date: 23 October 2000
Revision date: 6 January 2001
SECONDARY COIL CONSTRUCTION
GENERAL: Considerable care and a reasonable degee of skill must be exercised in the construction of Tesla Secondary Coils. They operate at RF frequencies and generate hundreds of thousands of volts. This page provides some of the construction details for one such coil which works at approximately 117kHz and generates in excess of 200kV.
Polyethylene pipe, length 1.1m, diameter 0.25m *
b. Cotton twine, length 800 metres, diameter 1.0mm
c. Copper wire, enamelled, length 800 metres, diameter 0.5mm
c. Varnish, Litre of oil based varnish.
*Polyethylene pipe is used for the coil former. The pipe I used was an off cut section of gas pipe obtained from a building site laying gas lines. The wall thickness is about 12mm. It is bright yellow in colour. PVC pipe may be used also, but its RF characteristics are not as good as those of polyethylene. The final Q of my coil was in excess of 200 at 117kHz!
** A fixture is similar to the one below is needed to mount and wind the coil on.
The fixture frame is made from Conti Board (particle or chip board). The shaft for the coil is 5/8" dowling, and the shaft for the spool of wire is 3/8" aluminium tubing. Two circular pieces of Conti board with 5/8" holes drilled in the centres were inserted in the ends of the coil former and held in place by three wood screws on each one..
1000 turns of twine was wound on to the former and sparingly varnished with several coats. This formed a track on to which the copper wire was subsequently wound. Considerable care was taken not to cross turns or miss a track. I used my left thumb to hold the wire in the track while turning the former with the right hand. At the end of every 50 turns I would place a piece of plastic electrical tape to prevent the wire from accidentially uncoilling. I then applied several generous coats of varnish to the coil. I used small terminal blocks at the coil ends. This was very tedious work, but the finished coil made it all worth while. It measured 50mH, self resonated at 155kHz and had a Q in excess of 200 at 117kHz (with a terminal of course)!!
I made a smaller coil 3" in diametre and 14 inches long using a cardboard former. It works at 325kHz. I will include details on its construction in this page at a later date.
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