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
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.
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 | Selftuning 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
Construction
22nd January 2009
I began the construction of the half bridge circuit in a small plastic box, the heatsinks are a Pentium II heatsink cut in half. The bridge is made fra 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 veroboard with a external 12VDC powersupply.
Troubleshooting
23. 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 ofcourse upset me when it happend 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 themself 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 bananaplugs 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 powerbar. 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 shortcircuit 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 shortcircuit 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.
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 interuptor 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.
I wanted to ask you what you think of Steves DRSSTC schematic with the flip flop circuit, so that the interrupter never shuts off the UCC’s. I came up with a way to use another 555 with the feed back as part of its timing instead of the 74HC109.
does it actually need a “flip-flop” device? because some times the output wont line up and will send out a very short on time
http://www.stevehv.4hv.org/DRSSTC1.htm
Hey Daniel
I am only working with his universal driver as Steve called his own older designs for obsolete compared to the new driver.
I am wondering, what is c4 for in the schematic, is it a dc blocking cap or it it used for something else?
Hey Marshal
Its a DC blocking capacitor that should stop the heavy DC currents from flowing at the rather low DC voltages that the GDT sees. If you have problems with lower values, try using a larger, up to some uF and with a 100nF in parallel, this should take care of resonance in the GDT primary drive circuit.
Hi Mads, I am looking to start experimenting with SSTC’s and was wondering if I could use a 36v supply for the half-bridge if I lowered the primary coil turns and perhaps made the secondary coil a bit smaller. I understand that I will get a much lower spark output from the secondary coil but I don’t mind too much as this would be my first time making a SSTC.
This 36v supply is 3 12v 7ah lead acid battery’s and I don’t need long runs from the SSTC whilst experimenting so I can afford to allow for a higher current draw in return for using a lower voltage.
Just wondering if that would work? And would I need to adjust anything else such as C8 and C9 in order to allow for more current to be drawn?
Thanks.
Hey Alex
I have limited experience with low voltage SSTCs as I have no problem using mains supply, as an electrician I am comfortable with it.
You could omit the capacitors and make the half bridge as this http://webpages.charter.net/dawill/tmoranwms/Elec_IndBridge.gif
You should properly look for some 100V higher current rating MOSFETs
Kind regards
Mads
Thanks for that Mads.
About using mains power, I am waiting until I can find/source a variac before I start using mains power with my projects. I am fine using mains for small low voltage step down transformers or items that have been commercially designed and tested for mains use, I am just slightly wary of connecting homemade circuits to it without a variac.
Plus I have my parents who don’t like the idea of me doing any electronics, seriously if a light-bulb blows or something happens they always blame me and my electronics! Talk about ignorance right.
Anyway enough ranting and on to finding a decent piece of tubing to wind my secondary coil onto.
Alex.
Hello, I want to ask if it is possible to run this design without a variac?
The question is if it is possible to run this SSTC directly of the mains 230 VAC with a bulb as current limiting for charging the capacitor in the start, and after the capasitor is charged, just bypas the bulb and run the tesla coil directly from mains suply, without using a variac?
Hi Benjamin
It is possible to run it as you say, but be aware that you have to design it carefully to run at full voltage from day one, doing first light and testing and tweaking a variac will save you some headaches.
If you don’t have a variac, maybe use a 230v to 48v transformer or something in that manner, for testing, else you just risk a BOOM at full voltage and will have to rebuild and fault find on burned tracks.
Kind regards
Mads