High Voltage Forum

Tesla coils => Solid State Tesla Coils (SSTC) => Topic started by: Laci on September 03, 2017, 08:25:15 PM

Title: SSTC (Not) Working Correctly
Post by: Laci on September 03, 2017, 08:25:15 PM

Hello Everybody!
I recently upgraded my half bridge SSTC to a full bridge,from an IR2153 to 2xIR2109.The half bridge worked very well almost 10cm long arcs to not grounded objects at rectified mains.
With the full bridge i get pretty weird results;it lights up a CCFL lamp bright,at every frequency-around 100kHz-400kHz(andjusted by the pot at the 555),but very tiny arcs.The current drawn is also the half of the half bridge current drawn(1A-half bridge,+-0,4A-full bridge).
I tried to change the number of primary turns,changing polarity,adjusting frequency,everything I could,but the results are at least half or less as good as the half bridge.
I checked every frequency at the gates of the mosfets,with a frequency counter and they are the same.Sadly,I do not have an oscilloscope so I think that it is pretty hard to find out what is making the problem.
As I said,the driver circuit changed,so I'm sure that the problem is with that,but do not know what...The mosfets are also heating up simultaneusly,so they should work correctly...
If you have an idea,how can I improve this design to work correctly,please reply :)
Thank you very much!

Title: Re: SSTC Not Working Correctly
Post by: Mads Barnkob on September 04, 2017, 11:31:53 AM

Are all MOSFETs heating up or maybe just 3 of them?

Is it polarity of the gate drive or polarity of the primary coil that you have changed? Your schematic is for sure wrong, you are driving both upper leg MOSFETs on at the same time and both lower leg MOSFETs on at the same time.

Since it oscillates, but draws very little power, it sounds like you are driving it out of phase, with wrong gate polarity or the supply to DC bus is not working and the energy transferred to the secondary circuit is only the capacitively coupled energy from the drive circuit.

Title: Re: SSTC Not Working Correctly
Post by: Laci on September 04, 2017, 02:31:11 PM

I do not use gate drive transformer.In theory,I think that the 74HC14 shifts the NE555's output level,and the IR2109 chips will never turn both the high- or low side mosfets on,since the input signal is inverted.The setup is also weak to drive a TV flyback transformer.

Title: Re: SSTC Not Working Correctly
Post by: Mads Barnkob on September 04, 2017, 02:51:40 PM

I completely missed the signal 1/2, so yes you have ofc taken care of the switching polarity.

Did you ground all the unused inputs on the 74HC14? If not, this could very well be the issue. There are other threads on the forum about that issue, like: https://highvoltageforum.net/index.php?topic=93.msg431#msg431

Title: Re: SSTC Not Working Correctly
Post by: Laci on September 04, 2017, 03:06:09 PM

I will try to ground the other pins!Also I found out,that the high side output of the driver ic is not working correctly:the low side output goes high whenever the input signal is low/ground,but the high side just makes a pulse,and goes back to low,not remains high,when the input signal is high.

Title: Re: SSTC Not Working Correctly
Post by: Mads Barnkob on September 29, 2017, 11:36:46 AM

Did it help to ground the unused 74HC14 input pins?

Title: Re: SSTC Not Working Correctly
Post by: CCX191 on September 30, 2017, 05:34:00 AM

Get a cheap DSO 138 oscilloscope :D

Title: Re: SSTC Not Working Correctly
Post by: Mads Barnkob on September 30, 2017, 11:56:12 AM

Quote from: CCX191 on September 30, 2017, 05:34:00 AM

Get a cheap DSO 138 oscilloscope :D

As long as the resonant frequency of the coil is not above 100 kHz, a DSO138 should be good enough, but it quickly begins to struggle above that.

I bought one and will write about it, once I get down through the pile of projects :D

Title: Re: SSTC Not Working Correctly
Post by: Laci on September 30, 2017, 02:02:42 PM

Thank you guys for being so helpful!:)
I'm upgrading to a better coil recently.A coil of 0.3mm magnet wire is coming,the primary is made of 6mm copper wire- 15 turns.I will make the secondary 110mm dia,550mm long,and around 1800 turns,as calculated.

I made my uploaded schematic on a perf board,but I realized that it's not working with the transistors,as they should.As the load on the IRFP460 full bridge I put two LEDs in different polarity,decreased the frequency to 1Hz and(if I remember),one of the LEDs was blinking,and the other was turned on fully,and never turned off.
I could't find the problem,so I made the circuit on a breadboard,now it seems working there.
The other problem:all of the IRFP460s are dead,due to my stupidity(or just they are crappy fake mosfets and give up easily....)

An oscilloscope could solve a lot of my problems,but I want to buy good one.

Title: Re: SSTC Not Working Correctly
Post by: Laci on October 10, 2017, 09:37:50 PM

So the magnet wire roll have arrive,0.3mm,636m.
My question is that 110mm diameter,550mm long,1850 turns or 160mm diameter,380mm long,1260 turns  secondary coil would work better for a SSTC or for a DRSSTC?

Title: Re: SSTC Not Working Correctly
Post by: Mads Barnkob on October 11, 2017, 10:03:36 AM

Quote from: Laci on October 10, 2017, 09:37:50 PM

So the magnet wire roll have arrive,0.3mm,636m.
My question is that 110mm diameter,550mm long,1850 turns or 160mm diameter,380mm long,1260 turns  secondary coil would work better for a SSTC or for a DRSSTC?

For a SSTC a smaller, not so tall, but lower diameter to height ratio is preferred. Something in the range of 1:2 to 1:3 ratio, since a SSTC needs a much higher coupling to perform than a DRSSTC, due to it operating with a much lower peak current(but high RMS current), it should give better performance with a smaller secondary coil, there is however also some increased spark length performance in longer secondary coils due to more secondary turns, but this increase is not that big and quickly diminishes when you exceed 1:4 or 1:5 ratios

A DRSSTC operates at very high peak currents and too high coupling will simply make it flash over between primary and secondary, but just the spark length that is achievable with a DRSSTC is another reason to make them longer, because if it is too short, all you get is limited spark length to ground :)

I would recommend going with:
a 1:4 ratio on the 110 mm diameter form, for 1330 turns, 440mm long winding (secondary circuit impedance around 47-49kOhm)
or
1:2.5 ratio on the 160 mm diameter form, for 1260 turns, 380mm long winding (secondary impedance around 61-70kOhm)

As a SSTC operates with long on-time, compared to a DRSSTC, I think the higher impedance secondary coil circuit would perform better. But I would someone else to comment on this, because I am not completely sure.

Regarding getting a good entry level oscilloscope, see the latest posts here: https://highvoltageforum.net/index.php?topic=107.msg883#msg883

Title: Re: SSTC Not Working Correctly
Post by: Uspring on October 12, 2017, 12:26:00 PM

Quote

As a SSTC operates with long on-time, compared to a DRSSTC, I think the higher impedance secondary coil circuit would perform better. But I would someone else to comment on this, because I am not completely sure.

