adding led lights on the side of fast track

Looking up your track piece, I don’t see any resistors.  The experts will help I’m sure.  The component identified in the pic is a diode that changes the center rail AC power to DC to power the leds. Size is to your taste.

TEDW, I don't know much about these things ,i thought it was a resister ,however i would like to be able to do this project just to give me something to do can you give me some idea of what size diode to use & does it matter which end gets hooked up to the center rail?

There should be a resistor somewhere.  If all those LED's are in parallel, with just a diode and 18 VAC on the track, those LED's will be launched into the middle of next week!  Parallel is a bad way to use them anyway, I'd wire strings of four in series with a small resistor and diode for each string.  That way you could balance the phases and not impart a DC bias on the track.  Imparting a DC bias on the track can't be a good thing, even for command.  You'd also use 1/4 the current with them in series.  I'd also probably add a 22uh choke somewhere if you run DCS, just to insure you don't screw up the DCS signal.

If you are running conventional locomotives and no command, you're going to have fluctuations in the voltage and brightness of the LEDs as you move the throttle up and down. To get near full brightness you have to run your trains at warp speed.   In any case, the easiest way to do that would be to just run an external power source to those LEDs. Use a diode and  run all 8 in series.  

I like TRAIN NUT'S idea about an external power source ,which i already have near where i want to put these led's ,i had forgot about that power source which i use to power some led's that i have running up both sides of two bridges on my layout ,tell me if this sounds ok to do ,i will order the pre-wired led's with the resister already  on each led & then hook them up positive to positive ,negative to negative ,is this what is called in series?, then  to the 12 volt dc power supply that i already have on the layout ? ,is this ok to do like this ?

If you use an external power source, the lights will be on when the external source is on, not when power is applied to the third rail; which I thought was your original idea.

LED's should ALWAYS have some sort of current limiting unless you are controlling the voltage to them to stay precisely within the narrow range of voltages so that the LED's run withing their ratings.  Typically, a series resistor is used to provide the current limiting.

With the pre-wired ones with the resistors already in place, you'd likely have to wire those in parallel as they're already current limited for 12VDC.

Dave ,you are correct that was my original idea ,but when Train Nut mentioned the external power source ,that sounded like an easier way for me to do it since i already had the power source there ,now for what may sound like a stupid question how do you connect the wires to run in parallel ?,& one more thing i want to mention is the external power source is a 12v,30 watt led driver which is currently supplying power to 11' of strip led's ,would this be able to power about 25 more led's & it is hooked up to a dimmer also.

Gerald Marafioti posted:

...if this sounds ok to do ,i will order the pre-wired led's with the resister already  on each led & then hook them up positive to positive ,negative to negative ,is this what is called in series?

GM,

What you describe is a parallel setup with all +'s together and all -'s together, then connect the all + to the +12V and the all - to the -12V

With a 12V DC power supply, and LEDs with resistors already built in to each one, you want to parallel connect the LEDs.

What is the effect you are looking for with lighted track?... just wondering.

EDDIEM,I am just looking for something to do on the layout, i want to put these lights in the middle of the 2 main line tracks under the 2 bridges i have ,i get bored when i have nothing to do it doesn't matter to me if it has a purpose or not ,i enjoy doing these things but with my very limited knowledge it is hard for me to do things so i try to get as much help as i can from the forum ,they have been very helpful to me in the past .So if what i described is in parallel ,can i just connect these to the 12vdc 30 watt driver that i have described above ?

gunrunnerjohn posted:

LED's should ALWAYS have some sort of current limiting unless you are controlling the voltage to them to stay precisely within the narrow range of voltages so that the LED's run withing their ratings.  Typically, a series resistor is used to provide the current limiting.

With the pre-wired ones with the resistors already in place, you'd likely have to wire those in parallel as they're already current limited for 12VDC.

With a  8 LEDs wired in series with a diode there is no reason to have a resistor in a circuit up to 18 volts.  No need to use LEDs with a built-in resistor either.  A plain ordinary $0.02 red LEDs are all you need. Looks like he says he's going to run on a Max of 12 volts so 8 leds in series with a diode would be fine. If he's using a 12 volt DC power supply no need for the diode either. Just wire them up in series and you're done.

To answer his question on series versus parallel.   Series is when you run the negative of the 1st led to the positive of the 2nd led. The negative of the second led to the positive of the 3rd led and so on. The last diodes negative would go back to your common terminal.

I don't understand why all this misinformation!  Do you know about the characteristics of LED's?  Here's the voltage/current graph for a typical red LED.

Note that at 2.0 volts the current is at the rated 20ma.  However, at 2.1 volts, the current has already skyrocketed to 40ma, twice the current rating of the LED.

In addition, if you string eight red LED's in series and connect them to 12VDC, they will light very dim, or quite possibly not at all.  12 / 8 = 1.5 volts on each LED.  Note the graph, at 1.5V the LED isn't drawing any current, thus it isn't producing any light.

LED's should last your lifetime if you don't abuse them, but I see people complaining about LED's burning out faster than incandescent bulbs, misusing them is the reason why.

Yes, I was not factoring in red for the color.  Red being one of the lower forward voltage LEDs, one 150- 200 ohm Ohm resistor wouldn't hurt.  However 18 volts with a red LEDs and a diode which reduces the voltage .6 - .7 volts,  plus the resistance of the wiring,  would not be a catastrophe. Would it shorten the life of the bulbs? Possibly? But it sure as heck wouldn't cause a catastrophic failure.  Add two more bulbs and he'd be absoluty golden!

It sounds like there is some confusion even among the experts ,so this makes it a little more difficult for me now ,this is what i think i am going to do ,i will order the led's with the resister already wired in ,then i will connect all the positives together ,then i will connect all the positives from the led's to the positive from the 12 volt dc power supply,then connect all the negatives from the led's together & connect them to the negative from the 12 volt dc power supply ,is there any reason this won't work ? If it won't work what am i doing wrong?

If you want the trackside LED's to come on with constant brightness when track voltage is applied, I would first rectify the AC track voltage and then run it through a 5VDC or 12VDC fixed voltage regulator chip followed by the correct resistor value to keep the LED current within the proper range.

Bob Walker, I have a dimmer switch on the control board for the bridge led lights ,this is where i would hook up the track side lights to this is the easiest way for me ,what you have suggested is a little over my head right now ,thanks anyway .

Here is a wiring diagram arranged for 8 red LEDs using a combination of serial and parallel circuitry. It is setup for 2 volt LEDs at 20ma each. The supply voltage is 12 volts. It requires 2 resistors of at least 220 ohms (use a higher value to reduce the brightness of the LEDs).

If you decide to get the LEDs with the resistors already attached, then you would wire them all in parallel as you have described.

CONSOLIDATED  LEO,  I will order the led's with the resisters ,this i think is the easiest way for me even if i should mess up the led's are not expensive ,so it wouldn't be a big loss but iam confident everything will work out ok,i have printed out your response & some others for future reference,one thing i will do is i am going to order a separate dc power supply,rather than using the one i have it will have enough power for more lights in the future if i need it. I will post how everything works out when i am done ,thanks to all who responded .