Re: K Quiz
Subject: Re: K Quiz
Date: Mon, 16 Jun 1997 16:39:44 +1200
From: "Malcolm Watts" <MALCOLM-at-directorate.wnp.ac.nz>
Organization: Wellington Polytechnic, NZ
Hi Bert and all concerned,
> > > k itself is relatively easy to measure and quantify. But as far
> > > as I know, the figure says nothing about _how_ the primary is
> > > coupling into the secondary. For example, I can score identical k's
> > > with a flat primary with the same outer dimension as that of the
> > > resonator when placed below the resonator as I can with a helical
> > > primary with the resonator sitting inside it (easy). Has anybody
> > > examined performance issues around the degree of coupling into say,
> > > just the bottom few turns vs a primary that loosely couples a long
> > > way up the secondary? I have a gut feeling that this may be a
> > > significant determinant of system performance given the normal high
> > > secondary Q's and the fact that all else being equal, performance
> > > for a given power input varies so widely in different systems.
> > >
> > > Malcolm
> > Hi Malcolm and All
> > I formerly used flat spiral coils. I now exclusively use cylindrical or
> > solenoid wound primaries. I have not taken the time and effort to
> > quantify my results but my gut feeling is that I get much better overall
> > performance with the cylindrical primaries. Usually the primaries are
> > about 4" to 6" larger in diameter than the secondaries and the
> > secondaries are set 2" to 4" above the top turn of the primary.
> > Skip
> Malcolm, Skip, and all
> This is one of those questions that really makes you go hmmm....! At
> first blush one would think that, if you've got equal coupling
> coefficients, it shouldn't matter. The coupling coefficient should only
> govern the relative amount of time that it takes to transfer the
> primary's energy to the secondary. However, I suspect that, in practice,
> it may indeed be more significant, since the secondary is not a simple
> lumped parameter inductor. The more localized the primary's magnetic
> field (as in a helical primary), the more concentrated the
> electromagnetic energy coupling into the lower sections of the
> secondary, and the more this would begin to look like a base-driven
> resonator. In fact, if taken to an extreme, you'd almost be
> approximating a magnifier - heavy magnetic coupling only to the lower
> section, and the remainder of the secondary behaving more like a
> base-driven resonator. Interesting speculations... Malcolm or Fr.
> McGahee, do your collected coil parameters give any clues?
> -- Bert H --
I knew this one would bounce back. Serves me right. Actually,
the type of primaries for the coils I am supposed to be charting was
one thing I never asked for. At the time I didn't think it was
important. I will reflect on this and try and get a couple of coils
charted per day. About time I finished all that.
I've often used helical primaries and have used them
exclusively in the mini-coil series. They certainly work OK. Perhaps
Gary Weaver's experiments might be telling us something (at least as
far as the secondary he tested them on goes).
It was really an off-hand query. I think computer modelling
would be appropriate for this one. Dr Rzesotarski might be doing some
of this as I type. In the meantime, I have some more stuff to think
about. See my post under the heading "more mini-coils".