I don't have any practical experience with SSTCs, but from calculations I believe, that the primary inductance can look almost completely resistive if driven at the right frequency and that secondary Q is above a certain limit. That would probably be an advantage in order to not have too much reactive current in the primary. The Q needed is about 2/k^2, where k is the coupling. Secondary Q depends on arc loading. For a given arc load it increases with less secondary inductance. A large Q will also increase the resistance seen by the driver. There is a limit to increasing Q or equivalently reducing secondary inductance, i.e. less turns, since at some point the voltage won't be large enough to cause breakout at all.

Another issue is getting the frequency right. The feedback adjusts to a 0 degree phase all over the complete loop. That usually works but might not result in quite the optimal frequency. I wonder if anybody has tried to add a manual phase shifter for optimisation.

That being said, this is all theory.

Title: Re: SSTC Not Working Correctly
Post by: Laci on October 13, 2017, 04:46:25 PM

Now i have the components for the secondary let's see what can I do :D
The coil,as calculated should be:125mm dia.,485mm long(1:3.88),1620 turns.

I hope,that if I can make it,it will work with a SSTC driver,then maybe upgrade to DRRSSTC...

Title: Re: SSTC Not Working Correctly
Post by: Mads Barnkob on October 14, 2017, 07:32:17 AM

Quote from: Laci on October 13, 2017, 04:46:25 PM

Now i have the components for the secondary let's see what can I do :D
The coil,as calculated should be:125mm dia.,485mm long(1:3.88),1620 turns.

I hope,that if I can make it,it will work with a SSTC driver,then maybe upgrade to DRRSSTC...

The secondary coil has a size that will make it useful for both SSTC and DRSSTC, but that primary coil might have too little coupling for a SSTC and way too high coupling for a DRSSTC. You can check the latter by plotting your coil dimensions into JavaTC and see the coupling vs. the suggest coupling.

Uspring, I will have read your reply a couple of more times before I can reply to it :)

Title: Re: SSTC Not Working Correctly
Post by: Uspring on October 16, 2017, 01:28:56 PM

Mads, sorry if I've been to opaque in my reply. From my point of view, a SSTC suffers in comparison with a DRSSTC, that the load to the bridge circuit, i.e. the primary, can look mostly inductive. In a DRSSTC that is compensated by the MMC. A mostly inductive load can have much current in it, which is not causing any real power output out of the bridge. The primary should look as lossy as possible, implying, that there is much power transferred to the secondary.

That requires a large influence of the secondary on the primary. A high coupling helps and also high secondary currents. Large secondary currents appear, when secondary Q is big. For a given arc load, this requires a not too large secondary inductance. For Qsec > 2/k^2, there is a frequency, at which the primary inductance is mostly cancelled by effects of the secondary current. At this point, the load to the bridge appears similar to that of a DRSSTC, i.e. an approximately sine wave current in phase with the bridge voltage.

The cancellation of the primary inductance can lead to high primary currents, so care must be taken in order not to overload the bridge. It can be considerably larger than the estimate Vinp/(2*pi*f*Lpri).

Possibly your coils already run like this. Do you have scope shots of the primary current of your coils, wrt to bridge voltage?

Title: Re: SSTC Not Working Correctly
Post by: Laci on October 16, 2017, 09:34:16 PM

The coil is made.I tried it with a slayer exciter circuit and I have a question.Why are the arcs large without topload at 3-5 turns primary,and weak with topload,but large again with topload and more(10+)primary turns?I thought it tunes automatically the primary frequency to the resonant frequency of the secondary,so why is it depending on the primary turns?

Title: Re: SSTC Not Working Correctly
Post by: Mads Barnkob on October 18, 2017, 10:07:11 AM

Uspring: So I was wrong about saying high impedance would be better, as that is quite opposite of a larger gauge secondary wire which would give a higher Q, also be able to carry more current etc.

I think my SSTC2 is around Q~140 and that is much higher than a conservative estimate of k=0.2, so that 140 > 50. That could also blow the MOSFETs when pushing out almost 500mm sparks :)

I only had a old analog oscilloscope back then, so that would be a good experiment for the future, so get it back out and hook it up to DSO, CT and Diff. probe.

Laci: A topload will represent a much bigger load to the energy source on the primary circuit, I think you are simply loading down the slayer exciter. So when you add more primary turns with the topload on, it is not as high currents flowing and it has a chance to actually deliver power to the secondary circuit.

Can you measure what resonant frequency it was running at, in the different setups?

Title: Re: SSTC Not Working Correctly
Post by: Uspring on October 18, 2017, 10:46:42 AM

Laci: You're right about the tuning not being dependent on the primary turns. I'd expect a larger primary current with with less primary turns, which might increase power throughput. The important term here is amp turns, which probably increases with less turns.
Adding a top load decreases secondary resonance frequency, which will also increase primary current, since primary impedance becomes lower with a lower running frequency.

The feedback will not always have the coil run at exactly the secondary resonance frequency. The condition for a working feedback is a 0 degree phase shift all over the feedback loop. I don't know, what your circuit looks like, but imagine, that the switching transistor is driven by an antenna. Then remove the antenna and replace it with a signal generator at exactly the same frequency, that the coil is running when using an antenna. The coil will behave as before and the antenna (now unconnected) will deliver the same frequency and phase as the signal generator. That shows, that the whole system phase shift between driver input and antenna output is 0 degrees.

The 0 degree condition is likely near the secondary resonance frequency, since the "whole system phase" varies strongly with frequency near resonance and the chance is high, that there is a frequency, that matches the 0 degree condition. That frequency might not be the best one for maximum power transfer between primary and secondary.

It's difficult to explain your observations without knowing the specs of your coil, e.g. feedback circuitry, inductances, capacitances coupling and such. You might try running a simulation.

Mads: Secondary Q depends mostly on arc loading, so it is probably much lower than that calculated from wire gauge and skin effects.

I don't quite understand your remark on loading down the slayer exciter. I'm not familiar with that circuit. How do you load it down aside from blowing up the transistor or overloading the power source?

Title: Re: SSTC Not Working Correctly
Post by: Mads Barnkob on October 18, 2017, 08:00:24 PM

Quote from: Uspring on October 18, 2017, 10:46:42 AM

Mads: Secondary Q depends mostly on arc loading, so it is probably much lower than that calculated from wire gauge and skin effects.

I don't quite understand your remark on loading down the slayer exciter. I'm not familiar with that circuit. How do you load it down aside from blowing up the transistor or overloading the power source?

Yes I was using unloaded figures here

From what I understand, the slayer exciter circuit is quite simple and not a big power pusher, that from its feedback oscillating nature has a narrow performance and can not keep up with feeding a larger capacitance, but I could be wrong :)

I recall back when I build SSTCs that larger toploads always meant trouble, but it could be as you describe that the higher primary currents was the real culprit causing flashovers as I caught on video at 3:37:

Title: Re: SSTC Not Working Correctly
Post by: Laci on October 18, 2017, 08:14:54 PM

So I made some measurements.The resonant frequency is 140kHz i think,but i'm not sure,because every frequency was measured with multimeter.The power supply is around 55 volts,large smoothing capacitor.
•Without topload:3 turns primary,current is 1A,and it outputs around 0.5cm arcs and they are pretty weak,can't pull a constant arc.With more primary turns,current drops,but the arcs gets more powerful,around 2cm.
•With topload <5 turns does not give any output,and by increasing the primary turns the current is dropping,arcs are increasing-the same thing as without topload,but the arcs are not as big as without topload,seems like it needs more primary turns with topload to work better.
The frequencies are pretty high(around 400kHz) in both cases,measured with multimeter so i think it's not accurate or it's not measuring what it should.

