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Ye good OL BRISG Tesla Coil

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Finn Hammer

Thu Nov 23 2006, 06:34AM

Registered Member #205 Joined: Sat Feb 18 2006, 11:59AM
Location: SkÃ¸rping, Denmark
Posts: 741

The way I see it, you can look at the coil on a micro level, this would be the SIDAC/TVS /Cpri/Rgate/Rdischarge and IGBT loop.
Or on a Macro level, which would include the PSU, smoothing caps (if any) and the charging choke.

On the micro level, the SISG is stable, I cannot think of a way the tank cap can recharge before the IGBT stops conducting.
But on the macro level it is prone to oscillate, at least with a single phase supply, and a smoothing cap.
With a stiff 3phase rectified supply, I assume that the firing rate will be determined by the time at which the tank cap can recharge. It will modulate slightly around the rectifier frequency. In the case of a 6 pulse rectifier, 300Hz. 600Hz if someone went over the hill, and built a 12-pulse rectifier.
I`m sure this will be investigated in due course.

Cheers, Finn Hammer

Steve Conner

Thu Nov 23 2006, 11:21AM

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

Hi Terry,

I didn't mean that there's anything wrong with the SISG. It works just like a static spark gap. What I mean is that DC resonant charging with a static gap, either regular or silicon based, is fundamentally unstable and not a good idea.

Terry Fritz

Tue Nov 28 2006, 05:32AM

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

Hi Steve,

I didn't mean that there's anything wrong with the SISG.

Yeah, I know...

I "still" don't know how PIRANHA works so good for current limiting and "ballast"... Let alone the voltage multiplication... Darn "computer" figured it all out... They are smarter than "me" now

I must think of a dual or even four MOT system based on PIRANHA... HARD to do since the "one" MOT system I have now will happily burn the house to the ground

But two MOTs could at least run to the house's circuit "fuse" limit...

Cheers,

Terry

Finn Hammer

Sun Dec 17 2006, 01:28PM

Registered Member #205 Joined: Sat Feb 18 2006, 11:59AM
Location: SkÃ¸rping, Denmark
Posts: 741

In another, more recent thread, Terry wrote:

Terry Fritz wrote ...

Hi,

I am working on PIRANHA III issues today. A dual MOT system that runs off a 120VAC 20A circuit with ease. It is in the 8 foot arc to ground range... About 2kW input at ~90% efficiency.

Cheers,

Terry

So I thought it about time to try for the SISG spark length record. I wound a 3000 turn secondary for the OL-BRISG, and loaded it down to 42kHz. Today, at 4.5kiloamps Ipri. I got 60 Inches out of it.

Do I hold a record?
15.6ÂµF @1050V, 300BPS takes 2.6kW, so it`s far from efficient.
Merry christmas to all from Denmark.

Cheers, Finn Hammer

Terry Fritz

Sun Dec 17 2006, 03:59PM

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

Hi Finn,

Mark Dunn's coil and mine only do about 4 feet. Marks coil runs at 14400 volts but his primary caps are small since the main coil used to use a conventional spark gap.

So you do indeed have the world's record at 60 inches by almost a whole foot!!

Cheers,

Terry

Steve Conner

Sun Dec 17 2006, 11:38PM

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

Congratulations and a merry Christmas to you too! It's interesting to see that your coil performs just as well as my OLTC2 did, even though the drive electronics are so much simpler and it only has a single brick. It used to give about 60" at 300bps too.

Of course, you can now do something I couldn't: increase the bang energy as much as you like by using a higher voltage tank capacitor and stacking bricks in series...

Terry Fritz

Mon Dec 18 2006, 03:06AM

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

Yes indeed!!!

The PIRANHA-III should use 15 x 1000V IGBT sections. I went to four SIDACs like Finn since it is far easier to deal with 1kV increments instead of 900V increments %:-)

The "limit" I ran into was available power. 2400W 120VAC 20A circuits are pretty common here but not much more unless you get into the 220VAC stuff (hard for a "party coil"

). It all works out well for 700A peak IGBTs.

But if Finn can drive 6X the current with bricks!! 4500amps at say 15kV is one heck of a spark!! With the low loss of the primary circuit, you can use a "really big" primary capacitor without hurting the primary "Q" much... Hard to say right off for an estimate of how many joules per bang there. I am thinking "enough"

So the "limits" seem to be available power, how big of primary cap you can afford to make, and if the coil itself will just go up in a ball of fire

I also note that with really big primary caps, open load peak to voltages get really high (Vo/Vi = k x SQRT(Cp/Cs)).

Merry Christmas to all!!!!

Cheers,

Terry

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