Re: Best cap size for a sync gap

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

Original poster: Malcolm Watts <m.j.watts-at-massey.ac.nz> 

Does anyone here have *proof* that the NST shunts are saturating or
is this just speculation? The reason I ask is that the shunts
actually have an airgap in series with them. I can certainly imagine
the main core approaching saturation.

Malcolm

On 3 May 2004, at 8:20, Tesla list wrote:

 > Original poster: Kurt Schraner <k.schraner-at-datacomm.ch>
 >
 > Hi Gary, Terry, all,
 >
 > the subject of best cap size for a sync gap and SLTR is stimulating,
 > and I like to add my SFr.0.01 to the interesting thread. Seeking a
 > well sized LTR value for my little coil UBTT (Uni-Bern-Tesla-Twin) and
 > a reply to Dan McCauley's overvolting question, I performed 29 SPICE
 > simulations, mentioned in my TCML posting of last September:
 >
 > http://www.pupman-dot-com/listarchives/2003/September/msg00311.html
 >
 > The sim's were for just for the _linear case_, where the NST
 > parameters (measured before) would not dynamically change. Meanwhile
 > the coil has been realized, and the calculated results, though in nice
 > agreement with reality otherwise, have taught me a different lesson:
 > The NST is indeed a more complex animal, than many of us might have
 > thougt before ;-). I experienced, and fully agree with those,
 > assigning magnetic shunt/core saturation in NST's a significant role
 > in TC use.
 >
 > The experimental results, compared to the simulation, were as follows:
 > In simulation a 230V/50Hz line power draw of ~880W / 1700VA
 > (PF=0.52)at an ~optimal setting of the rotary firing time of 4.2ms was
 > obtained. The experiment was showing 1300W / 1610VA (PF=0.807) at a
 > rotary setting of 3.6ms. No humming of the NST was heard, because of
 > the 1.5m-spark noise. The operation is stable and reproducible.
 >
 > The TC is powered by a 15/60 NST of Italian company FART. The SRSG
 > motor is fed via a phase-shifter of the John Freau type. The
 > phase-shifter can also be used to smoothly adjust the power input to
 > the coil. However I was scared adjusting the phase angle to the
 > predicted optimal 4.2ms, because of beginning safety-gap firing (2
 > brass balls of 0.5cm, adjusted ~10mm). A scope-shot of the charging
 > cycle at lower power may be had at:
 >
 > http://home.tiscalinet.ch/m.schraner/UpriC_oszi1304.jpg
 >
 > The charging circuit resonance, assuming linear behavior of the 15/60
 > NST (L.leak ~795H) and a 33nF primary cap would be about 31Hz. If
 > saturation brings the leak inductance down to 307H (38% of linear),
 > the cap would again be resonant! My 1300W operation of the NST might
 > imply a
 >      leak inductance of about 551H (69% of linear), leading to 37Hz
 > resonance - yet away from 50Hz, but the primary LTR cap value only
 > being ~1.8*Cresonant. Sooo... this alone shows SLTR experimenting
 > implies some risk, and should be performed cautiously. There certainly
 > are other effects, interwoven with the magnetically nonlinear behavior
 > of the NST. More thoughts, or even better: experimental info, would be
 > very welcomed to be seen appearing on this great list ;-).
 >
 > Data of the little UBTT may be supplied in a later posting, if of
 > interest. Two spark snapshots are here:
 >
 > http://home.tiscalinet.ch/m.schraner/1.06m_1332kl.jpg
 > http://home.tiscalinet.ch/m.schraner/TeslaAnVorlesung3kl.jpg
 >
 > The first pic shows operating the TC in single mode, in my lab; the
 > second in twin-mode at the Physics Institute of the Bern University,
 > during a lecture (sparklenghts: 1.06m and 1.3m respectively).
 >
 > Best regards,
 >                   Kurt
 >
 >
 >
 >
 >
 >
 >