Also,the height of the coil is 50cm,a bit taller then I described,because I wound it until I ran out of magnet wire.

Title: Re: SSTC Not Working Correctly
Post by: Laci on October 18, 2017, 09:26:42 PM

I'm also planning to buy some IGBT's.
I've seen which ones are good for tesla coils so I have a collection to choose:
HGTG30N60A4
IRGP50B60PD1
IGW60N60H3
and IGZ100N65H5XKSA1 which have very promising properties of 650V,100A,500W+,but I don't know its switching speed.

Which IGBT would be the best at >150kHz frequency in full bridge  configuration?

Title: Re: SSTC Not Working Correctly
Post by: Mads Barnkob on October 19, 2017, 09:22:56 AM

Laci: Could you also measure your power supply voltage for these experiments, because I think that you are loading that down so much that its voltage drops a lot and that is why you have no output.

Lets look at some parameters on the different IGBTs

IGBT	Vce____	Vce(sat)125Cmax	Icm____	Gate charge___	Combined switching time___	Switchng losses
HGTG30N60A4	600 V	2 V	240 A	300 nC	225 ns	1 mJ
IRGP50B60PD1	600 V	3.6 V	150 A	250 nC	180 ns	1.25 mJ
IGW60N60H3	600 V	2.2 V	180 A	375 nC	350 ns	3.5 mJ
IGZ100N65H5XKSA1	650 V	1.9 V	400 A	210 nC	480 ns	2 mJ

Vce(sat) is the voltage drop across the IGBT and the conduction losses are equal to Ohms law, so if this is 2 V and you have 100 A, 200 Watt losses, there is ofcause some derating in the link below that can be done due to short on-times. The lower Vce(sat), the better.

Icm is a good measure on hard you can push the coil, how much current you can conduct in the primary circuit.

Gate charge is a figure for the energy needed to turn the IGBT on, but also the same amount that has to be drained when turning it off, the large number, the better driver is needed.

Combined switching time is how fast you can switch the current on and off, the lower number, the high frequency is possible, for more details see here: http://kaizerpowerelectronics.dk/tesla-coils/drsstc-design-guide/igbts/

Switching losses is also very important, here you have to calculate how much power you have to dissipate from the IGBT to the cooling system (heat sink, water cooling, etc) in order to keep the die temperature rise within a acceptable limit, again see the above link for details.

IGZ100N65H5XKSA1 does indeed look very good, so does the others, but not IRGP50B60PD1, it has a too high Vce(sat). They will all be able to switch up to 300-1000 kHz(Fmax1), the limit you have to find is the power dissipation(Fmax2) to keep temperature rise within your design goal.

Title: Re: SSTC Not Working Correctly
Post by: Laci on October 19, 2017, 07:48:03 PM

I made a driver,with PLL halfbridge(irfz44),running everything on 12V,so I can tune the frequency and measure it.At a range of 150-160kHz,a fluorescent lamp is lighted up at almost  max. brightness,current drawn is at around 0.1-0.2A at 5+ primary turns and under that the current increases rapidly and does not increases the output power.I did not expected anyting better than this,because the setup was just made in order to check the secondary's resonant frequency.
The feedback for the PLL is also working,it adjusts frequencies as even high as 180kHz down to the resonant frequency (150-160kHz).

The previous slayer exciter test loaded the 55v PSU to 50V,so that was not the problem.Even if I shorted the collector to the + rail,no current was flowing,so I think that the 47k base resistor was too big.In this case without a signal from the base of the coil,the transistor never turns on,and with less turns,the induced current into the secondary coil is not big enough,to trigger the transistor I THINK... :o

My new question is how and what kind of varnish can I use to insulate the secondary coil?I visited some nearly electronics and hardware  stores and nowhere could I find varnish for magnet wire.I have nitro based laquer,but I do not know if I can use it for this or not.Actually I want to protect the coil,and prevent the pretty lose windings from overlapping,not to prevent it from too high voltage. :D

Title: Re: SSTC Not Working Correctly
Post by: Mads Barnkob on October 19, 2017, 08:31:02 PM

Try to look for a clear non-coloured polyurethane varnish, I have used some that was meant for boats or floors, just be sure it does not contain oil, some for boats does that and it has problems hardening up completely when there is nothing to absorb the oil (it properly would if it was used on wood). You should be able to find polyurethane varnish in all home improvement stores and paint stores.

I would like to use epoxy, but that is hard to come by in Denmark.

Title: Re: SSTC Not Working Correctly
Post by: Laci on October 19, 2017, 10:41:14 PM

This evening I ordered 4xIGZ100N65H5XKSA1 IGBT,calculated the maximum switching time which is around 800kHz so the switching should not be problem.Also bought some 74HC109N's to maybe upgrade to DRSSTC,if it will work as SSTC ;D
I will look for the type of varnish you said,and hopefully I can make the job.

Title: Re: SSTC Not Working Correctly
Post by: Laci on October 21, 2017, 05:10:53 PM

The secondary got 3 layers of acril-pulyurethane water based eco  varnish.It dried very fast and isolated,fixed the windings very good.I added an interrupter to the circuit,increased the voltage to 30V and got pretty good results,2-3cm arcs. :D
Here are some photos about the setup,and the GDT,which I'm planning to use.What is your opinion about it?

Title: Re: SSTC Not Working Correctly
Post by: Mads Barnkob on October 22, 2017, 07:22:51 AM

Good that you found a varnish that worked for you, 3 layers is good, normally I am also somewhere in that region with 2 to 6 layers of varnish, depends how much time I want to spend on it, and higher power Tesla coils also needs more layers, so a SSTC will do just fine with 3 layers.

Your breadboard setup can give you trouble when you start making longer sparks, with many long wires and leads to pick up the energy from the secondary coil, if you have problems with unstable control, try to move the electronics away or shield it with grounded aluminium foil.

Do you know what material type ferrite core you used for the GDT? At-least it does not look like a powdered iron core from a computer power supply (the yellow/green ones), but the windings itself look real good, for a half-bridge! :)

Title: Re: SSTC Not Working Correctly
Post by: Laci on October 22, 2017, 04:52:05 PM

I do not know the material of the GDT...It came out of an old pc.My friend found it in his pc,and he said,that some wires were twisted around it(probably the ATX PSU's wires).
The circuit is made on a breadboard,because I do not have any perf board.It will be upgraded soon.

