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Tesla coils => Solid state Tesla coils => Topic started by: Thunderstruck on January 21, 2019, 02:23:54 AM

Title: SSTC build as per Steve Ward's Mini SSTC - Final Design
Post by: Thunderstruck on January 21, 2019, 02:23:54 AM
Hello everybody,

First I would like to mention that I am aware that I am starting a new thread straight after a thread based on the same design, which could be considered as Double Posting. So I leave it up to the admin to allow it or not.

Anyway, after successfully building a SRSG Coil a few years ago, I decided to have a go at building a SSTC because it will allow me to experiment without a noisy spark gap, also everything is smaller and easier to handle.

For my first attempt I chose Steve Ward's Mini SSTC Design, it looks simple enough and easy to understand.
My understanding of electronics is OK, should be sufficient to build this circuit, but please forgive me if I ask a "dumb" question ( I'm only dumb till I get an answer  :) )
Anyway, I built the circuit and powered up the low voltage side to see if anything will go pop, aaand to my delight, there was no pops !
I recently got myself a new digital scope to replace a very basic CRO which is at least 25 years old, so this is a perfect opportunity to put it to a good use so I had a poke around to see how things are buzzing.
There are a few things that I do not make sense, perhaps of my lack of understanding, perhaps there is a fault somewhere, so I decided not to give it a full test until I get some clarification.
I hope somebody will be able to help me out with this. I used this fantastic feature on my new scope to capture a few screen shots ( what a great feature !!! )

Image 1 shows output of the 555 timer, looks ok, but it gets bit wonky at higher frequency
Image 2 shows UCC37322 output, so far so good
Image 3 shows UCC37321 output - that looks weird, tried another ic, same result. I would like your opinion on this one
Image 4 shows input signal on Schmitt trigger - from my ancient function generator
Image 5 shows output signal from the Schmitt - it is Schmitting quite nicely I think
Image 6 shows output from the UCC37322 with Schmitt only connected 555 has been disconected
Image 7 shows output from the UCC37321 with Schmitt only connected 555 has been disconected - Why is this not inverted signal ? I was
               expecting it to be...
Image 8 shows output on the UCC37321 / 22 with the 555 and Schmitt connected - What a mess... What is going on here ??

GDT is built and it works quite well, I tested it as per the instructions on another page ( with a function generator and a scope ).
I dare not plugging this thing in, because I reckon something will burn unless I clear this up.
Any help will be appreciated.


 
Title: Re: SSTC build as per Steve Ward's Mini SSTC - Final Design
Post by: Fumeaux on January 21, 2019, 10:41:25 AM
(*) I don't think your 555 timer output is working as intended. It should output something in the audible frequencies, not higher than 500Hz. Are you sure you have a cap where it states cap sub point? I'm not sure what it mean but look at this reference (http://kaizerpowerelectronics.dk/wp-content/gallery/2009_01_22_-_kaizer_SSTC_I/KaizerSSTCIdriverschematic.gif)
(*) The other thing is that the UCC's don't really like to be operated without any load. You don't have to use the GDT, as a high power resistor would be sufficient to provide a load (pls check with ohms law). If you use your GDT make sure to feed a "fake" feedback signal as the inductor would act like an open curcuit with DC (the UCC's don't like this too).

The first point should be able to fix your "UCC with the 555 and Schmitt connected" waveform.

I hope this helped, if you have more questions for me send a PM so I see it.
Title: Re: SSTC build as per Steve Ward's Mini SSTC - Final Design
Post by: Thunderstruck on January 21, 2019, 11:06:44 AM
Hi Fumeaux,

Ok, I will look at my 555 circuit, yes there is a cap on that sub point and a resistor on the resistor sub point. I connected those two with screw down terminals, because I want to be able to take them out easy in order to try different options - apparently spark characteristics change depending on values of that cap and resistor.
Honestly I can’t se how becuse 555 is there just to start the oscillations, after that the coil does it’s own thing so it will produce a spark depending on it’s own characteristics, regardless of a cap and a res in 555 circuit.
GDT is connected to the UCC’s so they are not running completely load free. I read somewhere that UCC’s can burn out without a load, so I had a GDT connected before I powered up the circuit.
But, I did not know that there should be a feedback from GDT. Should I just connect my signal generator to one of the windings and give it a square wave signal ?



Title: Re: SSTC build as per Steve Ward's Mini SSTC - Final Design
Post by: Mads Barnkob on January 21, 2019, 11:27:35 AM
Hi Thunderstruck and welcome to HVF!

