Re: Then what's the topload FOR?

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "davep by way of Terry Fritz <twftesla-at-qwest-dot-net>" <davep-at-quik-dot-com>

Tesla list wrote:
> 
> Original poster: "Christopher Boden by way of Terry Fritz
> <twftesla-at-qwest-dot-net>" <chrisboden-at-hotmail-dot-com>

> Been following the AC-DC thread...got to thinking.....
 
> Ok....by definition a Tesla Coil is an air-cored radio frequency RESONANT
> TRANSFORMER...right?

	Mostly.  cf the Corums Cavity Resonator approach.

> good
 
> Now, Resonant and Transformer both seem to indicate an AC thing to me, I
> have yet to see a DC Transformer (though I could REALLY use a few), or
> anything that resonates only one way never crossing a zero point.
 
> Ok....then, what's the toplaod do?

	Multiple things.  One common one is to 'shape the field'.
	Put another way:
		As voltage goes up leakage 'into the air'
		becomes a problem.
		This is worst from a pointy electrode.
		It is best (least) from a spherical, or squished
		spherical, electrode.

	Regardless of whether dealing with AC or DC this is true.  cf any
	picture of HV equipment.  Given a finite source of current to
	drive voltage up, minimizing leakage (large radius top load)
	increases voltage.

	Also, by fudging with the top load, one can fudge the
	free resonance of the secondary system, if that is seen as
	critical.  (I tend to think it is....)
 
> A Topload forms one side of a large air capacitor, cool, now, when the
> capacitor discharges (i.e. a streamer) it does this either into the air, or
> into a grounded object, the instantanious discharge would be DC because
> we're dischargeing a capacitor.

	...and, ac or dc, it leaks continuously.  leakage goes DOWN as
	radius goes up....
 
> But it's an AC system!???
 
> Ok, now if the topload stores energy until it overcomes the breakdown of the
> air and the maximum charge density allowed for the given curvature of the
> toroid the it has to be storing that energy during several cycles of the
> ringdown.

	I suggest that for usual coiling freqs a point thing will leak
	substantially in the course of a single 1/4 cycle.

	Also, streamer behavior may involve multiple discharges
	thru an existing, pre ionized, path.

> So...we're trying to charge a DC storage device from an AC supply...wouldn't
> this just result in a net charge of 0V?

> Think about it....

	Think about reducing leakage.
	Think about a trimmer cap on a secondary.
 
> Each bang in the tank circuit is of opposite polarity to the next.

	Seems to assume a synchronous gap....

> And Once the bang occures there is a fast ringdown into the primary
> coil of a damped AC waveform....everything is AC...each Bang is reversed,
> each cycle of the ringdown reverses....how the hell do we get a spark at
>all?

	??
	By exceeding dielectric strength of air.
	(over simplified, as many/most do not go TO something.)
 
> In theory, at least in my own warped and twisted head meat, we shouldn't
> have more than a few hundred volts, if that, ever seen in a topload.

	??
	In either the 'rf transformer' case or the '1/4 wave' case the
	voltage will rise to some large value.  In the rf transformer
	approach to modeling, cf turns ratio.  In the 1/4 wave
	approach, the math heads towards infinity...

	What limits it peak to '...a few hundred volts...'?

	best
	dwp