Kaizer SGTC I
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Introduction
This Tesla coil is my first and was build without any expenses worth mentioning, its the prototype from which I learned alot about Spark Gap Tesla Coils, high voltage and where to find components in household items and trash.
In the development the first version was more of a proof-of-concept model build only from old microwave ovens, televisions and cable.
Math and theory was not the leading part of this project in the start, but as optimizing went on I learned about tuning the Tesla coil for a better output, resulting in longer sparks.
Considerations
There is no protection against RF spikes going back into the High voltage supply and destroying it. Read more about the optimal setup in the Spark Gap Tesla Coil theory.
The secondary coil is limited by the amount of copper wire I had available from the cooling fan motor from a microwave oven. The diameter / height ratio of the secondary is far from optimal.
I used my flyback transformer as the power supply, it have a very limited current at about 1mA at 20kV, roughly estimated.
In the start I used homemade saltwater capacitors which are far from optimal.
Specifications
| High voltage supply | 20 kV from a flyback transformer |
| Primary capacitor |
8 nF MICA |
| Primary coil | inner 45 mm, outer 90 mm diameter, 1.78 mm diameter isolated copper wire, 6.6 turns. |
| Secondary coil | 50 mm diameter, 113 mm long, 800 windings, 0.127 mm enamelled copper wire. |
| Resonant frequency | Tuned at around 655 kHz. |
| Topload | 60 mm diameter sphere, tennis ball wrapped in aluminium foil. |
| Input power | Around 20 – 30 Watt |
| Spark length | up to 105 mm long sparks. |
Schematic
Construction
10th May 2008
The secondary coil was wound on a plastic tube, 50mm in diameter and 160mm in height. Its bottom was conical so practically there could only be wound wire on 110mm of the height.
The copper wire had a diameter of 0.127mm, varnished its diameter is 0.14mm, this very thin wire made it hard to wound nicely without overlaps.
It took me 2 days to wound the secondary coil, it was hard on the eye, arms and hand to do in one stretch. The plastic tube was mounted on a gear motor controlled by a frequency inverter so I could control the speed by a potentiometer.
11th May 2008
To keep the windings in place and insulate the coil it was varnished with common ship varnish, it was given a layer in the morning and one more in the evening.
12th May 2008
As the power supply I used my 20kV flyback transformer driver at 12Vdc input, the capacitor is a homemade saltwater capacitor with a capacitance of 2.7nF. The primary coil was wound of ordinary 2.5mm2 wire around a cut up soda bottle.
The topload is a sphere made of bobble wrap, tape and aluminum foil.
Spark gap is just 2 copper wires.
In the first test I could get 4-5mm sparks to a grounded object, the biggest problem was the too tight coupling between primary and secondary. Too tight coupling resulted in alot of racing sparks on the secondary coil, these are dangerous as they can destroy the thin wire on the secondary coil.
Here is a picture of some racing sparks I provoked to get a picture of it.
The primary coil was wound in a bundle and by adjusting the height of it, the coupling could be changed. It was now possible for 40mm sparks to jump to a fluorescent light hold in my hand.
15th May 2008
varnish, varnish, varnish, varnish, glue, glue and more capacitance…
The flyback transformer driver runs at 12Vdc input.
I made another saltwater capacitor and installed it in parallel with the other, the total capacitance was now 5.9nF.
As it can be seen in the pictures there is sparks or just “violet light” coming from other parts than the topload of the Tesla coil, its corona loss and decreases the spark length.
To isolate the secondary coil further it was given 4 more layers of varnish and the top of it was glued all over with hot glue. The metal cap was the new topload and 54mm sparks could be achieved.
28th May 2008
The flyback transformer driver runs at 17Vdc input.
85mm sparks can now jump to my fluorescent light.
The bottom from a beer can is the new topload, it results in some spectacular pictures, the higher voltage on the flyback transformer driver is the best improvement towards longer sparks, but also racing sparks on the secondary starts reappearing.
As it can be seen in the picture taken in the dark, there is still corona losses, and with this particular coil it will be impossible to avoid it at these driver input voltages. It is not easy to insulate 100kV. The following picture is taken with long exposure to show the corona around the coil itself, unfortunately its not as clear in the picture as seeing it live. The violet field around the coil is faint, but can be seen in the picture.
This picture is taken directly above the Tesla coils topload.
21st June 2008
I bought 10 old high voltage capacitors at 150 dkr (25$) for the lot, a real bargain in Denmark compared to the joy it has brought me. I only use one of them instead of the 2 saltwater capacitors. Its a Fribourg Condensateurs from 1961, 8nF rated for 20kV pulsedriving at maximum 2MHz.
A new topload was made from a tennis ball wrapped in aluminum foil, its not as smooth a surface as it should be, but it works.
The spark gap now consists of 2x WT20 tungsten welding electrodes, these are able of withstanding high temperatures without vaporizing as the copper wires were likely to do over time. There is still room for improvement on the spark gap as its still just a single jump static spark gap.
By calculating the Tesla coil in JAVATC I tuned the circuits to theoretically be in resonans, but its only approximating as the construction is far from precise.
With the new improvements 105mm sparks will jump to a grounded wire.
I took a series of pictures with different exposure times. Sparks are about 90mm long.
In the next picture racing sparks can be seen at the top of the secondary windings, without a breakout point or something to jump to, the energy build up is too large for the coil and its under a huge stress.
Conclusion
This small project started as a proof-of-concept model, to see if the theory I had learned would work in practice. It has come a long way since I started on it almost 2 months ago.
I learned alot more about the theory of the Spark Gap Tesla Coil, the math behind tuning the circuits and the importance of planning the design before building. This is no surprise. So there have been spend alot of time trying to optimize a Tesla coil build around a badly designed secondary coil, so the result will never be near optimal.
Despite all this, I am very satisfied with the results of 105mm sparks. There are several things to optimize in a final version of the Kaizer SGTC I, it would be a better spark gap, shorter and more suitable wires, shape of the primary coil and its coupling to the secondary and a topload with a smoother surface.
Demonstration
Posted December 13, 2009 by Mads Barnkob | Log in