you could get light from the LED w/o matching anode/cathode rule.
Oh yeah, the headlight/backup light outputs of a DCC decoder should be DC. The blue is around +12 volts and the white or yellow will go to ground when they are activated. I was thinking of applications like in passenger cars where there is no decoder and the power goes directly from the rail to the LED and resistor.
I'm sure I've seen this once or twice in the past. I often salvage stuff and test the LEDs to find out which way is right. I have had the odd one that worked both ways, though I think they were somewhat dimmer in the 'wrong' connection. As well as having different length legs some round LEDs (the dome shapes with a flange at the bottom) have a flat section in the flange next to ... either the cathode or anode :embarassed: (like I said, I'd test it and then know which polarity the flat was to be when I wire it in.)
