RE: Calculating Capacitance of solid disk

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

Original poster: "John H. Couture by way of Terry Fritz <teslalist-at-qwest-dot-net>" <couturejh-at-mgte-dot-com>


Bart, Dan, All -

One advantage of this new disc is that the capacitance can be easily
measured to check with what computer programs and estimates are giving.
There can't be many disc capacitance test that have ever been made so these
would be important tests.

One recommended test is the one that is shown in the "Tesla Coil
Construction Guide" page 14-13. All that is needed to find are two test
frequencies. The test should be made with a small TC with an operating
frequency of about 600 to 800 Khz. The frequency differencies will be small.

One capacitance equation for a disc from the TCBA News is

    pf = .35 d   where d = centimeters
                 and  pf = isotropic capacity

My dictionary defines "isotropic" as "exibiting properties (as velocity of
light transmission) with the same values when measured along axes in all
directions". This has confused coilers for years.

So we now have -
           Fantc       3.56   pf
           TCBA        3.556  pf
           Estimated   3.98   pf

It should be noted that when a toroid is placed on a TC secondary the toroid
capacitance is reduced because of the proximity of the secondary. However,
the toroid isotropic capacity to earth increases as it is brought closer to
earth. This means that the test resonant frequency will be LESS than
expected compared to the resonant frequency when the secondary has no
terminal. Don't let these resonant frequencies confuse the testing. If the
disc behaves like the toroid the testing should show that the disc capacity
is greater than what is shown above?

John Couture

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


-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Sunday, March 09, 2003 11:11 PM
To: tesla-at-pupman-dot-com
Subject: Re: Calculating Capacitance of solid disk


Original poster: "Barton B. Anderson by way of Terry Fritz
<teslalist-at-qwest-dot-net>" <classictesla-at-netzero-dot-com>

Steve,

You are correctly, I messed up the inputs. Yes, I put in meters instead of
inches. Thanks for paying attention and letting me know.

Now, with the "correct" inputs, computations for the 4" disc capacitance is:

System or Object Capacitance: 3.56 pF
Run CompleteTime elapsed: 2.1 secs

Take care,
Bart

Tesla list wrote:

 >Original poster: "Stephen Conner by way of Terry Fritz
 ><teslalist-at-qwest-dot-net>" <steve-at-scopeboy-dot-com>
 >
 >At 11:31 09/03/03 -0700, you wrote:
 >
 >>Original poster: "Barton B. Anderson by way of Terry Fritz
 >><teslalist-at-qwest-dot-net>" <classictesla-at-netzero-dot-com>
 >>
 >>Hi Dan,
 >>
 >>This is a nice function of Fantc. It can perform analysis of object
 >>capacitance for toroids, spheres, spheroids, discs, and cylinders (up to
 >>10 each of wanted). In this case, I simply computed the 4" disk
 >>capacitance. Here's the output at a detail 3 setting.
 >>
 >>Computing ..... please wait
 >>System or Object Capacitance: 140.08 pF
 >>Run CompleteTime elapsed: 2.1 secs
 >
 >
 >That's way too high! A disk that size should be way less than 10pF. are
 >you sure you didn't get inches and meters mixed up?
 >
 >Steve C.