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Re: secondary C
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.
>>
>>Mad Coiler
>>
>
>Hmmm, no one on the list knows how to calculate this?
>
>
Hello Mad Coiler,
Yes, there is a simple formula due to Medhurst. It is in the archives and
is repeated here for your convenience. Please note for future 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.