Re: [TCML] Tesla's topload

[jhowson4@xxxxxxxxxxx]

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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