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

["Dex Dexter" <dexterlabs@xxxxxxxxxxx>]

Curious things.
I have seen oscope waveforms of SG coil with coupling in 0.2 range and nothing strange I noticed.
Only faster ringups and ringdowns as expected.
If the coil with k=0.2 gives shorter spark output than with k=0.14 and power is adjusted to the level that there are no signs of corona elsewhere along the coil surface what does that means?

Dex  
   

--- resonance@xxxxxxxxxxxx wrote:



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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