# LED light help



## jgbeerman (Jan 6, 2010)

Evening Y'all-

I have some buildings all set to be lit up but I know nothing about working with LED lights. Does anyone know of a good source of information that could teach me how to install and work with them. Just want to make sure I do it right since the electrical part of this is my weak point.

Thanks


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## NIMT (Jan 6, 2011)

If you search LED on here you will find a ton of information to help you out!


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## T-Man (May 16, 2008)

Just buy a string of white LED Xmas lights.


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## jgbeerman (Jan 6, 2010)

Yeah I have decided to go with Xmas light strand but after that I am lost. Do I just cut them apart and extend the wire or do I pop the LED out and the solder the wire? And what is this business about resistors? Just trying to figure it out so I don't burn them out.

I read the wiki page on LEDs so I have a very basic understanding but not any specifics.


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## T-Man (May 16, 2008)

Use as is and just extend the wires. Don't cross them. That is the easiest way.

Read the 
post#8


Led use

Led revisited


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## tankist (Jun 11, 2009)

JB, if we know what is it you want to accomplish we can provide better answers.

as asked the answer is simple: get some leds from whatever source (xmass lights, old toy laying around, etc ), wire them to old power brick/cellphone charger, use led calculator (or this led array calculator)to calculate the current limiting resistor (mandatory).


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## xrunner (Jul 29, 2011)

jgbeerman said:


> Does anyone know of a good source of information that could teach me how to install and work with them.


Yea - the internet. 

It's simple - just Google LED tutorial or LED basics or any terms like that and you'll come up with a massive amount of beginner tutorials information. I don't mean to sound flippant, but it's really that easy to find info.


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## jgbeerman (Jan 6, 2010)

Ah tutorial, that was the term I could not think of last night!

Thanks for the input everyone


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## jgbeerman (Jan 6, 2010)

tankist said:


> JB, if we know what is it you want to accomplish we can provide better answers.
> 
> as asked the answer is simple: get some leds from whatever source (xmass lights, old toy laying around, etc ), wire them to old power brick/cellphone charger, use led calculator (or this led array calculator)to calculate the current limiting resistor (mandatory).


Tankist thanks for the information. What gauge wire would you recommend or does that not matter as much?


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## tankist (Jun 11, 2009)

does not matter at all, the smallest you have available : phone, network, old headphone wire, etc


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## gunrunnerjohn (Nov 10, 2010)

I use #32 wire-wrap wire for most of my LED lighting. It's more than sufficient for the current, and the small wire makes it easy to hide and route.


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## [email protected] (Jan 30, 2012)

Your Christmas strings are AC powered. You can cut and splice all you want. Just keep your pairs organized. I've also found some .89¢ LED flashlights and reading lights that work well.


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## gunrunnerjohn (Nov 10, 2010)

Actually, while the tree strings are AC powered, when you chop them up, you remove the structure that provided protection against reverse voltage for the LED's.

I think you need to decide how many LED's you need in a building, then work from there.


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## jgbeerman (Jan 6, 2010)

Okay quick update with a few more questions. I have done some reading and generally understand how to wire the LEDs and calculate values with Ohm's law.

What I am concerned with now is the actual power supply. All the articles I read talked about running the lights on a DC power supply. Any reason for the DC use and not being able to hook it up AC accessory?

Any recommendations for a power supply? Also do you generally do one switch for the whole layout or one per building?

Thanks again


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## [email protected] (Jan 30, 2012)

I will do some reading and experiments on this. I know that the little 2.4V bulbs have a shunt in the base that allows the series circuit to still work even with burned out lights. I have seen strings working with only four or five lamps lit. By, 'cut and splice' I mean that you can extend or shorten the length of wire between bulbs as long as you maintain circuit integrity. I have hundreds of old strings. I will get out the lineman's pliers.


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## T-Man (May 16, 2008)

If you use the string lights ,as is, a power supply is not a problem. All you need to do is extend the length of the wires. A 15 or 30 bulb string will go far.

