Re: [TCML] Sudden and unexplained destructive racing spark flashovers

[johnbrooks@xxxxxxxxxxx]

Keep eye out for electric boat (trolling) motor,,perfect
j.

On Tue, 07 Jul 2009 03:10 -0700, "DC Cox" <resonance@xxxxxxxxxxxx>
wrote:
> It's a right angle drive driven by a small 50 rpm gearmotor.  It runs the
> 3/8" brass rod (sec ground) up and down vertically.
> 
> It allows you to find the optimum sweet spot in only 5-10 minutes of
> experimenting while the coil is continuously running.
> 
> D.C. Cox
> 
> 
> 
> 
> On Mon, Jul 6, 2009 at 7:29 PM, Jim Mora <wavetuner@xxxxxxxxx> wrote:
> 
> > Hi DC, Et Al
> >
> > I don't understand your dynamic coil height changer. I have been doing it
> > the hard way (round PE or plexi spacers). I would like a dynamic method to
> > raise the secondary of my future VTTV 6" acrylic .125" form which will be
> > at
> > least 2" into the 8" solenoid. It would be nice to vary the height rather
> > than spacing for my 12".125" PVC coil. Neither coils are grossly heavy.
> >
> > Jim Mora
> >
> > How other do it are welcome. I suspect a longer former at the bottom for
> > stability is part of the recipe. Thoughts?
> >
> > -----Original Message-----
> > From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On Behalf
> > Of DC Cox
> > Sent: Sunday, July 05, 2009 9:04 AM
> > To: Tesla Coil Mailing List
> > Subject: Re: [TCML] Sudden and unexplained destructive racing spark
> > flashovers
> >
> > I'm just reporting from practical experience in coil building.
> >
> > If you exceed 0.14 in classic type coils, especially around 0.18 and above,
> > racing sparks will occur.
> >
> > There is no reason to exceed this coupling value.  If you do your output
> > sparks will diminish in length, not grow.
> >
> > I've attached a flexible shaft coupling to the base of various sec coils
> > and
> > dynamically elevated and lowered them while the coil is running.  Various
> > size coils, 4" dia to 24 inch dia.  In all case max spark length is
> > achieved
> > around 0.12 to 0.14 range.  I've carefully measured the k value at the
> > setting that we achieved the long spark length for a given coil.
> >
> > Oddly, it appears to be nearly a linear relationship.  A 24" dia sec
> > performs best with 9" of elevation.  A 18" dia. sec performs best with 6.5
> > inches of elevation.  9" dia sec works best with 3.25" of elevation.
> >
> > At around 0.18 to 0.2 range most coils started to exhibit signs of
> > excessive
> > corona and occassional flashovers.  I've repeated these experiments with
> > coils sizes ranging from 4" to 24 inch dia and the results seem to be the
> > same.  Excessive coupling produces diminished output spark lengths.
> > Carefull measurements with oscopes indicated the frequencies were starting
> > to split indicating power was being wasted by not going into the
> > fundamental
> > resonant freq of the sec inductor.
> >
> > Dr. Resonance
> >
> >
> >
> >
> > On Sun, Jul 5, 2009 at 3:15 AM, Dex Dexter <dexterlabs@xxxxxxxxxxx> wrote:
> >
> > > It's an experimental fact that too high coupling can be the cause of
> > > flashovers and racing sparks but...The point of max potential is at the
> > > terminal (top load) of the secondary in 1/4 wave resonance coils.Typical
> > > couplings used (0.1-0.2 range) can be hardly  high enough for the point
> > of
> > > max potential to be shifted somewhere else.Perhaps you are referring to
> > > increased secondary local voltage gradients vs higher coupling
> > > instead?That's a different thing and more possible to occur I think.
> > >
> > >
> > > Dex
> > >
> > >
> > > --- resonance@xxxxxxxxxxxx wrote:
> > >
> > > From: DC Cox <resonance@xxxxxxxxxxxx>
> > > To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
> > > Cc:
> > > Subject: Re: [TCML] Sudden and unexplained destructive racing spark
> > > flashovers
> > > Date: Mon, 29 Jun 2009 20:19:02 -0700
> > >
> > > Over coupling is one cause of racing sparks.  It produces more than one
> > HV
> > > point near the top 1/4 of the coil which can cause local ionization and
> > > eventual flashover in this area.
> > >
> > >
> > >
> > > Dr. Resonance
> > >
> > >
> > >
> > >
> > >
> > >
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