Re: Spheres vs Toroids (was - Source for Aluminum Spheres (up to12" threaded)

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

Original poster: "Malcolm Watts" <m.j.watts-at-massey.ac.nz> 

Hi all,
         To me, the best thing about a toroidal terminal shape is that
one can choose a ROC and capacitance independently. Long sparks =>
loads of available charge as well as voltage to induce ionization
some distance away so the two meet in the middle.

Malcolm

On 31 Oct 2003, at 14:34, Tesla list wrote:

 > Original poster: peter lawrence <Peter.Lawrence-at-Sun.COM>
 >
 > John,
 >       that's an interesting question. I have my own rule-of-thumb for
 > toroids (that
 > follows on the idea of secondary geometry recommendation of 3:1 to 6:1
 > aspect ratio):
 >
 > 	major diameter  around  75% to 95% of the TC secondary's winding length
 > 	minor diameter  around  75% to 125% of the TC secondary's diameter
 >
 > I think toroid's need to be sized based on the secondary coil geometery to
 > protect
 > the secondary from corona, and you get the capacitance you get and have to
 > design
 > around it.
 >
 > Using E-Tesla-6 we could plot the E-field around the TC for various toroid
 > geometries,
 > and see which has the best corona protection. It might also be able to
 > point out
 > which geometry best produces long horizontal streamers rather than strikes
 > to the
 > primary (just a thought...)
 >
 > -Peter Lawrence.
 >
 >
 > (major diameter = outside edge to outside edge, not center to center)
 >
 >
 >
 >
 >
 >
 >
 > Tesla list wrote:
 >  >
 >  > Original poster: "John H. Couture" <couturejh-at-mgte-dot-com>
 >  >
 >  > It is generally accepted that a toroid is better than a sphere for a TC
 >  > topload. But how do you determine the optimum toroid size because for a
 >  > certain size sphere diameter there are many different sizes of 
toroids that
 >  > have the same capacitance?
 >  >
 >  > For example if yon need a topload of 60 pf a sphere of about 43 inches
 >  > diameter will do the job. The possible toroids with the same 60 pf
 >  > capacitance are as follows.
 >  >
 >  >     3" x 70" toroid
 >  >     4" x 66"    "
 >  >     6" x 62"    "
 >  >     8" x 60"    "
 >  >     12" x 56"   "
 >  >     15" x 55"   "
 >  >     20" x 52"   "
 >  >
 >  > There are many other possibilities. The minor diameter will give a 
certain
 >  > breakout voltage and the major diameter will determine the  amount of
 >  > protection for the secondary coil. But how would you go about 
selecting the
 >  > minor and major diameters?
 >  >
 >  > I show a graph in the Tesla Coil Notebook with curves for spheres and
 >  > toroids. The graph makes it easy to find the toroids that have the same
 >  > capacity of a certain size sphere. However, I have never seen any
 >  > information or graphs that show recommended spheres or toroids for 
use with
 >  > a certain size TC to obtain the maximum spark length and also give the
 >  > proper protection for the secondary coil. It is obvious that if the 
topload
 >  > is too large the available TC power will not be capable of charging it
 >  > properly.
 >  >
 >  > John Couture
 >  >
 >  > -----------------------------
 >  >
 >  > -----Original Message-----
 >  > From: Tesla list [mailto:tesla-at-pupman-dot-com]
 >  > Sent: Saturday, October 25, 2003 3:01 PM
 >  > To: tesla-at-pupman-dot-com
 >  > Subject: Re: Source for Aluminum Spheres (up to 12" threaded)
 >  >
 >  > Original poster: Ed Phillips <evp-at-pacbell-dot-net>
 >  >
 >  > Tesla list wrote:
 >  >    >
 >  >    > Original poster: "Mccauley, Daniel H" <daniel.h.mccauley-at-lmco-dot-com>
 >  >    >
 >  >    >  >      Has anyone here ever compared large spheres with toroids
 > for top
 >  >    >  > loading of high-power TC's?
 >  >    >  >
 >  >    >  > Ed
 >  >    >
 >  >    > Toroids do much better than spheres.  I believe the first person to
 >  >    > start using toroids was back in the 1970's from
 >  >    > what i've read from Richard Hull's historical notes.
 >  >    >
 >  >    > Dan
 >  >
 >  >         In what way better?  Clearly they work just fine but wonder what
 > their
 >  > edge is over a sphere with the same breakdown voltage.
 >  >
 >  > Ed
 >
 >
 >