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Re: secondary C
From: John H. Couture [SMTP:couturejh-at-worldnet.att-dot-net]
Sent: Wednesday, November 12, 1997 5:20 PM
To: Tesla List
Subject: Re: secondary C
At 04:35 AM 11/12/97 +0000, you wrote:
>
>From: Mad Coiler [SMTP:tesla_coiler-at-hotmail-dot-com]
>Sent: Tuesday, November 11, 1997 7:39 PM
>To: tesla-at-pupman-dot-com
>Subject: Re: secondary C
>
>
>>From: Mad Coiler[SMTP:tesla_coiler-at-hotmail-dot-com]
>>Sent: Friday, November 07, 1997 12:09 PM
>>To: tesla-at-pupman-dot-com
>>Subject: secondary C
>>
>>Coilers,
>>
>> Does anyone have a formula for calculating the self capacitance of a
>>secondary coil? I have been making some small coils (6-12" tall) to
>play
>>around with different h/d ratios, etc. If there is a formula for
>>calculating a coils self-capacitance it would greatly speed up the
>>design process and tuning.
>>
>>Mad Coiler
>>
>
>Hmmm, no one on the list knows how to calculate this?
>
------------------------------------------------------
Mad Coiler -
The calcs are so well known by members of the Tesla List that everyone
expected the other guy would post the info.
There are several ways to find the self capacity of a Tesla coil
secondary. The Medhurst equation is the most popular.
picofarads = A x B + C
A = 5.08 R B = .0563 x L/R C= .08 + .38 x sqrt(R/L)
R = radius - inches L = length of winding - inches
When I was playing around with graphing the Medhurst equation using
Borland's Quattro I found that there was a strange hook in the curve when
wire lengths are less than 1000 feet with varying radiuses and lengths. In
some combinations the capacitance of the coil was greater as the wire length
decreased. This doesn't seem right but I have not made tests to verify this
condition. You may want to check this unusual result by building and testing
several small coils with large radiuses and small lengths. Set up the above
equations on a spreadsheet.
John Couture.