Ok, here's the disclaimer.
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I do not hold any responsibility or your use or misuse of this information, in any way. I am not a trained professional and I cannot protect you from the voltages that are part of this project, and any damage this project may cause, wether it be to animal or material. The user assumes all responsibility for the actions they take.
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Well, now that that's over, lets get on to what a tesla coil actually is.
A tesla coil usually has these key components:
*power source
*Switching circuit
*Resonant Capacitor (only for drsstcs, some vttc,s and regular spark gap type coils)
*Primary coil
*Secondary coil
The tesla coil was invented around 1891 by Nikola Tesla. His original intention for the device was to create a wireless energy distribution system. Unfortunately, his design could not send power at even close to reasonable efficiency, as the power was almost all being wasted on corona and arcing. Today, we coilers take this to an advantage.
But what males the tesla coil truly magnificent is the voltage it produces. A typical spark gap type coil takes (usually) the voltage from your wall socket, and steps it up to a couple thousand volts, where it then goes through the switching circuit, through the primary, and is seen on the secondary side as more that 200,000 volts! But how did tesla do this?
The answer is resonance. A resonant circuit, usually consisting of a capacitor and inductor, is much like a slinky. (stretched out) When you give it a push, it bounces back and forth losing momentum with each pass. However, if you keep hitting it every time it comes back, it will start to move really far back and forth at the same speed. (Or frequency) The frequency at which you hit it is it's resonance.
The secondary coil is like our spring. But how do we get voltage from it? Certainly not by hitting it. No, you have to use an oscillating magnetic field from the primary coil to excite it. A normal spark gap type TC would use a resonant capacitor and a spark gap to produce the oscillation, where as our coil (sstc) will use feedback from the coil itself to drive the primary. (using an antenna.)
~~for more info on how a tesla coil works, head on over to Richie Burnett's site or the wiki.
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Unfortunately, I cannot currently put up the steps to wind the secondary coil, but I will put up an intractable as soon as possible. But generally, what you need to do is wind many tight turns of thin magnet wire around a pvc form. Don't make it too tall. A good ratio for height is that the height is about 3 to 5 times the diameter.
Anyway, what you will get out of this coil is approximately 7-8 inch sparks. (Depending on how you set the interrupter) I'll go over this later, but for now, that is what you can expect. Trust me, you'll have fun.
*****EDIT: That mystery symbol appears because instructables cant handle the µ and Ω symbol in pictures. go figure! it works here.
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How many turns on the seconday?
If your interested:
Resonant Frequency: 231kHz (without primary windings)
Turns Ratio: 6.25:1300
Primary Inductance: 3.2uH
Glad your coil is on it's way.
The high voltage side behaves really strangely. When I measure the voltage across the Primary output, I get 8 volts. When I simulate the circuit (http://www.falstad.com/circuit/) the output starts strong but then the two .68uF caps lose their initial voltages and the output decays and ends up being about 8v. So theoretically my circuit is doing the right thing. When I connect one end of the primary output to mains ground, I can hear the current flowing at the 555's interrupt frequency. On a related note, it's a good thing I put fuses in this thing. Is the idea that the ~200kHz feedback from the secondary will make it through this decaying effect? Any suggestions?
I wouldn't count on it though.
I am an industrial electronics technician and don't need the step-by-step but a readable overall diagram would be quite interesting.
http://stevehv.4hv.org/SSTC5/miniSSTCfnlsch.JPG
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=495-3187-ND
But if you can't do that, you could try to series up two 1uF caps rated for > 120 volts in the place of each 0.68uF.
If you're absolutely sure about your soldering and are able to verify somehow that the circuit works, go ahead and and just hook it up. The variac is just a large safety buffer, and as long as you have some kind of circuit breaker, you should be fine. Best of luck!