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SSTC - What defines the spark size?

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MRacerxdl

Mon Feb 11 2008, 12:04AM

Registered Member #989 Joined: Sat Sept 08 2007, 02:15AM
Location: SÃ£o Paulo, Brazil
Posts: 476

Hi all, after a few tests with my SSTC, I really dont know what defines the spark size.

What I try to make:

Use IRFP250 and change to IRFP460 (150VDC). Nothing happened.

Get a bigger primary cap (Twice as original to be exact). Nothing Happened.
Get a bigger Secondary coil, with lower fres. I get a few less noise on the antenna feedback.
Higher voltage at IRFP460, POP. one IRFP460 as exploded! (200VDC)

Change the Interrupter frequency. Some progress but not too much, a few cm more.

Its a interrupted SSTC. I will make a new one, with protection diodes (There is a less expensive diode than MUR1560 to use on tesla coil?), and a fullbridge one. But I want to stop blowing all things :P

Someone knows what can I do for increase the sparks, I think its to low for the power input (500W)
Sparks to SSTC ground:

Video from sparks to ground (Audio Modulated Interrupter):

Video from Corona to ground (Low Interrupter frequency):

Thanks all for the help building that tesla coil, it has been a long time that I am trying made one, with help of people of 4hv I get this working :D

PS: With IRFP250 H-Bridge running at 110V mains Full Wave, and with interrupter, I didnt blow anything.

Kizmo

Mon Feb 11 2008, 07:32AM

Registered Member #599 Joined: Thu Mar 22 2007, 07:40PM
Location: Northern Finland, Rovaniemi
Posts: 624

Half wave DC gives longer sparks ;)

MRacerxdl

Mon Feb 11 2008, 07:40AM

Registered Member #989 Joined: Sat Sept 08 2007, 02:15AM
Location: SÃ£o Paulo, Brazil
Posts: 476

I forgot to say that, I have tryed to :P I get the sparks of Video (Audio Modulate Interrupter) I think I need to put it direct, without the Interrupter. But I blow the IRFP250 making that :P

Coronafix

Mon Feb 11 2008, 09:08AM

Registered Member #160 Joined: Mon Feb 13 2006, 02:07AM
Location: Melbourne, Australia
Posts: 938

Good ground is the beginning of good sparks.
HAve you added those MUR diodes yet? They will save your FETs.
Size of secondary and power input is another defining factor.

MRacerxdl

Mon Feb 11 2008, 09:43PM

Registered Member #989 Joined: Sat Sept 08 2007, 02:15AM
Location: SÃ£o Paulo, Brazil
Posts: 476

I didnt put the MUR diodes, for my first try, I didnt put it to low power test. How can I get a high power? because mine IRFP250 was running at 127VAC (150VDC) and I get only 3 A this means arround 400W.

There is a other diode that can I put, like the Super Fast Diodes of Computer PSU? (That have two big diodes in there that are 3A 400V (FR304) It can support 150A of peak. I wasnt try because it Super Fast not Hyper Fast like MUR diodes.

Coronafix

Mon Feb 11 2008, 10:26PM

Registered Member #160 Joined: Mon Feb 13 2006, 02:07AM
Location: Melbourne, Australia
Posts: 938

Those diodes aren't very fast, about 150ns.
I believe the recommended ones are 35ns.

Ken M.

Mon Feb 11 2008, 11:56PM

Registered Member #618 Joined: Sat Mar 31 2007, 04:15AM
Location: Us-Great Lakes
Posts: 628

My not so knowledgable experience says try a diggerent, preferably a larger toroid. MY SSTC was whipping out 9-13" arcs to air, then I added a toriod that was 1:4 ration on the sizes, and I believe I managed to 2x the arc length, I PRESUME this because before I added the torroid the arcs ONLY came off the breakout point which was focused upwards, But when adding the torroid, the arc still came off the breakout point BUt also came off the feedback antenna I'd say 4-7", got scared and killled the power, was afraid the arc would conect from antenna to torroid and blow up the semiconductors.

Terry Fritz

Tue Feb 12 2008, 06:42AM

Registered Member #393 Joined: Tue Apr 18 2006, 12:30AM
Location:
Posts: 297

Hi,

It's "firing voltage"!

In the case of the SISG, increasing the firing voltage 50% gets you 50% more spark length. A 200% increase in firing voltage gets you 200% more length.

Of course, a 2X increase in voltage is a 4X increase in power.

The SISG with its very low losses and very few variables makes the relationship of spark length to voltage and power very clear.

DRSSTCs play sort of tricks to mimic higher firing voltages.

Big toroids, bust through the air much better, but that is a bit different principle.

Terry - Far from dead, but just dormant

MRacerxdl

Tue Feb 12 2008, 07:52AM

Registered Member #989 Joined: Sat Sept 08 2007, 02:15AM
Location: SÃ£o Paulo, Brazil
Posts: 476

Here I get a few corona at antenna, but It was arcing for the air off the breakpoint (a screw pointed to the top). I was try to put 220VAC (300VDC) at my IRFP460 H-Bridge, but with 200VDC when I draw a arc, after I release it, it really blow the IRFP, like the photo :P

but it only blow only one IRFP, the other was G-D-S Short.

Dr. H.

Tue Feb 12 2008, 12:23PM

Registered Member #931 Joined: Mon Jul 30 2007, 05:25PM
Location: Bulgaria
Posts: 486

I agree for the toroid - with my coil (the thread about the completed SSTC) it is giving about 45-50sm with the toroid on the picture, and about 55-60sm when a put a second toroid over the first one. I would sugget usinng half-wave rectified (if you are not using an interuptor). It gives much better results. And for the blown mosfets - i think you are getting out of resonance. And put the fast diods acros the FETs. They will save you a lot of FETs

. Cheers Huben

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