Re: Redesigning/tuning a coil

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

Original poster: "Gerry Reynolds" <gerryreynolds-at-earthlink-dot-net> 

Hi John,

The coupling of an inverted conical primary is larger than a flatten version
of the same primary.   TC's are unlike conventional transformers where the
coupling coefficient affects the output voltage.  TC's are double tuned
resonant circuits and coupling coefficient has only secondary effects on the
output.  The reason for this is that TC's transfer energy and don't act like
a conventional turns ratioed transformer.  Discounting losses for a moment,
all of the energy in the primary will make its way to the secondary during
the ring down of the primary.  The coupling coefficient only affects the
time it takes for this energy transfer.  The secondary effect has to do with
losses in the primary circuit during this transfer so there is some benefit
in improved coupling to reduce these losses, but this is not of primary
concern.  An optimized TC maximises coupling just before the point of
causing racing arcs.  You may want to look at the archieves for a writeup by
Mark S. Rzeszotarski, Ph.D (I hope I'm remembering this correctly) on
inverted conical primaries.  Low power coils can benefit.  For higher power
coils, the raised primary can attract secondary arcs as well.

The inverse 4th power, I believe, is related to magnets (Antonio can comment
further on this).  Look at Chapter 3 equation 3-5 page 80 of your Jordan and
Balmain (my copy is 2nd edition) and evaluate the closed integral of H.dl =
I.  For an infinitely long wire, the H field will be I / (2*pi*r).  If the
length of wire is 5 times longer than the radius that the H field is being
evaluated at, this relationship will be 95% accurate.  A more accurate
evaluation is to use a current element (see equation 3-12 page 87) to
evalute the H field intensity.

Hope this helps,
Gerry R



 > Original poster: "john cooper" <tesla-at-tesla-coil-dot-com>
 >
 > Maybe I've a poor understanding of this but I've been laboring under the
 > impression that the sloped primary allows for a stronger coupling of the
 > prim to sec as it reduces the distance from those outside turns to the
 > sec.  It seems to me that the sloped prim may also 'shape the field'
 > somewhat or better direct it towards the sec.  My memory tells me that the
 > electric field diminishes as an inverse square function with respect to
 > distance, and that mag fields fall at an inverse cubed or 4th?  If a
 > tighter coupling than a flat prim would provide is not beneficial to a
 > particular coil then I can see that it wouldn't be of much use.  Have I
got
 > this all wrong, partly wrong?  I think I probably need to spend some
 > quality time with 'Electromagnetic Waves and Radiating Systems' by Edward
 > C. Jordan/Keith G. Balman to brush up on the basics.  Hmmmmm.
 >