# RE: secondary C

```From:	Mad Coiler [SMTP:tesla_coiler-at-hotmail-dot-com]
Sent:	Wednesday, November 12, 1997 4:21 PM
To:	tesla-at-pupman-dot-com
Subject:	Re: secondary C

Dr. Rzeszotarski and list,

Thank you for the Medhurst formula. I might have been able to find
this but I had not realized that "Medhurst" meant the internal
capacitance of a coil.
I had not realized that list members looked upon fictitious names as
bad. Some of my associates here tell me never to use my real name over
the internet. They are kinda overreactive anyways. Perhaps I should use
my real name in the future.

Tristan Stewart

>From:	Mark S. Rzeszotarski, Ph.D. [SMTP:msr7-at-po.cwru.edu]
>Sent:	Wednesday, November 12, 1997 6:06 AM
>To:	Tesla List
>Subject:	Re: secondary C
>
>>
>>>  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.
>>>
>>>
>>
>>Hmmm, no one on the list knows how to calculate this?
>>
>>
>Yes, there is a simple formula due to Medhurst.  It is in the archives
and
reference
>that many of us on the list prefer not to respond to individuals
without
>real names.
>
> Medhurst's formula:    C  = K x D
>
>where:  C = capacitance in picofarads
>        K = constant which depends on the ratio of the coil height to
diameter
>        x = means multiply K times D
>        D = solenoidal coil diameter in centimeters
>        H = coil height in centimeters
>
>        H/D       K
>        50      5.8
>        40      4.6
>        30      3.4
>        25      2.9
>        20      2.36
>        15      1.86
>        10      1.32
>        9.0     1.22
>        8.0     1.12
>        7.0     1.01
>        6.0     0.92
>        5.0     0.81
>        4.5     0.77
>        4.0     0.72
>        3.5     0.67
>        3.0     0.61
>        2.5     0.56
>        2.0     0.50
>        1.5     0.47
>        1.0     0.46
>        .90     0.46
>        .80     0.46
>        .70     0.47
>        .60     0.48
>        .50     0.50
>        .45     0.52
>        .40     0.54
>        .35     0.57
>        .30     0.60
>        .25     0.64
>        .20     0.70
>        .15     0.79
>        .10     0.96
>
>Reference:  H.F. Resistance and Self-Capacitance of Single-Layer
Solenoids,
>R. G. Medhurst, Wireless Engineer, February 1947, pp. 35-43, continued
in
>the issue: March 1947, pp 80-92.
>
>
>Regards,
>Mark S. Rzeszotarski, Ph.D.
>
>

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