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

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Original poster: Daniel Hess <dhess1@xxxxxxxxxx>


Gerry;

I was not aware that as the variac setting changes so does the phase 
relationship and/or the timing of the RSG. But thinking about it what you 
say makes sense because the only way I could run at full power (max variac 
setting) was to advance (present sooner) the RSG. It's just that as I 
advance, coil performance diminishes substantially. My goal is to retard 
for maximum performance but also to stay out of the racing sparks/safety 
gap firing realm. That's when Terry's note concerning really low K values 
caught my attention.

Speaking of, I tried to raise my secondary last night to shoot for looser 
coupling. When I built this coil, I specifically designed a method to 
easily raise/lower the secondary but only with about 6" of vertical travel. 
Alas, my current K setting was adjusted to .18 and was nearly all the way 
as high as it could go. I was only able to move the secondary up by another 
3/8" so probably did not lower the coupling by that much. It was 98 degrees 
in my sunny Texas shop last night so I didn't bother to measure the new K 
and will have to construct a new adjustable base before I can raise the 
coil beyond this point. Now Malcolm is suggesting some tests so I may hold 
off before going any further. I did run the coil at the new height but 
could not see any discernible difference. Again, based on my experience 
with this coil I doubt that the extra 3/8" changed the K that much.

Thanks so far for you help,

Daniel Hess



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06/15/2005 02:27 AM
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Re: ScanTesla program - Lowering the coupling may be better...




Original poster: "Gerry  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>

Hi Daniel.

I was meaning the main power variac setting.  You said you adjusted it
mechanically so you dont have the Freau controller.  The main power variac
setting will affect the phase of the charging waveform so you will need to
readjust the firing phase of the SRSG as you increase the variac output and
make a final adjustment at maximum output.  As the main variac output is
increased, the peak charging point will pull up in time and if the SRSG was
only adjusted at medium variac output, this will have the effect of firing
too late at maximum variac output and result in rough operation.  Some
power sources can saturate during this late timing thus reducing the
effective inductance of the power source.  This in turn can cause mains
resonance even though you thought you were LTR (called ferroresonance).  As
the power source inductance decreases, the charging peak will also pull up
in time and could cause the SRSG to stop firing entirely and result in
uncontrolled resonant rise.  Adjust your SRSG to fire sooner in the cycle
until the roughness disappears and see if you still have racing
sparks.  See interspersed comments.


>Original poster: Daniel Hess <dhess1@xxxxxxxxxx>
>
>
>Hi Gerry;
>
>motor under power, while the coil is operating. When I retarded the RSG
>motor (CCW) the performance of the coil increased dramatically but alas,
>eventually came the racing sparks and the cap safety gap began firing as I
>continued to retard.

This is exactly what I would expect.  When you retard too much (too late in
the cycle),  the charging wavefore also happens sooner (increased current
causes a different operating point on the B/H curve - beginnings of
saturation and reduced inductance) and the SRSG starts to miss.  Firing
after peak can be unstable if retarded too much cause changes in the firing
point also changes the timing of the charging waveform.  Rough operation
results and resonant rise causes the safety's to fire.


>To answer your last question, the operation sounded rough, very rough to
>me. I attribute this to the fact that the cap safety gap was firing 'all
>over the place.' But then again, the safety gap firing is akin to a
>misfire; You would expect rough operation under those circumstances, yes?

To me, it is a chicken and egg problem.  The misfire of the SRSG can cause
the safety to fire.  A safety firing occuring while the SRSG is operating
normally can also cause the SRSG to misfire.   A safety firing will
introduce a transient response with a timing different then when the SRSG
fires and screw up the charging waveform.  In either case, rough operation
will occur.

Gerry R.