[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

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



DC, I'm confused. How does Javatc predict 0.19 for a DRSSTC or any coil? The coil would have to be extremely large with the current algorithm (which needs work for larger coils). It's based on quenching seen on smaller coils at the moment. It really needs an update to include the type of quenching that is seen on good rotary gaps, large coils, and also DRSSTC's. BTW, Javatc gives a recommendation, not an "optimum" (just to clarify).

Anyway, the 0.19 number is freaking me out a little. Granted, DRSSTC's of decent size may do well here, however, Javatc simply should not be giving out that type of number in the recommended k output.

Bart B. Anderson

DC Cox wrote:
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
--
_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxxxxxx
http://www.pupman.com/mailman/listinfo/tesla

_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxxxxxx
http://www.pupman.com/mailman/listinfo/tesla




_____________________________________________________________
Washington DC's Largest FREE Email service. ---> http://www.DCemail.com<http://www.dcemail.com/>---> A Washington Online Community Member --->
http://www.DCpages.com <http://www.dcpages.com/>
_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxxxxxx
http://www.pupman.com/mailman/listinfo/tesla

_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxxxxxx
http://www.pupman.com/mailman/listinfo/tesla

_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxxxxxx
http://www.pupman.com/mailman/listinfo/tesla