*A MOT can kill you instantly or give you a really nasty shock and they are not toys, I have been shocked by one and it was freaking scary and painful so BE CAREFUL! i am not responsible to any damage caused!
Step 1: You Will Need
A light switch
A inlet from a computer power supply or something like it
A PFC capacitor (optional). 20uF at 250V+ should work just fine
Some .250" female spade connectors (bag of 50 for $2.20). You will also need some smaller ones for the inlet but I don't know what size
Some 14 awg wire. Speaker wire or an old power cord will work just fine
A 12" piece of 2 x 4
A soldering iron and solder
Some screws. I used #8 x 1/2" screws from Home Depot
Step 2: Position the Transformers
The first, and main thing to position are the transformers, everything else will be built around them. I prefer to put them on the right hand side of the board and have the all the other stuff in the left side. I put them primaries connections facing the back and the secondary connections facing the front. As you can see, the two transformers I am using are very similar except on has a small lip sticking out the side so I put this one on the left so the other transformer will over lap it and cover it up. Because one side of the transformer was on top of this lip it was uneven so I put a small piece of metal under the other side to level it out. After you have your transformers just the way you like them, leave the transformers on the board and use a sharpie to make marks through the screw holes on the bottom. After you have marked where the screws will go, remove the transformers and drill holes for them, then put them back on and screw 'em in.
Step 3: Position the Other Stuff
After securing your transformers, its time to install the switch. I had to cut the ground lug off the switch cause it was in the way, so i removed the screw and cut it off and put the screw in a hole near the top of the switch, i also cut off the two top screw holes. After that, the switch was ready to be put on the board along with the transformers. i bent the bottom two screw holes right at that line so that the switch would be slanted, i think this looks better and it a bit more convenient. I then marked the holes to screw the switch in and drilled them out but you must wire it up before you screw it in.
First off connect the neutral from the inlet to the bottom lug on the switch. Next connect a wire from the top lug on the switch with a spade connector on the end to connect the capacitor to (you will need to use the capacitor to measure your wire length). Next connect the live from the inlet to the other connector on the capacitor. Then connect the ground to the screw on the switch and another wire to the transformer cores, i just soldered it to the end on the secondary winding. Last thing is to secure everything, I bent a metal bracket from a transformer mount to fit the shape of the inlet and screwed into place to keep it from moving every time I pug and unplug it. I just used super glue to hold the capacitor...
Step 4: Wire Up the Transformers
Because we are using 120V transformers and I'm going to be powering it off 240V, you will need to wire them in series but you must wire them in phase otherwise you will just get little sparks. This simply means the two wires powering the transformers must be connected to the same side on each primary, look at the picture if you don't understand.
Connect the neutral and live wires coming off the capacitor to the to either the two left, or the two right leads on the transformer primaries, not one on left and right or vice versa. Connect the two other leads together and that will be it for wiring everything up.
I used thin steel wire to keep the wires neat and close together.
Step 5: 240V-120V Outlet Adapter
I don't think anyone will need this part but i wanted to share it with you. The outlet my dad made for the air compressor was close to a regular 120V outlet except one of the prongs was sideways so I had to build my own adapter.
I got the bottom of a wall wart that still had the prongs on it and i bent one sideways and made it as flat as i could, I then heated up a copper wire and melted it through the plastic for my ground. I got the end of an old extension cord that iv'e been saving for a long time and connected that so i could plug my 120V power cord into it.
Step 6: More Power
The two transformers alone can give some pretty nice arcs but some resonate capacitors on the output can give some much better arcs. All you need if four high voltage capacitors from the microwaves and wire them in series parallel and connect them to the output and the arcs can be drawn out much longer and also seems to draw less current. You could also just use one capacitor in series with the output but it will burn out pretty quickly. Putting the capacitors in series parallel does not change the over all capacitance but does increase the power they can handle. When drawing arcs, make sure to keep the metal casings on the capacitors touching or the cases will spark to each other.