Re: Then what's the topload FOR?

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

Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-qwest-dot-net>" <m.j.watts-at-massey.ac.nz>

Hi Chris,

On 15 Feb 2002, at 20:57, 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? 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?
> 
> 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.

It is important to be really clear about what happens and when. We 
are dealing with several elements where vastly different timescales 
are involved. In a typical disruptive TC with typically loose 
coupling, voltage across the length of the secondary oscillates with 
increasing amplitude at the system resonant frequency until the 
primary cap is empty. The accumulation of energy is a dynamic 
process. The terminal doesn't just gradually increase in voltage with 
a single polarity. Think of a swing swinging higher and higher as the 
person pushing the swing pushes with less and less oomph each time 
the swing reaches them until finally they push no more.
  
> But it's an AC system!???

But streamer formation takes place in *far* less time than the time 
per cycle of oscillation.
 
> 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.

Ringdown => that the terminal voltage is still oscillating, changing 
polarity, in accord with system Fr. Energy content remaining is 
reflected in the voltage the terminal reaches on each peak of a half 
cycle of oscillation.
 
> 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....
> 
> Each bang in the tank circuit is of opposite polarity to the next. 

Not necessarily true. You can successfully run a TC from a HVDC 
supply.

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?

You accumulate energy in the secondary system over several cycles of 
oscillation as it rings up in accordance with the primary's ring 
down. And if the radius of curvature of the topload is sufficiently 
small, the air around it will become ionized and form a streamer (or 
several). 

> 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.
> 
> I know I'm wrong (obviously) I just want to know why.

Does that help?

Regards,
Malcolm