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Why are breakout points required ...

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lpfthings

Wed Mar 24 2010, 09:03AM

Registered Member #1361 Joined: Thu Feb 28 2008, 10:57AM
Location: Cairns, Australia
Posts: 305

On most SSTC/DRSSTC's?

I know that they are used to control the spark breakout, and gives the spark somewhere to start from, but at such a high voltage, wouldn't the spark just break out anywhere from the toroid? Is it to direct the sparks away from the electronics underneath/primary or?

Cheers,
Dan

Luca

Wed Mar 24 2010, 11:07AM

Registered Member #2481 Joined: Mon Nov 23 2009, 03:07PM
Location: ITALY
Posts: 134

I have learned that without breakout you would have a too fast secondary voltage rise that would cause racing sparks on the secondary coil.

Anyway, I don't know why adding a breakout point slows the secondary voltage rise...

Regards,

Luca

Turkey9

Wed Mar 24 2010, 05:06PM

Registered Member #1451 Joined: Wed Apr 23 2008, 03:48AM
Location: Boulder, Co
Posts: 661

On a top load, the electric field is perpendicular to the surface. So on a sharp point, the electric field is concentrated. This means more potential at that point and thus the spark will break out easier. Same physics that makes corona form on sharp edges. Also, with a breakout the antena will pick up on the oscillations of the coil sooner (sometimes the antena won't pick up at all with just the topload).

Sulaiman

Thu Mar 25 2010, 06:37PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3141

My interpretation is that there are three voltage levels at the topload, in ascending order;
1) The voltage required to form the beginings of a spark by the sharp point
2) The voltage that the power supplied to the secondary can support whilst arcing/sparking
3) The voltage required to form the beginings of a spark by the smooth toroid

Voltage for case 3 is very much higher than 1 or 2 and may cause problems such as
racing sparks as above, higher voltage and/or current stresses in the primary and secondary components.......

Steve Conner

Thu Mar 25 2010, 07:05PM

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

That's correct as far as I know.

Except for one thing: Voltage 3 is only higher than voltage 1 the first time your Tesla coil fires upon powering it up. From then on, voltages 1 and 3 are the same, because the ionized remains of the old spark channel hang around between bangs and act as a breakout point for the next one.

Case in point, my DRSSTC will run happily without a breakout point, producing the same RF waveforms as it does with one, *if* it gets started successfully. If it doesn't, the discharge goes down the inside of the secondary instead, and I have about 0.5 second to turn it off before it goes on fire.

dex

Thu Mar 25 2010, 07:22PM

Registered Member #2566 Joined: Wed Dec 23 2009, 05:52PM
Location:
Posts: 147

Steve McConner wrote ...

That's correct as far as I know.

Except for one thing: Voltage 3 is only higher than voltage 1 the first time your Tesla coil fires upon powering it up. From then on, voltages 1 and 3 are the same, because the ionized remains of the old spark channel hang around between bangs and act as a breakout point for the next one.

Not quite.

Steve Conner

Thu Mar 25 2010, 09:00PM

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

Well, if that's "not quite" the correct explanation, then what is?

Richie Burnett first told me about this puzzling result, and I've seen it too: if the coil is capable of breaking out without a breakout point, then the secondary voltage and current waveforms, when you observe them with the coil sparking repetitively, are the same with the breakout point as without it.

I suppose this may not be true for untuned primary SSTCs where voltage 2 (as Sulaiman calls it) is much smaller than voltage 3. These coils just blow their MOSFETs if you take the breakout point off. But for a properly designed classical SGTC or DRSSTC, voltages 2 and 3 are about the same, and the breakout point is just there to direct the sparks in a safe direction.

It may also be untrue if the coil operates at a low break rate and everything has time to deionise in between bangs.

Dr. Drone

Fri Mar 26 2010, 12:29AM

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

lpfthings

Fri Mar 26 2010, 05:31AM

Registered Member #1361 Joined: Thu Feb 28 2008, 10:57AM
Location: Cairns, Australia
Posts: 305

I accidently had a non-breakout point spark from my TC today, and it didnt seem to harm it for the 3 bangs or whatever I left it on for.

Thing is with my DRSSTC, it doesn't run at a high frequency, maybe 1 or 2 BPS.

Thanks for the explanations :)

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