Tech Forum

The Tesla coil uses a resonant transformer, with tuned primary and secondary coils, to produce high-frequency current at very high voltage. A resonant transformer is like a child's swing, or pendulum; by pushing repeatedly at just the right time on each cycle, the pendulum can be made to swing much farther than from any one push. Also, as in the case of a pendulum, the trick is to give a short, sharp push and to let go, which may be done in a Tesla coil using a spark gap that is conductive for only a part of the cycle. When the circuit is broken, the high dv/dt (rate of change of voltage) in the inductance of the primary circuit creates a high-voltage wave. In addition, like any transformer, the Tesla coil multiplies the output voltage by the turns ratio of the primary to the secondary coil.

A simple Tesla coil could be made from an electromagnetic door buzzer, below.

(Buzzer, from http://radiology.rsna.org/content/suppl/2011/03/16/radiol.11101899.DC1/FigE2.gif)

Though the battery might be just 1.5 volts, a 60-volt neon lamp could be lit by connecting it to the contact and spring strip. Here, the high voltage is due to the high dv/dt as the moving spring strip suddenly opens the circuit. Winding a secondary coil with many more turns over the existing primary coil would increase the output voltage on the secondary by the turns ratio. Placing the right value of capacitor across the primary coil to tune it to the self-resonant frequency of the secondary would increase the voltage yet more.

See http://en.wikipedia.org/wiki/Tesla_coil and http://www.hvtesla.com/tuning.html for more information.

Go to the following web site by Kevin Wilson. It is very well done and has a nice and brief explanation of the theory of operation and how to build it safely. http://www.teslacoildesign.com/