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Messages - Thunderstruck

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1
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 !

2
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...

3
Beginners / Re: Keep or throw away ?
« on: February 07, 2019, 12:20:52 PM »
Excellent ! Thanks for the info.
DRSSTC is a bit too complex for me right now, i need to get my simple SSTC working first, then hopefully I can move onto something more challenging.

4
Beginners / Re: Keep or throw away ?
« on: February 07, 2019, 11:27:44 AM »
Thanks for the info, next up, we have some legless components

3 x G40N60UFD Ultra Fast IGBT
2 x F30U60DN Ultra Fast Recovery Rectifiers

Are these any good for SSTC ? With this much speed I’ll be surprised if they aren’t !!
They test OK, and yes I know they should live in an anti static bag  ;D, which they do.

5
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.

6
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 ?

7
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...

8
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.

9
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?

10
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  :)

11
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 ?

12
@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  :)

13
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 ?



14
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.

15
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....



16
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

17
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....


18
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...

19
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

20
Beginners / Keep or throw away ?
« on: January 24, 2019, 11:21:11 AM »
Hello,
These components have been hanging around my workshop for a while.
They look like something that could be used for a cool project but some of them are complete mistery.
Image 1 - I thought these are large IGBT's but they are definitely not.
Images 2 and 3 - Large capacitor bank of unknown rating
Image 4 - another large cap

Please let me know if any of these are worth keeping

Yes, I know that the mouse can be used as a pointing device, it is there fir scale  ;D

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