Running 12 volt "stuff" with computer power supply

[kickngas]

I am planning on tapping off the computer power supply to run my LED's on my CP buttons.

[MrSaLTy]

It really depends on how many LEDS you want to run.... most LEDS draw about 20 ma.  Look at your power supply and see what the rating is on the +12v rail and try to guess how much you computer draws and see how much room you have..... my guess is you can run quite a few.  You can also run them off of the +5v rail also but you just need different resistors on them.  Your power supply should be rated in amps and 1000ma=1amp.

[tristan]

The amount of power draw would be negligible on most ATX power supplies, even running 24+ LEDs. I've wired up UV LEDs inside a computer, and I've never even thought about how much power they use. I do tend to use quality power supplies though, and newer CPUs and chipsets require a good amount of 12V power.

[Bill Mote]

So, you're tapping into the orange lead that goes to the motherboard?  You're not worried about that at all?

Also, can anyone provide the formula for figuring out which resistor(s) to use for any given LED setup?

dot

[88mph]

So, you're tapping into the orange lead that goes to the motherboard? You're not worried about that at all?

I just daisy chain onto one of the power connectors going to one of my hard drives.  The yellow wires are 12 V.  Nothing to worry about there.  I wouldn't mess around with the big connector that goes directly to the motherboard..

-88mph

[MrSaLTy]

You can use this page to figure out your resistor value assuming you know the forward voltage for the LED and its current rating.

http://linear1.org/ckts/led.php