It is good that you make a new thread, instead of high jacking another thread. While its the same build, its most likely not the same problem, also who wants 100 pages long threads to look for answers in when searching from google :)

There is nothing wrong with the 555 running at up to the resonant frequency, that is just running it in CW mode, which would be better to implement by tying UCCs ENBL to on all the time instead, as the 555 properly cant handle the resonant frequency well enough over such a wide span. The 555 interrupter is only turning ENBL on/off on the UCCs to interrupt the CW mode and spare the MOSFETs from heavy heat dissipation due to conduction losses.

Fumeaux raises a few good points about UCCs destroying themselves if used without a load, they can simply oscillate into MHz region with their own output capacitance/inductance and burn to the ground.

You can just hook it all up driver -> GDT -> MOSFET gates, without mains power, then you have the UCCs running under right conditions and use a signal generator to simulate the antenna feedback. If you hook it all up with secondary coil in place and such, the driving energy from the GDT to MOSFETs can actually supply enough current to "leakage" drive the resonator as I demonstrate here:

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Title: Re: SSTC build as per Steve Ward's Mini SSTC - Final Design
Post by: Fumeaux on January 21, 2019, 11:38:28 AM
My point was that if you have the working frequency too close to the interrupter frequency you won't get a clear viewing on the osci, as the output is too unpredictable and not periodically.
Title: Re: SSTC build as per Steve Ward's Mini SSTC - Final Design
Post by: Thunderstruck on January 22, 2019, 12:30:49 AM
Hi Mads,

Thanks for your comment, what would be an ideal frequency for the 555 ?
I noticed that 555 is connected to the enable pin of the UCC’s and it did cross my mind that it will switch them on and off at a given frequency but I could not understand why ( I mentioned that im OK with electronics, there is lot to learn )
From your comment I gather that is to allow the transistors to “take a break” so they do not overheat.
Thinking along those lines, there must be a frequency that is optimal for that job ?
Title: Re: SSTC build as per Steve Ward's Mini SSTC - Final Design
Post by: Fumeaux on January 22, 2019, 01:00:53 AM
There is no ideal frequency, but the problem is, that when the signal frequency (signal generator) and the interrupter frequency (555) are too close together you won't be able to see either on an oscilloscope. The signal frequency is typically between 200kHz to 600kHz (for sstc) and the interrupter/enable pin is there to well interrupt the signal. Typically the interrupter goes only up to 300Hz.

And the funky waveform you see comes from the fact, that the signal and interrupter frequencies are not matched and the interrupter can turn on/off mid pulse, resulting in the chopped up squarewave. This not the big of a deal if the interrupter does that every now and then (300Hz), but at 24kHz it does the copping pretty much every cycle => funky waveform | slower interrupter => better/normal waveform

In my video in the background you can see the waveform on my oscilloscope. There is the ontime with very fast switching (for me 130kHz) and an off phase. This on off is around 40Hz.
PS: I swear I didn't find a scope shot of an interrupter. This is not just self promotion.
Title: Re: SSTC build as per Steve Ward's Mini SSTC - Final Design
Post by: Thunderstruck on January 22, 2019, 02:37:15 AM
Ok, I’m starting to understand what the problem is, my 555 is going too fast.
So, jobs to do :

- Make 555 output about 300 Hz
- Feed between 200 to 600 kHz into the antenna
- Check output on UCC’s

I thought that the 555 becomes irrelevant once the coil starts, but now it all makes sense.
Things you learn...  :)
Title: Re: SSTC build as per Steve Ward's Mini SSTC - Final Design
Post by: Thunderstruck on January 22, 2019, 12:18:18 PM
As planned I carried out some tests, and I think I made some progress.

Image 1   I slowed down the 555 to around 300 Hz
Image 2   Connected 350 kHz signal to the antenna
Image 3   Schmitt output at 350 kHz - looks a bit messy
Image 4  UCCxxx22 output - also messy
Image 5  UCCxxx21 output - messy, but a LOT cleaner than before
Image 6  Both UCC's together ( xxx22 CH1, xxx21 CH2 ) apart from that weird waveform, I am really pleased to see that now I can see inverted signal on UCC xxx21

Next job is to figure out the reason for that bad signal form on the  UCC's.
I disconnected the 555 and fed exactly the same signal from a generator, UCC output did not improve.