Title: Re: SSTC Not Working Correctly
Post by: Laci on October 24, 2017, 07:04:56 PM

The 4 transistors have arrived.I'm a bit worried about the 4th kelvin pin,because I do not know what is it,but it's shorted to the emitter and the datasheet says that they are not exchangeable.
An oscilloscope is getting pretty necesarry,and I'm going to buy a cheaper,because it should be enough for me.I found the 3 cheapest scopes in the EU which are two hantek:DSO5072C and DSO4072C and UTD2102CEX.
I think that the DSO4072C would be the best choice,due to its frequency generator function,but its also a bit more expensive than the two others.Which one of the other two would you recommand?

Also,is it important to mount so high power transistors like these on big heatsink,while running SSTC?

Title: Re: SSTC Not Working Correctly
Post by: Mads Barnkob on October 25, 2017, 07:31:46 PM

If the ferrite core came from a ATX power supply, there is a good chance that it is powdered iron and NOT useful for a GDT working at hundreds kHz in a SSTC.

Just bend the kelvin leg the opposit way or snap it off completely if you are not going to use it. If you want to learn more about kelvin connections: http://www.powerguru.org/kelvin-emitter-configuration-further-improves-switching-performance-of-trenchstop-5-igbts/

How are the prices on DSO5072P and UTD2102CEX compared to a Rigol DS1052Z? The first two has remarkably low memory record depth of only 40k points and 25k points. Hantek gives a lot more detailed technical specifications than Uni-Trend, so just on that point I would choose Hantek over Uni-Trend.

Title: Re: SSTC Not Working Correctly
Post by: Laci on October 25, 2017, 10:22:26 PM

Well,I bought the DSO4072C  8)
The item's location is in Germany,but the seller is based in CH,so I hope,that they will send the scope from Germany....
Hopefully I will get it in 1-2 weeks,so I will have the chance to finish the project before nov.10 for a physics demonstration in my school. :)

Until then,thank you very,very much for the help!

Title: Re: SSTC Not Working Correctly
Post by: Laci on October 30, 2017, 09:43:54 PM

I'm back again :)
I have some good results at a halfbridge of IRP240's,70V.The full bridge of the new mosfets is also made,i will test it and upload pics tomorrow.
One thing that is interesting is that without resonance cap on the primary,the results are not even nearly as good as with it.2x0.15uF 250V capacitors are connected to 11-13 turns primary gives the best results.I'm thinking why not buy some components to upgrade to DRRSSTC? :) So I have the following questions:
1.Would be good 2x 942C20P15K-F capacitors in series as resonance capacitors?
2.What type of ferrite ring should i buy for the current transformer and for the GDT?
 If you can,please send the accurate models of the ferrite rings,so i can buy them on mouser.com.

Title: Re: SSTC Not Working Correctly
Post by: Mads Barnkob on October 31, 2017, 09:13:59 AM

You do not have a resonant capacitor in a SSTC, you have a DC blocking capacitor.

If you upgrade it to a DRSSTC, be sure to use a DRSSTC driver, else it will be a short life for your IGBTs, do not use MOSFETs in a DRSSTC, they have a much too high conduction loss at those peak currents.

2x 942C20P15K-F is what I used in my small DRSSTC2, so it can be good enough for smaller coils.

This would be a suitable physical sized, N30 material and a permability AL value of 5750: https://www.mouser.com/ProductDetail/EPCOS-TDK/B64290L674X830/?qs=sGAEpiMZZMt1hubY80%2fs8DEvGx1xc7EcUsoMlWTaffs%3d   and a datasheet for it: https://product.tdk.com/info/en/documents/data_sheet/R3600x2300x1500.pdf

Title: Re: SSTC Not Working Correctly
Post by: Laci on November 01, 2017, 06:37:24 PM

Well some things happened since the day before yesterday...The oscilloscope have arrived,full bridge of IGBT's was made.Sadly its not working.I think that the IR2109 can't output enough current,because the waveform at the gate is anything,but not a square wave.I think that I will buy the ferrite rings,resonance capacitors and UCC37322 & UCC37321 chips this evening.
An other thing:I replaced the IRFP240's in the halfbridge circuit with an IRFP350 and a FQA24N50F just to try the circuit on mains.Firstly i connected a light bulb as a ballast to see if it is working.It was and produced great,around 5cm arcs.Then I removed the light bulb.What would you expect?Well...more than 20cm arcs started shooting out from the breakout point.It was exciting,at least for me...Of course the transistors died pretty fast,as always,so I could not make a picture or video.It was all good,and working until I put my hand so close to the interrupted arcs,that I almost touched the topload.At a point I heared a bang,the 3.5A fuse blown up,then the mosfets shoretd out.
It was a great experience,but I wonder why the transistors blown up?Please tell me if you know :)
Also,I'm not using isolation transformer and the coil is grounded to mains ground.

Title: Re: SSTC Not Working Correctly
Post by: Laci on November 01, 2017, 07:11:30 PM

Here is the photo of the full bridge and the other is the high and low side waveform,the upper is the low side.

Title: Re: SSTC Not Working Correctly
Post by: Mads Barnkob on November 03, 2017, 03:19:56 PM

Congratulations on making long and delicious sparks :)

The IRFP350 only has a continues rating of 10 A and pulsed 64 A, they properly died from over current. Your hand near the secondary circuit will also change its resonant frequency, but I do not think that should have resulted in phase shift/hard switching and therefor cause the explosion.

You are entirely right about that gate drive not being sufficient to drive anything, but to keep the switches in linear mode where they die from too much heat from conduction losses.

Title: Re: SSTC Not Working Correctly
Post by: Laci on November 03, 2017, 06:49:32 PM

I hade some UCC's from the past,but they are not working.Now I got a single new 37321,hooked it up to a test circuit.I added a 1uF film capacitor to the power rails,and connected it to the GDT,the other end to ground.When I touched the input pin,a large current started to flow,and the chip acted as the others:driving large every time if I connect them to a power supply.I've seen somwhere,that it's not easy to kill chips like these.Am I the master of the chip killing,or they are not dead,just acting weird?Also,what about dead time of the IGBT's at a GDT?

Title: Re: SSTC Not Working Correctly
Post by: oneKone on November 04, 2017, 09:18:13 AM

Hi Laci.

My experience with the ucc3732x driver chips is that they need an input or they'll fail, almost oscillate themselves to death! I've killed a few like this so i've always made sure they've had a driving signal. another thing i use is a dc blocking capacitor but i don't know if this still applies to when only using one chip as you've described. Hopefully this helps in some way. 

Title: Re: SSTC Not Working Correctly
Post by: Laci on November 05, 2017, 02:10:06 PM

As a test,I connected the PLL to a bd139 & bd140 and through a 1uF cap to rhe GDT and the other end of the GDT to ground.It draws around 200mA,and the signal at the IRFP240's gate in halfbridge looks like on the picture.However, if I connect a load to the halfbridge,no current is flowing.Everything looks working,and I don't know what is the problem...

Another thing that I've realised,why the transistors blown up two times,when I connected the DC blocking or resonance capacitor:the resonant frequency of the secondary is 150kHz,but the primary's was a way more higher,but as stupid as I am,I blown up 4 transistors,instead of at least tune a proper primary-secondary resonance.Now I measuerd  the primary's resonant frequency and at a point it's 144kHz which should be good at long sparks right?Also,the previously posted GDT problem is still not solved...

