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



Original poster: "John H. Couture" <couturejh-at-mgte-dot-com> 


Peter -

The optimum toroid size and the proper TC secondary protection are up for
grabs. With Paul N. interested in the problem it appears that progress will
be made in this direction. I wiil be anxiously waiting to see what he
discovers.

John Couture

--------------------------


-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Friday, October 31, 2003 4:35 PM
To: tesla-at-pupman-dot-com
Subject: Re: Spheres vs Toroids (was - Source for Aluminum Spheres (up
to12" threaded)


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