Tesla Coil 2003 Constuction

Tesla Coil

Here is our Tesla Coil. It is a DC powered unit. Our configuration is built on three levels. The secondary(red vertical tube), toroid and primary are located on the top level. The tank capacitor, charging reactor, and Rectifier Board are on the middle level. The power transformers and current limiting inductor are on the lower level. The Rotary Spark Gap is on the floor in front of the unit.

The coil resonates and 383 kHz and requires about 1300 watts of power. We achieve a first notch quench. The ring-up occurs in ~6 cycles(~15.5 uS) and the ring-down in ~10 cyclces(26 uS). Streamers are 16 to 20 inches in length.

Tesla Coil
Tank Capacitor

Tank Capacitor & Charging Circuit

The tank capacitor is an 18 nF parallel plate capacitor constructed from aluminum flashing for the conductor and polyester sheeting for the dielectric. The charging reactor is 7500 turns of #30 ga wire on a pair of gapped U-100 cores. It has an inductance of 31 henries. The diode was constructed from a series of 1000 Volt diodes with smoothing resistors and capacitors in parallel with each diode.

Power Transformers

The transformers are (4) MOT's with the secondaries wired in series and a center tap to ground between the middle two. The transformer primaries on one side of the center tap are wired in parallel and the other two are wired anti-parallel. Each transformer has a turns ratio of approximately 17.5 so we get 4X17.5 = 70 times the voltage in the transformer secondary/primary. The current limiter is #14ga wire wound on a gapped U-100 core to get 15 mH. With this configuration we draw about 13 amps and and the transformer primaries see 100 Volts AC. Mains power is 120 VAC. A contactor and 12 VDC control circuit(for safety) are not shown.

Power Transformers

Full Bridge Rectifier

The Rectifier Bridge is made of (4) series of 1000 volt diodes with smoothing resistors and capacitors in parallel with each diode. Filter capacitors(with parallel bleed resistors for safety) are located on the DC side of the Rectifier Bridge to reduce ripple. Input to the board is 7000 VAC(3500 VAC to ground - 2 legs out of phase). Output from the board is +5000 VDC and -5000 VDC for a total of 10,000 VDC.

Tesla Secondary & Toroid

The Secondary is 1-7/8" Dia X 12" lg on a Polyethylene tube(1200 turns of #30 ga wire). The toroid is made from 3"dia dryer vent duct. It is 16" OD. The toroid is thus known as 3" X 16". The computed capacitance of the toroid is 16.9 pF. The Secondary has as computed inductance of 8mH and a computed capacitance of 4.4 pF. The total predicted capacitance of the secondary circuit is 21.3 pF. Calculated Reactance at resonance is 19K Ohms and resonance is predicted at 386 kHz(Actual 383 kHz).

Secondary & Toroid

Tesla Primary & Strike Rail

The primary is 8 turns 1/4" copper tubing spaced 1/4" apart and mounted in a 30 degree involute cone configuration. It is tapped at 4-3/4 turns so that the primary circuit resonates at the same frequency as the secondary circuit. The outermost loop of tubing is the strike rail which is connected to RF ground and protects the primary from stikes.

Rotary Spark Gap

The rotary spark gap consists of two tungsten electrodes. Brass screws mounted in a polycarbonate disc pass between the electrodes and close the circuit. The motor operates at 1725 RPM and there are 16 brass screws in the disc. This gives a spark gap break rate of 460 BPS.

Rotary Spark gap
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