Mike and Alan's Tesla Coil Site

Introduction

We're based on the Isle of Anglesey, North Wales. Alan lives on the south-west coast, and I'm a few miles north in the village of Rhosneigr.

I'm a software engineer by profession (that's a computer programmer in the old money) and amongst other hobbies, have built lots of electronics projects over the years. They've been mainly digital stuff, so tesla coils are a refreshing change. In the tesla building partnership, I do most of the constructional work.

Alan owns and runs a company specialising in wiring harness manufacture. He's the expert scrounger in the partnership, sourcing the materials and components needed. He's obtained near impossibilities such as the pole transformer and the 20A variac that will form components for the second and very much larger tesla coil. More about that later.

Mark I Specification

Our first coil is largely based on Nick Field's design, which was published in Everyday Practical Electronics magazine (EPE), March 2001 issue. We've substituted a larger neon sign transformer though, replacing the 10kV 50mA version described in the article with a 10kV 100mA version, also supplied by Tunewell Transformers. Additionally, we've replaced the original aluminium foil coated discharge sphere with a toroid made from a 1 metre length of 4 inch diameter corrugated aluminium vent tubing.

It was completed in late 2001 and has proved to be very reliable, the only problems being an occasional blown fuse in the controller and the static gap requiring periodic adjustment. We've had strikes of just over 1 metre, which is pretty spectacular (and very noisy!). The last image in the series below was a distance of about 80cm, the target being a lager can, earthed to encourage a strike.

The main components:

Transformer - Tunewell 10kV 100mA NST
Static Spark Gap - 7 off 22mm dia x 120mm long copper tubing
Capacitor - 3 x 16 47nF 1.5kV strings in series giving 15.6nF at 19.2kV
Primary Coil - 10 turns 6.5mm copper refrigeration tubing
Secondary Coil - 800 turns 0.6mm magnet wire on 4 dia x 20 inch former
Controller - 8A variac with safety cut-outs as per Nick Field's design

Results

Mark II

The next attempt is slowly coming together. The lastest major component completed is the primary coil, which is constructed from 8mm microbore copper tube, mounted on uPVC supports. The base is from an old circular table and, being some sort of resin moulding, is lightweight. Since the primary coil image below was taken, I've added a safety strike ring and terminal connections to complete the assembly.

The secondary coil former is a length of sewerage pipe, which Alan scrounged from a roadside repair in Southern Ireland. After several coats of polyurethane varnish, it was wound in a surprisingly short time (around 2 hours) with 18swg enamelled wire, using a modified wire reeling machine and two pairs of hands. A couple of coats of varnish were applied while it was rotating, with a warm air blower encouraging the drying process.

I've been experimenting with a rotary spark gap, but have had problems trying to get the motor to lock on to the mains frequency (50Hz). The motor I've used is a capacitor-start 3000rpm 120v ex-computer disk drive, using a step-down transformer. From various bits of information gleaned from the web, I gathered that to convert it to salient pole operation, the rotor required flats machining (for a 3000rpm motor, 4 flats at 90 degrees to each other) which I've done, using the machine shop at the local college. However, it doesn't seem to reach 3000rpm, as I've used a neon connected to the mains power as a strobe, and I don't get a stationary image of the rotor shaft. Ah well, that's what experimentation is all about!

We've found a possible capacitor (50kV, 1uF) sourced from Ebay. This is probably a higher value than I would have chosen, and not as versatile as the MMC (multi-miniature capacitor) pack used on the first coil which could be configured to different values, but it seemed too good to pass over. We'll see how it performs.

Once we've built the toroid (this will be 12 inch ducting, with an outer diameter of around 41 inches) we'll probably try a test run using the transformer, capacitor pack, gap and controller from the first coil.

The main components so far acquired or built:

Transformer - English Electric 5kVA 11kV/250V circa 1960
Variac - Zenith Electric Co Ltd 20A 0-270V
Secondary Coil - custom-built 66 inch length by 12.5 inch dia, 1200 turns of 18swg
Primary Coil - 18 turns of 8mm copper tubing, 42 inch outside dia

I'll post pictures of the main components as the building work progresses

Mike and Alan's Tesla Coil Site

Introduction

Mark I Specification

Results

Mark II

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