Title: Re: SSTC build as per Steve Ward's Mini SSTC - Final Design
Post by: Mads Barnkob on January 22, 2019, 12:25:58 PM
How sure are you about your GDT being suitable? To me it looks most like the first case here in Richies GDT troubleshooting: http://www.richieburnett.co.uk/temp/gdt/gdt2.html
Title: Re: SSTC build as per Steve Ward's Mini SSTC - Final Design
Post by: Fumeaux on January 22, 2019, 12:38:27 PM
Looks good. Currently you dont have a 50/50 pwm but if you have the antenna connected and the coil running it should solve itself. For now it could help to increase the voltage output of your signal generator if possible, if not it's not a big deal either.

The second thing is the bad waveform on your output. It may be due to a unsuitalbe core, as Mads pointed out, or, and something similar happend to me, it could be due to too little capacitance on the 12V rail, which causes the voltage to dip too low during switching of the UCC's. Try to find something between 100-1000uF and put it between 12V and GND. [Scope shots of the 12V rail before and after pls]

PS: Can you post a photo of your gdt for "remote diagnosis"?
Title: Re: SSTC build as per Steve Ward's Mini SSTC - Final Design
Post by: Thunderstruck on January 22, 2019, 12:39:07 PM
Mads, you had exactly the same link posted before on another thread, it looked interesting so I connected my signal generator to one coil of my GDT and scoped the other two, they looked quote good which makes me think that my GDT probably works ok. My opinion might be wrong.

Waveforms you see are directly from the outputs of the UCC’s, so signal going into the GDT is wrong, I did not even bother checking the output - it is probably tragic.
I would like to get a nice clean signal from the UCC’s before I move onto the next component, otherwise I will get lost...
Title: Re: SSTC build as per Steve Ward's Mini SSTC - Final Design
Post by: Thunderstruck on January 22, 2019, 01:11:25 PM
I used this core:
https://www.jaycar.com.au/l15-35x21x13mm-toroid-or-ring-cores-pk-2/p/LO1238
Title: Re: SSTC build as per Steve Ward's Mini SSTC - Final Design
Post by: Mads Barnkob on January 22, 2019, 02:07:41 PM
That is a L8 material ferrite/iron powder ring core, that material is not suitable above 100 kHz, as you can see here its initial permeability start dropping hard after 300 kHz: https://www.forward.com.au/pfod/HomeAutomation/BLEHighPowerLightSwitch/M7_HY2_ferrites.pdf

Get one with a Ui/AL value around 4000-5000, follow this excellent guide: http://thedatastream.4hv.org/gdt_parts.htm

 
Title: Re: SSTC build as per Steve Ward's Mini SSTC - Final Design
Post by: Thunderstruck on January 22, 2019, 09:38:27 PM
I guess I was wrong regarding my GDT. I just ordered a couple of these as per your advice:
https://au.rs-online.com/web/p/ferrite-rings/2120910/?relevancy-data=636F3D3126696E3D4931384E525353746F636B4E756D626572266C753D656E266D6D3D6D61746368616C6C26706D3D5E2828282872737C5253295B205D3F293F285C647B337D5B5C2D5C735D3F5C647B332C347D5B705061415D3F29297C283235285C647B387D7C5C647B317D5C2D5C647B377D2929292426706F3D3126736E3D592673723D2673743D52535F53544F434B5F4E554D4245522677633D4E4F4E45267573743D3231322D30393130267374613D3231323039313026&searchHistory=%7B%22enabled%22%3Atrue%7D
Title: Re: SSTC build as per Steve Ward's Mini SSTC - Final Design
Post by: Thunderstruck on January 24, 2019, 06:35:01 AM
Drying Secondary is taking up space on my bench, so I can't work on the circuit until it completely dries...
Title: Re: SSTC build as per Steve Ward's Mini SSTC - Final Design
Post by: Mads Barnkob on January 24, 2019, 07:51:11 AM
That is a fine looking secondary, how many layers of varnish will you end up giving it? And what type did you use?
Title: Re: SSTC build as per Steve Ward's Mini SSTC - Final Design
Post by: Thunderstruck on January 24, 2019, 08:16:50 AM
For this coil I used Polyurethane varnish, I’m already on my 4th layer.
Usually I use Ultimeg varnish - designed for the electrical industry to resist high voltages.
I do not expect a huge output on this coil so I did not want to use expensive material.
Secondary on my SRSG TC is done with Ultimeg and it works really well.
Title: Re: SSTC build as per Steve Ward's Mini SSTC - Final Design
Post by: Thunderstruck on January 25, 2019, 11:40:25 AM
As Fumeaux suggested, I took some measurements of voltages at different points.
Just remember that I am still learning to use my new digital scope, apologies if something does not make sense.
From what I see and understand there is a bad noise problem, comments are appreciated.

