Author Topic: My First SSTC (and exploding IGBT's)  (Read 4046 times)

Offline Dylan Burger

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My First SSTC (and exploding IGBT's)
« on: March 16, 2017, 06:47:19 AM »
This coil looks somewhat like junk, but thats probably because I started designing it when i was 11 or 12.It was originally intended as a spark gap coil, but due to the cost of NST transformers here (not to mention HV caps...) I opted to convert it to a SSTC.

I have a small issue where the output of this coil is not very good, 3cm max at resonance, (~140khz) with 110v input.

[EDIT] - I finally got a scope. Gate waveforms and more are at the bottom!

I am unable to rewind the secondary coil at the moment. Partly because I cant find anyone to supply me with enough wire, additionally , the .51mm wire it is currently wound with was gifted to me by a friend who can no longer source wire for me.

This is what happened to my  40N65FL2 IGBT's recently when I decided to run my coil after the rebuild :


The drive circuitry is a CD4046 based PLL driver, it uses antenna feedback and UCC37322P /UCC37321P gate drive IC's and a home made GDT from some old stuff laying around. I have no oscilloscope so all i can measure is the frequency response it can provide ( how stable output voltage is in reference to a sweeping frequency). Voltage was a good constant 12V out from 40Khz to 200Khz, so I suppose its alright. I really need a oscilloscope XD. The interrupter is just a 555  limited for <50% duty cycle via diodes.

Now for the schematic :


I have all the values the same as in this schematic , except for the cap on pin 6 & 7 of the CD4046 (I replaced that with a 1.5nF to get 100-150Khz on my coil) and I dont have a cap in the GDT circuit, my resistor there is 15R. I use a full bridge rectifier , and I also added some zeners and protection stuff on the IGBT side of the GDT.

It looks like this :


Now for coil specs :

Topload :

Toroid. Made from 8cm diameter ducting, inner diameter is 18cm and outer diameter is 36cm.  the center plate is 6cm thick, made from a empty spool that had wire on. It is wrapped in a fine aluminium mesh i bought at a hardware store, because the ducting was a cheap plastic and it started to burn off the silver coating as soon as it arced.

Image of topload here :


Secondary :

11cm x 54cm (actual winding size)
11cm x 66cm (tube length)
Wire is 0.51mm (or 24 Gauge ?) and i calculated around 1100 turns on the secondary.

With topload , resonance is at ~115Khz (using JavaTC)



Primary :

18cm diameter.
8 turns 6mm copper tubing
18mm turn to turn spacing (25 mm center of tube to center of tube)
21cm tall



The driver board / box , and GDT :

A CD4046 PLL driver


555 Interrupter


Laptop variable output power supply (regualted, set at 15V)


Terminals ,switches and pot's :  (left to right)
Antenna , pulse width, pulse frequency, on/off toggle, phase adjust for CD4046, Phase lock indicator, interruptor/CW toggle


GDT :


Tuning and setup :

First I did was to hook up all my measurement equipment (amp meter and frequency counter ) then power it up with 20VDC, in CW mode, i sweep the pot till i get a current spike, do a variety of different frequency measurements to determine if the driver is at resonance with the secondary. Bumped up the voltage to 50VDC , retuned and then hooked it to a 220 to 110v step down transformer (quite large and bulky).
Then I powered it on and started to find the tap point in CW mode.  Each time it was for around 10 seconds on time. IGBT's did not get hot.
I switched over to pulsed mode and had a very short pulse , about 3 seconds apart. When i got to the point that i removed 2 + 1/2 turns, turned it on , and POP, instantly had fried IGBT's. Throughout this entire process , arcs did not break out by themselves , nor did the arcs exceed 3cm. It was in resonance, because it was the peak at which it would produce something, i just had to start decreasing turns on the primary to be able to pump more power through it.

[EDIT] - Here are some scope shots of the gate drive signal

This is after GDT - when driving a load with the mosfets. (gate and source pins)


And the same signal on the other mosfet (Gate and Source pins, due to the triggering the waveform is not inverted)


This is what is going into the GDT.


--NOTE--

I cant find the photos i took of the waveform after fixing the waveform and squaring it up (by means of zenner diode clamping) -
and until i get my hands on a dual channel scope i dont think ill be able to see if there is overshoot or not. I tried to compare rise and fall time for the signal but it seemed identical to me.

Here is a link to a gallery containing photos of the coil, and its main parts.

