This instructable will show you how to make an external ATX power supply.
Now many other people have done something like this before, mine is different in the way that the power supply is replaceable and the case and many of the parts came from an old computer (yay recycling).
As you can see, the main reason why I built this is to power my camera for some time lapse and some long exposures, something the batteries just coulden't do.

Step 1: Parts

Ok let's get started. You will hear this alot in this 'structable but if something isn't clear in my pictures or my description, check some other great people that have done ATX mods, their instructions are better than mine.

Now, parts, I just went to the shack and grabbed all the stuff I needed, you can slowly gather the parts from used audio amps and stuff, but I kinda needed this to work soon so I just bought it. Total cost was near $25 but I had a few of the needed parts already.

You will need the usual 10ohm 10watt sand resistors
LED's
Solder
a switch (I made the mistake of buying a lit switch, the extra load to light the switch won't turn the PSU on, so get just a regular switch. As an override, I just shorted out the terminals, I'll get a different switch later)
other random stuff, you should probably read through this whole thing before starting your project.

Step 2: Starting the Build and Cutting the Case

First up is the case, I just took an old cd drive and removed the metal housing, makes a nice project box.

Then the ATX connector from an old busted motherboard. A big tip for removing the connector, do it pin by pin, take the plastic thing and just pry it off the board, then you are left with a bunch of metal pins, then de-solder and remove them, then push them back into the connector, some of the pins might not fit very well, just add some superglue so they don't fall out when you plug in the connector.

And finally the heatsink from the smaller section of the motherboard... you'll know what I'm talking about when you look at it.

Ok now, you got your parts and now you need to cut the case, draw out how you want it and take your cutting tools (dremmel, drill, zip saw, file, whatever) and chop the holes.

Step 3: Attach All Your Stuff

So connect all your wires and stuff.
The led's just pop in, so does the switch.
For the ATX connector, I put it in the hole and put some JB weld along with it to keep it there.

The terminals are a bit special, I noticed that just putting them in, the metal case would conduct electricity and short everything out.
So I took a bit of plastic tubing (also called weedeater gas line that I meant to install in the trimmer last season)
And used it to insulate the binding posts. (see pics)

Also check out the pic with the heatsink. You might have to drill out the holes at the edge to make the bolt fit through, as you can see it just is right on the resistor.

Step 4: Solder Your Wires (ZZZzzzz...)

Yes this is the most boring part.
But first, you have to decide what voltages you want, i only had 4 posts so I can have 3 different voltages. If you get more posts, you can add more voltages, you can also just add more if you want (which I intend on doing later)
I chose 3.3 (for my camera) 5v (kinda like a half dead 9v) and 12v (need to run an old CB radio and test car radios)
There are plenty of other instructables that will show you how you should wire up your switch, and which color of wire does what, I'm not going to repeat that here. That's what science is, if it works, you don't have to keep doing the same experiment over and over just to prove to yourself it works. (E.G. the baking soda and vinegar experiment, EVERYONE knows that works, and yet they still have kids figuring it out)
/rant
Ok now get to soldering, I salvaged my wire from an old christmas light set.

Step 5: Finished and Final Remarks

Ok, your done, close up your box, put some screws in it. And brush away the dust.
Test (using resistive setting) each terminal to the case (if it conducts, re-do the tubing and make sure it's insulated good)
The case is NOT ground for one reason only, if the case was ground and a voltage terminal came loose, it would short out. Now since the case is not grounded, then a voltage terminal can come loose without messing stuff up (just test it every now and then)

I ran it all night and it was fine, I pointed the PSU exhaust down the inside of the case to make sure the heatsink stays cool. Even without it I would say it's fine. I might throw an old laptop fan in there just to make me sleep better.