Image 1 - Output of LM7812
Image 2 - Output of LM7805
Image 3 - Voltage at 555 ( trace is a bit dim, I later realised that I can make it brighter )
Image 4 - Voltage at UCCXXX22
Image 5 - Voltage at UCCXXX21
Image 6 - Voltage at SCH Inverter
Title: Re: SSTC build as per Steve Ward's Mini SSTC - Final Design
Post by: Fumeaux on January 25, 2019, 12:57:14 PM
That looks quite good. Is it while having a gdt connected and a generated signal for the feedback? If so, there shouldn't be a problem. Maybe add three 100nF ceramic disc capacitor on the lm7812 input, output and the lm7805 output for filtering the sharp spikes.

The reason I said it was because I had 2 Volts of ripple on my 12V line. That was at ~130kHz, and the higher the frequency the more often the ucc's switch -> more drop. But I guess you are fine.
Title: Re: SSTC build as per Steve Ward's Mini SSTC - Final Design
Post by: Thunderstruck on January 25, 2019, 01:29:31 PM
GDT is connected, but there was no feedback signal to the antenna.
Do you think it will make a lot of difference ( feedback signal )
I will have a go at at that tomorrow...
Title: Re: SSTC build as per Steve Ward's Mini SSTC - Final Design
Post by: Fumeaux on January 25, 2019, 02:02:16 PM
There is a huge difference between oscillating and not oscillating, as every switch (on to off, off to on) for the UCC's draws a bit of power. You don't need an extra feedback signal if you have a coil running. But, no feedback signal (real or fake) -> no oscillation -> no current draw
Title: Re: SSTC build as per Steve Ward's Mini SSTC - Final Design
Post by: Thunderstruck on January 25, 2019, 10:18:51 PM
I am waiting for a proper toroid cores to arrive, Mads noticed that my current core is not suitable for frequencies needed. They should arrive next week.
I do not have any 24 awg wire for the windings, I used slightly thinner wire in my current GDT, do I need to compensate for this ? Maybe I should use slightly thicker wire ?
Im sure there is maths behind this  :)

My secondary is almost finished, last polyurethane layer is drying as we speak.
For a primary coil, is it better to use solid core copper wire or multistrand is ok ?
My SRSGTC uses 6mm copper conductor for primary windings, that seems to work well....

Title: Re: SSTC build as per Steve Ward's Mini SSTC - Final Design
Post by: Mads Barnkob on January 28, 2019, 09:22:54 AM
AWG24 is plenty for a GDT, it can continues carry 4A, your average current is lower than that. Thicker wire for higher current capability, but you will sacrifice some coupling for that. So it is best to use the smallest possible both for not using a overly large/expensive core just to fit the wire. I make almost all mine from Ethernet cable, which varies from 24-26AWG.

Skin effect due to high frequency makes the use of solid copper conductors non-ideal due to the most of it not carrying any current, but at least the thermal mass or the copper can help cool down between the pulses. Hollow tubing has the advantage that you can run water cooling through it.

So I almost always use tubing, its easy to bend, its cheap from the scrap yard, you can water cool it if necessary etc. For SSTC I use regular machine tool wire as there is no need for tuning taps and tight coupling is needed, so might as well use a wire with already added insulation on it.
Title: Re: SSTC build as per Steve Ward's Mini SSTC - Final Design
Post by: Thunderstruck on January 31, 2019, 12:28:02 AM
Thanks Mads, my new cores just arrived, so soon I’ll be able to test my waveform with proper GDT ( I hope it will be good anyway  :D )
They are blue - that’s a good sign, and all the way from Czech Republic to Australia
Title: Re: SSTC build as per Steve Ward's Mini SSTC - Final Design
Post by: Thunderstruck on January 31, 2019, 11:40:32 AM
Ok, I made a new GDT, using new cores and this time I used magnet wire. I scoped the gates of the Mosfets and I do not know what exactly is going on.
Signal does not look clean at all
I was expecting inverted signals, but they look the same.

I'm starting to think that there is something seriously wrong with my circuit....


Title: Re: SSTC build as per Steve Ward's Mini SSTC - Final Design
Post by: Fumeaux on January 31, 2019, 11:53:40 AM
First of all I think the waveform is good enough to drive mosfets.