Title: Re: SSTC Not Working Correctly
Post by: Mads Barnkob on November 05, 2017, 10:30:25 PM

How much can we trust the voltages shown in the oscilloscope shot?

Ch1 is 20V/div and Ch2 is 2V/div, so you properly have no voltage at all driving one leg of the half bridge.

You do not tune a SSTC primary circuit, you only vary the amount of primary turns in order to decide/limit the current that can flow in it.

Title: Re: SSTC Not Working Correctly
Post by: Laci on November 09, 2017, 10:39:17 PM

A few things happened again.The GDT problem solved,because I made a halfbridge on a breadboard with IRFZ44N's and it worked pretty good,but with the IGBT's the signal was not even like square,probably due to the poor design and the BD139-140 output stage.
New components have arrived.
Ferrite toroids(3x): https://www.tme.eu/gb/details/tx42_26-3e25/ring-ferrites/ferroxcube/tx422613-3e25/
Capacitors for DRSSTC(3x in series): https://www.tme.eu/gb/details/phe450rd6220j/standard-foil-polypropylene-capacitors/kemet/phe450rd6220jr06l2/

And other chips.I put together a PLL based IR2109 full bridge driver circuit on a perfboard.Sadly,the output of the IR2109 was not enough for the IGBT's,so I bought 2x IR2184 and added them to the perfboard.I will test it tomorrow.

Yesterday I created an arduino based interrupter with bps+duty cycle control and SD card music play function.Since I don't have optical fiber,I will connect the interrupter to the main driver circuit via some kind of insulated cable .

Tomorrow I will try to make the CT and the GDT.What is your opinion about the toroids?Can I use them for both the CT and the GDT at 150kHz?(Since the secondary res.freq. is 150kHz)

Title: Re: SSTC Not Working Correctly
Post by: futurist on November 10, 2017, 01:24:36 AM

3E25 toroids will be fine for both GDT and CTs. I use them too for CTs, and even worse N87 material for GDT

Why not invest in fiber optic transmitter/receiver? They are not that expensive:
https://www.ebay.com/itm/2x-AGILENT-HFBR-1414T-TX-FIBER-OPTIC-TRANSMITTER-160MBD-8-Pin/182851049308
https://www.aliexpress.com/item/HFBR-2412TZ-RECEIVER-FIBER-OPTIC-5MBD-TTL-ST/32709652010.html

Especially because arduino won't like EMI from the coil. I have one as fan speed controller and bus precharge controller, and it kept resetting on ground strikes before I added various protection to reset pin, etc.

Title: Re: SSTC Not Working Correctly
Post by: Laci on November 10, 2017, 10:36:54 PM

I've made the GDT :) !What is your opinion about it?The first scopeshot shows the unloaded GDT,the other one the GDT with an IGBT connected to it,which probably loads down my scope's built in 50R impedence function generator.

Title: Re: SSTC Not Working Correctly
Post by: Mads Barnkob on November 11, 2017, 01:28:43 PM

Remember to mark up the phasing of the GDT windings, before twisting it all together, makes it much easier to avoid mistakes later on.

For your next GDT, I would advise you to use a complete network cable, normally I parallel all the white/colour wires and use the 4 coloured pairs for the gates, this gives a nice and sturdy primary winding that can conduct some current, heat up less and has high coupling to the secondary windings.

(https://highvoltageforum.net/proxy.php?request=http%3A%2F%2Fkaizerpowerelectronics.dk%2Fwp-content%2Fgallery%2F2009_08_27_-_kaizer_drsstc_i%2FIMG_2683.jpg&hash=52b0cf62a5ff6eee6b515fd492214208ebbd7402)

Square wave looks fine and despite your signal generator might be weak, its actually doing a fair job driving that gate! But I would not recommend that you continue to use it for that, did you insert a 50 Ohm resistor in series with the primary to match the output impedance of the signal generator?

Looking forward for the coming updates :)

Title: Re: SSTC Not Working Correctly
Post by: Laci on November 13, 2017, 10:07:52 PM

Updates again.
I hooked up the GDT to the IGBT full bridge.The driver circuit was the PLL circuit,with the UCC chips converted to another perfboard.
At the beginning,I experimented with the GDT phasing,but it was not working,so I made some changes and marked the cables from one end.Additionally,I have a question:is that a problem if I have single coil connected to the UCC's instead of two in parallel?
The phasings looks correct,the waveforms also OK i think,but it doesn't outputs anything to the primary.The chips heats up pretty fast,especially the UCC37321.The current starts from 2A and drops to around 1A in around 10 sec.,while the chips heats up uncomfortably hot.The old chips were died,as I expected,when I put them in the socked,they exploded like a firecracker...
I see a problem on the waveform:it's around 2V at 2V/div so 4V.It should be the same as the UCC's 12V rail right?And what is the current drawn of the UCC's in your circuits?

Title: Re: SSTC Not Working Correctly
Post by: Laci on November 13, 2017, 10:14:03 PM

Photos:

Title: Re: SSTC Not Working Correctly
Post by: Laci on November 14, 2017, 09:02:10 PM

Well...I'm about to give up this project...Nothing is working :(

After I removed the zener diodes from the IGBT's,the fluorescent lamp started to light up.
Since I'm an idiot,I directly shorted one of the UCC's 6 & 7 pins to ground.After I fixed it,the coil started to work pretty well.The UCC's didn't died and I made some changes to the fullbridge.
It was working nice on the 18V laptop battery charger.I still couldn't connect the zener diodes,because with them high current started to flow in the driver circuit,so I think that they shorted the transistors gate to emitter at such a high frequency.
Then I connected my 55V transformer to the fullbridge.I pressed the driver circuit's power button.Immediately very high current started to flow to the IGBT's.I turned off very fast everything.
Next I disconnected the transformer and turned on the driver circuit alone.Around 1.5A started to flow,and guess what?Two IGBT's were completly shorted.

Altought,the GDT worked pretty well,the signals were good,in phase.After fixing the wrong connection on the perfboard,the driver circuit drawed around 0.4A and the UCC's heated up slower.

As a last hope,I'm gonna check if the other two IGBT is good or not.If yes,then rebuild the whole thing as a halfbridge.If not then just use my remaining 2xIRFP460.
I'm really disappointed,but I should expected these fails to happen.Hopefully this forum will help other peoples to learn about my problems and they will not make the same mistakes as me...

A question is still existing:why the IGBT's blew up?And why the thing was not working with zener diodes?I think they died due to gate overvoltage.I've seen,that in other schematics two zeners are used in opposite direction.Did this caused the death of my IGBT's?

Title: Re: SSTC Not Working Correctly
Post by: Mads Barnkob on November 14, 2017, 09:17:02 PM

A single wire primary on the GDT is not a problem unless it really heats up or has a high resistance. It all depends on the load the GDT has to drive, did you calculate how much driving power is needed? ( http://kaizerpowerelectronics.dk/calculators/igbt-gate-drive-calculator/ ) This will also give you an idea on how much power the UCCs draw.

