Electronic – Advantage of rotary spark gaps in tesla coil design

The output from a tesla coil is indeed ac but it's a lot higher than 60Hz. Using a 50 or 60Hz supply is convenient because it has the power to generate a decent charge into a capacitor that connects through to the primary via a spark gap. See this explanation for starters.

The primary coil (via the spark gap) resonates with the primary capacitance and this forms a parallel tuned circuit. For high-Q parallel tuned circuits, the current that flows between primary coil and capacitor is very high and usually tens to hundreds of kHz.

This generates an alternating magnetic field that impinges on the 2nd coil. This second coil has much higher Q than the first coil and is tuned by the capacitance of the large terminal to ground. It is also a parallel tuned circuit and when tuned to be at the same frequency as the primary resonance produces rather large voltages that most of us have seen on videos.

All this happens at very much larger frequencies that AC mains. Normally, on tesla coil demonstrations, a medium voltage dc supply is used to charge C1 up to the voltage needed to break-down the spark gap.

As an aside, I've used low voltage tesla coils (tuned primary and secondary coils) to couple useful amounts of energy across a 40mm gap to power electronics on a rotating machine. OK they don't use the spark gap to initiate a spark but they do use exactly the same principle. There is also a lot of talk about using this technique to power lamps wirelessly. I don't think it will replace wires though because energy transfer is fairly inefficient.

That is a disaster waiting to happen. Here are just a couple of the problems:

• You can't use galvanized steel bolts for your spark gap. They'll quickly overheat, erode, and the wooden base will probably catch fire. Also, the zinc plating will burn off in a cloud of toxic fumes. Try a Richard Quick gap or a sucker gap.
• You can't use microwave oven capacitors as your primary capacitor. They can't handle the high peak discharge currents and will explode, showering the room with hot oil.
• The hookup wire you've used to interconnect the tank components is too thin.
• The primary (the ~6 turn coil made from copper tubing) is probably tuned incorrectly. You need a movable tap.
• The primary-secondary coupling is too high.
• A single MOT has too low of a voltage. It's not impossible to build a working Tesla coil with a single MOT, but it's quite challenging and from the pictures it is very obvious that you don't have the experience needed.

I am very worried for your safety. You should do more research, starting with this safety guide: http://www.pupman.com/safety.htm You should start off with a different high voltage transformer - a 12 kV, 30 mA neon sign transformer (NST) will be both much safer and easier to get working. MOTs take no prisoners.