Re: Capacitance of toroids

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Mddeming@xxxxxxx 

In a message dated 2/8/06 11:17:38 A.M. Eastern Standard Time, 
tesla@xxxxxxxxxx writes:
Original poster: "Adriano Mollica" <adriano.mollica@xxxxxxxxxxx>

Hello to everyone,

I almost finish the construction of my TC, but i have a little problem.
I need a top load of 29pF, than i think is ok, and i'm going to make it by
using a extensible aluminum pipe, that is pretty cheap and easy to put in a
toroid shape.

My question is, how can i calculate the capacitance of that toroid I'm gonna
build?

i found on internet two different way to calculate it, but  both use only
two parameters witch are , in one case: internal diameter and external
diameter, or in the other case: external diameter  and size of the pipe.
  And of course, i obtained 2 quite different measurements. What i need, is a
formula that use all three parameters together: inside diameter(d) ,
external diameter(D), and size of the tube(x).

do you know the answer?

thanks, Adriano


Hi Adriano,

Since D-d=2x there are really only two parameters. Some formulas use 
the external diameter of the toroid and some use the center-to-center 
diameter, which is, in your notation (D+d)/2. Some formulas are 
worked out in inches and others in meters. Make sure you know which 
conventions and units the  poster of the formula is using. Of course, 
these formulas are only exact for a toroid infinitely distant from 
any other object and the result will vary with the geometry of your 
coil, size and position in the room and proximity of any grounded 
object, but they give good first approximations.

Matt D.