Kaizer DRSSTC IV

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

Introduction

DO NOT REPLICATE THIS PROJECT!

If you do anyway, be aware of large switching transients that may damage nearby electronics, read this entire article before proceeding.

The idea to this coil came with Steve Ward showing off his first QCW DRSSTC that used a buck regulated DC supply to ramp up the supply voltage along with a long on-time to grow straight and very long sparks compared to the secondary coil length.

I thought it could be done simpler, yet with less control, by using the rising edge of 50 Hz mains supply voltage. From start of the sine wave to the top it corresponds to a on-time of 5000 uS and to be able to use large IGBT bricks the frequency would have to be kept down. Sword like behaviour of sparks is however mostly seen at above 300-400 kHz, where as lower than that results in more branched sparks.

 

Considerations

A high impedance primary circuit is needed to keep peak current at a level that the IGBTs can handle to switch for very long pulses, for a DRSSTC, up to 5000 uS. In order to get enough primary windings, I went for a upside-down U shape primary as a regular helical coil with high enough coupling would quickly get as tall as the secondary coil itself.

To use 3 IGBT bricks in parallel it is important to ensure as even current sharing as possible, this is done by mounting them close to each other on the same heat sink, drive them from the same gate drive transformer with individual gate resistors matched as close as possible.

Steve Wards universal driver 2.1b only has a robust enough 24 VDC section to run up to about 300 uS on-time with large gate capacitance, when trying to run with longer on-times than that, the 24 VDC 1.5 A regulator is now longer enough to supply the needed current. A external 26 VDC 8 A power supply is used instead and output stage will have to be reinforced to conduct higher currents and dissipate more heat.

 

Specifications

Bridge 3x  SKM145GB123D IGBT bricks in a parallel half bridge configuration
Bridge supply 0 – 260VAC through a variac
Primary coil 21 turns of 8 mm copper tubing in a up-side-down U shape
MMC 10 strings in parallel of 10 in series Kemet
R474N247000A1K
 capacitors for 0.047 uF at 9000 VDC, 280 A peak and 40 A rms rating.
Secondary coil 160 mm diameter, 330 mm long, 1500 windings, 0.2 mm enamelled copper wire.
Resonant frequency Around 100 kHz.
Topload 100 x 330 mm spun aluminium toroid.
Input power 10BPS, 500 cycles, 50A limiter: 750W at 260VAC at 3A.
Spark length Up to 500 mm long sparks.

 

Schematic

Bridge section

Driver section

Same as Steve Wards universal driver version 2.1b. Just made on single sided PCB without SMD components and the 24VDC part has traces reinforced, MOSFETs heat sinked and uses a external power supply. A external 26VDC / 8 Ampere power supply is used to ensure that under voltage will not be a problem, at least not before something starts to smoke.

 

Construction

31st October 2011
I put the bridge together on a heat sink with 3 phase rectifier used with all inputs in parallel for 1 phase supply and connected all 3 half bridge IGBT bricks in parallel with 3 straight bus bars. All recycled components from a DC link inverter.

Designed staccato PCB as the old layout used in my VTTC I was on a vero board. A optical output was added to use the interrupter with a standard DRSSTC driver.

Started construction of the secondary coil.

2nd November 2011

Etched PCB board for staccato controller.

Finished winding the secondary coil. It was made with a total of 1500 turns of 0.2 mm wire and dimensions 160 x 330 mm. Varnished the secondary coil with polyurethane varnish.

3rd November 2011
The secondary coil was given a second thick layer of varnish, not the most pretty job as I tried to pour as much varnish on as possible and let it rotate and settle it around the coil by itself. As the secondary coil was not completely in level it result in a little running, but overall a fair result of adding a lot of thin varnish.

Finished assembly of the staccato controller and bench tested it.

The project got shelved due to starting on a new job, after a long rest of over 3 years the box with parts was once again brought out in the light and construction could continue.

7th March 2015

Etched driver PCB and started populating the board with all passive components.

6th October 2015

Construction of a very cheap MMC from capacitors that was bought from a 10$ ebay auction for 100x Kemet R474N247000A1K, rated for 900VDC 28 A peak and 4 A rms. A easy and uniform construction, with current sharing in mind, is to construct it around a round piece of wood or plastic tube.

