On a Colorado mountaintop in 1899, Nikola Tesla transmitted electrical power over a distance of 25 miles without the use of wires. How did he do it? He did it with a device of his own invention known as the Tesla coil.
Tesla coils are a regular feature of science and industry museums because of their great visual effect; they shoot off huge sparks at a great distance. One day, a few years ago, I decided to attempt to build one. I was successful, but not after almost killing myself in the process. The rest of this writeup consists of notes from this experience consisting mostly of instructions on how to build your own and avoid killing yourself in the process. So... *ahem*
How To Build Your Own Tesla Coil
... and not kill yourself while doing it
... or just have a hearty laugh at 18thCandidate's misadventures in electricity fundamentals
Warning: Following these instructions is very dangerous and potentially stupid. I shocked myself while building this strongly enough to cause a bit of smoke to escape my body and singe some of my hair. It could have been much worse. If you actually attempt to build this thing, PLEASE BE CAREFUL!
Disclaimer: Neither 18thCandidate nor E2 at large have any responsibility over what happens to you if you follow these instructions. If you follow them, you are the only person liable for any damage that occurs because of it, whether personal, punitive, or property damage.
Now... let's get down to business
Before you start, I recommend reading up on basic electrical wiring. Some of this description might confuse you if you aren't familiar with the fundamentals of electricity and simple electrical engineering.
I should also note that this isn't an exact replica of Tesla's monstrous coil. It is much smaller and will work in the privacy of your own home or garage. It also uses DC current instead of AC; this way, the current is steady and doesn't alternate, catching you by surprise. Don't worry, the effect is still quite nice.
The first thing you will have to do is head down to your local Radio Shack (or your preferred electronics store) and pick up some parts. That's right, you're going to journey into that region in the back of the store with lots of capacitors and resistors and stuff. I would suggest getting an employee to help you, especially since a part or two will probably have to be ordered. Here's what you'll need. I should remind you that these are taken from my notes and off of several old receipts; the part descriptions may be out of date. Your friendly Radio Shack employee should be able to help.
A 27 ohm / 10 W resistor
A 240 ohm / 10 W resistor
A 50 V / 6 A breaker
A 8000 microF / 35 V capacitor
Two 2N3055 NPN semiconductors
A 24 V / 5 A transformer
A TV flyback transformer
Plenty of coated copper wire
An aluminum rod
A simple switch
A power cord plug-in
A piece of perfboard (see Lesson #5 below)
Lesson #1: Do NOT attempt to use a wall socket for your power until you are dead sure the circuit is complete. I tried using a cut-off power cord from an old fan and used it for an incomplete circuit; stuff started burning immediately.
Lesson #2: Tesla coils and Dr. Pepper do NOT mix! While plugged into the wall, I was startled by the reaction that my coil gave. I jumped up and grabbed it just as my Dr. Pepper spilled on the circuit. I proceeded to see a great deal of stars before falling over. I woke up a few minutes later with some singed hair, coughing a tad of smoke up. Keep beverages away from your coil, ESPECIALLY when delivering power to it!
Now, take four pieces of the wire, strip off their coating, and wind three of them around one side of the TV transformer and the other around the other end. Lots of wraps are good. My suggestion is to put this transformer on some sort of slightly elevated wood base of your own construction; don't let it touch anything else metallic.
In the end, you want ends of wire sticking out in eight places: one at each end (from the single wired side) and six in the middle (but probably near the ends). You'll want a decent length sticking off at each place. The electricity will pass from wire to wire, so as long as they're all stripped, the scheme doesn't matter.
Connect the first wire to the single end of one of the semiconductors. Take one of the two exit paths of the semiconductor and attach the second wire from the side of the coil. Take the third and fourth wires and repeat this with the other semiconductor.
Lesson #3: Don't hook up any power yet. Wait until the end. No matter how badly you want to throw some power into the mix, all you'll do is blow up parts if you put power in now. I learned this after three trips to Radio Shack.
