Installing LED's

[chad thomas]

LEDs don't have a voltage rateing. They are current dependant. And they can be dimmed by lowering that current with a variable resistor. Be sure and use a 470 ohm resistor (yellow-violet-brown) in series with the variable (5K ohm should suffice for the variable) to protect the LED (assumeing 18V source). It dosen't matter which side of the LED you put the resistance as long as it is in series. The polairity of the LED power does matter but if you hook it up backwards it will not harm it, it just will not work. You can also use the AC output of the power supply, then polairity will not matter, the LED will only light up dureing the right polairity of the cycle. The blinking will be much to fast for the human eye to see.

[rrinker]

 Be VERY careful witht he variable resistors. Most typical colored LEDs are about 2.1 volts, most hite types are 3.1-3.5 volts. You need at least that much voltage, plus a resistor to limit the current - ALWAYS. The variable resistor will be easy to drop below the minium required for a safe current limit - and poof goes your LED.
 The only way to really 'dim' an LED is to modulate the power to them. Instead of constant power, you use a circuit to turn the power on and off. The closer the on time approaches constantly on, the brighter the LED appears. This technique actually works very well.

                                           --Randy

[Vail and Southwestern RR]

The anode goes to the positive side, most likely the red wire, but it would be good to verify that.  Don't forget to put a resistor in series to limit the current, or you may blow the LED almost instantly.

Google is your friend:

http://metku.net/index.html?sect=view&n=1&path=mods/ledcalc/index_eng

 

[rudywa]

OK I got some info on the site with the PDF from Tony's here is the simple question...I have a red and a black lead coming off a 12v dc power adapter, i.e. radio shack type with the plug cut off...how do I attach the anode, cathode? Anode being the longer wire. And the positive.

[Anonymous]

Although I have not tried it, I bought a bag of variable resistors from radio shack for less than $5.00 for 20.  I 'm going to try them out by hooking them up to an LED to see if I can vary the resistance and dim the LEDs oight output.  Most LEDs work around 1.5 volts so I'm using a 0 to 100k ohms resistor to get the output I should need.  I'll try this out & see what happens.  Tweet

[Blind Bruce]

Rudy,

What the boys said is absolutely correct. I also want to point out that each diode has a maximum current that it can handle. If you do not know this value, start with a very large resistor like 2.2k and work your way down in value till the desired brightness is attained. The more current that you put through the diode, ie less resistance, the brighter it will glow UP TO A POINT! Then it will destroy itself.

BB 

[MisterBeasley]

Also, LEDs are not "omnidirectional" light sources like incandescent bulbs.  They put out a fairly tight "beam" of light.  This makes them ideal for headlights in locomotives, but less desireable for interior building illumination.  You could, of course, mount the LED pointing straight up and put aluminum-foil "mirrors" on the ceilings to bounce the light around inside.

Also, standard LEDs are a very white, "hot" color.  The yellow tint of incandescents is far more natural inside a building.  You can get the "golden white" LEDs, but they're more expensive.  (The make very nice loco headlights, though.)

[stokesda]

Rudy,

If you want lighted buildings, you might be better off using incandescent lamps instead of LEDs. The disadvantages of LEDs for applications like this are that are that light from an LED is directional, which means that it's focused in one particular direction rather than giving off an equal amount of light in all directions. That's why it's good to use for flashlights and locomotive headlights, but might not be so good to use for lighting a room. Also, white LEDs are kind of pricey and put off a bit of an "unnatural" bluish light. There are "yello-glo" LEDs available, which put off a more "realistic" white light, but they are usually even more expensive than the regular white LEDs.

All the same, if you want to get some good basic info on LEDs and their use, take a look at the following:

http://www.tonystrainexchange.com/technews/install-leds-decoders.htm

www.richmondcontrols.com

 

[Anonymous]

If you are asking, can I dim LED's, the answer is not much.

For the most part LED's are either on or off. They require a minimum voltage to 'fire'.

Generally a 750 to 1000 OHM resistor in series with the LED is required when using up to 12 volts dc or so. The large value of the resistor will allow some dimming but no way like a incandescent bulb.

You can experiment with the resistor value but do not expect a big difference in the output of an LED.

[mikesmowers]

   rudy,  LEDs are not dimmable as those in yout buildings. You will need to hook them up through a resister depending on the voltage of the LED what size of a resister you will need, also keep in mind that a LED (Light Emitting Diod) Is a diod and the current will only go through in one direction What voltage is your power pack and what voltage are you LEDs. Let us know some more details and we can certainally help you.    Good luck.     Mike

[rudywa]

OK, I know very little about LED's I would like to use them for special effects on my layout, question is; are there simple beginner's instructions on the web for rookies to learn how to hook them up?, I was thinking of using a spare power pack that I light up my buildings with small bulbs now on the DC side so I can dim them to look more realistic. Any ideas about beginner instructions?