The resulting MMC has a capacitance of 0.047 uF at 9000 VDC, 280 A peak and 40 A rms rating. Which is spot on for this coil to be running with design goal primary inductance of around 100 uH, 300 A peak, 5000 uS on-time and maximum 10 BPS.

11th October 2015

Construction of acrylic primary supports, that has 21 slots and is formed for a up-side down U shape primary coil. A way of getting a large primary inductance and still maintain a certain distance to the topload as the secondary coil is very short.

The supports are made by hand using a saw, file and drill press.

16th October 2015

Getting the coil winded from the inside and out was no easy task, the whole large roll of copper tubing is heavy, easily bends too sharp and is like a spring. It will lock itself in the wrong slots and it can be a very frustrating piece of work. The complete result is however worth the effort, it looks smooth and even.

As the slots was not made to snap the copper tube in, from shear fear of cracking the acrylic, I made a small hole behind each slot that made it possible to tie each turn at each primary support, with a little piece of copper wire it is secured from deforming the coil.

As water cooling of the primary coil is going to be a must with the long on-times, simple clamps was made from copper sheet and two screws the fastens the 4 braided copper flexible wires to the tubing. The same 4 braided copper wires was soldered to the MMC terminals, as even as possible distributed around the circular copper wire terminal.

Having made the MMC on a wooden stick makes it easy to mount with two wooden blocks with holes in for the extra length of the round rod.

29th December 2015

Driver board populated with all active components. 24 VDC regulator is left out as this will be supplied externally from a 26 VDC, 8 A power supply. All traces related to the 24 VDC is reinforced by soldering a 0.5 mm2 copper wire along them. Four 2200 uF 35 VDC capacitors was added to the underside of the board, one at each N- and P-channel MOSFET. All output stage MOSFETs have heat sinks mounted.

All these precautions are hopefully enough to ensure no under voltage or over heating situation is possible when running at 5000 uS on-time.

25th July 2016

The coil have been put together with power supply, bridge, driver, platforms, secondary and topload. Two fuse holders for large bussman fuses was used at the end of the flexible copper braids for primary tap.

7th October 2016

First test of the coil after all the components have been put together, there are still a few things not in place, but it is good enough for initial testing.

The first test is without power on the DC bus. This is solely to test if the driver and power supply is good enough to drive the 3 IGBT bricks’ gates in parallel with a satisfying gate waveform. The following oscilloscope shots show the coil being driven at 5 ms on-time at 100 BPS, corresponding to every rising edge of the half wave rectified 50 Hz mains supply.

The following months, where I had only little time to do more testing, I could not get the coil to run properly with power on the DC bus. I could measure oscillation at the resonant frequency, but nowhere near enough for the coil to actually produce a output ever so slightly or just so small as to light up a close by fluorescent tube.

I tried running the coil with added 6000 uF capacitance, with normal interrupter, with and without DC bus snubber capacitor, with much fewer primary windings etc. I did a lot of changes to it, so it would be more like a regular DRSSTC, than a QCW, little did it help and I did not get much further before putting it away for Christmas holidays.

26th March 2017

After some online discussions as to what the problem could be, and showing off the coil for the first time, it was suggested that the regular 1:1000 cascaded current transformer for feedback was simply not delivering a strong enough signal as a high impedance coil naturally works with a much lower peak current. From the thread on the forum here https://highvoltageforum.net/index.php?topic=24.0 it is decided that I will try to make a new 1:50 turns ratio current transformer to see if increased feedback will help the coil oscillate.

The only capacitance on the DC bus was a 0.68 uF snubber capacitor, this was also increased to a 10 uF capacitor bank of MKP film capacitors. A small amount of energy storage is needed to make the phase correction driver able to run stable.

First light was achieved with some 20 cm long sparks, remember that the coil is far from tuned for maximum performance and the input voltage was only 200 VAC.

1st April 2017

I made a wide range of secondary and primary circuit measurements to find the resonant frequencies, as the U-shaped primary makes it difficult to simulate with tools like JavaTC.

