Re: Coupling Questions & coil measurements
Higher values of coupling would apply to magnifier design where k should be
around 0.6 for optimum operation. For normal TC oscillators k should always
be in the general range of 0.18 to 0.22 with 0.2 being a normal design
parameter to strive for.
Yes, it is true there are certain values of k that do work better but only
in tightly coupled resonance transformers. Above 0.6 the next value that
works best is 0.9 but that value is not readily obtainable in most designs
unless you are running coilform diameter around 2.50-30 feet in dia. The
exact reasons for this go into 2nd order and partial differentials which are
not easily discussed without a lot of time and a big chalkboard.
From: Tesla List <tesla-at-pupman-dot-com>
To: tesla-at-pupman-dot-com <tesla-at-pupman-dot-com>
Date: Monday, August 09, 1999 4:04 AM
Subject: Coupling Questions & coil measurements
>Original Poster: Ross <ross-o-at-mindspring-dot-com>
>I have a few questions about coupling. I have measured the resonant
>freq of the primary and secondary according to the technique described
>in Malcolm's Electronics World (*) paper. I checked the coupling using
>the technique where you run 5-10A of 120VAC through the primary and
>measure the voltage across the secondary (**).
>In my reading, I have found several references that discuss "Magic K"
>values. Brent's book explanation says that Magic Ks relate to even
>integers (multiples) of "RF cycles". That makes no sense to me because
>"RF cycles" are different for each coil and it's unique Fsec.
>The paper "Tesla Transformers" by Von Werner Heise also describes
>"values of K to strive for". One of the magic K values is 1.33. I have
>helped measure K on 3 well performing coils in the last week and all had
>a K value of almost exactly 1.33!?! The coils varied in size from 3 ft
>long secondaries to secondaries as tall as me. I may be
>misunderstanding Mr Heise, but it seems that his argument is based on
>first notch quenching.
>Can someone explain why some of these K values are supposedly better.
>Has anyone seen evidence of superior performance after moving from a sub
>optimal K to a "magic" K? In other words, is it an artifact of the math
>or does it really matter?
>On a similar topic, I'm not sure that I understand the "double hump"
>response. Can someone please describe how the resonant freq of the
>primary/secondary system is different from the resonant freq of either
>circuit measured independently and how this relates to coupling?
>Once I get more of this figured out, I hope to devote a web page to
>proper Tesla Coil measurement techniques and interpretation. I intend
>to discuss it in layman's terms and then spend a little time describing
>the differential equations and showing how a few things are derived (for
>us engineer/math types). If anyone already has a page like this, please
>let me know. Also, any references to this type of information is
>(*) Electronics World + Wireless World, March 1995
>(**) I will drop this on my page at
>Making arcs in SoCal,
>Huntington Beach, CA