Hi everyone.I have an Atlas Master series GP40 with the dual mode #342 decoder. Works a treat and is a superb locomotive. I wanted to add some ditch lights, but before that I tried researching about the decoder and found there are function C & D outputs for exactly that purpose.To test these I first clipped on some LED's (with 1K resistors) onto function C&D outputs and set the necessary CV's. They worked fine. I really wanted to use some grain of wheat lamps I had so I next clipped on some 12v mini lamps directly. Things worked great for a few minutes before one lamp stopped working, after another minute or so the other stopped. I removed the lamps and checked them out with a battery and they were fine so the problem seemed to be on the decoder. I went back to the LED's and they worked but were now very dim now. I checked the voltage out of the C&D pins with a meter and I seem to be only getting around 2~4V. It was definitely higher before as the lamps and LED's were much brighterAny thoughts on what I have done to the decoder? Did I overload something? The lamps are 12v 60mA, so I think those and the function A & B LED's should be around 150mA the manual says is the max.
I am somewhat electrically competent btw. So this is not a simple mistake of wiring things up incorrectly.
Thanks all!Sean
Sure sounds like you overlaoded the function outputs. On caveat on light bulbs - they ahve a high inrush current when cold. They might draw 60ma lit, but when first turnign on they can draw a lot more, which is why some resistor is often suggested even for bulbs rated at the full decoder voltage.
Also check the decoder ratings. There are usually 2 for functions - one is the max per function output, and the other is the max for all functions combined. For example, there may be a 6 function decoder with 150ma per function but 500ma total - so while on any one function you have have a 150ma load, you can;t have that much on all six of them.
If you still want ditch lights, you'll probably have to repalce the decoder. Check out one of the TCS ones, which have settings to handle LEDs for effect lighting, they'll work very well with LEDs and still have a nice flashing effect. The 'dim' setting on TCS decoders is adjustable so that it actually can dim or turn off an LED. Their instructions show suggested values for using LEDs or bulbs.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
Thanks for the prompt reply Randy. I dropped the resister value and used 3mm yellow LED's and the lights work fine. Still not as bright as before or as I would like of course, but I have something that works. I will definitely take you up on the advice of using resistors with bulbs going forward. Sure doesn't look like there are any "user serviceable" parts there!