Re: Formula for self C of a Coil (not Medhurst)

To: tesla-at-pupman-dot-com
Subject: Re: Formula for self C of a Coil (not Medhurst)
From: "Ed Phillips" <evp-at-pacbell-dot-net> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)
Date: Wed, 26 Apr 2000 19:16:23 -0600
Approved: twftesla-at-uswest-dot-net
Delivered-To: fixup-tesla-at-pupman-dot-com-at-fixme

> Just correct me if I'm wrong, but I heared/read that Medhurst derived the
> "self capacitance" and its formula from experiments he made - he
> calculated the coil inductance and then measured its self resonant
> frequency. From these values he dervied a theoretical value for "self
> capacitance", the theoretical capacitance that would together with an
> ideal inductor give exactly that resonant freq. Doing lot's of experiments
> with different sized coils, he made up the table and formula

	Absolutely correct; the table came first and then was fitted with a
simple formula.


> 
> So, how far is the "self capacitance" from the "true" coil capacitance
> anyway? Is there a way to determine the "true" capacitance at all?

	How do you define "true capacitance"?????????  The normal engineer's
way is that capacitance which, when placed across an inductance equal to
the low-frequency inductance, gives the observed SRF.  Since the "real"
capacitance is distributed, can't think of any other definition.

Ed