Making a Good Toroid

Date: Wed, 08 Feb 2006 09:04:31 -0700 - Subject: Capacitance of toroids - Original poster: "Adriano Mollica"
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 aluminium 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

Original poster: "C. Sibley"
Isn't internal diameter essentially a function of the external diameter and tube diameter?

Internal D = External D - 2xPipeD

Basically if you have any of the two you can derive the third measurement. You don't need all three...

Curt.

Original poster: "Gerry Reynolds"

Hi Adriano,

You don't want to calculate the capacitance of a stand alone toroid. The calculation needs to be done in presence of the secondary and surrounding environment. There are several tools available to do this. JAVATC is the one that I am familiar with and is a very accurate tool. BTW, inside and outside diameters, and major and minor diameters are two ways to describe a toroid. Javatc uses major and minor diameters.

http://www.classictesla.com/java/javatc.html

Gerry R.

Original poster: Vardan <vardan01

Hi Adriano,

It is a complex problem. It depends on the coil dimensions and even some on the size of the room the coil is in. But there is a program here that does it to within about 3%:

http://hot-streamer.com/TeslaCoils/Programs/E-Tesla6.zip

It finds the capacitance be working out all the electrostatic fields and such:

http://hot-streamer.com/andrewb/

This is the original DOS based program, but it still runs fine under Windows too. there are text files in the zip that tell how it works.

There is also an on-line JAVA program here that can do it:

http://www.classictesla.com/fantc/fantc.html

http://www.classictesla.com/java/javatc.html

I have a coil I tune by raising or lowering the top terminal and it works very well. But you do have to get it set up right to begin with to be sure it will tune in the range you need. The above program will help a lot there.

Cheers, Terry

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.

Original poster: "D.C. Cox"

Use sec coil form dia. x 3 or 4 for major toroid dia., and then use major toroid dia. to minor toroid dia. of 3:1 ratio to determine correct sizing of toroid. x 3 gives more streamers and x 4 gives single longer streamers. Depends on what you like.

Dr. Resonance

>Original poster: "C. Sibley" <a37chevy@yahoo.com>
>
>Isn't interal diameter essentially a function of the external diameter and tube diameter?
>
>InteralD = ExternalD - 2xPipeD
>
>Baciscally if you have any of the two you can derive the thrid measurement. You don't need all three...
>
>Curt.>>