The measurements was done with secondary in place inside the primary. But secondary ground was unconnected and primary circuit was left open loop by removing the tapping point. I am not sure if this is the correct method, as resonant frequencies are much different when measured with secondary ground or primary loop closed, this is because energy is then transferred between the two resonant systems. The results could however vary with 10-20 kHz compared to the open loop measurements…

Secondary circuit test results
Setup with a 80 cm long wire with 3 bend wires hanging over and pointing down to be “branches”. Signal from signal generator connected to ground terminal on the secondary coil, ground left floating. Signal into oscilloscope captured from open loop probe hanging next to secondary coil.

Unloaded result: 101 kHz, 80 cm wire result: 91 kHz and 80 cm wire with branches result: 88 kHz.

Primary circuit test results
Setup with signal generator and oscilloscope connected across the primary LC circuit and with a jumper across the IGBTs to have a closed loop. Signal generator is connected through a 10K resistor.

Primary resonance with secondary ungrounded – 7th turn from bottom 102kHz, 6th turn from bottom 96kHz, 5th turn from bottom 90kHz and 4th turn from bottom 86kHz.

Rest of the measurement results did not have individually saved oscilloscope shots, so here is a overview of the primary tapping frequencies.

I recorded video from oscilloscope and spark formation (dark dark video, blerg, sorry). There are 4 tests where primary is tapped at 96 kHz, 90 kHz, 86 kHz and last at 65 kHz, where it for reasons I still do not fully understand, performed the best! This is a huge detuning compared to the loaded 88 kHz secondary measurements. I also tried all the taps between 86 kHz and 65 kHz, with only increasing performance until I could detune it no further.

The staccato interrupter is not particular stable and does not really give a good clean 5ms on-time, it starts conducting before the zero crossing, possibly due to non-adjusted phase correction on the driver, this will get looked into next time its running. Waveforms are highly distorted, peak currents are low in the magnitude of 50 A peak. (Blue 100V/div inverter output – Yellow 100A/div current – 5-6 ms on-time)

and also some close up pictures of the beautiful sparks, still much shorter than what I expected, but maybe the very high impedance primary circuit just limits the current way too much, future experiments would be with a step up transformer for a higher primary peak voltage.

4th April 2017

From last nights experiments, I think that this idea might work on a small scale, the peak currents drawn by this large coil simply creates too large switching transients.

I tried tuning the coil at 120 kHz and 130 kHz, way above the estimated loaded secondary resonant frequency of 88 kHz. It performed better than ever before at 120 kHz tap, which properly makes a little sense compared to the better performance at 65 kHz, it certainly does seem to be a harmonics pattern here. But I do not think I can tap it any further down on the inner side of the primary coil right now.

There was however also much higher current draw, loud clunks from the variac and lights dimming! The voltage spikes on the mains supply are at levels where my voltmeter was damaged in my variac. This is also why I call quit on the project as it is, its future will be rebuilding it to a conventional, properly PWM controlled, QCW.

I had sparks fly out to about 50 cm as it can be seen in the video

Conclusion

So far the prototype has worked and shown that the concept works. The spark formation is more straight than first anticipated, as most QCW coils operate above 300-400 kHz to get long sword like sparks. It is however clear that the sparks produced by this coil, resonating below 100 kHz, is swirling a lot.

Tuning is very different from a regular DRSSTC where the sweet spot that produces the longest sparks at the lowest current can be within a few centimetre on the primary coil. Here I could get the same performance over a wide span of 60 kHz, tapping the primary anywhere would give me around 30 cm sparks, but it was easy to recognize when a true sweet spot was found, as the very abrupt current draw could be heard clearly from the variac clunking loudly and lights dimming slightly.

The switchings transients are however a great danger to nearby electronics and is of a magnitude where filtering is properly not enough, certainly it is not a solution to add more passive components to counter a problem that can be completely eliminated by using a different topology and have a control scheme that can control a ramped voltage from a capacitor energy storage, like the class D amplifier, phase shifted or PWM controlled QCW coils demonstrated by other Tesla coil builder.

I wanted to try this method, to see if simplicity could do the same job, it could not.

