Low Voltage DC Interrupted SSTC's (Tefatronix, Skori)

[Magneticitist]

For anyone who may be interested in small coils like me I made a single video showing the output of 3 different variations of what I've basically been calling a Tefatronix style circuit, which is sort of a simplified Skori driver. Tried to make timestamped links but it didn't work. These are really handy for using 30V DC supplies or so. I think I've seen a couple iterations on forums but there aren't many around the net it seems. Figured I would post something here before I put these coils away for a while.

Tefatronix circuit at http://tefatronix.g6.cz/display.php?page=sstc4&lang=en
is a really good baseline for this circuit to see how it works.
Skori and Tefatronix have the most impressive results I think and Skori has a lot of detailed explanation of his drivers on his webpage.
http://skory.gylcomp.hu/tesla-ml/index.htm
http://skory.gylcomp.hu/tesla/mini_tesla.html

You can see that it is self oscillating with secondary feedback using a 1:1 transformer or thereabouts to drive a push-pull stage. This means that you can more or less build a 'high power Slayer exciter' with just a small GDT and extra mosfet. I have been making these circuits for a while and find them to be a great way to get fun discharges from low voltages or pull ZVS-like arcs from small coils. Most of them had been thrown together only experimenting with the GDT and primary. With a dual resonant primary one can run at 12V and get inches of arcs. It is also common to see sword-like discharges from these circuits. These can be tuned to run continuous anywhere in the realm of 1v to 30V or so before pulling in excess of around 10A but it is all around better to run them interrupted where one may want to sacrifice running continuous for longer arcs. This is like an in-between circuit to play with interrupted arcs after building a Slayer Exciter but before going to a high voltage half bridge.

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The first coil is the smallest I've made so far and it's just a bit tinier than Tefatronix's. I usually run this ungrounded but adding the ground slightly improves performance. I use a TL494 to interrupt all of these via a 12v regulator. There is some slight primary arcing where the topload is just too close.
This uses IRFZ44N mosfets (this circuit at 26V or so is reaching about the ceiling with these)
Secondary is 1 x 1.2 inches using 40 AWG wire
The GDT is about 9 turns bifilar
Primary is 5+5 interleaved windings and center tapped similar to Tefatronix' flat cable primary

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@2:48
Second coil is a bit larger at about 2 inches tall and 1.7 inches wide also using 40 AWG. There are two chokes on the input allowing for a primary without a center tap. It seems increasing this secondary to a slightly larger size can also increase the output considerably.
It uses 3x 18650's to make a fully charged 12.6V battery which feeds a 35v max boost converter.
I set the max voltage on this to around 26V to avoid possibly damaging the 12v regulator and the mosfets.
Again using IRFZ44Ns and about a 9 turn transformer for feedback and gate driving. Everything could be made so much smaller than I have here but I'm not very good at condensing.
Primary is 2 turns of 12 AWG.
This was meant to be dual resonant but I damaged the first coil and left the capacitor. Still works.
It will run CW at around 12V for short periods but heats up the small heatsink quickly without a fan.
This circuit taught me that with just the right tuning (which I only saw for a little while before being unable to reproduce it) a dual resonant SSTC of this size can produce something like 3 inch discharges at only 12-13v on the bus. That had ultimately destroyed the small series capacitor I was using and I settled for this more reasonable output. It's not easy to get Skori's results at 12-18V but, possible of course.

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@5:03
Third coil is the largest iteration I've made of this circuit but it also gives me the longest discharges at about the 30V-50V intended max input voltage. I've ran it up to about 60V before it started having trouble but was able to pull 6 inch arcs at 50V and have had it tuned just right to where it could barely stretch out 6 inches at a high duty cycle low bps @30VDC.
It uses IRFP250 mosfets and an IRFZ44N for interrupting
The transformer is a small 1:1 of probably 25-30 turns I pulled from some board
Currently about 8000uF on the bus
Circuit is dual choke fed with a 4 turn primary and incrementally tuned series capacitor with an additional parallel 5nF or so. It is currently tuned to where the breakouts are longest at 30V-50V but could still tune it for pretty good arcs at around 15V-24V.

I think this kind of arrangement allowing for a higher voltage bus ceiling is a good in-between circuit
where one can get more than puny arcs at under 50V which is what may be close to the ceiling of a 'safe' or more commonly attainable DC supply voltage.

[Gisho]

Thank you for all this info ,I'm thinking of replicating this build but can I use a 555 timer interrupter instead? I've heard that this should go well with the fets at 10% duty cycle
Pls give me any tips as I have mediocre knowledge in electronics, It would be very helpful  

[Magneticitist]

555 would work fine. I'm careful with my potentiometer when using the TL494 and not limiting the max duty cycle, but have found some arrangements can handle temporary CW at lower voltages such as 5v-12v without needing an insane sized heatsink and active cooling. I have one I run in CW from a 30V 5A supply which in reality pushes about 33V at 6A or so. I keep the fets on a large heatsink and it can run indefinitely. As for the interrupter you may want to invert the signal with a small transistor so an LED indicator makes sense since the interrupter mosfet needs to be on all the time to force the push-pull fets low. I just wire my pot 'backwards'.
It's often easy enough to trial and error a couple primaries as far as coupling distance and then play with the height it sits along the secondary. A regular single conductor can be used for the primary. There seems to be certain phase-shift it tends to run at for longest arcs depending on the GDT used and for me they usually don't seem to reach out well til about 24V and higher. I made a couple using IRFP260's that would pull some nice hot arcs at only 12v or so and pulled about 10A in the process. Another thing to remember is to have the voltage divider on the mosfet gates set properly. You want to start at no voltage across them and slowly increase it looking for oscillation. Shielding can also be tricky with these so try not to create long leads and keep everything tight and short as possible. I've often tried to run wires to pots and the interference became a problem in the interrupter.