There might be one of these things wrong:

I guess you could try if you have a short from + to -
(with a 12V supply and a lightbulb between supply and +)


If there is, you have your GDT connections switched.
Title: Re: SSTC build as per Steve Ward's Mini SSTC - Final Design
Post by: Teravolt on January 31, 2019, 06:19:26 PM
keep in mind that if your probe grounds are to long fake induced voltages can apper on your scope diplay. close your ground to the tip and see if you can pick up noise around your circuit. other problems might arise from ground loops.
Title: Re: SSTC build as per Steve Ward's Mini SSTC - Final Design
Post by: Thunderstruck on January 31, 2019, 10:07:55 PM
Thank you for your comments. Fumeaux, I will try the light globe test as you suggested.
The way I understand the GDT windings, first one is connected to UCC’s, second is connected to Mosfet 1 and third is connected to Mosfet 2 but it is swapped / twisted ( maybe I got this bit wrong ).
Thinking about it, I probably got it wrong right there....

Teravolt, I noticed that  the waveform changes as I move the ground leads around, so you are probably right about picking up noise.
Title: Re: SSTC build as per Steve Ward's Mini SSTC - Final Design
Post by: pentode on February 01, 2019, 08:30:26 AM
If the GDT connections are both in phase you will blow your mosfets
as both will be switched on together !
Title: Re: SSTC build as per Steve Ward's Mini SSTC - Final Design
Post by: Fumeaux on February 01, 2019, 09:19:21 AM
Actually not, as the lightbulb is not a short curcuit.
Title: Re: SSTC build as per Steve Ward's Mini SSTC - Final Design
Post by: Thunderstruck on February 01, 2019, 11:10:49 AM
Ok, I went back over the circut, and yes I swapped one of the GDT windings - the one that goes onto the gate of Q2. It is meant to be reversed, but I reversed it twice ::).
I fixed that, now I got inverted signals on the gates !

Then I decided to connect it to my lab power supply instead of mains, and to my surprise nearby fluorescent tube STARTED LIGHTING UP !!!! YAY !!

I increased the voltage to about 30V and managed to get a small zap from the secondary breakout point.
I noticed that the current draw was about 2 Amps, and it was pulsing.
Forgot all about the run time, had it on for about 5 min continuously, before realising that I might fry something.
Mosfets got pretty hot Q1 more than Q2, fortunately I fitted a large heatsinks so they did not fry.

What would be next step before I connect it to my Variac ?


Title: Re: SSTC build as per Steve Ward's Mini SSTC - Final Design
Post by: dexter on February 01, 2019, 12:15:44 PM

What would be next step before I connect it to my Variac ?


in nearly all my antenna feedback SSTC's i had to reverse the polarity of the primary side of the GDT so that the primary coil is in phase with the secondary coil
If the phasing is wrong the output of the coil will be very small to the point i had to draw an arc in order to see it but as soon i fixed the phasing i got few cm streamers even with around 30V on the bridge.
Title: Re: SSTC build as per Steve Ward's Mini SSTC - Final Design
Post by: Fumeaux on February 01, 2019, 12:19:20 PM
Does it run with antenna feedback already or still from a function generator?

In order to decrease the current draw you can:

experimental: You can just add windings or build a new primary (with taps).
technical: Calculate the primary reactance and adjust it, to achive a wanted current draw. Mads discussed the powercalculation here https://highvoltageforum.net/index.php?topic=455.msg2763#msg2763 (https://highvoltageforum.net/index.php?topic=455.msg2763#msg2763)
Title: Re: SSTC build as per Steve Ward's Mini SSTC - Final Design
Post by: Teravolt on February 01, 2019, 06:33:27 PM
When you fire it up make shure tha any of that noise doesn't and couse ant shoot trough in the fets. Is there any dead time betwean each fet turning on?
Title: Re: SSTC build as per Steve Ward's Mini SSTC - Final Design
Post by: Thunderstruck on February 02, 2019, 08:32:42 AM
@Dexter,
Seems like GDT is working fine, waveform on Fet gates is correct, so I think i got the GDT right this time.

@Fumeaux,
Function generator was not connected at all, that is probably why Q1 was heating more than Q2.
I connected the generator today, and - NOTHING, absolutely no activity. Then, I decreased the frequency to about 200kHz, and the nearby fluorescent tube lit up along the entire length, current draw went up as well, but no sparks.
Both Fets were equally warm. I’ll have to do some maths to work out the current draw as you suggested.

