SSTC Micro

[jockoFergy]

Hey everyone!
   After months of tuning and measuring voltages I finally got my Micro SSTC to spit some fire, but could be better... I am using Steve Wards micro almost exactly, except my interupter 555 has adj feq and duty cycle. I can add schematic if need be but my question might be easily answered, so Ill start off simple... so i got some 3 cm breakouts which is an achievement for me but i noticed when i touch my flathead to the trimmers(both for freq and duty cycle) the streamers double in size. I'm wondering, does that mean something with my ground isn't optimal? If its not that simple i'd be glad to post my schem, pics of coil and scope. running at around 300 kHz btw...
Thanks in advance!
Jocko

[Mads Barnkob]

Hi Jocko and welcome to HVF!

Your body is a capacitor in the high frequency world, you act as an amplified feedback signal injection into your circuit.

Try to increase the feedback in the antenna to the driver circuit by having it closer to the secondary coil.

Please do post pictures, video and everything else you want to share.

[davekni]

The 555 in Steve's circuit appears to be used to start the oscillation, not as an interrupter.  Your version should work as long as the 555 frequency is somewhere near the coil resonant frequency.  Your issue could be that the coil is running at the 555 frequency instead of resonance.  As Mads suggests, placing the antenna closer should help, causing antenna feedback to override the 555 frequency.  (That's the circuit intention, for the antenna to override.  That happens more easily the closer the 555 frequency is to resonance.)

[Magneticitist]

Yea the 555 is there to just kickstart/maintain the oscillation and feedback and is supposed to help keep it stable when loading it but I've found it unnecessary so long as I start the circuit up. Steve set the 555 at around 300khz or so which is close enough to the resonant frequency of the coil to get the feedback to take over properly. I added a 74hc14 instead although that isn't really necessary either. The antenna feedback can get wonky but it works well enough if arranged properly. Using some type of ground plane seems to help as well as placing the antenna of a certain length at just the right location near the coil. Steve has the enable pin tied to the input on his circuit but you can separate them and add your interrupter addition to control the enable pin. 

I noticed recently his website is down but luckily it's archived on the waybackmachine for anyone interested https://web.archive.org/web/20190111164436/http://stevehv.4hv.org/SSTCindex.htm

[jockoFergy]

HI and thank u for taking a look!
So I did some further readings with the scope and my coil is actually running at 994 kHz! One thing i did notice however is when i do in fact touch the trimmer POT current draw climbs to 2.95 amps, at 31.5 volts btw, AND... this time the large resistor going from the interrupter output to the antenna started smoking and pretty much melted. So, bear with me cuz I'm no EE, self taught with physics background and a LOT of trial and error (and watching Kaizer P.E. vids!)  That's gotta be coming back from the coil right? Its 1,000,000 ohm resistor. So since the coil is running at it's own freq and not the interrupter then I need to move the antenna further from the coil rather than closer correct?
Oh I tried to take a picture with my phone to show the breakouts but while touching the trimmer POT it doesn't matter how far back I go, the phone goes crazy and will not cooperate... I need either to buy a camera, or make a friend to snap the pic... so sad... that I dont mind, that is. No time for friends, way too obsessed purturbating the ether with forces of epic proportions!
Anywho, I'll leave a pic of my setup at least, might help your diagnosis. One other quick thing... was watching diodegonewild solid state TC and he used an IR2153 which is a half bridge driver with built-in pulse generator. That seems like the most awesome convenient chip EVER. Do yall advocate or condone using this over uc37321 and separate pulse gen reasons why it's good or not ideal?
THANK YOU ALL AGAIN.
PS nothing against anyone else, I appreciate all input and help but just gotta say, Mads and Magneticist, huge fan, your content is what got me into this whole world of awesome, and it's all I ever wanna do with my free time now... like unhealthy obsession! K b4 it gets weird I'll just say yall are fricken awesome, and thanks...

[Rowdy]

his time the large resistor going from the interrupter output to the antenna started smoking and pretty much melted. So, bear with me cuz I'm no EE, self taught with physics background and a LOT of trial and error (and watching Kaizer P.E. vids!)  That's gotta be coming back from the coil right? Its 1,000,000 ohm resistor. So since the coil is running at it's own freq and not the interrupter then I need to move the antenna further from the coil rather than closer correct?

Ok maybe a typo here but are you talking about R5 or R1? One is a 10K and the other is 100K.
Maybe try this to adjust pots...
https://www.mouser.com/ProductDetail/Bourns/H-90?qs=nS9uH9%252BmxhzS2pH7coy5Fw%3D%3D
But sounds like thats not only the problem. Take your time and check your wiring and part values, I know
I have put in the wrong parts a time or two 

[davekni]

IR2153 is self-oscillating, so designed for open-loop uses.  It could be sync'ed to a Tesla coil with feedback, but it's not quite as easy.  Depending on gate charge, it would overheat at higher frequencies.  Looks like it's targeted to 20kHz-100kHz applications.

