Dan's Conventional Tesla Coil

My First Conventional Tesla Coil

Introduction

Alright, living in a small townhouse I was forced to work on solid state tesla coils. But enough is enough. Time to go for the

big streamers. Big arcs! Here you can see my first conventional tesla coil in progress. All components are now complete and

I only have to start installing and connecting the "guts" of the coil which will be placed underneath the table.

Click here for Tesla Coil System Schematic

HV Power Supply

15kV, 60mA Franceformer Neon Sign Transformer (NST)

Calculated Output Impedance = 250k ohms

NST Filter

For the Neon Sign Transformer (NST) filter, I decided to go with Terry Fritz's design. The picture above is my unfinished

NST filter board. The fully adjustable safety gap shown is made up using 1/2" corona balls. This filter, however, was never

used in my design.

Click here for the NST Filter Schematic

Primary Tank Capacitor (MMC)

The primary tank capacitor I am using is the MMC capacitor shown above. Using a synchronous rotor spark gap (SRSG),

the LTR (larger than resonance) capacitor size required for a 15kV, 60mA NST calculates to be 0.0277uF.

To create this new MMC, I used twelve (12) 0.33uF, 2kV capacitors in series to create a 0.0275uF, 24kV MMC.

The capacitors used are GE 42L3332, 0.33uF, 2kV Poly Capacitors. These can be obtained at Newark Electronics

(www.newark.com) for about $4.50 each.

Synchronous Rotor Spark Gap (SRSG)

Well, like everything else with this coil, I have changed my overall design of the SRSG. The new design will

incorporate two stationary electrodes up front using a rotor with a conductive ring as shown in the picture below.

Since there is much greater rotational weight (conductive ring, hex bolt electrode holders), I've decided to reduce

the rotor size from 7" to 6" diameter to reduce stress on the motor. The motor bracket itself is made of PVC. Also

note the nylon screws in the front. This prevents arcing of the rotor disk to the motor.

More information regarding this SRSG can be found here.

Specifications:

Motor: 1/25 HP Hysteresis Synchronous Motor (1800RPM)

BPS: 120

Primary Coil

The picture above is a close-up view of my primary coil. It is a pancake primary design with 13 turns of 0.25" diameter

copper tubing spaced 0.25" apart. Also shown is the strike rail which floats about 2 inches above the primary coil. This is used

to help prevent the secondary from arcing to the primary. When building your strike rail, remember that it should not be a closed

loop. Plus the gap between the loop should be far enough apart so voltage doesn't arc across it. The supports are made up of

Ultra High Molecular Weight (UHMW) Polyethlene. This material was basically chosen for its availability and price even though its

dielectric strength is superior to that of delrin, nylon, pvc, etc...

Control Box

Here is the control system for my tesla coil. There are two circuit breakers, one controlling the

SRSG (synchronous rotary spark gap), and the other controlling power to the primary circuit. A

simple relay latch control scheme is used to turn the tesla coil on and off, and there is also a safety

key switch to prevent unauthorized use.

Secondary Coil

1000 Turns, 23.5" Winding Length, 4.5" diameter PVC

Secondary self-resonant frequency: 340 kHz

Secondary resonant frequency with 5x20" toroid topload: 195 kHz

Resonant frequency of secondary coil was determined using the following method. An oscillator was connected in series with

a 1k, 0.5 watt resistor which was connected to the base of the secondary coil assembly. A multimeter was connected to secondary

side of the 1k resistor and the ground lead of the multimeter connected to the negative output of the oscillator. (Note: There is no

connection between the secondary coil and the negative output of the oscillator) At resonant frequency, the voltage read at the 1k

resistor will be at a minimum since current through the resistor will be at a maximum at resonant. I simply adjusted the the oscillator

until this minimum was found. The following picture shows my resonant frequency test set-up.

Top Load

At first, I attempted to build my own toroid from scratch, but quickly gave up on the endeavor since my homemade toroid looked like a complete

heap of garbage. I'm already about $1200 in the hole for this project, so I might as well have a sharp looking toroid on top. Since commercially

spun toroid were about $425.00 for a 5" x 20" toroid, I've decided to go with D&M High Voltage in Florida for a nice 5" x 20" toroid which only

cost about $79.95 (not including shipping). To be honest, I was skeptical at first, but after receiving the toroid, I am extremely impressed. They

did an excellent job and the toroid looks fantastic. I'll definitely be going back to them for other toroids.

Additional Photos (Click to enlarge)

More to come soon . . .

Last modified August 16, 2005 08:05:21 PM