Untitled Document

	Tesla coil
	I have planned to build my own coil for a long time, but this summer I was fortunate to have all necessary parts needed for building one. It's a dream come true! First of all I needed a winding apparatus to wind my secondary coil on. My father had an old wooden lathe (homemade ecostyle =)) that he didn't need. It had no motor just the frame and bearings (from a motorblock and a bicycle). I found one old washing mashine motor that I did use and some wheels, also from washing mashines. WM-motors is constructed to be run with two speeds. One for normal washing and the other for centrifuge. I had to get the speed down to about 20 rpm. So I used three wheels (diffrent size in diam.) and straps to get the speed down to about 14 rpm (bearing for the middle wheels is from a water pump). I also installed a pedal from an old singer sowing mashine to be able to gain control over speed and start/stop. It took me about three weeks to finish this lathe. Coilwinding became much easier with this apparatus :-)
		Secondary coil consists of 800mm PVC duct 160mm in diameter. Winding the secondary took about three hours. Six thin coats of polyurethane varnish was applied while coil still rotating to get an even layer. I used 1kg of 0,45mm (25AWG) varnished copper wire. This resulted in 699,4m copper wire and 1392 turns. The ends were plugged with 5mm polyacrylate plates glued in place with superepoxy. I used two M8 bolts for mounting coil and toroid. Calculated inductance is 62,69 mH and selfcapacitance 11,83 pF which translates to about 184,8kHz. Additional top load does however lower resonant frequency to about 121,5kHz.
	The toroid for this coil was made from one aluminium cake form (95mm in diam.) and kitchen aluminium duct tube (110mm in diam.). Toroid capacitance was calculated using Mark Rzeszotarskis equation (all calculations made with wintesla 5.0) Further improvements is to make a larger toroid which comes on top. This is to get larger capacitance and lower the resonance frequency of the coil and get better sparks.
		Primary coil consists of 15 turns of ~4,7mm copper tubing used in automobiles as breaking tubes. Spacing between turns is 6mm. Coil is tapped at 6,2 turns to match the resonance frequency of the secondary coil. I used eight pieces of 2cm thick polyacrylate plastic as support. Strike rail is 10mm copper tubing about 600mm in length. Strike rail is elevated about 10cm from primary coil.
	Power supply consists of four neon sign transformers rated at 4kv @ 50mA each. They are coupled in series and parallell to give 8kv @ 100mA. I use two 20uF PFC capacitors and a line filter. Nst:s are made with automatic current limiting, which makes them arcproof. Next summer I intend to swith out the Nst:s for Mot:s (Microwave Oven Transformers). I may use about six of them, four to get 8kV at higher currents and two as current ballast on the mains side (in series with primary shorted).
		To protect the NST:s I used the Terry Fritz NST-filter design, which consists of varistors, capacitors, resistors and of course a safety gap. Safety gap is made of sandpapered cloath hangers =). They had a thick layer of paint, which I removed by fastening the knop in the drill and sandpapering it with 150, 300, 400, and finally with 1000 mesh sandpaper.
	The HV capacitor bank consists of 24 0.15uF @ 2kV metal film capacitors coupled to give 0.100uF @ 12kV. This is a bit low on the voltage tolerance side (recommended is about 40kV), but it worked great. Propably thanks to the bleeder rresistors. Over each cap is three 10 MOhm resistors coupled in series to give 30 MOhm. They are slided into a 3mm PVC-tubing to prevent from disharge between capacitor and bleeder resistor. What I didn't expect hovever while running the coil was that it would disharge between the capacitor bank terminals (about 40mm apart). This resulting in a loud bang. I will have to install a polyacrylate plate between terminals to prevent this in the futhure. As seen i the picture caps are mounted in place with M5 bolts and connected with 1mm bare copper wire.
		I used a Synchronous Rotary Spark Gap to achieve maximum performance with this coil. It cinsists of a salient pole motor and a disk made of 10mm plywood (impregnated with harts), a disk of 2mm alu, 4 rotating electrodes (M8 acid resistant bolts), and 2 static electrodes made of the same acid resistant bolts (only longer). I found out that motor will sync easiest in anti-clockwise direction.
	Control box includes 10A variac (for power control) and emergency stop button.
		Finished secondary coil with toroid mounted. Left picture shows entire setup with control box. Some parts needed for this project was ordered through ebay seller rainylk (http://stores.ebay.com/TeslaStuff)