Your high 994kHz operation may be due to wiring inductance.  I see one 2200uF cap hanging off the circuit with wires.  At least some supply bypassing needs to be on the board (short wires for low inductance), especially at the regulator (U1) input and output and across the gate driver supply and ground pins.

Is it 10 ohm resistor R3 that is hot?  That would be expected at 994kHz.  It requires a lot of power to turn on and off the large FET gate at high frequency.

What are the spec's of your secondary (and primary) coils?  The image looks like a long secondary of fine wire for high inductance and low frequency.  (Adding a top load further decreases the secondary frequency.)  That raises another issue that could be causing high-frequency oscillation.  The antenna may be coupling to the primary rather than to the secondary, so oscillating at the primary frequency.  1MHz may be reasonable for the primary coil and 1nF C3.

[Magneticitist]

It's great there are still people messing around with this stuff and still highly experienced people willing to help cause I only have so much of a clue. I hadn't played around with the antenna feedback too much because I wanted to use a CT instead but I did notice how easily it can get thrown out of wack without careful placement though. Came to the conclusion something like the common use of an actual extendable antenna which can be articulated around may be a good way to go about it to find an appropriate spot. As for your increased feedback when touching the pots, you might want to try to arrange the setup in a way where you're not moving your hand real close to the antenna. When it comes to touching the pots you only need to do that once anyway and the coil doesn't need to be running because you're just trying to produce a set frequency. Better to not use pots at all unless testing resistance before changing out to a set value. If you're still currently using Steve's exact circuit more or less which doesn't implement interrupting, you want the coil running at its own frequency. The 555 timer is always putting a weak 300khz or so signal into the gate driver so if for some reason when say pulling an arc, the coil wants to kick out of self oscillation, the 555 timer signal will be there to kick it back in immediately. Hard to really tell how it would all work out til tidying it up after double checking all wiring. The circuit itself is pretty neat and convenient and if say running from a decent DC supply can be condensed down rather small.

[jockoFergy]

Very helpful thank you all. The resistor that burnt up was 100k R1. And yes tall skinny thin wire secondary. Funny thing it wasn't the one I built originally for this project. The one originally built matched Steve's pretty close. the circuit matches his so perfectly cuz I just couldn't get mine to work so gradually as I got more and more frustrated, my logic was there must be something I'm doing wrong and since I cant figure it out, it got closer and closer till exact same. After that it still didnt work so started just using other coils I had wound already, along with trying different primaries (solid, stranded, Cu pipe, diff gauges, etc) and got lucky honestly, and got tiny breakout. After that something clicked. So now I gotta tidy up the circuit and see how it goes. As far as using the pots, no I dont ever adjust it really. It wasn't that it was a problem, actually opposite! I WANT the results i get from touching it, minus the fried resistor.
  I'll post some pics when it's done. As soon as i get the ucc37321 gate drivers I'm moving on to half bridge! Resonance is crazy y'all! The universe was built on constructive interference!  Cant get enough of this shite!

[Magneticitist]

I first tried doing things like running the antenna wire to chunks of metal like heatsinks, then did the same for the bottom of L2 and sort of moved them around each other various ways while observing the output. I think I had something wonky going on. Eventually at a certain voltage the bottom of L2 caught fire trying to char its way through the wooden platform base to get to the antenna which was touching a heatsink also laying on the wooden base. For that brief moment when the two met through a small link in burning carbon the output went insane lol. I only caught it out of the corner of my eye while I was panicking to hit the off switch but it was an order of magnitude greater in output. I guess for that moment I was getting direct feedback from the bottom of L2 without any current limiting but I wouldn't expect it to run that way for long, although I kind of wonder how that would fare on the Micro SSTC given the low input voltage. When I eventually moved to the CT feedback it seemed like it wasn't really easy to position the antenna in a way where I would get the same output. I've talked to some people who make the antennas seem easy and others who don't like dealing with them at all. I've seen builds where the bottom of L2 just floats all by itself with a little corona on the tip and the antenna is some short piece just stuck out toward the side. A buddy I know who is a skilled tinkerer had troubles with it even after a lot of work and what looked like logical layout and positioning. Progress is made either way you look at it regardless of plasma output though!

[davekni]

The bottom of L2 needs to be grounded as shown in Steve's schematic.  (You may get some results with floating, as it still couples to ground a bit through capacitance to L1.)

An antenna needs to couple to the top of L2 more than L1.  It's the L2 resonance that needs to be driven to get performance.  If the antenna is too close to the L2/C3/Q1 connection, then the circuit may oscillate at the primary L1/C3 resonance.

That long secondary with fine wire will resonate at a relatively low frequency, probably too low to be effective for the high-frequency primary.  Use javaTC or whatever to calculate L2 inductance and resonant frequency with the top load.  Then change back to something in the 300kHz range.

There is some circuit wiring error for R1 to be smoking.  R1 connects between driver chip pin 2 and ground.  The driver chip would be toast long before its pin 2 has enough voltage to fry R1.