RE: Toroid Capacitance

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

Original poster: "Terry Fritz" <teslalist-at-qwest-dot-net>

Hi John,

At 06:35 PM 7/20/2003 -0400, you wrote:

>Terry -
>
>The toroid capacitance reduction will always be a guesstimate at the TC
>design stage because of it's nebulous nature. The reduction is caused by
>surroundings that have unknown variable electrical capacitance effects and
>the effect of these variables on the toroid can only be approximated. The
>reduction changes every time the surroundings change and this changes the
>resonant frequency.

I would not call it "nebulous" ;-))  When I made my OLTC coil, knowing the 
toroid capacitance and Fo frequency was very important "before" the coil 
was built.  If it was more than about 5% off, I could not tune the 
coil.  In that case, the primary frequency was fixed.  The "only" tuning I 
had was raising and lowering the toroid.  So I found the Fo frequency of 
the primary and calculated the range of secondary tuning for the toroid 
being in the low, to high positions.  The programs turned out to be 
accurate to within 1% in that critical case.

Programs that use the numerical methods of E-Tesla6 don't "guess".  The 
secondary voltage profile is derived from Paul's secondary simulations and 
the rest is pure number crunching.

E-Tesla6 certainly takes into account "surroundings".  When I took the OLTC 
to the Tesla meetings, I had to account for the size of "Bills Garage" and 
pre-tune the coil for that "space".  The surroundings appear to be "ground" 
as far as the coil is concerned.


>Why should a coiler care about the toroid reduction? It should be noticed
>that the capacitance of the toroid has some effect on the output spark
>length. Ignore the toroid reduction and you get less spark. The larger the
>toroid capacitance the higher the voltage and the longer the spark.

"Big" toroids do seem to do much better.  The system certainly has to tune, 
and the toroid seems to like "one" long arc.


>I have also found that one of the apparently easiest TC tests is to
>determine the resonant frequency of a TC after it has been built. However,
>the accuracy of the test can vary over a wide range. Before toroid
>reductions and resonant frequencies will make sense a standard method of
>testing for the resonant frequency will have to be established.

??  The methods in your books do fine...  The streamer adds about 15% to 
the secondary capacitance.  So the primary has to be tuned about 7% low in 
frequency.  Those of us with scopes and frequency counters can measure 
tuning frequencies to within like 0.01%.  Far more than needed...


>Because all TC programs can only approximate the toroid capacitance
>reduction at the time the TC is being designed the effective toroid
>capacitance and the resonant frequency in the program may or may not have a
>large error. At present the Paul N. TSPP appears to give the most accurate
>results.

Paul's programs do rule!! ;-))  But after things get better than about 1% 
in accuracy, it just don't matter to the practical coil builder ;-))


>The JHCTES program resonant frequency in the outputs depends on the TC
>designer's estimate of the Secondary Terminal input to the program so the
>accuracy can vary. If the designer is experienced and very lucky the toroid
>reduction and the resonant frequency could be 100% accurate, however, the
>odds are high against it. One way to improve this program accuracy is to use
>the data you can get from Terry's E-Tesla6 program and add it to the JHCTES
>program.

Bart has gone a long way, if not the full way, toward this end:

http://www.classictesla-dot-com/fantc/fantc.html

Bart's Java program pulls it all together.  Using the basic program's of geoTC:

http://www.abelian.demon.co.uk/tssp/geotc/

Also note Bart's related graphs at:

http://www.classictesla-dot-com/sim/ctop.html



>Bart Anderson and I are working on making the JAVATC program the best
>available for designing Tesla coils. This program has worked very well in
>the past, however, at present like all other programs the toroid reduction
>is the weak link. We expect that this will be improved by using the TSPP
>program.

Oh!  maybe you are ahead of me here ;-))

Toroid reduction "does" require heavy number crunching...  But there are 
not "that" many variables so maybe a generalized "fast" equation can be 
found using the available information and tools.  Note Paul's big data base 
of simulated coils at:

http://www.abelian.demon.co.uk/tssp/vsd/

Cheers,

         Terry


>John Couture
>
>-------------------------------
>
>
>-----Original Message-----
>From: Tesla list [mailto:tesla-at-pupman-dot-com]
>Sent: Saturday, July 19, 2003 6:18 PM
>To: tesla-at-pupman-dot-com
>Subject: Re: Toroid Capacitance
>
>
>Original poster: "Terry Fritz" <teslalist-at-qwest-dot-net>
>
>Hi John,
>
>The capacitances of toroids, coils, and their combination is well known and
>understood.
>
>If one takes say a 20pF (free space) toroid and adds it to a coil with a
>Medhurst capacitance of say 15pF, The combination will (in fact must) have
>significantly less capacitance.  Maybe like 27pF.
>
>All these can be calculated with E-Tesla6:
>
>http://hot-streamer-dot-com/TeslaCoils/Programs/Programs.htm
>
>Cheers,
>
>          Terry
>
>At 05:52 PM 7/19/2003 -0400, you wrote:
>
> >All -
> >
> >Have any coilers found that the Toroid free space capacitance is reduced
> >when the toroid is placed on the secondary coil?
> >
> >John Couture
> >
> >-----------------------------------