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Re: Spice simulation pictures
Tesla List wrote:
>
> > Subject: Re: Spice simulation pictures
>
> >From sgreiner-at-mail.wwnet-dot-comSun Oct 13 22:22:02 1996
> Date: Sun, 13 Oct 1996 09:56:45 -0700
> From: Skip Greiner <sgreiner-at-mail.wwnet-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: Re: Spice simulation pictures
>
> Tesla List wrote:
> >
> > >From lod-at-pacbell-dot-netWed Oct 9 22:54:10 1996
> > Date: Mon, 09 Oct 1995 21:26:28 +0000
> > From: GE Leyh <lod-at-pacbell-dot-net>
> > To: tesla-at-pupman-dot-com
> > Subject: Re: Spice simulation pictures
> >
> > Dave Huffman wrote:
> >
> > If you visit ftp://d0huff.fnal.gov/ftp you should find the JPGs
> > > along with the spice demo I used. The schematic/spice file is there
> >
> > Nice simulations! I was wondering if you have tried to more closely
> > model the secondary coil, that is to represent the self-capacitance
> > as distributed along the secondary rather than as lumped at the end.
> >
> > I've been playing around with PSPICE, and I think that I might have
> > an explanation for why larger toroids yield better output. This
> > effect has been observed empirically by many coilers, including the
> > folks at the TCBOR, and has confounded me for quite some time, since
> > if you add capacitance to the output the voltage there must decrease,
> > if energy is to be conserved.
> > As it turns out, a Tesla Coil will only act like a resonant xfmr if
> > the sec capacitance is concentrated at the top, just like in your
> > PSPICE model. By contrast, if you distribute the capacitance evenly
> > over the sec coil then it starts to behave as a tapered transmission
> > line, which produces less output. A tapered xmsn line is not as good
> > because it always stores at least part of its energy in the magnetic
> > field, and so never at any instant in time is all of its energy
> > present solely in the electric field, where it would produce output
> > voltage. So by adding more and more capacitance to the top, the
> > currents at all points along the coil are brought into phase,
> > yielding the best output voltage. More C past this point should
> > start to degrade performance.
> > How much C is optimum? Still working on that one, but it's probably
> > more than an 'proportionally sized' toroid would provide.
> >
> > -GL
>
> Greg
> This discussion seems to infer that the length of the TC when using the
> transmission line analogy is something other than 1/4 wave long. My
> understanding of transmission lines is that he energy transmitted down
> the line continously transfers between the magnetic field and the e
> field. If the TC secondary is indeed 1/4 wave long then it appears to me
> that it would certainly be possible to have all of the energy in the
> transmission line concentrated at the top of the secondary in the
> e-field without the need for a large toroidal capacitance. A previous
> discussion has touched on the need for a physically large discharge
> discharge electrode to prevent premature breakout so I won't go into
> that here, but if a way could be found to make a true 1/4 wave secondary
> without the need of a toroid to tune it AND a way to prevent premature
> breakout without a large electrode our TCs might end up looking entirely
> different.
>
> Comments and flames, please
> Skip
Skip,
Once again, take a coil, any coil, with or without terminal capacitance.
Ground the base. Shock excite it. It will with out fail resonate at
its natural 1/4 wave frequency. No tuning is required with terminal or
anything! It is unavoidable and impossible for the resonator system to
due otherwise! Also the maximum voltage point will always be at the top
of the system, provided that you are not dragging the system to another
frequency by forcing in huge amounts of mistuned, coupled energy via a
magnetic or direct coupled source. If the shock excitement is tuned to
the same frequency as the resonator, then we are really cookin'.
The addition of a toroid is never, ever needed to TUNE a resonator,
unless the primary tap and input capacitor are cast into an epoxy block
and will forever remain invariant. The addition of a terminal will
always detune or change the RESONAOTR SYSTEM'S natural period of
oscillation. A complete Tesla coil system can be tuned by varying any
ONE of the following, provided all the other components are set in stone
and are forever invariant.
1. Change the input capacitor,
2. Change the primary inductance,
3. Change the resonator coil in any way,
4. Change the terminal capacitance.
Under no circustances will a quarter wave transmission line with a coil
in it, anywhere, ever equal a wire path length of 1/4 wavelength. Only a
rigid piece of straight conductor floating in the vacuum of outer space
has any chance of approaching this value.
Richard Hull, TCBOR