Re: OLTC update

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

Original poster: "D.C. Cox by way of Terry Fritz <twftesla-at-qwest-dot-net>" <resonance-at-jvlnet-dot-com>


You might also consider an extra large ferrite core in only the first 4-6 in
of the sec. coil.  Ferrite would only be perhaps 20% of sec. coil dia.  This
would help drop opr. freq perhaps into the range of your primary system so a
nice primary load of perhaps 20-30 turns could occur.

I'm far from being a solid state engr. so this is only a suggestion for
consideration of those actively working on this device.

Best regards,


Dr. Resonance





----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Sunday, August 11, 2002 4:52 PM
Subject: Re: OLTC update


> Original poster: "tesla by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<tesla-at-paradise-dot-net.nz>
>
> Hi Terry/List
> The idea of tuning by selecting the Number of IGBT's operating seems
great.
> You could possibly have "tuning " IGBTs which have much smaller caps which
> are selected just to tune the coil.
> Best
> Ted L in NZ
> PS thank you for sharing your work with us all
> ----- Original Message -----
> From: "Tesla list" <tesla-at-pupman-dot-com>
> To: <tesla-at-pupman-dot-com>
> Sent: Monday, August 12, 2002 7:05 AM
> Subject: Re: OLTC update
>
>
> > Original poster: "Paul Nicholson by way of Terry Fritz
> <twftesla-at-qwest-dot-net>" <paul-at-abelian.demon.co.uk>
> >
> > I guess the main difficulty with the OLTC is that a large primary
> > cap is required in order to get a decent firing energy.  Thus an
> > impractically small primary inductance is called for.
> >
> > Barry wrote:
> >
> > > Would it be easier to build a secondary that couples to a
> > > higher harmonic of the primary?
> >
> > Hmm.  Putting the energy into a primary (or any coil) by
> > connecting a charged cap across its ends tends to excite the coil
> > at its lowest resonant mode, which is what we'd call its Fres.
> > Only a little of the firing energy goes into higher modes
> > of the primary.
> >
> > To excite the primary at a higher mode (not a harmonic), one way
> > would be to simultaneously discharge several caps, strategically
> > placed along the winding, alternated with ground connections.
> > The initial firing energy would be shared across all the caps.
> > This would seem to be feasible given the use of semiconductor
> > switches.
> >
> > Apart from the difficulty with tuning, so far so good.
> >
> > The problem then is to couple effectively to the secondary. Now
> > with the primary at a higher mode, current in parts of the primary
> > will tend to be pulling against current in other parts of the
> > primary as far as the inductive coupling to the secondary
> > quarter wave is concerned.  And as the mode number gets higher,
> > the overall cancellation of the field from the primary becomes
> > more complete.
> >
> > Therefore, it would be necessary, in order to obtain a cooperative
> > field from each half-wave current segment of the primary, to
> > reverse the winding sense between each firing cap.  But doing so
> > would destroy the transmission line properties which were giving
> > you the particular mode, and the system degenerates almost into
> > a set of parallel primary windings, each with its own personal cap.
> >
> > So to persue Barry's rather interesting idea, I think it would be
> > necessary to make sure that the secondary was closely coupled to
> > only one half-wave's worth of the primary, and that the rest of
> > the primary contributes relatively less to the coupling.  Acmi
> > can be used to model the coupling to a secondary from a primary
> > which has caps placed along it's length, so long as these caps are
> > large compared to the self-C of the primary itself, which it's
> > safe to assume.
> >
> > Note that this might not be possible with traditional spark gaps
> > because of the need for simultaneous switching.
> >
> > Apart from tuning, I think the other main problem with this
> > approach would be how to ensure that large amounts of energy don't
> > converge onto a single cap of the primary, which it's perfectly
> > free to do so once the thing is released into resonance - given
> > unpredictable reflections from the top of the secondary.  We
> > wouldn't want any of the caps to suddenly find itself carrying
> > a whole lot more energy than it started out with.
> >
> > But then we do have scope for controlling the timing of the
> > switching, so maybe things could be controlled automatically
> > somehow.  If you get into that sort of territory, you can
> > conjecture building up a traveling pulse waveform along a primary,
> > by firing caps consecutively, so that the energy is built up
> > into a single broadband pulse.  You'd set things for a steady
> > impedance transformation along the way, and the primary would
> > couple to or merge into a secondary, which would continue the
> > impedance transformation (by some cunning choice of coil profile)
> > to give a single huge voltage pulse at the top.  Picture a deep
> > atlantic wave approaching a beach, rolling up in the shallows,
> > trading width for height.  The deep sea wave sees a gradual
> > impedance change as the beach applies some extra boundary
> > conditions.  Surfers know the beaches with the best profiles -
> > wonder what shape of coil would turn a long duration, low-voltage,
> > high-current, broadband pulse applied at one end, into a short,
> > high voltage, low current pulse at the other.  Note that this is
> > quite unlike a normal TC.  We're now firing up multiple resonant
> > modes, and timing them so that they momentarily converge to a
> > single giant voltage pulse at one end (preferably the far end)
> > of the coil.  But before anyone gets too excited, there are some
> > problems with this approach and it's not likely to give you any
> > more topvolts per joule than a regular TC, if my sums are correct.
> >
> > But, I think I like Barry's idea, because it opens up some
> > interesting possibilities.  Whether it would bo any better than,
> > say, a normal primary with lots of separate caps and switches
> > paralleled across it would have to be considered.  All in all,
> > I'm following this OLTC stuff with great interest.
> > --
> > Paul Nicholson
> > --
> >
> >
> >
> >
>
>