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SSTC/DRSSTC without breakpoint

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MRacerxdl

Wed Mar 26 2008, 11:39PM

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

Hi all,
I saw on the most part of the forum (and the web too), that all Solid State Tesla Coils needs to have a Breakout point, because without it I can kill the Mosfets/IGBTs.

But I found 2 guys on youtube that have made a DRSSTC and a SSTC without breakpoint.
How can it be done?

DRSSTC:

SSTC

Thanks

...

Wed Mar 26 2008, 11:42PM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

You just need to make sure that the radius of curvature on the torrid is sharp enough that you can still have breakout. On my pllsstc I used a piece of 1/4" of copper pipe which allows me to run without the breakout point.

MRacerxdl

Wed Mar 26 2008, 11:53PM

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

Hmm, you mean I need to calculate the toroid radius to some kV of breakpoint? Using the Toroid as the breakpoint?

Ken M.

Thu Mar 27 2008, 12:24AM

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

Hey mastre.... I'd like you to check this post out

, look at the authors name and then look at your videos and the author of those videos, yes the authors names are SLIGHTly different but the coils look the same, also if you look at the author of the videos "salvaged PS" vid and then look at the forums authors avatar. See any resemblances?

HV Enthusiast

Thu Mar 27 2008, 01:03AM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

Breakout points are used because it reduces a lot of stress on the components. Considering the IGBTs and MOSFETs are already stressed to the max, adding a break-out point is simply a no-brainer and can get you magnitudes greater reliability for a given toroid size.

Plus, i think all of us here have probably run DRSSTCs without break-out points. Its not difficult, but it just overstresses components.

Coronafix

Thu Mar 27 2008, 03:30AM

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

The second link has a breakout point.

Tom540

Thu Mar 27 2008, 05:25AM

Banned on 3/17/2009.
Registered Member #487 Joined: Sun Jul 09 2006, 01:22AM
Location:
Posts: 617

lol those are my coils. It has to do with how powerful your igbt's are and the toroid size. If you aren't loading the thing down with a monster toroid you can achieve breakout without a point. You also need optimum coupling. I had an SSTC a few years ago that used a full bridge of irfp450's with voltage doubler running at 400bps that could achieve breakout without a point. heres link

and the small one without a breakout point

MRacerxdl

Thu Mar 27 2008, 09:34AM

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

Good work Tom540! These are very good coils!

Someday I will try to make one sstc without breakpoint, First I need to make a new secondary coil.

Steve Conner

Thu Mar 27 2008, 01:27PM

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

My DRSSTC works without a breakout point, although it tends to flash over down the inside of its secondary former instead of breaking out from the toroid. I once had the breakout point fall off in the middle of a run!

If you have a current limiter fitted, nothing bad will happen to your silicon. If it arcs over, or the current limiter kicks in before it breaks out, then you might want to try a smaller toroid.

Marko

Thu Mar 27 2008, 02:53PM

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

For most typical SSTC's, running without breakout point is a very hazardous condition which should be avoided.

When the coil is not loaded by streamer it's Q may go up several tens of times, which means that base (series) impedance of the secondary will decrease by same amount, down to about the AC resistance of the coil!

If you were already running your mosfets at edge of their ratings and the coil fails to break out, they are doomed instantly.

And even if your inverter survives, and coil still fails to break out, nearly all power put into system would be dissipated in the resistance of the coil, which would very quickly destroy itself in that state.

It is possible to run a SSTC without breakout point but at very reduced input voltage, or even direct base drive without primary at all (to give the same stress to the inverter it would normally have with streamer load). Resonator would produce very high output voltages but you wouldn't be able to see any significant sparks form it because any breakout would instantly kill it's Q.

I'd say it's one of major limitations of usual SSTC topologies like bridges or class E, is that they simply can't tolerate no load conditions without reducing the input voltage into the inverter.

For DRSSTC I believe, (hope someone can correct me) it would be opposite, since with no load the low impedance of the secondary would actually kill down the primary tank's Q and current would grow much slower than in normal operation.

Still very high voltages, as in or more than in normal operation would build up on the secondary and without streamer to grow and load it down it would be expected to find another way to discharge itself!

At least that's how I interpret what steve observed.

To compare, the primary current f the DRSSTC jumps when secondary gets heavily loaded or shorted (arc to ground), while typical SSTC would see highest base impedance with secondary shorted (most coils wouldn't be able to oscillate in their fundamental mode in this condition, though).

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