The free opening on your two semiconductors should each have a wire running out; these should connect together with spare room to some sort of ground. A good choice for this is a metal frame of some sort (steel is good if you can get some); ask your friendly Radio Shack helper for some more details.
Lesson #4: Don't leave out the grounds, but don't do something dumb either like installing a high-quality system for what is basically a fun project for a rainy afternoon. Make sure you have a good grounding system, but don't overdo it. I wound up putting my wiring within a frame made out of steel and attaching all the grounds to it; a good chunk of spare steel and some solder should do the trick.
Now, for wire number five off of the coil: take a small additional piece of wire (stripped clean) and connect these two pieces, with wire number five attaching right in the middle of the small piece, leaving two open ends. Take the sixth wire from the coil, attach it to the 240 ohm resistor (we want the bigger resistor closer to the coil), and then attach one of the two ends of the fifth wire to the other side of the resistor. Take the one remaining free end you have left, attach the other resistor to it, and then put an unterminated wire on the other end of that resistor.
Lesson #5: If this is intended to be more than a one-shot deal, ask your friendly Radio Shack helper about perfboard to mount most of this wiring on. It's definitely useful, and actually makes the task of wiring much easier as well.
Now go back to that sixth wire and strip an area in the middle (between the coil and the resistor) clean as a whistle. Tie on a wire here for later use. Now, the wire hanging free at the other end of the resistor chain should have another wire attached to it, with enough free space hanging to attach ground #2.
The seventh wire from the coil should also be attached to the frame as a grounding.
Now, take the remaining end of the wire from the resistors and attach it to the negative end of the capacitor. Take a wire and attach it to the positive end of the capacitor, then take another wire and tie this wire, the wire tied onto the sixth wire, and the wire attached to the capacitor together at a point. You should now only have one wire hanging free and another wire hanging off of the coil. Trim the one hanging off the coil to an inch or so in length and don't worry about it for the time being. This is the point where sparks will start to fire off when you're finished.
Lesson #6: You NEED a breaker of some sort between your coil (most of which is done) and the wall socket. Doing it without a breaker results in resistors blowing up, a small fire, lots of smoke, an angry and intoxicated sibling shouting at you, a call to the fire department, and being late for a date. oh, the memories...
Attach your free wire to one point on the breaker. On the opposite point, attach a wire, then attach this wire to the ground. The other two points on the breaker should also be attached by a wire, but the middle part of this wire should be wound around a transformer.
Take two pieces of wire and attach them to a switch. Take one end of this and wrap it around the free end of the transformer. Take the other end and attach it to the wall socket as the directions state. Take one last piece of wire, wrap it around the same end of the transformer as the switch-attached wire is, then attach the other end to the other prong of the wall socket, following the socket directions.
And you're done. Whew.
Take a deep breath, make sure the switch is OPEN, and plug it into a wall socket. Nothing should happen. If something has happened, unplug it quickly and try to figure out where you went wrong.
If everything looks good, get away from the bigger transformer and hit the switch. After a second or so, sparks about 6 inches to two feet should start shooting off of the free wire. Marvel at the beauty of wireless electricity. My coil still works after four years, at least the last time I tried it.
Lesson #7: If it doesn't work, don't worry about it. I had to try roughly fifteen times from scratch to get this to work. I recommend searching around for Tesla coil references on the web, and visiting the local library, too; there are lots of approaches to building a coil.
Lesson #8: This coil is not a toy. Don't leave it out where your six year old nephew can plug it in, flip the switch, ooh and aah at the pretty lights, then get the shock of a lifetime, followed by an episode of screaming and a disgruntled father looking angrily at his mysterious coil-building brother... ah, the memories
This concludes our lesson for today. Thank you.
Note: These are experimental notes as I tried various things. I am NOT an experienced electrician by any means! This was purely the results of my dabbling in electricity over one long summer with lots of idle time. If an experienced electrician wants to rewrite this, feel free! I also welcome comments, however serious or sarcastic, via /msg. | 
