RE: Toroid Capacitance Equations

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

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


Dr. Resonance -

The "D" is not a factor but is the overall large diameter of the toroid.

  6" x 24" Toroid  pf =(2.0233)(D^.8085)
                      =(2.0233)(24^.8085)
                      = (2.0233)(13.0587) = 26.42pf (INCA 26.20pf

  12" x 48" Toroid pf = (2.0586)(48^.8365)
                      = (2.0586)(25.4893) = 52.47pf (INCA 52.43pf)

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

When the toroid minor diameter is not 3,6,12, or 20 you have to extrapolate
between the given minor diameters on each side of the equation diameters.
For the 7" x 30" toroid proceed as follows.

The 7" x 30" toroid capacitance is between the following capacitances.

  6" x 30"  Toroid pf = (2.0233)(30^.8085)
                      = (2.0233)(15.64) = 31.64pf (INCA 31.60pf)

  12" x 30"  Toroid pf = (2.0586)(30^.8365)
                       = (2.0586)(17.2033) = 35.41pf (INCA 35.455)

The 7" x 30" toroid capacitance is between 35.41pf and 31.64pf = 3.77pf
        (7-6)/6 = .1667 x 3.77 = .6283 + 31.64 = 32.27pf (INCA 32.40pf)

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

The 8.5" x 34.5 toroid capacitance is between the following capacitances.

   6" x 34.5" Toroid pf = (2.0233)(34.5^.8085)
                        = (2.0233)(17.512) = 35.43  (INCA 35.535)

   12" x 34.5"  Toroid pf = (2.0586)(34.5^.8365)
                      = (2.0586)(19.337) = 39.81  (INCA 39.80)

The 8.5" x 34.5" toroid capacitance is between 39.81 and 35.43 = 4.38pf
          (8.5-6)/6 = .4167 x 4.38 = 1.825 + 35.43 = 37.26  (INCA 37.59)

By "shielding" factor I believe you mean what I call the toroid capacitance
reduction when the toroid is on top of the TC secondary coil. I have found
this reduction to vary from about 10% to 30% with real coils. This wide
range in capacitance is due to the variety of the surroundings that affect
the capacitance  around Tesla coils when they are tested. For small toroids
on large secondary coils the capacitance reduction may be negligible. This
reduction can only be determined by actual proper testing of finished coils.
For the latest info refer to my post to  Peter Reid under Subject "First
Light for 10" Coil" 12/24/2003.

Please let me know if you have more questions.

John Couture

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



-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Tuesday, December 23, 2003 6:18 PM
To: tesla-at-pupman-dot-com
Subject: Re: Toroid Capacitance Equations


Original poster: "Dr. Resonance" <resonance-at-jvlnet-dot-com>



John:

Can you pass along the "D" factor for the following additional sizes:

24 inch x 6
30 inch x 7
34.5 inch x 8.5
48 x 12 inch


Do you usually subtract 10% as a "shielding" factor when the toroid is atop
a coil?  Typical would be coilform size = 1/2 toroid major dia.

Dr. Resonance

Resonance Research Corporation
E11870 Shadylane Rd.
Baraboo   WI   53913
  >
  > To All -
  >
  > Over the past years I have collected about a dozen various equations for
the
  > capacitance of a toroid. The accuracy of these equations vary greatly and
  > none of them are very accurate for a particular toroid. I have found that
  > having only a single equation for all sizes of toroids that give accurate
  > results requires a very complicated equation. In order to simplify the
work
  > of calculating the toroid capacitance I have found that 4 simple
equations
  > can give acceptable results.
  >
  > The 4 equations are for toroids with minor diameters of 3", 6", 12", and
  > 20". The equations do not give the exact capacitances that Antonio's INCA
  > program (meters) shows but they will be very close. In fact the equations
  > will give good accuracies for minor diameters that are between the
3,6,12,20
  > inch if you extrapolate between the capacitances obtained for these minor
  > diameters.
  >
  > d = Minor diameter in inches
  > D = Major overall diameter in inches
  > Note that D must be at least twice d.
  >
  >     d = 3"    pf = 1.6079*(D^0.8419)
  >     d = 6"    pf = 2.0233*(D^0.8085)
  >     d = 12"   pf = 2.0586*(D^0.8365)
  >     d = 20"   pf = 2.2628*(D^0.8339)
  >
  > The Toroid Capacitance Graph in my TC Notebook shows four capacitance
curves
  > that were made before INCA's exact capacitances became available. The
  > Notebook curves were made from equations that are similar to the
up-to-date
  > ones shown above.
  >
  > If you have any questions please let me know.
  >
  > John Couture
  >
  > ------------------------------------
  >
  >
  >