What happened, or why, I dont know. Was it the short pulse that caused a voltage spike ? Lack of freewheel diodes causing a short in the IGBT body diode ?

Thanks all for reading. I appreciate any help.
« Last Edit: April 07, 2017, 12:00:26 PM by Dylan Burger »

Offline Mads Barnkob

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Re: My First SSTC (and exploding IGBT's)
« Reply #1 on: March 17, 2017, 01:35:47 PM »
I do not have any experience with PLL driven SSTC's, all my SSTC's used a circuit based on the SSTC schematics from Steve Ward.

One thing that strikes me is however the very loose coupling between primary and secondary coil, the setup you have right now is much more suitable for a SGTC/DRSSTC, which is also where you had it from. If you take a look at the SSTC's at my website, you can see that I use a very tight coupling where the primary coil is wound directly onto the secondary coil with only 4 layers of plastic sheet in between.

As to why the switches explode...

Wrong phasing of the GDT, so that both switches are turned on at the same time or off at the same time, but just a little energy is let through, enough for small sparks.

Antenna feedback is not stable, raise the antenna further up the secondary coil.

Have you tried using MOSFETs instead of IGBT?
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Offline Dylan Burger

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Re: My First SSTC (and exploding IGBT's)
« Reply #2 on: March 17, 2017, 04:00:11 PM »
I do not have any experience with PLL driven SSTC's, all my SSTC's used a circuit based on the SSTC schematics from Steve Ward.

One thing that strikes me is however the very loose coupling between primary and secondary coil, the setup you have right now is much more suitable for a SGTC/DRSSTC, which is also where you had it from. If you take a look at the SSTC's at my website, you can see that I use a very tight coupling where the primary coil is wound directly onto the secondary coil with only 4 layers of plastic sheet in between.

As to why the switches explode...

Wrong phasing of the GDT, so that both switches are turned on at the same time or off at the same time, but just a little energy is let through, enough for small sparks.

Antenna feedback is not stable, raise the antenna further up the secondary coil.

Have you tried using MOSFETs instead of IGBT?


I am currently on the lookout for a oscilloscope, so as soon as i get one i can determine more or less whats going on. After that i will probably upgrade it to a DRSSTC using Steve's Universal Driver or something similar.

It used to be a pancake coil , I then made the helical coil thinking I would up my coupling more. Ill get some nice insulated cable and wrap another primary onto the secondary to see what I can achieve.

I have made doubly sure of GDT phasing, by means of physically checking each spool on the GDT and with my DMM ( short two wires together and read the voltage diff on the other end - The higher voltage compared to the other way around means they are 180 deg out of phase)

I will try that as soon as i can order some more switches. Ill probably go with IRFP460's this time. I'm getting tired of IGBT's XD

Yes, I used to run this coil on IRFP460's with stellar explosions, blowing legs off the MOSFETs and sometimes they just die and blow the trip switch. It seems to me I either lack snubbing somewhere or my driver is not functioning... Ill test both conditions if i can get a scope to test it with :)

On a side note - here is a video with the coil running the best I've ever got it to. ( Its semi DRSSTC with a small cap in series with the primary - which is a recipe for explosions as well...) -excuse the family in the background... I also get zapped by the earth wire XD-

/>

Offline Dylan Burger

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Re: My First SSTC (and exploding IGBT's)
« Reply #3 on: March 18, 2017, 09:18:20 AM »
You are probably expiriencing cross conduction in your switching device.
its a good idea to run it at low input voltages and scope for how long a igbt stays open.
if this is more then 50% of the frequency (so something like 60% on 40% off) you found the problem.
this can be solved by making the gate turn on slower and discharge faster.
also you might need to check the phasing of the primary/current transformer as the small sparks could also indicate that the primary/current transformer is out of phase with the secondairy.



Thanks, I'll check it out. Might be getting a scope today so I'll see what I can find.


As for adding dead time, I have a 10ohm resistor in parallel with a uhf diode to charge the gate slow and discharge very quickly. Whether or not it works will be determined by oscilloscope as soon as I get one.


I don't have Current Transformer feedback (yet), at the moment I'm using antenna feedback. I'll try switching the primary phase around and see what it does.