UCC chips should NEVER be running without a load connected to their outputs, if you have this, it is almost guaranteed that they are destroyed. What happens is that the high output current capability of the IC can self oscillate with the stray inductance/capacitance at its connections, into MHz frequencies and it will just do this until it burns out.

Regarding the output voltage, are you sure you are not short-circuiting anything with those connections to the oscilloscope? You should not measure the primary side of the GDT, but the secondary side, this is where you have to check for your good looking gate switching waveform and adjust gate resistor accordingly to minimize ringing at turn-on.

Do not worry too much about small failures, we have all been there and I also used to have a mountain of burned silicon :) It takes exploding parts to build knowledge. Keep up the good work and experiments!

Edit: regarding exploding IGBTs/zener diodes, this is almost always two things, wrong phasing so that you are turning on two wrong switches at a time and they short circuit the power supply across themself and die or too much current.

Do not think that just because you test the bridge at 12V that it is switching correctly, that voltage is so low that even if its short circuiting the IGBTs could very well just dissipate the power, but with higher voltages they will go puufff!

Title: Re: SSTC Not Working Correctly
Post by: Laci on November 14, 2017, 09:55:14 PM

Thank you for the reply!
I'm upset,because Friday I could show it on a physics presentation and things are not going very well.
I should start everything from the beginning and upgrade everything lineary.The only thing that worked very well,was the halfbridge with the IR2109 bootstrap.That worked more than 1 minutes :O But as always,that also died...

Quite a lot of SSTC's and DRSSTC's are made with halfbridge.I want to go back to that and make it working.Only if that is done,then upgrade.

The resonance capacitors are like addiction to drugs for me.Almost every time,when some arcs are coming out from the secondary,I connect them to the primary.This way failure is guarantied,which is a routine for me.

I send some pictures of the fullbridge.Tomorrow some pictures will be uploaded about the GDT waveforms.Maybe test some bootstrap circuits,remove the died two IGBT from the heatsink.

Title: Re: SSTC Not Working Correctly
Post by: Laci on November 17, 2017, 09:37:27 PM

Hmmmm......
The full bridge got repaired,by removing the 2 dead IGBT and replacing them with 2x1uF MKP caps.Driver circuit was the same,PLL driven UCC's and as interrupter a simple 555 astable multivibrator,then Steve Ward's interrupter with burst mode.
It was working nice and good at 55V.Then I increased to mains rectified with 60W lamp in series.
Strange things started to happen...It was working sometimes,and sometimes not.The current into the halfbridge was measured with a multimeter.It started to randomly jump up,and reached my meter's limit.
While this was happening I heared clicking sounds coming under my workbench.I looked down,and saw an interesting thing:The HV was arcing from the mains ground(the bottom of the secondary)to the neutral.
Then I wake up in an other world and realised the big deal.I WAS RUNNING THE TESLA COIL ALL THE TIME WITHOUT GROUNDING THE SECONDARY.

The problem was my wall outlet's connector multiplier or splitter or whatever it's called,because it's cable doesn't contained the 3rd ground wire...

I fixed this problem quickly,then started running the thing interrupted.Steve's interrupter resulted awesome looking and sounding sparks,,but not really long ones.So I made the astable multivibrator for higher duty cycle.The result is shown in the video;around 20 cm sparcs.

One active problem is the feedback.When a put my hand closer to the coil,the arcs lenght increases.I already had this problem,and I thought it was repaired by a solder connection.Is this normal?


I'm gonna upload a picture of my planned CT to use.What is your opinion about it?

Title: Re: SSTC Not Working Correctly
Post by: Laci on November 17, 2017, 09:40:13 PM

Video: https://mega.nz/#!MfollKQK!felQUB7hoZHNeaBLQouAqYp8BmTamvcU1xY57miKpZ4

Title: Re: SSTC Not Working Correctly
Post by: Laci on November 17, 2017, 09:48:22 PM

And the sad thing comes again.I kinda finalized this SSTC,so it would be possible to show it to other peoples in a school presentation,but that ended this day,and I had to say to my physics teacher,that I couldn't make it....

Title: Re: SSTC Not Working Correctly
Post by: futurist on November 18, 2017, 12:50:22 PM

Don't worry, I'm sure you'll have another chance of presenting your project and that your teacher understands that building SSTC isn't a piece of cake

Title: Re: SSTC Not Working Correctly
Post by: Laci on November 18, 2017, 02:58:03 PM

Yes,it's not easy at least for me.The system is down again,due to my stupidity,because I disconnected the interrupter and the breaker popped.One of the IGBT's died.

Now I can relax a bit,and focus on other things.I'm proud,that I could make a pretty good SSTC.The driver circuit works great.The IGBT's gate waveform was really good(see the picture).The interrupter is OK,but without shielding anything,or optical fiber connection,it isn't stable.

I still have quite a lot things to upgrade.I'm planning a DRSSTC,but it wouldn't be a good idea to run it on a IRFP460 halfbridge...

Many thanks for this forum,and for everybody who helped me to get here!I will not leave,just take a break,until new transistors will arrive :)

Title: Re: SSTC Not Working Correctly
Post by: Mads Barnkob on November 18, 2017, 05:23:18 PM

You have learned a lot of lessons and that is more valuable than having a kit work in the first go :)

You are absolutely right about IRFP460s not going to work in a DRSSTC, MOSFETs have no place in switching so high peak currents, just do a quick calculation with on-resistance and peak current so see that you are trying to dissipate the heat of the sun in a glass of water.

Have a nice break and certainly looking forward to help you build a DRSSTC :)

Title: Re: SSTC Not Working Correctly
Post by: Laci on December 02, 2017, 08:10:32 PM

While I'm making the DRSSTC,I also rebuilt a fullbridge of 2xIRFP460 and 2xIRFP240,since I had these transistors.It still works very good.The power supply is around 120V,by putting some transformers in series,and it's still working after two days,which is a record for me :)
The interrupter is my scope's built in,connected to the UCC's enable pin,but I want to audio modulate it.The audio modulator in the Kazier SSTC 2 looks promising,but I would like to have cleaner sound,not the midi-interrupted type.Do you have any idea?

Title: Re: SSTC Not Working Correctly
Post by: Mads Barnkob on December 03, 2017, 08:02:06 PM

Quote from: Laci on December 02, 2017, 08:10:32 PM

While I'm making the DRSSTC,I also rebuilt a fullbridge of 2xIRFP460 and 2xIRFP240,since I had these transistors.It still works very good.The power supply is around 120V,by putting some transformers in series,and it's still working after two days,which is a record for me :)
The interrupter is my scope's built in,connected to the UCC's enable pin,but I want to audio modulate it.The audio modulator in the Kazier SSTC 2 looks promising,but I would like to have cleaner sound,not the midi-interrupted type.Do you have any idea?