Demonstration

There is not a overall demonstration video yet, but the 3 videos from research development above.

Kaizer DRSSTC II

Introduction

I wanted to build a small DRSSTC in a few days without having prepared anything, most parts are reused or scrapped from things I have found and saved.

 

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

 

Considerations

I was nervous that the metal enclosure for the driver was too close to the primary coil and would absorb some of the energy, first tests show no sign of heating of the metal.

I made the bridge section entirely on a normal one sided PCB and was not too sure if the traces were thick enough to withstand the high peak currents or keep a low inductance layout. It all seems to work without problems.

 

Specifications

  Revision 1 Revision 2
Bridge 2x G12N60C3D IGBTs in a half bridge configuration 2x IXGN60N60C2D1 IGBTs in a half bridge configuration
Bridge supply 0 – 160VAC through a variac, 6A rectifier bridge and 2x Aerovox 410uF 430V filtering capacitors in parallel.  0 – 210VAC
Primary coil Flat primary. Inner diameter 70 mm, Outer diameter 187,36 mm. 6 turns 1,78 mm copper wire (2,5 mm²), turn spacing 8 mm. Tapped at 4.8 turns.  
MMC 2 in series Cornell Dubilier (CDE) 942C20P15K-F capacitors for 0.075uF at 4000VDC rating.  
Secondary coil 50 mm diameter, 200 mm long, 1430 windings, 0,127 mm enamelled copper wire.  
Resonant frequency Around 327 kHz.  
Topload 40 x 215 mm aluminium tape on a Styrofoam toroid.  
Input power 250BPS, 250uS on-time, 68 primary cycles, 300A limiter: 120VAC in.  350BPS, 120uS on-time, 35 primary cycles, 280A limiter: 210 VAC in at 2A. 420 Watt.
Spark length Up to 240 mm long sparks.  Up to 370 mm long sparks.

 

Schematic

The driver is a variation of Steve Wards universal driver and beneath you can see the bridge schematics.

 

Construction

13th August 2011

Optimize driver PCB, design bridge PCB, toner transfer to PCB.

14th August 2011

Etch PCBs, assemble bridge PCB completely, half done with driver assembly. Heat sinks, electrolytic capacitors, voltage splitting capacitors and rectifier bridge are all salvaged components. Materials for building a enclosure and base is found. Lexan salvaged from LCD monitors is used for the base and some normal house wiring is used for the primary coil.

 

15th August 2011

Winding CTs for feedback and OCD, building enclosure and base, driver PCB assembled.

 

16th August 2011

Driver PCB fault finding and testing, enclosure and base building. I had forgot to add the trace that resets the OCD on the driver board after I moved it while optimizing the board layout.

 

17th August 2011

Complete construction and ran first test, no first light.

Some more detailed pictures of topload, secondary with terminations and primary coil.

Flat primary. Inner diameter 70 mm, Outer diameter 187,36 mm. 6 turns 1,78 mm copper wire (2,5 mm²), turn spacing 8 mm.

50 mm diameter, 200 mm long, 1430 windings, 0,127 mm enamelled copper wire.

40 x 215 mm aluminium tape on a Styrofoam toroid.

 

28th August 2011

First light, phasing of feedback transformer was wrong.

3rd September 2011

24 cm sparks, running 250uS, 68 primary cycles, 120VAC in, 268A primary current. 250BPS.

 

Here is a scope shot of the primary current waveform and a zoom of the same.

 

4th September 2011

I blew up both IGBT transistors running at the same settings as above on the 3rd September 2011, but at 160VAC input, nothing violent, just a flash and all was silent.

I will rebuild the bridge with IXYS IXGN60N60C2D1 IGBTs, which will hopefully make the bridge indestructible compared to the size of this Tesla coil.

11th September 2011

Rebuild the bridge and spent the day fault finding on the circuits as it did not work, turned out to be a 33V Zener diode on the bridge board that was short circuited.

 

16th September 2011

I recorded some data from different settings and came up with following before admitting that my heat sink is just too small. Further tuning is till needed, I hope it can do better and it seems to never go higher than 280A primary current.

