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SSTC: base feed transformer

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Dr. Dark Current

Mon Dec 03 2007, 03:49PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

So has anyone tried this actually? Basically you use a step-up ferrite transformer connected to your bridge that feeds the base of the secondary winding. It should have two advantages over "direct drive" primary winding: 1) no pri-sec flashovers 2) greatly reduced magnetizing/reactive current.
One disvadvantage would be that the ferrite xfmr would have to handle the power of the coil so it would be probably quite big and xpensive. But for small <400W coils the transformer could be a flyback core, core from SMPS etc.

I think I will try it but I need some help on design of the transformer, how big pri/sec ratio should I aim for, how many prim. turns etc.?

Spedy

Mon Dec 03 2007, 04:27PM

Registered Member #964 Joined: Wed Aug 22 2007, 12:39AM
Location: Stockton, CA
Posts: 134

Interesting concept, like a ferrite-cored Tesla Magnifier. I would do some research on those before getting into this project, but It'll sure be cool!

Steve Conner

Mon Dec 03 2007, 04:31PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Alan Sharp tried it in the 1990s. It was a disaster, IIRC.

We know a lot more about solid-state coiling now, though. But bearing in mind the required fairly high base feed impedance, the transformer design will probably still be pretty difficult. You might struggle to get low enough leakage reactance, low enough self-capacitance, and adequate flashover clearance at the same time. Bear in mind that flybacks self-resonate at frequencies much lower than Tesla coils.

Marko

Mon Dec 03 2007, 07:02PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Hey, I just needed a thread like this..

I'm also very curious about possible use of a transformer.

I don't think transformer needs to have high turns ratio, like 1:10 should give plenty of voltage to drive some good power.

Regarding coupling, it should in any case be much better than air core

But with proper winding technique it can be reduced to nil.

From what I know there should be much less stress on the mosfets and even heavy hard-switching (audio modulation and etc.) should work much better for higher powers.

I tried to get Chris

to think about the idea, but I don't think he got me seriously.

If magnetizing current could be reduced to negligible value, I thought that audio-modulation could be much easier. The driver behind the ferrite transformer would basically be a class D amplifier.
I'd really like to see a CW coil pumping half a meter long audio modulated arcs.

But all this needs expert opinion...

Alan Sharp tried it in the 1990s. It was a disaster, IIRC.

Hmm... as far as I see, he used series capacitor on the transformer primary? I don't think DRSSTC with ferrite transformer would fare well.

Marko

Dr. Drone

Mon Dec 03 2007, 09:25PM

Registered Member #290 Joined: Mon Mar 06 2006, 08:24PM
Location:
Posts: 1673

Marko

Mon Dec 03 2007, 09:51PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Christopher Miles wrote ...

Marko wrote ...

Hey, I just needed a thread like this..

I tried to get Chris

to think about the idea, but I don't think he got me seriously.

Marko

Ohhhhhhhhhh I am interesting for sure; however, I have a few projects that will fill my plate for the next year, wheeeeeeeee.

Hey, why not build a little proto yourself and see if you can keep the magic smoke in?
If a little coil works, maybe can make bigger?

I can fund the project as know $ is tight. I am sure we have just about all you need in our garages in Az. to start the project out?

Cheers,
Ch

Sir, I'll try something in along with my SSTC development!

I actually have a ready transformer I could try this with, although I fear output voltage may be a bit too high...

And I could try one of smaller secondaries with it. I need more of Steve's opinion, though.

If basic magnifier proves to work well I can go to audio modulation, but that's probably not a close future,

BTW, you have your big VTTC to finish!

Marko

Dr. Drone

Tue Dec 04 2007, 07:05PM

Registered Member #290 Joined: Mon Mar 06 2006, 08:24PM
Location:
Posts: 1673

Reaching

Tue Dec 04 2007, 08:09PM

Registered Member #76 Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458

hrhr, thats a really nice idea and i have to try it out immediatly.
i have some half and fullbridges already finished and 2 really large ferrite cores which can handle 3kW+ each .

lol, just think about a fullbridge with smoothed dc running on 200khz in a 1:10 transformer, feeding the base of the resonator with 3kV+ .. thats weird lol but i like it

colin heath

Tue Dec 04 2007, 10:19PM

Registered Member #123 Joined: Fri Feb 10 2006, 12:58PM
Location:
Posts: 162

hi all,

This has been done successfully. i haven't got the link to it anymore but will try to find it on net.

It was quite a powerful coil

heres the link on hacked gadgets as his site appears to be gone.

cheers

colin

Bennem

Wed Dec 05 2007, 06:42AM

Registered Member #154 Joined: Sun Feb 12 2006, 04:28PM
Location: Westmidlands, UK
Posts: 260

His name is John Tomacic.
He had a web site with pictures and some information
on his SSTC coil.
I'm not sure if the site is still up and running though.

Mel.

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