Re: [TCML] Tesla's topload

[DC Cox <resonance@xxxxxxxxxxxx>]

I had a large coil once with a pair of stacked 34 x 8.5"toroids.  The total
cap of the stack increased 50% with the second toroid added due to the
shilding effects from upper toroid to ground.

Dr. Resonance




On Sat, Apr 9, 2011 at 12:29 PM, <jhowson4@xxxxxxxxxxx> wrote:

> Well Steve, experimental evidence and experience always supersedes theory.
> Being an individual who wants to go into the field of high voltage research
> upon graduation, I am going to have to play with that software you have. =)
>
> So I guess the real question is, where is the charge going? Since it does
> not seem logical that a 50% decrease in surface area would yield only a 10%
> -15% decrease in capacitance. So something else must be going on here.
>
> I suppose that the most logical explanation would be that charge is
> actually being stored on the interior of the structure for these open
> geometry designs. Maybe due to the incompleteness of the conductor Faraday's
> law does not apply with the same rigor as it would in a solid sphere model.
>
> Just out of curiosity how does the total surface area of your electrodes
> compare to that of a solid model.
>
> I am willing to bet that if 2 5-10 degree sectors centered on the radial
> line between each element were removed from each ring. (you would have to
> reconnect the now 2 conductors somehow) that the capacitance would remain
> about the same as previously calculated.
>
> This would be a test of the fact that charge is not really going to be
> stored directly in between each element. And might work to support the idea
> that charge is actually being stored on the interior, by showing that the
> total used surface area of a ring toroid is roughly equivalent to 10-15% of
> the exterior surface of a solid toroid.
>
>
> Questions for another day I suppose. =)
>
>
>
> Thanks,
> John "Jay" Howson IV
>
>
> ----- Original Message -----
> From: "Steve Ward" <steve.ward@xxxxxxxxx>
> To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
> Sent: Saturday, April 9, 2011 11:43:24 AM
> Subject: Re: [TCML] Tesla's topload
>
> My experience with using both solid and ring toroids is that the
> capacitance
> of my ring design was only about 10-15% less than the solid toroid. This
> was for a 42" OD x 10" cord toroid using 7 x 1" rings (so roughly 50% of
> the
> surface area was metal). Of course using more rings approaches the same
> capacitance of the solid surface toroid.
>
> Jay's logic is pretty much in agreement with mine, but i wouldnt have said
> this is a "drastic" decrease in capacitance, but rather a "slight"
> decrease,
> and maybe his mental model exaggerates the effects of shielding and surface
> geometry. I of course used FEM to do a study for optimizing my ring toroid
> for parameters like total capacitance, breakdown voltage, material cost,
> and
> labor. FEM removed the need for me to guess at the charge distribution, it
> let me see where i was most likely to get breakout. For my design, 7 rings
> worked out to be the best compromise i thought. Indeed the breakdown
> voltage is lower as rouge sparks from the end opposite of my breakout point
> are more frequent than when i used my "solid" toroid (corrugated tubing
> with
> foil tape). The spark performance is still just as good, though.
>
> Once again, you can get free 2d FEM software from:
>
> http://www.femm.info/wiki/HomePage
>
> Tesla coils are solved using an axis-symmetric solver, in case you were
> wondering how to handle it in 2D. Unfortunately, this means you cant handle
> something like Tesla's bumped topload, need actual 3D for that.
>
> Steve
>
>
> > This is all for a mostly solid object though.
> > For a ring toroid the effective capacitance decreases, because of the
> small
> > element size the shielding plays a really important role in how the
> charges
> > are distributed.
> >
> > is the charge going to be directly between two elements, no because that
> is
> > an unstable situation.
> > what about on the interior of the element array, not so much because that
> > would not jive with Faraday's laws
> >
> > so you are limited to the charge having a maximum on the outermost
> > conductor that will decrease as it approaches the hypothetical surface
> the
> > elements are trying to make.
> > this drastically reduces the surface area and thus also drastically
> reduces
> > the capacitance
> >
> > Thanks,
> > John "Jay" Howson IV
> >
> >
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