Thank you for your response! :)

Offline Acid Byte

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Re: My First SSTC (and exploding IGBT's)
« Reply #4 on: March 18, 2017, 01:52:50 PM »
You are probably expiriencing cross conduction in your switching device.
its a good idea to run it at low input voltages and scope for how long a igbt stays open.
if this is more then 50% of the frequency (so something like 60% on 40% off) you found the problem.
this can be solved by making the gate turn on slower and discharge faster.
also you might need to check the phasing of the primary/current transformer as the small sparks could also indicate that the primary/current transformer is out of phase with the secondairy.

i had the same issues.
fixed this by slowing down the gate charge but making the discharge faster
« Last Edit: March 18, 2017, 02:02:20 PM by Acid Byte »

Offline Acid Byte

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Re: My First SSTC (and exploding IGBT's)
« Reply #5 on: March 18, 2017, 03:01:39 PM »
You are probably expiriencing cross conduction in your switching device.
its a good idea to run it at low input voltages and scope for how long a igbt stays open.
if this is more then 50% of the frequency (so something like 60% on 40% off) you found the problem.
this can be solved by making the gate turn on slower and discharge faster.
also you might need to check the phasing of the primary/current transformer as the small sparks could also indicate that the primary/current transformer is out of phase with the secondairy.



Thanks, I'll check it out. Might be getting a scope today so I'll see what I can find.


As for adding dead time, I have a 10ohm resistor in parallel with a uhf diode to charge the gate slow and discharge very quickly. Whether or not it works will be determined by oscilloscope as soon as I get one.


I don't have Current Transformer feedback (yet), at the moment I'm using antenna feedback. I'll try switching the primary phase around and see what it does.


Thank you for your response! :)

Let me know what fixed your problem :)
And your welcome.

Offline Mads Barnkob

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Re: My First SSTC (and exploding IGBT's)
« Reply #6 on: March 20, 2017, 10:37:05 AM »
Reversing the phasing of the primary coil is one of the first things to try out when starting up a new coil, but that would normally never lead to switch failure/explosions, just very small output.
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Offline Dylan Burger

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Re: My First SSTC (and exploding IGBT's)
« Reply #7 on: April 07, 2017, 10:26:23 AM »
Alright - General update : (Ill append to my original post as well)

I have acquired an oscilloscope - though its an analogue 10Mhz i believe it will do the job well enough.

I have scoped my gate drive circuitry and noticed an odd waveform. I fixed it by altering the resistance that feeds into the GDT.
I also noticed a nice square wave on the FET/IGBT side. slight ringing. But as soon as I power this thing on with some load the gate waveform goes nuts. I cant square it up at all. Stray inductance maybe ? or interference ?

Ill attach scope shots to the main post. I was running these tests with small mosfets i had around - im ordering IRFP460's soon.
Can you guys maybe suggest an IGBT suitable for my use ? I was thinking of using these :  FGH60N60SMD (ebay link)





You are probably expiriencing cross conduction in your switching device.
its a good idea to run it at low input voltages and scope for how long a igbt stays open.
if this is more then 50% of the frequency (so something like 60% on 40% off) you found the problem.
this can be solved by making the gate turn on slower and discharge faster.
also you might need to check the phasing of the primary/current transformer as the small sparks could also indicate that the primary/current transformer is out of phase with the secondairy.



Thanks, I'll check it out. Might be getting a scope today so I'll see what I can find.


As for adding dead time, I have a 10ohm resistor in parallel with a uhf diode to charge the gate slow and discharge very quickly. Whether or not it works will be determined by oscilloscope as soon as I get one.


I don't have Current Transformer feedback (yet), at the moment I'm using antenna feedback. I'll try switching the primary phase around and see what it does.


Thank you for your response! :)

Let me know what fixed your problem :)
And your welcome.

To add, I still need to scope out how my driver will behave and what waveforms ill get when my new switches arrive, but for now im stuck with no fets or IGBT's . Ill update here as soon as I have built everything again. Thank you for your help :)

Reversing the phasing of the primary coil is one of the first things to try out when starting up a new coil, but that would normally never lead to switch failure/explosions, just very small output.

Turns out that reversing the primary on my coil has little effect on output (at 50v input). There was more heating in the switches though.
Thanks for the assistance mads :)


Offline Acid Byte

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Re: My First SSTC (and exploding IGBT's)
« Reply #8 on: April 08, 2017, 03:15:49 PM »
i have never seen this gdt you have used before.
maybe the core is what is causing the problem?
https://postimg.cc/image/d08tw9t97/

Offline Dylan Burger

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Re: My First SSTC (and exploding IGBT's)
« Reply #9 on: April 08, 2017, 05:41:13 PM »
i have never seen this gdt you have used before.
maybe the core is what is causing the problem?
https://postimg.cc/image/d08tw9t97/

It was a transformer I found in my junk box and decided to try it. I cant even remember where I salvaged it from.How would I be able to test if the GDT is the issue ? It has four coils on it with the same turns on each. I paralleled two to make it a 1:2:2 GDT. Currently , with the GDT connected to my mosfets, the wave is nice and square, the issue comes in when the FET's start pushing a load that the drive (and output of the FET) goes whacky.

