Tesla Coils

Tesla coils are the amatuer experimenter's easiest and hardest way of getting into the hundreds of thousands of volts, even millions of volts. It all comes down to the type of tesla coil being built. But first, you have to understand how a (conventional) tesla coil works in the first place.
	Tesla coils are air cored resonant transformers. Resonant, basically meaning 'in tune', and transformer meaning the things you find in almost every household appliance. They're used to step up/down voltage. In the case of a tesla coil, the voltage is stepped up. To hit an electric circuit into resonance, two basic components are required. A capacitor (something which stores energy in the form of an electrostatic field) and an inductor (stores energy in form of a magnetic field).
The capacitor in the tesla coil is used for storing the energy, while the inductor (or primary coil) is used to provide mutual inductance to the secondary coil. In order to discharge the capacitor's energy into the primary coil, we need some form of an interruptor. The difference in interruptor design separates the many different types of tesla coils.	The good ol' beer-bottle capacitor setup
The spark gap being tested, notice the arcs between	The old, traditional way of tesla coiling was to use a spark gap for an interruptor. A spark gap is simply a gap between two electrodes, connected to certain points in the circuit. When the voltage over these electrodes exceeds a preset amount (usually a couple thousand volts), the electricity jumps across, and discharges the capacitor's energy straight into the primary coil. This then provides a voltage spike across the secondary coil much like a transformer action. This voltage spike also appears across the toroid (top of the secondary coil), and is discharged from there.
I have to admit I didn't put much effot into designing and constructing this tesla coil, so please put up with the dodgy bits and pieces. Anyway, onto my coil... the first thing I did was to make a beautiful secondary coil. This bugger took about 4 hours just to wind the wire on. Its probably the most rewarding thing in the world though, to finish winding a secondary coil. All up, it's 30cm long, with 1200 turns of 22 gauge wire. Coated in polyutherane varnish.
Next come the supports for the primary coil. The primary coil wire is quite thick, since it has to carry hundreds of amps due to the capacitor discharge.	1. A long piece of wood is filed down at specially marked sections
Here's a closeup of the filed down bits	2. It's then cut into four sections. Theres a 30cm ruler for scale.
3. All four sections all glued onto a ceramic board base.	4. Time to wind the wire. The thick 10 gauge wire is very hard to work with, and screws are used to secure it to the base.
5. The completed primary coil	A closeup of the screw in method of mounting the wire.
Thats the hard bits done... the toroid came next on the list.... I took a joy trip to the local ventilation ducting store (yes there is a store like this in Darwin) and found myself a meter of 4 inch ducting. Guess how much that costed me...... $22!!! And that was half price too (the guy was very nice and gave me that discount when he heard about such a strange use for ducting pipe). The ducting is coiled around into a doughnut shape, and covered in aluminium foil.
The primary and secondary coils mounted into position.	The setup with toroid, primary coil and secondary coil all secured together.
The high voltage transformer took a bit of scrounging to find. These aren't your little square transformers you find in your VCR player, these are big things that are used in the powering of large neon tubes. So I called up the local neon sign manufacturing company (yes, we also have one of those in Darwin) and they gave me a used transformer for $20. Not bad. There it is on the right, with numourous danger signs to stop idiots from turning it on and frying themselves. This particular unit takes in 240V and outputs 15kV (15,000V) at 30mA.
	Erm, the next bits you've already seen.. I mean the capacitor and spark gap. I put those images up the top of this page somewhere. So I'll skip that bit and go straight to the finished thing. Actually I don't have a picture of this, but have some of the tesla coil in action though. Like the one on the left. Complete dismal performance for its size. But hey, it still makes 25cm topload to ground arcs, and 7cm corona discharges (like in the photo).
And this is a long exposure with me swinging a grounded rod beside the topload. Notice the ground arcs visible this time. The corona discharge is there again because I forgot to take the discharge rod off the topload. This setup is completely ridiculous in terms of spark length, however. It should be capable of up to 40cm arcs to ground, but I guess you get what you work for.
Overall the performance was not satisfying, but it was fun to build nevertheless. What else can I say?	This space left intentionally blank