Re: ScanTesla program - Lowering the coupling may be better...

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Original poster: Daniel Hess <dhess1@xxxxxxxxxx>


Terry;

Re; your comment,

"But it suggests that "very low" coupling may be a good thing....  Like a 
coupling of 0.03!!!"

I noticed something just this past weekend which seems to support the idea 
that lower coupling might be better. About a year ago I built a SRSG for my 
coil and designed the motor to fit in to a cradle so that it could be 
rotated to provide a means to advance or retard the firing angle. I used a 
stepper motor assembly to rotate the motor in its cradle but never got 
around to building the stepper motor controller. So in the meantime I just 
adjusted the motor manually in a trial-and-error fashion until I got (what 
I believed was) the best output. This past weekend I finally completed the 
controller and for the first time was able to adjust the SRSG on the fly 
and some things became readily apparent.

For one thing it turns out that my original static setting was too advanced 
and as I began to retard the setting and it came in to tune, the sparks got 
longer, brighter, it got louder (goodness) but I also began to develop 
racing sparks along the secondary and for the first time, the cap safety 
gap started to fire. I tried to gently push it a few times and the racing 
sparks and cap S-G firing were consistent and proportional to the degree 
that I retarded the SRSG. Even at lower power settings on the variac where 
I wasn't getting the racing sparks the cap safety gap went ballistic! Could 
the firing angle of the RSG have any bearing on resonance between C1 and 
the NST secondary? (my C1 is an mmc @ .049 uf and the NST is a 15,000 x 
.120) Or put another way; perhaps the angle of the RSG has no bearing on 
the resonance between C1 and the NST but running it so far advanced 
attenuated any naturally occurring resonance?

Years ago, I set the coupling of this coil to one of the magic K values of 
.18 using the suicide cord method. (applying 120 VAC to the secondary and 
measuring the induced voltage in the primary, then computing the value of K 
and adjusting the coil height to the desired value. .18 was as tight as I 
could go since any setting higher introduced severe racing sparks in this 
coil.  I was disappointed that I could not achieve a higher coupling but 
wrote it off to the physical dimensions/parameters of the secondary, that 
had provided a ceiling which prevented me from going to a tighter coupling. 
But it never occurred to me that perhaps a LOWER  K value might allow me to 
retard the SRSG to a close-to-max position sans the racing sparks!

I'll whup out my suicide cord later this week and readjust to the next 
lower magic K value (or maybe several steps down) and post the results 
soon. BTW, I attached a scale and pointer to the body of the gap motor so I 
can reference how far I've rotated it and in which direction. The scale is 
really handy because, if I ever get totally out of tune the scale allows me 
to quickly return to my starting point.

Daniel Hess



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06/10/2005 09:43 PM
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Re: ScanTesla program - basically working!!




Original poster: Terry Fritz <teslalist@xxxxxxxxxxxxxxxxxxxxxxx>

Hi All,

I note that the ScanTesla program is repeating something the MicroSim
modeling suggested months back, but I ignored...

The MicroSim model took all day to work by "hand"...  ScanTesla took 35
seconds while I "watched" ;-)))

But it suggests that "very low" coupling may be a good thing....  Like a
coupling of 0.03!!!   I am guessing that this would ring the primary to
"very high" voltages and give very high secondary voltages (and probably
good sparks ;-))...  The model suggest that this is a fairly "optimal"
power transfer (and significantly better!) situation for getting really
high top terminal voltages even with a significant streamer load...  Lp is
pretty much set for the Fo frequency since the coupling is so low...

Much much to ponder.......

Cheers,

Terry