This is my first solid state Tesla coil, so I went with a sturdy and proven schematic made by Steve Ward. After all, a lot of other coilers have replicated this circuit with great success and therefore it is easy to find information how it works and how to troubleshoot it.
High Voltage Safety
WARNING!: Working with electricity is dangerous, all information found on my site is for educational purpose and I accept no responsibility for others actions using the information found on this site.
Read this document about safety! http://www.pupman.com/safety.htm
One of the differences from the original circuit is that I use 230VAC input instead of 115VAC. So capacitors and MOSFETs have a higher voltage rating. I will change the interrupter to be able to go down to a very low break rate.
|Bridge||2x IRFP460s MOSFETs in a half bridge configuration|
|Bridge supply||0 – 230VAC from a variac, 8A rectifier bridge and 330uF smoothing capacitor0 – 325VDC on the bridge.|
|Primary coil||115 mm diameter, 1.78 mm diameter isolated copper wire, 10 windings.|
|Secondary coil||110 mm diameter, 275 mm long, 1000 windings, 0.25 mm enamelled copper wire.|
|Resonant frequency||Self tuning at around 250 kHz.|
|Topload||100 mm small diameter, 240 mm large diameter, toroid.|
|Input power||Continues Wave mode: 1000 W at 230VAC input voltage.|
|Spark length||up to 250 mm long sparks running interrupted.|
All unused input pins of a 74HC14 has to be tied to ground, floating inputs and a noisy environment is a recipe for trouble. Therefore noise can get coupled between the gates internally and make the whole IC not work properly.
22nd January 2009
I began the construction of the half bridge circuit in a small plastic box, the heat sinks are a Pentium II heat sink cut in half. The bridge is made from copper wire size 2.5mm² / AWG14.
The bridge is made from a 8A bridge rectifier with 330uF 450V smoothing capacitor, two IRFP460 MOSFETs with MUR1560 diodes, two 0.68 uF 400VAC film capacitors for the voltage splitter and 10R gate resistors.
The driver circuit is made on vero board with a external 12VDC power supply.
SSTC Problems and Troubleshooting
23rd January 2009
When I first tried to run the driver circuit separately to test the driver before connecting it to the MOSFETs, it only resulted in the MOSFET driver chips (UCC37321/UCC37322) catching fire and burning up like a small volcano. This did of course upset me when it happened once more when I had changed the chips. This led me to seek help and I learned that running the driver chips unloaded, without a MOSFET or GDT connected to the outputs, the chips will oscillate into oblivion and burn them self down.
With the complete circuit put together it all worked except the primary coil was phased wrong, but it was no problem since I used banana plugs for the primary connections.
I ran the coil as CW (Continues Wave, non interrupted so its switching at its resonant frequency) to stress it to its maximum, which also did result in failures at 230VAC in, drawing around 4 to 5A.
The secondary coil was grounded to the mains ground in my house, but by accident I were using a plug without a earth connection in, so the secondary earth was arcing to the phase and neutral in my power bar. Pushing around 1 kW into this rather small circuit with passive cooling became enough combined with HF noise on the phase and neutral and one of the MOSFETs exploded violently and the other died silently. Here I discovered my design did not make it easy to change the MOSFETs, a important thing to consider in future constructions.
For the next couple of days I could not get the coil to work again. Everything in the driver circuit was changed and measured with a oscilloscope without finding anything out of order. It was first when I by accident measured short circuit connections with a DMM that I discovered one of the secondary windings on the GDT was not connected to the MOSFET, it was because the gate resistor was destroyed from the short circuit of the MOSFETs. Changing the 10R resistor made the whole thing work like a charm again.
Here are some pictures from the first light, input power is from 30VAC to 230VAC at up to 5A.
SSTC Audio Modulation
I use a audio modulator made by the user Reaching (Martin Ebbefeld) from 4hv.org.
For sound input I use a cheap children’s keyboard from a toy store. Its far from perfect for the job, especially because its waveform is highly distorted. It does not deliver clean tones ,but seems to involve a lot of modulation inside it to simulate different instruments. But its cheap and expendable.
Watch the film and look at the schematics for more about the audio modulation.
Building this clone of Steve Wards SSTC5 was a great introduction to solid state Tesla coils. I now have a understanding of how it works from interrupter to driver to bridge.
Further projects with this circuit will be a complete rebuild with audio modulator and a full bridge of MOSFETs, this will be a separate project.
In thew following videos, the SSTC I is playing music from the interrupter shown in schematic for the SSTC II.