What is a Tesla Coil?
A Tesla Coil is an air-cored, resonant transformer. It is capable of producing very high voltages, and visual discharges. They are mostly used for hobby, but are also used for research, lightning testing, and special effects.
Here is how these beasts work...
The 120 volts in your house is stepped up via the Neon Sign Transformer, to over 10,000 volts @ 30-60 mA. This voltage charges the tank capacitor, until the voltage stored in it reaches a level high enough to jump the spark gap. When the air between the spark gap becomes ionized, it conducts very well. This acts like a closed switch, and shorts out the transformer. All the energy stored in the tank cap is dumped, through the spark gap, and into the primary coil. This creates a ring of magnetism around the secondary coil. The secondary coil absorbs this magnetism, and stores the voltage in the toroid. When the secondary absorbs more energy, and stores enough voltage in the toroid, that immense voltage will break out into the air as a large spark, or streamer. During this very fast process, some things can go wrong. If the spark gap is set too wide, or fails to fire, for example, the voltage in the cap or NST can reach several times the normal level. This should cause the safety gap(s) to fire, releasing that voltage to ground, thus saving the cap or NST from death.
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