You can power them with anything you want. It all depends on how you want to wire them. In ac when the are wired back to back they blink, but it is so fast you cannot see it.
Generally the LED is low amperage at .02 amps. S0 that is 50 bulbs per amp.
WHen the transformer breaker activates you have gone too far.


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## jgbeerman (Jan 6, 2010)

T-Man that makes a lot of sense just to add some extensions in instead of cutting it apart. This way I can just plug the strand right into the wall and just add a switch to it turn the lights on.

Fantastic! Thanks!


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## fotoflojoe (Dec 31, 2011)

I use old computer ribbon cables (floppy disk, IDE Hard disk, etc) for wiring LEDs. Having worked in IT, I've got tons of them laying around. Simply peel off what you need - just like a pack of Twizzlers. One cable can yield up to 24 pieces of wire 18 inches long. More than enough for most projects.


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## gunrunnerjohn (Nov 10, 2010)

I have tons of ribbon cables as well, but the wire-wrap wire is really fine and very easy to hide. It's also a lot more "workable" than the ribbon cable strands.

I have a ton of WW wire left over from a former life as well, so I'm all set.


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## Mike S (Mar 6, 2012)

You should have no problem running the LEDs off of an AC source like that. As LEDs are diodes, and diodes can be thought of as a 'one-way valve' for electrical current, you will only have to ensure that the orientation of all of the LEDs is the same.

Make sure you limit the current provided. One LED running on a 20V source should have a 1K ohm resistor (brown-black-red colour code) in series with it to limit current to 0.02A.


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## gunrunnerjohn (Nov 10, 2010)

Mike, you're forgetting one little detail. LED's have a reverse voltage maximum, typically in the 5-7 volt range. Running them off 20 volts will be hitting them with roughly 28 volts reverse voltage, far in excess of their ratings. LED's don't behave like traditional diodes, they have some unique properties.

In these scenarios, I recommend either a series diode or wiring dual led's with opposite orientation in parallel. LED's wired this way protect each other from reverse voltage.


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## Mike S (Mar 6, 2012)

Ah...good to know! Don't (really) have to think about the reverse voltage when you only play with DC...


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## T-Man (May 16, 2008)

Of course you do!!!!!!

How do you reverse an engine???

You switch track polarity and reverse the voltage. 
You must have DCC, How quickly these converts forget.

I don't mean to get on your case, so forgive me.


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## Mike S (Mar 6, 2012)

I was referring to reverse voltage across an LED and not having to worry about that when only using DC with LEDs...though I see the ambiguity in how I said it!


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## T-Man (May 16, 2008)

I find it interesting on how many ways there are to wire them up. On my table I show examples on some.

Here is the ac set up











A rail DC setup. . 










The motors have voltage spikes and a capacitor helps


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## gunrunnerjohn (Nov 10, 2010)

T-Man, the cap would be an even more effective spike suppressor if you put it after the resistor directly across the LED.  That way you have the resistance of the resistor to balance against the impedance of the cap. I'd recommend a tantalum cap for the application.


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## T-Man (May 16, 2008)

That sounds great. The motor mounted LED without any power supply for chips has always been a problem. They just don't last. 


How small of a cap can I use?? This is for DC HO operation.


I have them in the pci range from a batch I bought. They are really small.


The picture was made up from a previous discussion so it was an improvement over anything I had before.


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## gunrunnerjohn (Nov 10, 2010)

You can probably get away with 1uF tantalum caps, they would present a pretty low impedance to a fast spike. It also depends on the value of the resistor, obviously the larger the resistance, the more effective a given capacitance will be. For noise immunity in many aerospace applications, I used to use 10 ohm resistors and .1 ceramic caps. That knocked down most of the high frequency spikes pretty well. I'm thinking LED's with their low reverse voltage immunity might want a little more protection.

Another effective protection for an LED is a reverse protection diode across it. Both would probably be great protection.


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