@Teravolt,
I would like to be able to answer your question, but I do not understand “dead time” I’ll google it and see if I can figure it out. This is my first SSTC, I’m OK with electronics, but nowhere near where I would like to be.
I built SRSGTC - mechanical switching, mechanics I understand very well  :)
Title: Re: SSTC build as per Steve Ward's Mini SSTC - Final Design
Post by: Fumeaux on February 02, 2019, 08:51:33 AM
Desdtime is the time between one mosfet turning off and the other on. As both fets are connected to the same gdt they both get the same drivesignal. As far as I am concerned, there is no deadtime, which makes the curcuit a bit less efficient, but thats not a problem. If you wanted to implement deadtimes, the driver would have to become quite complex.

And you can try to reverse your gdt connections. Then you should get an output.
Title: Re: SSTC build as per Steve Ward's Mini SSTC - Final Design
Post by: Thunderstruck on February 02, 2019, 11:12:46 AM
Desdtime is the time between one mosfet turning off and the other on. As both fets are connected to the same gdt they both get the same drivesignal. As far as I am concerned, there is no deadtime, which makes the curcuit a bit less efficient, but thats not a problem. If you wanted to implement deadtimes, the driver would have to become quite complex.

And you can try to reverse your gdt connections. Then you should get an output.

I suspected exactly that, but wasn’t sure. In that case it would be easy to measure the “deadtime” on the scope, however in my case it wouldn’t be easy because waveform is so messy.
When you say reverse the GDT connections, do you mean rotate the GDT 180 degrees ?
Title: Re: SSTC build as per Steve Ward's Mini SSTC - Final Design
Post by: Fumeaux on February 02, 2019, 12:47:00 PM

I suspected exactly that, but wasn’t sure. In that case it would be easy to measure the “deadtime” on the scope, however in my case it wouldn’t be easy because waveform is so messy.
When you say reverse the GDT connections, do you mean rotate the GDT 180 degrees ?


Yes you can measure the deadtime that way.

I suspect that your feedback is out of phase. Therefore by switching the connections it could improve your output.
Title: Re: SSTC build as per Steve Ward's Mini SSTC - Final Design
Post by: dexter on February 02, 2019, 02:57:06 PM
@Dexter,
Seems like GDT is working fine, waveform on Fet gates is correct, so I think i got the GDT right this time.

The waveform on Fet's gates will be correct regardless if the phasing is not
Depending on how you connected the primary and secondary sides of the GDT (especially when the leads ate twisted) and the way you connected primary coil to the bridge you can end up in a situation where the signal picked up by the antenna is in anti-phase with what you have on primary coil.
When this happen you get just a small glow at the breakout point. This is easily countered by reversing the connections A and B
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Title: Re: SSTC build as per Steve Ward's Mini SSTC - Final Design
Post by: Thunderstruck on February 03, 2019, 12:19:35 AM
Dexter, Fumeaux,

I just switched the primary winding on the GDT, there is better output now, when connected to my function generator, at about 340 kHz I can see small streamers on top of the secondary ( worth mentioning that I do not have a top load yet, but I have 150mm metal sphere that I intend to use ).
Sparks will jump across 30mm gap to a piece of metal held close.

At about 30V DC it draws about 2.5 A
Slowly going in the right direction I suppose  :)
Title: Re: SSTC build as per Steve Ward's Mini SSTC - Final Design
Post by: Mads Barnkob on February 03, 2019, 10:42:33 AM
Getting 30 mm sparks from 30VDC in is a good indicator that everything is right.

As you ramp up the voltage you will most likely see some unstable interrupting, sputtering sparks etc. Try to adjust the position of the antenna if this happens. The same applies if you see sparks or too much corona on the antenna tip.

Reversing the GDT primary or the primary coil itself has the same result, I almost always ended up reversing the primary coil as it was easiest for me with my circuit layout.

We need pictures of sparks! :)
Title: Re: SSTC build as per Steve Ward's Mini SSTC - Final Design
Post by: Thunderstruck on February 03, 2019, 09:37:58 PM
Well, unfortunately that did not go so well, I slowly increased the power, started getting longer sparks, and then C8 started smoking.
It is rated over 400V, I do not understand why did it go up in smoke?
Title: Re: SSTC build as per Steve Ward's Mini SSTC - Final Design
Post by: Fumeaux on February 03, 2019, 10:14:18 PM
Do do know how your waveform on the mosfets looked while operating?
Was it like this or 50/50 on-off-time?



That might explain, why only one cap started smoking, or maybe it was a productionfailure and not your mistake.

Do you have an idea at what voltage and what current the cap blew?
I suppose it could have been too much current for the little cap.

