27 October 2000


General: The Terminal provides the capacitance for the Secondary Circuit making it resonant to a particular frequency (117kHz in our case). It can range from about 10 to 100pF and more depending on its physical shape and size. Tesla Coilers usually use either spherical or toroidal shaped Terminals. They need to be made of some kind of metal such as aluminium or copper and should be smooth without sharp points.

Spherical and Toroidal Terminal Formulas for capacitance:

Terminal Voltages:

There are two types of voltage specifications: Potential (V) and Electric Field (E) Volts per metre. The Potential on any terminal is a function of the electrostatic energy it contains and its capacitance. The energy (joules) comes from the primary circuit, and the capacitance is as determined above.This seems to be where the laws of physics regarding conservation of energy and some Coilers part company. One does not get millions of Volts out of a terminal, but 100's of thousands. On the other hand, one can get in excess of a million Volts per metre field intensity at the surface of a terminal.This is where the terminal ionizes the air about it and the charges break free to make those lovely sparks.

Case in Point:

The primary circuit has a 0.05uF capacitor and a 10kV rms Neon sign transformer. At the instant of spark gap firing the capacitor has about 12kV charge (14.14kV peak voltage available). Using the formula below, the energy in the capacitor available for transfer to the Terminal via the coils is 3.6 Joules.

Even assuming no losses and the terminal capacitance is 50pF, the Terminal Voltage potential works out to 379kV using the same formula above manipulated to make Voltage the dependent variable. By doing the following, a much easier formula for determining Terminal Voltage is produced:

Remember, there are circuit and radiation losses, so the actual Terminal Voltage Vs will be somewhat less than the 379kV calculated.

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