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Makers and Making: LED Home Lighting convert 120V AC to 12V DC?
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djmorice
Mar 31st 2009
So I want to make a cool light for my dining room at my new house and I wanted to use LED's. But, I would really like for it to work with my light switch. So basically, I need to figure a way to convert 120V AC to 12V DC for the LED's. I plan on keeping it installed at my house, so it needs to be safe too.

This is my first project like this, so this might be a newbie question. But, could someone help me out?
Odin84gk
Apr 1st 2009
You have two options: Use a 12v wall-wart style plug.
Or, you create a resistor-divider to step it down.
The 12v wall-wart might be the best way to go if you are unfamiliar with electricity.

A better suggestion would be to buy some LED Christmas lights.
 Stokes
Apr 1st 2009
Here's one instructable that uses the reactance of a capacitor instead of a transformer or resistors:

http://www.instructables.com/id/AC-Powered-White-LED-Circular-Magnifier-Work-Lamp/
Odin84gk
Apr 1st 2009
That one took me a minute to remember my basic circuits:

Rcap = 1/(2 * pi * frequency * capacitance)
Rcap = 1/(2 * pi * 60 * .47uF) = 5643.8 ohms
Current Through LED's = (Vac - (VdropLED *NumberOfLEDS))/impedance
Current Through LED's = (120 - (1.6 * 15))/5643.8 = 17mA
Peak Current = (120*sqrt(2) - (1.6*15))/5643.8 = 25.8mA

So, yes, a capacitor would be an acceptable alternative. Remember to use a poly film or ceramic cap, and not a standard polarized electrolytic.
 Stokes
Apr 1st 2009
Heh, I had to do the same thing... I was originally baffled by the schematic.
jschuch
Apr 6th 2009
*LOL*

So was I. 8-)

That's cool, but you'd still be monkeying around with 110VAC. Personally, I'd find a used laptop power supply.

John
Makerdino
Apr 6th 2009
Buy an adapter that screws into the light socket that has a 110v plug socket in it from a hardware store. Plug a small 12 volt power supply into it, then wire up your lights to the When you flick the switch it energizes the power supply and your LEDs turn on. Simple, and it'll cost you less that $20. :)
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