Maybe look into Polypropylen-Capacitors that can be used for pulsed applications, and maybe something with a higher voltage rating. (Replace both caps at once ;))
The first one I found was this: WIMA MKP1J036806F00KSSD
Title: Re: SSTC build as per Steve Ward's Mini SSTC - Final Design
Post by: Thunderstruck on February 04, 2019, 03:59:23 AM
Waveform was exactly like that, but I did play around with the pots while the coil was running.
As they say hindsight is always 20/20, cap I used is probably not suitable, it is Polypropylene but voltage is only about 300V AC.
https://au.mouser.com/ProductDetail/Illinois-Capacitor-CDE/MPX684K305G?qs=HXFqYaX1Q2ycCo06bCS07Q==

I ordered caps you suggested, they seem like a good choice, I also ordered a pair of Fets, just in case I blew one up.
I did not check yet if I fried them or not.
I can’t remember exact voltage at the time, but Variac was supplying about 70-80V.

Worth mentioning that my coil would not run without the function generator connected to the antenna.
Title: Re: SSTC build as per Steve Ward's Mini SSTC - Final Design
Post by: Fumeaux on February 04, 2019, 08:42:30 AM
Worth mentioning that my coil would not run without the function generator connected to the antenna.


Title: Re: SSTC build as per Steve Ward's Mini SSTC - Final Design
Post by: Thunderstruck on February 04, 2019, 11:17:29 AM
Worth mentioning that my coil would not run without the function generator connected to the antenna.
  • I think you should get that working with a priority. Did it only work with the function generator before you swapped the gdt connections or after doing so? Or have you tried it? Swapping the connections should have made it work.
  • And as far as I can remember you don't use a topload at the moment? That could be a problem for the feedback as well.
  • Have you decreased the current draw? You said you wanted to, but did you also do it?
  • When you have it running again, run it for a short period of time and feel if any component got warm. And film the sparks :)

It never worked on it’s own, always with the FG connected.
Swapping the connections made it produce a better discharge, but with the FG only
That is right, no top load yet, I have a metal sphere that I can use, about 120mm dia
Well, as far as the current draw is concerned, It was going high, about 4A at 30V. Then, next time I tried it stayed at about 2.5A, I thought that it “sorted itself out”, so I decided to try doing a full test - aaand things fried.

I just investigated the circuit and found that both Fets are gone, in addition to the smoking caps.

As you suggested , I should have sorted out that duty cycle, currently it is about 60% ( which makes me think that is why Fets died )

UCC***22 is at 61%
UCC***21 is at 39%
I have no idea what controls their duty cycle or how to adjust it ! Might be obvious, but I’m not afraid to admit that I do not know.

If I feed sine wave signal into the antenna, inverter outputs a nice square wave at 50% duty cycle, it is 50% at pin 2 of the UCC’s, but they change the duty cycle.

Replacement parts should be here by Friday, so I get to try again  :)
I find all this rather interesting...
Title: Re: SSTC build as per Steve Ward's Mini SSTC - Final Design
Post by: Teravolt on February 04, 2019, 07:31:29 PM
hear is some web sights to show you what dead time is and circuits for implimetation


https://www.eeweb.com/profile/paul-clarke/articles/switching-fets-and-dead-time

https://electronics.stackexchange.com/questions/281248/how-do-i-delay-mosfet-turn-on-without-slowing-down-the-rise-time

https://www.researchgate.net/figure/Conventional-dead-time-control-circuit-a-schematic-representation-of-the-conventional_fig7_263150695

http://www.modularcircuits.com/blog/articles/h-bridge-secrets/h-bridge-control/

this is one of Steves earlyest  circuits and has its set of problems a universal driver circuit is more advanced and has more protecive fetures like overcurrent
Title: Re: SSTC build as per Steve Ward's Mini SSTC - Final Design
Post by: Mads Barnkob on February 04, 2019, 09:25:09 PM
You have to understand that driving it with a function generator it will never be able to adjust itself to the changing resonant frequency of the secondary circuit. As the sparks grow the secondary circuit is loaded and its resonant frequency starts to drop. This happens at every single cycle, so it is critical that you get the antenna feedback to work as the first thing.

You are stressing your primary circuit by switching a large current that can not get magnetically coupled to the secondary circuit and transferred on to be sparks, instead the large circulating current in your primary circuit is destroying your components.
Title: Re: SSTC build as per Steve Ward's Mini SSTC - Final Design
Post by: Thunderstruck on February 04, 2019, 11:38:43 PM
Teravolt,  thanks for the links, a lot of interesting reading there. I have some time to read before my components turn up.