Offline Mads Barnkob

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Re: My First SSTC (and exploding IGBT's)
« Reply #10 on: April 08, 2017, 07:12:59 PM »
Good that you got a oscilloscope! My own first one was also a analog 15 MHz, two channels though, but it is vital to just be able to see one thing at a time, at the right sample rate and bandwidth. It will do just fine for almost any Tesla coil stuff, getting a expensive DSO is just to make life easier :)

It looks like a filter choke ferrite and bobbin, it will properly be good enough, maybe on the low side speaking of permeability, but good enough frequency wise, which is also indicated by your square waveform. But the cross section is on the low side, you do risk not having enough electromagnetic energy transfer and maybe its suffering from saturation.

It sounds like you do not have galvanic isolation and something is not correct with the windings of that GDT.

Are you sure it was 4 separate coils to start with? If you paralleled two coils, that could only be used for the primary, and then two singles for the MOSFETs, that would make it a 2:1:1 GDT and actually drive your MOSFETs with half the voltage of what your drivers are driving the GDT with.

So maybe that is your only problem, that the GDT is outputting a insufficient voltage to drive the MOSFETs properly under load?
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Offline Dylan Burger

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Re: My First SSTC (and exploding IGBT's)
« Reply #11 on: April 08, 2017, 07:42:54 PM »
Good that you got a oscilloscope! My own first one was also a analog 15 MHz, two channels though, but it is vital to just be able to see one thing at a time, at the right sample rate and bandwidth. It will do just fine for almost any Tesla coil stuff, getting a expensive DSO is just to make life easier :)

It looks like a filter choke ferrite and bobbin, it will properly be good enough, maybe on the low side speaking of permeability, but good enough frequency wise, which is also indicated by your square waveform. But the cross section is on the low side, you do risk not having enough electromagnetic energy transfer and maybe its suffering from saturation.

It sounds like you do not have galvanic isolation and something is not correct with the windings of that GDT.

Are you sure it was 4 separate coils to start with? If you paralleled two coils, that could only be used for the primary, and then two singles for the MOSFETs, that would make it a 2:1:1 GDT and actually drive your MOSFETs with half the voltage of what your drivers are driving the GDT with.

So maybe that is your only problem, that the GDT is outputting a insufficient voltage to drive the MOSFETs properly under load?

Yes , I am quite happy with it. And it came with a x10 probe. This thing is able to measure (tested to) 400v with that probe. So , I am rather impressed. All the reading i did on scopes led me to want to build a attenuation box for it XD But it seems that wont be necessary now.

Oh cool, i never thought it could be a choke :) I did a part search for any number I could find on it. Google turned up nothing. Next step for me would be to try and find a decent ferrite toroid I suppose ? (if the current GDT fails to comply of course).

Ill do some tests and see what i can find.

Yes, the coils were two separately wound coils, but there are four former slots. I cut the series connection and used them each as a individual coil.
Kick me if I'm wrong, But if i parallel two coils (to make a primary) - then the winding resistance would be half of the remaining two ? Essentially then it would be 0.5:1:1 or 1:2:2 ? or is it solely dependent on the amount of turns?  Voltages (measured by scope) on the mosfet side (if memory serves correctly) is around 20v. ill do some proper tests tomorrow, i cant put a load on the GDT though because i have no FET's  ;D

Offline Mads Barnkob

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Re: My First SSTC (and exploding IGBT's)
« Reply #12 on: April 08, 2017, 07:58:56 PM »
Just be aware that a attenuator does not provide isolation from higher voltages, a differential probe is a much better idea, but also costs a lot of money.

I missed that you paralleled them and not in series, but that just makes it 1:1 GDT then, it is a turns ratio voltage product. Around 10-20 turns should make a good GDT for a SSTC, you could also calculate it: http://thedatastream.4hv.org/gdt_index.htm
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Offline Dylan Burger

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Re: My First SSTC (and exploding IGBT's)
« Reply #13 on: April 08, 2017, 08:07:48 PM »
Indeed, I have been very wary of what i connect my scope to. I have also seen the differential probes, quite expensive, Probably because of the price of the equipment it goes with.

