Re: [TCML] Re: Position of baffle inside secondary

["Dex Dexter" <dexterlabs@xxxxxxxxxxx>]

Thanks for the references Dr. R.
Does any of them have mentioned issue of tesla coil racing sparks ?
My impression is that 1/4 wave tuned coils need to be powered near their maximum capability for racing sparks to break out.
Well,quite an interesing remark can be found in the famous Tesla's patent too.
 http://www.google.com/patents?id=m7R9AAAAEBAJ&printsec=abstract&zoom=4&source=gbs_overview_r&cad=0

"The adjustments should be made with particular care when the transmitter is one of great power,not only on account of economy,but also to avoid danger.I have shown that it is practicable to produce in a resonating circuit EABB'D immense electrical activities,measured by tens and even hundreds of thousands of horse power,and in such a case,if points of the maximum should be shifted below the terminal D,along coil B..."

Somehow I feel Tesla is not talking about 3/4 wave resonance mode here.And having on mind this patent directly concerns Long Island coil which was not supposed to hurl sparks (I think) in operation,I have another question.
Could it be after all that current computer models overlook something regarding propagation of higher overtones and their interaction even without spark loading?

Dex 
--- resonance@xxxxxxxxxxxx wrote:

From: DC Cox <resonance@xxxxxxxxxxxx>
To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
Cc:
Subject: Re: [TCML] Re: Position of baffle inside secondary
Date: Thu, 16 Jul 2009 17:07:55 -0700

Terman's Radio Engineer's Handbook has a lot of work on this subject.
Morecroft and Drude also did a lot of pioneering work in early radio
engineering with regard to coupled circuits.  Coursey's "Electrical
Condensers" is also full of information regarding early wireless systems
using fairly tight coupling and medium power (10-30 kVA) systems.

If you can handle the math it's clear. Basic calculus and summations, etc.

If not, just consider using what we've found seems to work best.  0.12 to
0.14 for normal spark gap excited oscillators, and slightly higher in
DRSSTC systems.  I use 0.18 for most of my DRSSTCs and would never go above
0.2 for this type of design.  JAVATC does predict 0.19 as optimum for many
of the DRSSTC
designs I've done, but I prefer to stay slightly lower and avoid problems.

You also have to carefully consider the power level you are running.  If you
put 30 kVA into too short a coil, hence overdriving it, you will experience
problems.

Regards,

Dr. Resonance




On Thu, Jul 16, 2009 at 12:45 PM, Dex Dexter <dexterlabs@xxxxxxxxxxx> wrote:

>
> Dr Resonance,Paul Nicholson,
>
> That sounds very interesting althought I admit I don't get a clear picture
> from the description.
> Did they measured these  effects in detail back in early 1920s?This would
> be another surprise if they did.
>
> Dex
> --- resonance@xxxxxxxxxxxx wrote:
>
> From: DC Cox <resonance@xxxxxxxxxxxx>
> To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
> Cc:
> Subject: Re: [TCML] Re: Position of baffle inside secondary
> Date: Tue, 14 Jul 2009 15:38:25 -0700
>
> The sparks start to diminish in length when the systems are too tightly
> coupled because overcoupling causes the main resonant freq to begin
> splitting into to separate component frequencies.  Increase values of k and
> the split becomes more pronounced.
>
> Wavelength is tied to freq via the velocity of wave propagation, usually
> around 0.96 x C (speed of light) for a classic coil.  In classic fashion
> the
> large inductance of the sec coil tries to delay the ability of current flow
> to produce a magnetic field, hence the slightly lower than theorectical
> velocity.
>
> Each of these two separate component frequencies causes the potential
> distribution along the sec coil to occur at different 1/4 wavelengths in
> accordance with their specific
> frequencies.
>
> If you have the top of the sec hitting best resonance at one freq, and
> another point down from the top hitting another resonant peak, then the
> potential distribution is hitting
> peaks at various points, usually 3/4 to the top of the sec coil.
>
> The localized peak potentials may begin cycles of constructive and
> destructive interference which leads to local ionization along the top
> areas
> of the sec coil.  When this occurs the path to the lower (near ground
> potential) areas of the coil shortens and massive ionization begins
> occuring.  This collective process is called "racing sparks".  The air is
> now overstressed and can cause breakdown (as example) from top 3/4 winding
> to lower 1/4 (near ground) winding.
>
> This process really isn't anything new as it was well documented in many of
> the old wireless textbooks circa 1915-1925, Morecroft, et. al.
>
> Most of the 1980 thru 1990 ARRL Radio Amateur's Handbooks also contained a
> section on the undesireable effects of overcoupling between two
> magnetically
> linked inductors.
>
> Dr. Resonance
>
>
>
>
> On Tue, Jul 14, 2009 at 12:46 PM, Paul Nicholson <tcml88@xxxxxxxxxxx>
> wrote:
>
> > Dex Dexter wrote:
> >
> > > I was surprised to learn of the existance of the optimum
> > > coupling with respect to the best performance of SG coils.
> >
> > Theoretical considerations must be guided by the hand
> > of practical experience here.   It is regularly but not
> > always observed that onset of racing arcs limits coupling.
> > Nobody knows why this is.   High k leads to fewer cycles for the
> > energy transfer, but all the voltages and currents remain about
> > the same - at least at the fundamental operating frequency.
> > So why should racing arcs and flashover appear?  Unknown.
> >
> > > But even if the conditions are such that secondary itself
> > > is free from undesired discharges ,beyond certain coupling
> > > point spark lenghts might start to diminish!
> >
> > Here too, the reasons are unknown.  Coupling affects the
> > envelope of the RF, and therefore perhaps the ability to build
> > long streamers.  Little is known about how the coil/topload
> > combination interacts with its irregular and complicated spark
> > loading.  So many variables involved, instrumentation is a
> > challenge, and realistic modelling of the TC/spark interaction
> > is, well, a pipe dream.
> >
> > Nobody has yet had the audacity to square up to these problems.
> >
> > I think that practical experience has led to 'typical' TC
> > design rules that (re)produce coils which are probably close
> > to optimum.  I don't think there's any yet-to-be-discovered
> > recipe that will go way beyond the present state of the art.
> > Our inability to explain why a certain range of k is desirable,
> > and so on, is merely an embarrassment to theorists, rather than
> > a hidden key to great new performance.  Perhaps that thought
> > is why nobody is pushing these boundaries of our understanding.
> >
> > (Not to mention the hideous cost of a digital scope with enough
> > RAM to capture the entire bang waveform at high time resolution!)
> > --
> > Paul Nicholson
> > --



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