Re: TC vs MAG
From: Malcolm Watts[SMTP:MALCOLM-at-directorate.wnp.ac.nz]
Sent: Tuesday, August 26, 1997 5:16 PM
Subject: Re: TC vs MAG
> > My answers for what they're worth....
> > > From: bmack[SMTP:bmack-at-frontiernet-dot-net]
> > > Sent: Sunday, August 24, 1997 10:37 PM
> > > To: tesla list
> > > Subject: TC vs MAG
> > >
> > > hello all
> > >
> > > I've been reading references here and there on the list to
> > > magnifiers and secondary windings of TC's.
> > >
> > > To the best of my understanding, the difference between the
> > > mag and the TC is that the mag uses tight HF transformer coupling
> > > (as tight as air core gets-that is) and uses an additional quarter wave
> > > resonator in series with the Hf transformer secondary. This additional
> > > resonator should have as little magnetic coupling as possible as to
> > > avoid damping. Right so far?
> > Yes. Except that in a sense, the resonator is coupled to the driving
> > system as long as the gap is alight since the two are _electrically_
> > coupled. You can reach k > 0.9 in an air-cored transformer quite
> > easily.
> > > My questions are: >
> > > 1) Is the mag secondary quarter wave resonant, or is the turns ratio
> > > the main issue here?
> > Turns ratio. Ideally the driver is a voltage source. In practice, it
> > never is because the primary cap is not a voltage source. For a
> > tightly coupled driver, you can tune the primary to the resonator and
> > virtually ignore the secondary.
> > > 2) If it is quarter wave, the sum length is half wave which should
> > > give poor results. Is there some phase abberation that makes this
> > > work?
> > This is really only an issue in a loose coupled system where the two
> > secondaries appear to form a single resonator.
> > > 3) Some coilers don't get seem to get too fussy about the actual
> > > wire length used, rather they use a "magic number" of 900 turns.
> > > Maybe I'm too theoretical, but I ALWAYS calculate the wire length
> > > to get a "ballpark" idea of free resonance, THEN go for optimal
> > > aspect ratio. I would like your opinions on this.
> > The 900 - 1000 turn guide allows a fair amount of inductance without
> > the wire become too small and hence excessively lossy. Wire length
> > is really a bygone era thing. I use the Lself and Cself of the
> > resonator to calculate Fr. Works every time for every resonator I've
> > ever built.
> > > 4) In some low power table tops I've built, it was noted that
> > > the resonant freqency was very sensitive to the actual wire
> > > length.
> > > In fact the secondary could be in two or more sections separated
> > > by about a foot (didn't try longer) and still maintained a frequency
> > > realtionship to pure length!
> > Well, it will to some extent. If you work through Wheeler's Lself
> > formula you can see why. What you have done is to reduce the
> > inductance by separating the winding into pieces but at the same
> > time, you have increased Cself by maing the thing taller.
> > > These models used small top capacitances.
> > > Thus my confusion about the magnifier concept.
> > What k was the system running at?
> > >
> > > Thanks in advance,
> > >
> > > Jim M
> > IMHO,
> > Malcolm
> > Thanks for the info, Malcolm!
> The k on that particlar event was more like 0.4.
> I guess I missed something in the colorado spring notes.
> I remember reading Tesla's measurement for k at some point
> was 0.6 while doing "extra coil" experiments. This brought
> me to the idea that it was not a critical element to the
> magnifier concept. Later on, however, he does make the
> stipulation of tight coupling, but don't recall seeing any actual
> measurement recorded.
k = 0.6 (or is it 0.65?) is a "magic" coupling constant. In a
lossless circuit, energy transfer from primary cap to resonator is
effected in just *one* cycle of oscillation. k's of this order are
crucial to making magnifiers more efficient than two coil systems.
There is a series of magic k's, 0.4 or thereabouts being the next one
in the series. The efficiency comes from removing energy from the
losses in the primary as fast as possible. Since k is related to
relative coil position and system geometry, it is clear that reaching
this k in a two coil system designed to produce sparks is not on
because the primary would be covering a fair proportion of the
resonator (and of course the output discharge would not get any
further than the primary coil being the closest object to the
> Also, you mention that the secondary and the resonator are
> electrically coupled during a gap fire.
I meant to imply that the *primary* is coupled to the resonator
during gap fire. The secondary is always electrically connected.
> Does this imply that a
> magnifier will be less efficient at increased BPS ?
No. As Richard Hull will tell you though, efficiency when running
tight k's is heavily dependent on gap quenching ability and using
high BPS _effectively_ is also heavily dependent on good quenching.