Re: Redesigning/tuning a coil

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

Original poster: "Malcolm Watts" <m.j.watts-at-massey.ac.nz> 

On 21 Apr 2004, at 7:53, Tesla list wrote:

 > 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.

Actually, instantaneous loading in conjunction with the coupling
coefficient affects the output voltage in all transformers. TCs ring
up like they do because they are mostly unloaded by resistive
elements during that time. Not so different.

Malcolm


 > 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. >
 >
 >
 >