Re: Recycled: Measuring Coupling Coefficients
From: Malcolm Watts[SMTP:MALCOLM-at-directorate.wnp.ac.nz]
Sent: Thursday, December 04, 1997 10:52 PM
To: Tesla List
Subject: Re: Recycled: Measuring Coupling Coefficients
> From: John H. Couture[SMTP:couturejh-at-worldnet.att-dot-net]
> Sent: Thursday, December 04, 1997 2:44 PM
> To: Tesla List
> Subject: Re: Recycled: Measuring Coupling Coefficients
> At 01:40 AM 12/4/97 +0000, you wrote:
> >From: Malcolm Watts[SMTP:MALCOLM-at-directorate.wnp.ac.nz]
> >Sent: Wednesday, December 03, 1997 4:19 PM
> >To: Tesla List
> >Subject: Re: Recycled: Measuring Coupling Coefficients
> >Guess I have something to say here:
> >> From: John H. Couture[SMTP:couturejh-at-worldnet.att-dot-net]
> >> Sent: Monday, December 01, 1997 11:27 PM
> >> To: Tesla List
> >> Subject: Re: Recycled: Measuring Coupling Coefficients
> >> fixed coupling and be independent of frequency . However, if the TC
> >> capacitor is changed and the operating frequency changed the coupling would
> >> also be changed without changing the physical characteristics or geometry of
> >> the coil. Has anyone ever checked this?
> >My experiments suggest k is purely related to coil geometry and
> >proximity given that Ls and Lp are *fixed*, not "variables". If you
> >alter geometry of either coil or coil proximities to one another, Lp
> >and Ls don't change but k does and hence Lm must. It is worth noting
> >that unless you know how many turns you will be using on that 15 turn
> >primary, you can't pre-calculate k either.
> Malcolm -
> Your comments prompted me to go back and review the K factor again. I
> think you are correct (K related only to geometry) because as I pointed out
> in another post the frequencies (F) cancel out in the test equations.
> However, this does not happen in the following:
> K = 1/sqrt(Qp x Qs) Q = 6.283 F L / R
> This situation requires more study. What are your comments ?
I have just posted a fairly weighty piece on coupling in reply to
someone else. That k in your equation above <> k = M/SQRT(Lp.Ls).
That k is more correctly labelled kc and is a dimensionless number
that you can relate to k (magnetic) to determine the behaviour of the
circuits and in fact, the overall bandwidth of the coupled system.
kc is a variable, k is not.
For kc > k, the circuits are undercoupled (Q's are abysmal and
either poor to begin with or decimated by heavy losses). In this
case, energy transfer from pri to sec never goes to completion as
energy is lost faster than it is transferred. Completely useless for
TCs if this is how the system behaves prior to spark production.
For kc = k, coupling is critical. Circuit bandwidth is at a minimum,
transfer time = infinity in the lossless case. Equally useless for
TCs if this is how the system behaves prior to spark production. This
is the *ideal* case for spark loading (allows first notch quench to
be achieved easily).
For kc < k, the circuits are now overcoupled and a complete transfer
from one to the other with the minimum losses the Q's can allow now
occurs in a finite time, the time becoming progressively shorter as
k gets larger. As kc gets smaller and smaller regardless of k,
efficiency climbs towards 100% (infinite Q's = zero losses).
Brilliant for TCs prior to spark production. And in fact if you
scope the system, you will find that you *have to* meet this
condition if your system is to produce sparks at all. The presence of
this condition is signalled by the production of the DSB envelope.
What you are seeing is 100% transfer minus losses.
> Regarding your other comment on "you can't pre-calculate K either" I would
> point out that the JHCTES TC computer program will first calculate "how many
> turns you will be using on that 15 turn primary" and then will determine the
> K factor. In other words the program is doing what you say is necessary to
> calculate the K factor.
> I think there is much more to the K factor and other TC parameters than
> what coilers (myself included) think they know. Unfortunately the Radio and
> EE Handbooks do not cover Tesla coils so coilers have to rely on the Tesla
> List and the few books specific to TC design and theory
> John Couture.
The comments above apply strictly to two coil systems.