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Tesla Coils
and
Spun Aluminum Toroids
Click here for Efficiency Theory
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New size spun aluminum toroid with pristine brushed finish. 2.25" x 8" with 1/4" center mounting hole.
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I've been studying and building Tesla coils for over 25 years. One of my goals is to achieve better efficiencies and to determine the relative importance of the various factors that contribute to the coil's efficiency. There are many coiling myths out there, and I enjoy discovering them, and benefiting from the knowledge gained in the process.
I've done a comparison of high and low breakrates for low powered coils up to 1500 watts or so, and it appears that the low breakrates (around 120 bps) are best. When running NST powered TC's, it often helps to use a synchronous rotary spark gap running at 120 bps, although folks have also obtained excellent results using single air blast static gap arrangements. In any case, non-sync rotaries should not be used with NST's because it tends to destroy them under some conditions.
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4" x 13"
Pristine Brushed Finish
1/4" center mounting hole
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5" x 16", 1.75" x 6", and 4" x 13" toroids shown below
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Spun aluminum toroids are the "gold-standard" of topload excellence for Tesla coils. The roots of the spark streamers glide around over the toroid surface rather than staying stuck at one spot as when corrugated toroids are used. Generally for a given spark streamer length, a smaller spun toroid can be used. If a corregated toroid is used, it will need to be larger. Spun toroids are excellent for Tesla coils, vacuum tube Tesla coils, or as sub-toroids below a larger toroid, and for marx generators and other high voltage projects. The metal half-shells fit together and form a flat seam which does not interfere with the sparks. The sparks glide over the seam as if it wasn't there.
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At left is a small synchronous rotary spark gap that I built which features a lexan rotor, a small 1/20th HP sync motor, and spinning electrodes which are made from steel bolts. The AC phase is adjusted by rotating the motor in its cradle while the coil is turned off. Lexan can melt, so the heat build up must be monitored to be sure it doesn't get too hot, but I haven't had any problems with it getting too hot.
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40A, 250V line filter
can be seen to the right
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Here is the completed TT-42 tabletop TC which gives 42" sparks from a 12kV,30ma robust NST. There are about 1300 turns of 28awg magnet wire on the secondary form which is a 4" by 19" pvc pipe. The primary uses 14.5 turns of 10awg solid pvc coated grey ground-type wire on a lexan form. The lexan is supported above a Y shaped piece of wood which is supported by 3 legs from an old TV. The capacitor is a 0.0147uF, 45kV rated, Maxwell cap. I just use safety gaps to protect the NST. NST's should be used only with static gaps or with a sync gap as I am doing here. A non-sync rotary gap will tend to destroy an NST. I use one of my small toroids below my main 4" by 13" toroids, to keep the sparks away from the primary.
In my older coil which had a taller 23" secondary, the small toroid was not required.
The main purpose of the smaller toroid is to raise the height of the main toroid to prevent sparks from striking the primary.
As a test, I recently installed a 6" x 24" smooth spun toroid in place of the 4" x 13" toroid. This gave 44"+ sparks, but gives only one spark streamer. A corrugated
toroid gave only a 42" spark. TT-42 sync rotary
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