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Introduction
The idea was to build a very small and compact tesla coil as a gift for my mother that is working with various science classes for the lower grades in the public school.
This is a very similar driver circuit, the same as used in Kaizer SSTC I. This time I have just made a PCB board containing both driver circuit and bridge.
Considerations
I knew this would get claustrophobic with so little space for a complete interrupter, driver and bridge.
Using the enclosure as the heat sink is the reason why a low break rate is chosen, so avoid excessive heating.
Specifications
| Bridge | 2x IRFP460 MOSFETs in a half bridge configuration |
| Bridge supply | 230VAC directly from the wall, 4A rectifier bridge and 330uF smoothing capacitor |
| Primary coil | Rev 1: 55 mm diameter, 1.38 mm diameter isolated copper wire, 10 windings.Rev 2: 80 mm diameter, 1.38 mm diameter isolated copper wire, 10 windings. |
| Secondary coil | Rev 1: 50 mm diameter, 200 mm long, 1430 windings, 0.127 mm enamelled copper wire.Rev 2: 75 mm diameter, 165 mm long, 1500 windings, 0.1 mm enamelled copper wire. |
| Resonant frequency | Rev 1: Selftuning at around 470kHz.Rev 2: Selftuning at around 180 kHz. |
| Topload | Rev 1: Made of two bottoms from beercans, 65mm diameter and 30mm in height.Rev 2: 45 x 152 mm turned aluminum toroid. |
| Input power | Interrupted mode: ?W at 230VAC input voltage. |
| Spark length | Rev 1: up to 140 mm long sparks.Rev 2: up to 250 mm long sparks. |
Schematic
Construction
21st July 2009
I designed a compact single sided PCB that contains both driver and bridge section on a mere 65 x 75mm board. Here is newly etched board, traces are abit shaky as I have drawn them all by hand.
The MOSFETs uses the enclosure as a heatsink, I sanded down the paint for metal contact and use pads to isolate between MOSFETs and enclosure.
BPS is kept low, but can be varied from 4 to 20 BPS, to avoid excessive heating as the enclosure is not an optimal heatsink.
In the bottom of the following picture you can see the bridge rectifier mounted to the enclosure and the input filter for 230VAC in. The red wires lead to the 330uF/400V smoothing capacitor and the 100nF/1600V Rifa capacitor is the DC blocking capacitor in the primary circuit.
The coil is connected directly to 230VAC without any kind of voltage regulation and also requires a external 12VDC supply for the driver.
Antenna and primary coil connections are temporary solutions for the sake of demonstrating the tesla coil in working order. A fold out antenna from a small radio or such will be added later. Some kind of support with bananajacks with a secondary and primary coil mounted on will be added, to avoid wrong phasing of the primary coil.
Here the complete setup is size compared to a 330ml beercan
Sparks
Here is one of the more spectacular spark pictures I have taken, in my eyes it looks like a demon waveing its arms over the head which also have a distinct face with glowing eyes and a open mouth, or maybe I am just seeing things from inhaling too much ozone 
24th July 2009
I borrowed a expensive macro lens for my Canon 350D camera and took some pictures with great details of the sparks, very sharp pictures!
Revision 2
1st August 2009
Doing a short demonstration I adjusted the antenna with my hand while the coil was running, this resulted in unstable oscillations and the bridge was shortcircuited. I am now replacing the destroyed MOSFETs and here I can feel the disadvantage of servicing on a compact design.
A new secondary coil is in the making, it is wider, shorter and have half the resonant frequency of the first. It will be fitted nicely on a piece of plexi for a complete look.
19th August 2009
The new secondary is finished, it took me over 8 days to the winding as it is very intensitive to wind with such a thin wire. Keeping the wire tight, windings tight to each other, not pulling the wire too hard from the spool, watch for jams and overlaps and it all have to be done with a bright light very close to get a good view.
It uses the topload from my VTTC I, a 45 x 152 mm aluminum toroid, with this it have a new resonant frequency around 180 kHz.
It is all fitted onto a piece of plexi with addtional protection around the primary connections so it no longer possible to touch any conducting part of the primary circuit.
Conclusion
I am very satisfied with the final result, that I got to fit everything and use the enclosure as a heatsink turned out real good. Heating is not a problem with runtimes at about 2-3 minutes which is also the durations its been built to be demonstrated for.
Enclosure dimensions are 125W x 80D x 50H mm.
Demonstration
Revision 1
Revision 2
Very nice work. I hope to have my minni sstc going soon.
Please help. I need a little info. I cant get this coil to fire without touching and holding the antenna first.
I used your schematic to a tee. I also tried switching the antenna coupling diodes to 5 v zeners, Still no luck.
Thanks again. CJ
Have you tried moving the antenna closer to the secondary coil?
My antenna is often within 6 – 8 cm from the coil and will occasionally have a bit of corona at the end
Thanks, I will try that tonight.