Mads, now I understand why driving the circuit from the FG is not a good idea - it does not allow itself to self-tune.
I still do not understand why UCC’s output 60/40 waveform, is this because I’m driving the circuit from the FG ? Will this change once I get feedback circuit working ?
Ideally it should be 50% duty cycle, right ?
Title: Re: SSTC build as per Steve Ward's Mini SSTC - Final Design
Post by: Mads Barnkob on February 05, 2019, 08:44:28 AM
Teravolt,  thanks for the links, a lot of interesting reading there. I have some time to read before my components turn up.

Mads, now I understand why driving the circuit from the FG is not a good idea - it does not allow itself to self-tune.
I still do not understand why UCC’s output 60/40 waveform, is this because I’m driving the circuit from the FG ? Will this change once I get feedback circuit working ?
Ideally it should be 50% duty cycle, right ?

You function generator could easily put out a waveform with a duty cycle distribution like that, that all depends on who you set it up.

A resonator like the Tesla coil secondary circuit or a GDT can never run at anything else than 50/50% duty cycle with some natural added dead-time from magnetizing currents shifting phase etc. So the feedback will always be tied to the sinus waveform of the secondary.
Title: Re: SSTC build as per Steve Ward's Mini SSTC - Final Design
Post by: Thunderstruck on February 05, 2019, 09:25:47 AM
Thanks Mads, it's clear now. My FG is ancient, no data display, just an on led and a large knob, so yes, it might be doing strange things.
In the meantime I organised a top load 150mm and 180mm spheres ( 8pF and 10pF or thereabouts ).
Fitting for a breakout point on top.
Title: Re: SSTC build as per Steve Ward's Mini SSTC - Final Design
Post by: Thunderstruck on February 11, 2019, 11:55:44 AM
Well, I spent most of my weekend building a new circuit, trying to make it a bit neater than the first one.
I did not like the waveform in my first circuit it was really ugly. Despite my best efforts, my new circuit produces exactly the same waveform.
I think I spent enough time on this project, It is a fairly simple circuit, but I cannot make it work.
What hope do I have of making something more complex if I cannot built this ?
Time to give up electronics and keep going with mechanical switching I think...
Title: Re: SSTC build as per Steve Ward's Mini SSTC - Final Design
Post by: Laci on February 11, 2019, 04:28:24 PM
Can you send us some pictures about your complete setup?It's often hard to solve a problem for the first try,some time for thinking and compatible components does the trick! :)
Title: Re: SSTC build as per Steve Ward's Mini SSTC - Final Design
Post by: Mads Barnkob on February 11, 2019, 10:58:06 PM
I feel your frustration and believe me, I have been in the same place with so many projects. Just let it rest for a week or two if its driving you mental, then return to it with new ideas and energy.

The SSTC is quite sloppy in its design and stability, so the more complex DRSSTC can often be easier to find errors on as its better specified what signal is needed where.

Just give us some more details and we see if we can help you get this thing running!
Title: Re: SSTC build as per Steve Ward's Mini SSTC - Final Design
Post by: Thunderstruck on February 16, 2019, 02:16:27 AM
I tried one more time, I started getting some output and then everything went quiet - probably burned out fets, because heatsinks were too warm for 10 second opertion.
Well, I head enough and put the entire thing into the rubbish bin to stop myself spending any more time and money on this project.
I learned a few things about electronics from this project, I also learned that I am not capable of building a simple circuit. My ambition was to build a large coil based on UDD 2.7 - I even bought all the components and pcb’s. That is far more complicated circuit and I have no chance in hell to make it work.

Anyway, thanks for your help guys and apologies for wasting your time !
Title: Re: SSTC build as per Steve Ward's Mini SSTC - Final Design
Post by: Mads Barnkob on February 16, 2019, 12:50:30 PM
I tried one more time, I started getting some output and then everything went quiet - probably burned out fets, because heatsinks were too warm for 10 second opertion.
Well, I head enough and put the entire thing into the rubbish bin to stop myself spending any more time and money on this project.
I learned a few things about electronics from this project, I also learned that I am not capable of building a simple circuit. My ambition was to build a large coil based on UDD 2.7 - I even bought all the components and pcb’s. That is far more complicated circuit and I have no chance in hell to make it work.

Anyway, thanks for your help guys and apologies for wasting your time !

Not always a bad choice to clean the table and walk away for a bit. Give it a few weeks and then start building your DRSSTC, if you already have the parts, just get going :)

I am struggling hard right now to fix my own DRSSTC1 that just blew the bridge on me, its been 3 long days of trying to get it to run again and I am also frustrated, but I keep going and I try to document my steps through it, so it can get online and help others.

I hope to see you back building the DRSSTC!