The audio modulator I used in the SSTC2 is a midi-like interrupter as it does PWM and interrupted tones, there is not much difference in sound from this and a pure MIDI modulator, except the MIDI modulator has better and more precise tone control, which actually sounds better :)

You are properly asking for FM modulation like sound, like the one you hear in a Class E Tesla coil, you could take a look at the LTC6992 IC that Acid Byte uses in his SSTC, that might just be the thing for you: https://highvoltageforum.net/index.php?topic=164.0

Title: Re: SSTC Not Working Correctly
Post by: Laci on December 15, 2017, 05:52:37 PM

I think this project is done :)
I've put everything together on Tuesday and everyhing was working.On the next day I showed it on a physics demonstration,it was working without problems for hours!
Yesterday I made a small modification:added the 3x220nF resonant caps to the primary.It was awesome!Around three times larger arcs than before,up to 40cm!Sadly,I today killed the mosfets,because I pulled an arc direcly from the topload by a long wire and probably a high peak current killed the mosfets.Otherwise it was working amazingly wel.I think this setup is much more stable than anytime before,but I really want to know the difference between the DC blocking cap and the resonant cap.Does just the driving circuit make the difference?

Anyways now I can continue the making of the DRSSTC.IGBT's will come soon,probably not the same ones as before,probably IGW60N60H3's or HGTG30N60A4D's...
A short question about that:what kind of caps can be used in the 1.3b driver's gdt driver section?

Title: Re: SSTC (Not) Working Correctly
Post by: Mads Barnkob on December 16, 2017, 04:23:23 PM

The difference between a DC blocking capacitor in a SSTC and a resonant capacitor in a DRSSTC is actually not that big, they are most likely both MKP type and could be the same capacitance.

You can have a 1 uF DC blocking capacitor in a SSTC and also a 1 uF resonant capacitor in a DRSSTC, but what makes the difference is the inverter impedance, which is calculated from inverter voltage output divided by inverter output current. A SSTC has a low current compared to a DRSSTC.

The reactance Xc of a DC blocking capacitor should be many times smaller than the inverter impedance, where in a DRSSTC the reactance is much higher due to smaller capacitances in the MMC, but to go back to our example of 1 uF DC blocking vs. 1 uF resonant capacitor, a small SSTC would maybe be 320V/10A so 32 Ohm impedance but the large DRSSTC using 1 uF resonant capacitor could be 564V/2000A so ~0.25 Ohm impedance.

The reactance Xc = 1 / (2 * pi * frequency * capacitance), so the higher capacitance, the lower reactance at the same frequency.

Title: Re: SSTC (Not) Working Correctly
Post by: Laci on December 16, 2017, 09:33:09 PM

So basically a capacitor in the primary circuit doesn't effects the primary resonant frequency,and the important thing is to drive it at the secondary's resonant frequency?

Title: Re: SSTC (Not) Working Correctly
Post by: Mads Barnkob on December 16, 2017, 09:41:46 PM

Quote from: Laci on December 16, 2017, 09:33:09 PM

So basically a capacitor in the primary circuit doesn't effects the primary resonant frequency,and the important thing is to drive it at the secondary's resonant frequency?

Not if there is a huge mismatch between inverter impedance and capacitor reactance, then it will just behave as a DC blocking capacitor, which is only there to protect the MOSFETs from a saturated primary coil (preventing explosions).

Title: Re: SSTC (Not) Working Correctly
Post by: Laci on December 16, 2017, 09:46:34 PM

I calculated my designs properties.At 150kHz,330VDC rectified mains,the 3×0,22uF caps have 23 ohm reactance.So if I remove one from the three,the current and the arcs size should increase?

Title: Re: SSTC (Not) Working Correctly
Post by: Mads Barnkob on December 17, 2017, 09:34:08 AM

Quote from: Laci on December 16, 2017, 09:46:34 PM

I calculated my designs properties.At 150kHz,330VDC rectified mains,the 3×0,22uF caps have 23 ohm reactance.So if I remove one from the three,the current and the arcs size should increase?

In theory yes.

But you are only going to be blowing up MOSFETs when you try to run a MOSFET inverter for a SSTC as a DRSSTC.

As the primary current goes up, the losses in a MOSFET versus a IGBT is very different!

A MOSFET has a fixed on-resistance and this is the root cause of heating problems with high currents, the fixed voltage drop of a IGBT makes it have a lot less conduction losses than the MOSFET, at high peak currents.

Title: Re: SSTC (Not) Working Correctly
Post by: Laci on January 03, 2018, 08:06:32 PM

The oneTesla interrupter is done on a breadboard.Here are two short videos about it running.I was changing the on time,to see if the audio quality is better at lower on times or not.The popping sounds are existing at me too,and also at high on times the higher tones gets distorted,like in the Pirates of Caribbean.
*Running at a halfbridge of 2xIRFP460.

https://mega.nz/#!EWBkgADC!LDEw2XMfGtdSZRNl6JwAd5hNmV-WHBNajizALh813NI

https://mega.nz/#!MbZRBZQI!Vikm4im2t40Qc0l12D8tJiDiLgcfKILILvruWl-_BJI

Title: Re: SSTC (Not) Working Correctly
Post by: Laci on March 10, 2018, 08:34:18 PM

Since I got 10 IRFP460,why not rebuild a SSTC driver?!I made a full bridge of them,more less accordingly to Mads recommendation,with thick wire and without perfboard.Also made a full bridge rectifier with 5 caps in parallel for a total of 1200uF.I put them into a nice enclosure,with full/half wave rectification(120/60Hz) and a switch,which bypasses the 330ohm resistor responsible for slowly charing the caps.
Actually I am sad,because 5 transistors and 4 TVS diodes died in a row.Two of the transistors died violently and three of them silently,as well the diodes.The 440V TVS diodes always died when I played midi with high on time from the interrupter.The first transistor died because of a spark to ground (which will probably be a new post),then the next two pair simply exploded at low bps,then I stupidly after replacing the transistors touched the "snubber caps" which of course got connected to the gate of one mosfet.Silent death.Then replaced the transistor,but not the protecting zener diodes which killed the new mosfet...It's a really bad idea to work with these kinda things when you are tired...

Title: Re: SSTC (Not) Working Correctly
Post by: Laci on May 13, 2018, 09:51:35 PM

While being busy with school,I had a bit of time to continue this "never ending" project.Made a new IRFP460 bridge again on perfboard,but with 2 sides(halfbridges)on a heatsink to make the replacement easier.
Another important thing is that I got a new grounding.Instead of the mains ground now I have around a 50cm "U" form steel sinked in the ground and connected to the bottom of the secondary through around a 7m long,really thick 3in1 cable with the wires paralleled for lower resistance.
The driver circuit is the UD1.3 with antenna feedback,without current transformers.The interrupter is the oneTesla with pretty low on times,probably the default settings,for DRSSTC.The whole driver is poorly insulated from the tesla coil,not sure if that's a problem or not.
The main issue is the current drawn.Using my newer primary with the thick wire(6 turns)the rms current is not enough to blow a 1A fuse and the arcs are not really good,maximum 10cm(1/5 of the secondary).The midi sound is already too loud.Don't get me wrong,not for me,but for my neighbours. :P
I assume that the low on time of the interrupter prevents the arcs to grow,because with such a thick and just 6 turns primary the current flowing into it should be way to higher even at SSTC operation.How else can I increase the arcs lenght?Any tips would be appreciated.
Also the main motivation is the Kaizer SSTC II and oneKone's SSTC at the arcs to secondary size,which is around 1:1 in both cases,right?