I peak Voltage in, AC Current in, AC Burst length BPS Watt, AC Spark length, mm
280 210 0,5 120 200 105 274
280 210 0,75 120 300 157,5 290
280 210 2 120 350 420 354
280 210 4 120 500 840 370

200 BPS, 274 mm sparks.

 

350 BPS, 354 mm sparks.

 

500 BPS, 370 mm sparks.

 

Here is the current waveform which pretty much stayed the same doing these tests, also a better quality picture of the sparks.

 

Additional tuning gave me much better results in the form of almost the same spark output at lower on time, lower peak current and lower power in.

Here it is a screenshot of a spark going out to 337 mm running 70uS on-time, 260A peak current, 300 – 400 BPS at 260VAC at 0.5A.

 

Conclusion

Revision 1

It is no problem building a small DRSSTC in a few days with some previous knowledge and a off the shelf secondary coil.

In the future I will properly not make another Tesla coil with TO-247 IGBTs, I need some more overhead with the way I push my Tesla coils.

 

Demonstration

28th August 2011

First light

 

3rd September 2011

Came out a bit dark, but shows 24 cm sparks, running 250uS, 68 primary cycles, 120VAC in, 268A primary current. 250BPS.

 

16th September 2011

37 cm sparks, running 120uS, 35 primary cycles, 210VAC in, 280A primary current. 200 – 400 BPS.

 

16th September 2011

33,7 cm sparks, running 70uS, 260VAC in, 260A primary current. 300 – 400 BPS.

14th February 2012

Playing Doom 1 – Episode 1 soundtrack with my new midi modulator.

Kaizer SSTC III

Introduction

The idea was to build a very small and compact Tesla coil as a gift for my mother that works in various science classes for the lower grades in public school.

This driver circuit is very similar to the one used in Kaizer SSTC I. This time I have made a PCB containing both driver circuit and bridge.

 

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

 

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, to 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: Self tuning at around 470kHz.Rev 2: Self tuning at around 180 kHz.
Topload Rev 1: Made of two bottoms from beer cans, 65mm diameter and 30mm in height.Rev 2: 45 x 152 mm turned aluminium 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 and PCB files

PCB file for ExpressPCB

 

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 a bit shaky as I have drawn them all by hand.

The MOSFETs uses the enclosure as a heat sink, 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 heat sink.

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 banana jacks 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 beer can

 

Sparks

Here is one of the more spectacular spark pictures I have taken, in my eyes it looks like a demon waving 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 short circuited. 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 acrylic for a complete look.

 

19th August 2009

The new secondary is finished, it took me about 8 days to do the winding as it is very intensive to wind with such a thin wire. Keeping the wire tight, windings close 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 aluminium toroid, with this it have a new resonant frequency around 180 kHz.

Top of secondary was filled with epoxy to insulate the brass bolt from the inside of the secondary and the bottom earth connection is fastened with a nylon bolt.

It is all fitted onto a piece of acrylic with additional protection around the primary connections so it no longer possible to touch any conducting part of the primary circuit.

 

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 and its not 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.

 

Conclusion

I am very satisfied with the final result, that I got to fit everything and use the enclosure as a heat sink turned out real good. Heating is not a problem with run times 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.

Revision 2 looks even better, performs better but was also a lot of work to wind the new secondary with such a thin wire.

Demonstration

Revision 1

Revision 2

Kaizer SSTC I

Introduction

This is my first solid state Tesla coil, so I went with a sturdy and proven schematic made by Steve Ward. 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.

 

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

 

Considerations

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.

The interrupter will be changed to go down to a very low break rate.

 

Specifications

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.

 

Schematic

All unused input pins of a 74HC14 has to be tied to ground, floating inputs and a noisy environment is a recipe for trouble. The noise can couple between the gates internally and make the whole IC not work properly.

 

Construction

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.

 

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.

 

Sparks

Here are some pictures from the first light, input power is from 30VAC to 230VAC at up to 5A.

 

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 and its not 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.

 

Conclusion

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.

 

Demonstration

In thew following videos, the SSTC I is playing music from the interrupter shown in schematic for the SSTC II.