I just installed an NCE D13SR decoder in one of my HO gage P2K FA's and replaced the headlight bulb with a 12vdc LED as I do in all my installs. The LED won't light and even after trying a second one, still no light. Finally I decided to test the voltage output from the blue and white/yellow wires on the decoder, thinking it may be 1.5 - 3.0 volts. They both were at 13.6 volts. Is this normal for NCE decoders? I didn't see anything in the literature stating voltage output. All of my other decoders; Digitrax, Soundtraxx, and Soundtraxx Tsunami work with the 12 vdc LED's.
-Bob
Life is what happens while you are making other plans!
Function output on NCE decoders is 12-13 volts. There are no 12v LEDs. Some may have factory installed resistors but they all must have resistors.
Jay
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That is normal for many decoder, 12 to 13 volts. All the decoder instructions I have seen are like that. The ones with 1.5 volt and three volts for LED's spell it out. I just looked at the PDF for that decoder. Seems very clear.
Either you burnt out the LED's are have them wired in reverse.
What is the brand of 12 volt LED's? I have not seen any for sale yet.
Rich
If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.
Perhaps you have the LED polarity backwards. An LED won't light if it is not connected to the correct polarity.
The LED's I use are from LED-Switch Co. and they sell online and on Ebay. I have used them in many of my locos and they are 12 volt, with built-in resistors. They look just like a normal 3mm LED. I will check the polarity on the one installed now. I could easily have switched the wiring when soldering them. Here is a link to the 12 volt LED's.
http://www.led-switch.com/12%20volt%20LED.htm
You guys were right, I had the LED wired backwards! Don't know why I did that, I have installed dozens of LED's and never thought I had it backwards? Thanks again,
Just for the record, aside from decoders with regulated 1.5 and 3 volt pads, a decoder's function output if 1.5 volts less than the track voltage. As not every system puts the same voltage to the rails, it's always a good idea to find what your system puts out.
Some systems put out around 18 volts on the rails which would give you around 16.5 volts on the function pads. The majority of systems will have closer to 14 volts on the rails which would give you around 12.5 volts for the function outputs. This can be very important if you are using bulbs.
Mark.
¡ uʍop ǝpısdn sı ǝɹnʇɐuƃıs ʎɯ 'dlǝɥ
Mark,
That is a good point, I have been using 12 volt LED's for my headlights and never checked the actual voltage from the function wires. 13.6 volts may be pushing the limit on a 12 volt LED? They are bright but a warm white. I haven't had one fail yet so I guess they operate OK on a little over their rating.
-*Bob
Do they specify what resistor is in them to make them "12V" LEDs? I'm willing to bet it's somewhat less than 1K
Probably still OK though.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
Randy,
I contacted LED-Switch and they said they thought it has a 500k resistor built in and they were rated for 12-15 volts. This was just an email response, no documentation.
farrellaa Randy, I contacted LED-Switch and they said they thought it has a 500k resistor built in and they were rated for 12-15 volts. This was just an email response, no documentation. -Bob
500 ohms maybe, but definitely not 500K (500,000 ohms) !
Sorry, that was 500 ohms, not 500k?
If the LEDs are 3.5V drop like most white LEDs, I wouldn;t go above 16V to those if it's a 500 ohm resistor - that's right at 25ma which is usually the limit for white LEDs.
I have about 12 of these in my locos (some are backing lights) and none have burned out yet, but I am assuming they are all running about 13 volts. What I like about them is not having to fit a resistor in where there isn't much room and they have a nice warm white color. I do like some of the yellowish headlights on a few of my Spectrum locos but they aren't as bright.
Just when I thought all was good, the decoder wouldn' t fit with the body shell installed. Had to replace wiith a Digitrax DZ123, but now all is good. The older FA's with the motorized fans don't have much room left unless you cut the weight off.
Take out the fan mechanism and just attach the fan blade to the roof, you can't hardly see it turn anyway.
Good idea Jay, I may do that on my second unit (A-A). Will have to see how much room is left with the mechanism removed. The NCE decoder was too long to fit at the other end behind the cab wall.
Is this output 12V AC or DC
Mike Dickinson
MichaelWD Is this output 12V AC or DC Mike Dickinson
A decoder's function outputs are DC.