Title: Re: SSTC (Not) Working Correctly
Post by: Mads Barnkob on May 17, 2018, 11:02:01 AM

Are you using a DRSSTC UD1.3 with antenna feedback to drive a SSTC? I never heard of that before and maybe you have some timing issues with coil being driven off resonance or the very low on-times for a DRSSTC is too little for a SSTC.

In music mode you should expect shorter arcs, than what you can get when pushing it in interrupted mode, as you have more charge on the topload.

It seems like you have metal enclosures on everything, just get them grounded to the same ground rod as your secondary coil and you should avoid too much interference. But just a metal enclosure in itself will help a lot.

Title: Re: SSTC (Not) Working Correctly
Post by: Laci on May 17, 2018, 03:15:12 PM

Right,the signal is received from an antenna.Not sure if it makes any difference,but it works this way too.With current transformer feedback the oscillation is not starting on it's own so I tried this.Also the first set of transistors has blown up.Some weird phenomena were happening with the coil.The arcs were not so big so I uploaded the code to the arduino with the lookup table scale 10 for longer on time,but without longer arcs,just higher current drawn.The arcs stopped when I was pulling an arc,moving the antenna-no effects.
Just as an experiment I removed the topload and added a anorher smaller coil to the top of the secondary.This doubled the size of the arcs and the current and sadly killed the transistor at the second midi song with the maximum on time(~350uS).3 transistors died and the zener diodes at one side.I assume that the high magnetic field got into the GDT and without grounding it easily got to the transistors.

Since the inverter is screwed again but I have the IGBTs,I wonder if this inverter design is good for a DRSSTC or not?
By the way thanks for the reply again,Mads!

Title: Re: SSTC (Not) Working Correctly
Post by: oneKone on May 17, 2018, 03:50:45 PM

you've mentioned that with CT feedback the oscillation will not start, did you try changing the phasing of the CT? also is the driver self made or bought? the antenna feedback could be causing some feedback errors.

another thing (sorry i have not re-read your thread) are you using a tank/resonance capacitor? if so how have you tuned your primary to the secondary? 

Title: Re: SSTC (Not) Working Correctly
Post by: Laci on May 17, 2018, 04:44:16 PM

The driver is self made.I think that the phasings were shifted,but I was not paying much attention to this,because I thought that using antenna is the same thing.Not sure if current feedback works with SSTC.

I was using capacitor with the primary in the past,but that was unstable,simpy due to the antenna feedback.Some mosfets died that way too....

Title: Re: SSTC (Not) Working Correctly
Post by: Laci on May 27, 2018, 06:39:11 PM

After two days running at 180V,two IGBT died when I connected the inverter to rectified mains.Probably because I just hooked up a capacitor to make it double resonant,or because the GDT flashed over(I noticed this yesterday).Anyways as last attempt I replaced the failed halfbridge with a capacitor voltage divider and it is working now for 3 days!Well,it is not working now,because the driver has an issue;a smoothing tantalum capacitor shorted out and I have to replace it,but also upgrade a bit on the design and use a transformer instead of the ATX PSU.
I tried several things with this inverter,so far so good,it works like a charm expect the flashovers from secondary to primary even after decreasing the turns on the conical primary.
Yesterday I was looking for those fake QCW interrupters to create long and straight sparks and ended up with a combined Kaizer VTTC staccato controller and loneocean's RSSTC3 interrupter.I made this circuit on a breadboard,it was not working as it was supposed to,but probably due to bad connections on the breadboard.While testing it produced 40cm straight arcs to ground,which I think is really good.Sadly at this point the capacitor blew up and I couldn't make a video of it.

I have a video with 8 primary turns and with the complete conical primary.With that amount of turns doesn't exist flashovers,but with 4-5 turns the flashovers were significant.
I don't know why is the inverted working better with 2 transistors instead of 4!?In comparison with the fullbridge now it has +-325V/2 so like +-162V across the primary instead of the +-325V.Double the voltage,double the size of the arcs,if the inverter is working correctly,right?

https://mega.nz/#!ZeJVnKoR!FvYfJYxrESm7BmyOdQYU9mSWFapb9-rF1G6Ag1iQua4

Title: Re: SSTC (Not) Working Correctly
Post by: Laci on June 27, 2018, 04:47:10 PM

Here comes some more updates!After a month the coil is still going strong,it has no problems and produces decent sparks.I suppose the full bridge blown up by an arc-over from the secondary to the primary,with the halfbridge the arcs flow through the capacitors instead of the transistors,blowin' them up.
A couple of pictures taken by my friend:
(https://i.imgur.com/l4BBJ4i.jpg)

(https://i.imgur.com/nj5iWkz.jpg)

Title: Re: SSTC (Not) Working Correctly
Post by: Mads Barnkob on July 01, 2018, 01:09:57 PM

Quote from: Laci on May 27, 2018, 06:39:11 PM

After two days running at 180V,two IGBT died when I connected the inverter to rectified mains.Probably because I just hooked up a capacitor to make it double resonant,or because the GDT flashed over(I noticed this yesterday).Anyways as last attempt I replaced the failed halfbridge with a capacitor voltage divider and it is working now for 3 days!Well,it is not working now,because the driver has an issue;a smoothing tantalum capacitor shorted out and I have to replace it,but also upgrade a bit on the design and use a transformer instead of the ATX PSU.
I tried several things with this inverter,so far so good,it works like a charm expect the flashovers from secondary to primary even after decreasing the turns on the conical primary.
Yesterday I was looking for those fake QCW interrupters to create long and straight sparks and ended up with a combined Kaizer VTTC staccato controller and loneocean's RSSTC3 interrupter.I made this circuit on a breadboard,it was not working as it was supposed to,but probably due to bad connections on the breadboard.While testing it produced 40cm straight arcs to ground,which I think is really good.Sadly at this point the capacitor blew up and I couldn't make a video of it.

I have a video with 8 primary turns and with the complete conical primary.With that amount of turns doesn't exist flashovers,but with 4-5 turns the flashovers were significant.
I don't know why is the inverted working better with 2 transistors instead of 4!?In comparison with the fullbridge now it has +-325V/2 so like +-162V across the primary instead of the +-325V.Double the voltage,double the size of the arcs,if the inverter is working correctly,right?

https://mega.nz/#!ZeJVnKoR!FvYfJYxrESm7BmyOdQYU9mSWFapb9-rF1G6Ag1iQua4

Great that you get all the small errors sorted out and keep the coil running!

Half the primary turns does not nescasarily mean double the current, you also have some stray inductance in wiring and bridge, but you are pushing much higher currents through the transistors and it most likely what is blowing them up. While you have two transistors in series conducting the half the voltage, the current through them is the same as if a half-bridge was driving the same load, but the power dissipation is lower.

Great video with a good clear MIDI like sound reproduction.

You should challenge your photographer friend to get crystal clear single spark shots and he will soon realize that it requires one hell of a camera :D