My Tesla Coils

Over the years I have built a number of coils, unfortunately not many were too good. Fortunately I don't have pictures of them, so instead I intend to give details of more recent coils and current projects.

TC2

Secondary

For this coil I started with the secondary, with the intention of deciding on the drive and primaries later. From previous projects, renovating old items of electrical apparatus, I had a number of part reels of wire, mostly double cotton covered (dcc). I also had a number of possible formers, mostly fairly large, but I instead decided to use a 2.5"o.d. cardboard mailing tube. I know a lot of people don't like this material, but I have always had success with it. To improve the material I impregnated it with poyurethane varnish, diluted equally with white spirit. It was then coated with a further three coats of undiluted varnish.

The secondary winding consists of about 800 turns of 38swg dcc. For a larger coil this would be far too thin. This gives a winding length of 12", with .5" space at either end. The winding was coated with clear polyurethane, the first coat being diluted 50/50. Five further coats were put on, with a light sanding using fine wet & dry paper between coats. A small brass bracket was epoxied to the base end to act as the connection. At the top, a disk of thick card was glued on, and a turned wooded insulator glued to its centre, with a disk of copper 2.25" dia. on top as a terminal. A helical coil of 16swg bare copper was used to connect the top of the coil to the top terminal.

Topload

Various toploads have been used. The simplest to make were based on polystyrene foam toroids obtained from a local craft shop. They were covered with aluminium foil, using double-sided tape. A central; disk of card, also covered in foil was force fitted into the centre of the toroid.

Primary

The primary coil was made as an inverted cone, with a former fabricated from four triangles of mdf drilled to accept the 18swg wire. In its current configuration the coil is mounted at the base of the secondary, and it has 12 turns, 4"dia. it can be tapped as needed for tuning purposes.

Spark Gap

Various spark gaps have been used. None of them showed a significant improvement over a simple static gap made from two L-shaped brackets fitted with 0.25" brass bolts as the electrodes.

Capacitor

I have used several different capacitors with this coil, starting with salt water, then flat plate polythene, followed by a self fabricated one made from double sided fibreglass printed circuit board. When I first suggested this to other coilers they were somewhat doubtful, but in my experience it had a number of advantages. I have found it to be less lossy than salt water caps. It is less inductive than some forms of rolled caps, and it is certainly a lot less potentially messy than oil filled caps. I will add details of the construction after I have made my next one, as I plan to take pictures at each stage, and I have one or two ideas for minor improvements. The cap used with this coil is 2n2F, and has been tested to 30kV pulsed.

Power Source

So far this coil has been powered using the output of an old induction coil, and a solid state flyback circuit; both with their outputs rectified.

Results

Clear coronal discharge to air. 4" arcs to a grounded wire. Able to light a 24" fluorescent tube without connection, hand-held at a couple of feet.