1.3 F.A.Q.

A Tesla coil is a high voltage, high frequency resonant air core transformer. It was developed by the Serbian born inventor Nikola Tesla in the 1880s. It was originally created to serve as a transmitter for the wireless transmission of electrical power. The idea of wireless power transmission never caught on mainly due to lack of funds. The true Tesla coil had three coils, a primary, a secondary, and an extra coil which is called the Tesla magnifier.

Today Tesla coils serve little practical purpose. There are a few practical purposes for them however. They are used to simulate lightning strikes to test aircraft hulls, and power distribution equipment. They are also used in the film industry wherever good lightning like discharges are needed. An example of this would be in the movie "Terminator 2". Most coils built today are 1/4 wave coils which do not make use of the Tesla magnifier coil. Tesla coils are fairly easy to build with readily available components. The normal hobby Tesla coil setup consists of a high voltage step-up transformer which has a secondary voltage of 5000-15000 volts AC. Neon sign and oil burner ignition transformers are commonly used. Almost all of the other components are made by the builder.

The theory of operation of a Tesla coil is not too difficult to understand. The most basic Tesla coil system consists of a high voltage step- up transformer, sparkgap, capacitor, primary, secondary, and output terminal. First the capacitor is charged until it the air around the sparkgap breaks down and forms a conducting channel. The capacitor discharges rapidly into the primary coil and a magnetic flux is built up around the primary coil. The flux then collapses and charges up the capacitor again. The capacitor then discharges into the primary again. This forms what's called an LC (L stands for inductance and C stands for capacitance) oscillator. This cycle goes on until there is not enough power left to jump the gap. The capacitor then is charged by the high voltage transformer and the cycle repeats over and over again. You can think of the primary, sparkgap, and capacitor as a radio transmitter. The secondary can be thought of as a radio receiver. The resonant frequency of the secondary is determined by it's capacitance which is derived from the output terminal, the capacitance of the secondary winding, and the inductance of the secondary. If the resonant frequencies of both the primary, capacitor, and sparkgap circuit (also called a "tank" circuit) match with the resonant frequency of the secondary coil then high voltages will be induced in the secondary due to the effect of VSWR, or the standing waves in the coil. What happens is there is sparking that occurs at the output terminal. Understanding this is not required to build a sucessful Tesla coil, although it does help to know some of the theory.