Ah, alright. Thanks for that! Ill probably be rewinding it sometime soon, or at least heavily loading it. Ill pull some specs from the IRFP460 datasheet and try to duplicate it with some resistors and caps  ;D 

[Edit] :

While removing the primary coils i noted my GDT had about 42 turns on it. To get a sufficient 1:2:2 GDT i am planning on winding 20 turns of bifilar wound magnet wire.Would this be sufficient ?
« Last Edit: April 09, 2017, 08:30:44 AM by Dylan Burger »

Offline Mads Barnkob

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Re: My First SSTC (and exploding IGBT's)
« Reply #14 on: April 09, 2017, 09:25:45 AM »
42 turns is too much. You need to calculate it and make it the right way :)

You could play around with this little spreadsheet calculator that I made for GDTs, it is made in openoffice but I think you can import it to excel if needed, else google drive's spreadsheet editor can read it fine.
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Offline Dylan Burger

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Re: My First SSTC (and exploding IGBT's)
« Reply #15 on: April 09, 2017, 09:58:11 AM »
42 turns is too much. You need to calculate it and make it the right way :)

You could play around with this little spreadsheet calculator that I made for GDTs, it is made in openoffice but I think you can import it to excel if needed, else google drive's spreadsheet editor can read it fine.

Alright , thanks for all your help so far :)

Ive been taking a look at your spreadsheet-  is there a way i can calculate Ae and AL ? Or can I rather measure inductance and plug it into the table ? I do not have a LCR meter , but there is a way to calculate L with a scope and frequency generator.

I have attached a link to waveforms of my current GDT - loaded with a 10nf capacitor, and a toroidal GDT , also with 10nF capacitor. I notice that i did mess with the Volt per div setting, it was to see how square the wave actually is after the cap was connected.

« Last Edit: April 09, 2017, 06:52:48 PM by Dylan Burger »

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Re: My First SSTC (and exploding IGBT's)
« Reply #15 on: April 09, 2017, 09:58:11 AM »

 


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post Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
[Electronic circuits]
T3sl4co1l
September 16, 2019, 06:59:12 AM
post Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
[Electronic circuits]
davekni
September 16, 2019, 04:18:26 AM
post Re: My second DRSSTC
[Dual Resonant Solid State Tesla coils]
davekni
September 16, 2019, 02:49:28 AM
post Re: Large Ferrite Core with IGBT-Brick Driver
[Transformer (ferrite core)]
davekni
September 16, 2019, 02:43:18 AM
post Re: Homemade HV transformer
[Transformer (ferrite core)]
davekni
September 16, 2019, 02:36:17 AM
post Re: adventures in homemade flyback bobbins.
[Transformer (ferrite core)]
davekni
September 16, 2019, 02:26:40 AM
post Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
[Electronic circuits]
petespaco
September 16, 2019, 01:50:19 AM
post Re: UD2.7 Gate Signals
[Dual Resonant Solid State Tesla coils]
coilinator
September 15, 2019, 08:22:47 PM
post Re: My second DRSSTC
[Dual Resonant Solid State Tesla coils]
erdal
September 15, 2019, 02:09:17 PM
post Re: Homemade HV transformer
[Transformer (ferrite core)]
AlexanderHun
September 15, 2019, 10:39:29 AM
post Re: Homemade HV transformer
[Transformer (ferrite core)]
ElectroXa
September 14, 2019, 07:01:28 PM
post Re: adventures in homemade flyback bobbins.
[Transformer (ferrite core)]
AlexanderHun
September 14, 2019, 06:59:13 PM
post Re: Homemade HV transformer
[Transformer (ferrite core)]
AlexanderHun
September 14, 2019, 06:43:15 PM
post Re: Homemade HV transformer
[Transformer (ferrite core)]
ritaismyconscience
September 14, 2019, 06:35:32 PM
post Homemade HV transformer
[Transformer (ferrite core)]
AlexanderHun
September 14, 2019, 05:05:00 PM
post Re: UD2.7 Gate Signals
[Dual Resonant Solid State Tesla coils]
profdc9
September 14, 2019, 04:50:10 PM
post Re: UD2.7 Gate Signals
[Dual Resonant Solid State Tesla coils]
coilinator
September 14, 2019, 08:42:55 AM

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