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High Voltage Page
500,000 Volt Tesla Coil (1995)
This Tesla coil was designed to run on a 900 Watt neon transformer. Unfortunately, all I had was a 240 Watt neon transformer, which was still enough to generate 175,000 Volts with streamers up to 18" long. It cost about $50 to build (not including the neon transformer). 
Fundamentals of the Tesla Coil
A Tesla coil is a high voltage transformer with an air core. The primary and secondary coils each have inductance and capacitance so they function as an LC circuit with its own resonant frequency. The primary capacitance comes from a capacitor that discharges across the spark gap when the voltage is high enough. The secondary capacitance comes from the coil itself and the sphere or toroid at the top. When both circuits have the same resonance frequency, the oscillations efficiently contribute to the induced voltage.

Tesla Coils
This was my first Tesla coil built in 1994. It didn’t work very well. The picture on the right shows a rotary spark gap that was used.

Here is my second Tesla coil built some time around 1994. The secondary coil is 3.5" diameter × 14" tall and has 996 turns. The original design was closely modelled after Gordon McComb’s book, Gadgeteer’s Goldmine. It never worked very well, but I think it will work quite nicely now that it has been modified. The left picture shows the original coil and the right picture shows the new modified design.

This was my third Tesla coil built in 1995. This is the same coil as shown at the top of this page. The design was based on John Couture’s Tesla Coil Design Manual (1992). The secondary coil is 5" diameter × 20" tall and has 508 turns. It is interwoven with fishing line and coated with enamel to improve the insulation between turns.

This miniature Tesla coil was also built some time around 1995. The secondary coil is 1.625" diameter × 6.375" tall and has 1080 turns.

Van De Graaf Generator
Useful Formulas
There are plenty of other great web sites for designing Tesla coils so I will just summarize some basic formulas here:
Notation: these formulas use the following notation:
Design Formulas:
Capacitance Formulas:
Inductance Formulas:
See also my Tesla coil rendering with magnetic field.
Other High Voltage Links
Bert Hickman’s Teslamania Site  World’s largest Jacob’s Ladder, Lichtenberg Figures, Coin Shrinking
close lightning photo  by Kane Quinnell
Tesla Technology Research  the world’s largest Tesla coil, 13 MV, 55' sparks, 125 kW, by Bill Wysock
ball lightning created in a lab  YouTube video
Peter Terren’s Mad Science Page  3 kW Tesla coil, Magnetohydrodynamic (MHD) drive, home made lasers
Twin Tesla Coil  nice table top Tesla coil by Sam Barros
Ball Lightning  created in the lab, see also Sam Barros’ experiment
Lifters  electrostatic flying capacitors
Electric Arc Furnace (EAF)  YouTube video, used for melting recycled steel, 600 V x 135 kA = 81 MW
