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

[DC Cox <resonance@xxxxxxxxxxxx>]

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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