# LED and AC is there a way?



## ColenJacksdad (Aug 24, 2010)

Is there a way to wire up LED's to an AC current?


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## The Pod (May 19, 2008)

I have not tried this.

And would not recommend it. Although the above link may work, it would most definitely be alot safer to power your LEDs using a AC to DC transformer instead.


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## Jack Stevens (May 19, 2010)

ColenJacksdad said:


> Is there a way to wire up LED's to an AC current?


What are you trying to accomplish? A single LED or a string of them?

There's no reason you can't, as long as you take reasonable safety precautions. You have to keep in mind the voltage drop and current draw of each LED. If you are running multiple LED's, and the current draw on each is the same, you can just total the voltage drop.

OK, a single LED, red, typically 2.5v forward voltage drop, 100 ma. That gives you a current draw of 100 ma, or .1 amp. 120 volts AC is 120 volts RMS; you need to plan for peak voltage to keep from blowing the LED. If I remember my math correctly, to figure peak voltage given the RMS voltage, you multiply by 1.414, which gives you 169.68 volts; round that to 170 volts.

170 volts peak - 2.5 volts drop across the LED = 167.5 volts to drop, with a current of .1 amp.

You use Ohm's law to figure the value of the resistor you need; I found a brief description of that at http://www.play-hookey.com/dc_theory/ohms_law.html I've never used that site before; it's just something I pulled up in Google.

R=E/I, or R=167.5/.1, so the resistance value would be 1675 ohms. Round that to 1700 ohms.

I don't think that's a practical application, because to calculate the wattage of the resistor, you do P=I*E, or Power (Watts)=Current times Voltage, or .1 x 167.5, which is 16.75 watts. A BIG resistor. Use it for illustration only. I'd do a 20 watt resistor as a safety factor. A 10 ma draw LED would result in a 2 watt resistor, but it'd be considerably dimmer.


So, as I said, what's the application?


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## Vafik (Sep 28, 2010)

There are ways of doing this. My Xmas lights are LED and use just a standard plug for 120 AC. But the problem is when using AC and not DC is that the LED doesn't stay on consistently. They actually flash at such a high rate you don't really notice it unless you or the light is moving. That's b/c of the alternating current. If you plug some LED Christmas lights in and move your head from side to side you can kinda notice the flashing effect it gives off. Your best bet is DC "direct current" for a better result from the LED, it will be a constant on with no strobing. If your looking to light just one or two LED's, why not wire it up with batteries. Just hit up a radio shacks parts selection for LED's, battery holders, switches and resistors if needed.


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## ter_ran (Jan 14, 2006)

The Pod said:


> I have not tried this.
> 
> And would not recommend it. Although the above link may work, it would most definitely be alot safer to power your LEDs using a AC to DC transformer instead.


*I have done this AC to DC transformer/power supply hack many of times with items that require 3v(Props usually requiring two standard 1.5v AA or AAA batteries) and 4.5v(Props usually requiring three standard 1.5v AA or AAA batteries). It will work as long as you keep the wattage and amps withing specified output ratings. I actually buy alot of 3v, 4.5v and 6v DC power supplies used at my local flea market or swapmeet. Sometime I have been lucky and found a few at garage sales! Hope this helps! Best of luck to ya!*


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## Xane (Oct 13, 2010)

Make sure you test them with a multimeter before wiring them into anything important. If they're not "regulated" then if the amperage drawn is too low the voltage spikes. I bought 4.5v adapters from Parts Express and they tested out at about 8.4v after I melted a (luckily cheap, replaceable) LED light. The customer service was excellent and I had no trouble returning them. This was my fault, since the product description does not say it is regulated. I only mention the company name in case you see it on their website and are tempted to buy it since it's cheap (Radio Shack sells regulated 4.5v for $20 ) - I'm sure the product works fine for something that's explicitly labeled 4.5 v / 500mA.


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## Biggie (Jul 29, 2009)

This is why I have a giant box of AC/DC wallwarts in the basement, ohms law is your friend by the way. 

Get yourself an Instructables account if you don't have one yet, amazing DIY site. Used to be easier to navigate around, but everything is there.

http://www.instructables.com/id/Using-AC-with-LEDs-Part-1/

You can find Part 2, 3, and 4 in the sidebar


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