Re: Dimensions of my flat spiral coil

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

Original poster: "Peter Lawrence by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Peter.Lawrence-at-Sun-dot-com>

Dave,
     the problem may be that the formula uH = R^2*N^2/(8*R+11*W) was
found empirically (inductance of lots of coils where measured and a formula
that computed those inductances from the coils' dimensions was guessed at
until one was found to agree "reasonably" close to measurement).

The range of dimensions tried during this empirical exploration may not have
been wide enough to be accurate for your coils, for example yours have nearly
a zero inside diameter, but those may have been left out of the original
experiments.

Also, to predict resonant frequency another formula is needed for self-
capacitance, which as far as I know no one has ever tried to either guess
empirically or derive from EM principles for flat spiral coils.

-Peter Lawrence.

PS,  I have two different LC meters, which give different L measurements on
one of my coils (off by a factor of three!!!). I'm certain that one of those
meters is broken in at least one L range. 



>
>Even without running the above coils, just the fact of the inductance
>measurements is odd in itself.  A single wound coil yielded, in this case, a
>7 to 1 gain over the calculated inductance.  In the wye coil, each wire
>measured close to the calculated inductance, but there were three of them.
>
>I am very interested to hear the explanations for the discrepancies between
>actual design and calculations from the skeptics.  If everything we need to
>know about coils is already known, what is the simple answer to these
>measurements?
>
>When I characterized the frequency of the single wound coil, the resonant
>frequency band was from 50KHz to 100KHz.  But I can't make the coil operate
>at that frequency.
>
>I look forward to your report as to the characteristics of your coil.
>
>Dave
>