Remember when Scott Bogard wrote:
Adding a top load lowers the tesla coils resonant frequency, what about
adding a bottom load? Would
putting a toroid or some kind of capacitor between the coil and ground
lower the coils resonant frequency?
At first glance it didn't seem like much of an idea. But it *did* get me
to thinking:
Could one run a "transmission line" from the topload to another toroid
some
distance away? And then use breakouts on this second topload to force it
to
act as the main discharge point? Seems safer and easier than a magnifier
configuration, but with all the spacing benefits. Plus easier to make and
transport two separate small toroids than one big one.
Bart didn't think much of this:
Not sure. I doubt it. The transmission line would likely be the breakout
point if of a 2 coil
systems normal turns. Note in maggy's, the driver has >only 200 to 300
turns.
The extra coil is the high turn coil. If the driver
had high turns, the transmission line would be a serious breakout problem.
What appears good in visualization is rarely true in reality (physics is
the
cause).
Well, guess what? It works *very* well, thank you!
I've been having chronic problems with my Pig SISG killing itself by
secondary strikes hitting the electronics under the primary. So a few weeks ago,
I set up my "extra" toroid and gave it a try!
I kept my "good" toroid (very smooth home made 8" x 36") over the
secondary. I had a spare "ugly" 8" x 36", so I located it at the same height, but
70" away (center-to-center, so 34" edge-to-edge). I put the "extra" toroid on
a piece of 8" PVC pipe. I connected the two with a piece of 4" OD aluminum
flexduct.
Despite the much smaller radius of curvature, at no time did any
streamers come from the 4" flexduct.
With a breakout point on the "extra" toroid, all the streamers came from
the extra. When I started pushing way too much power into the coil, a few
streamers occasionally came from the main toroid to an unlucky piece of nearby
plywood sheeting. But one doesn't usually put 8 kVA into a 6" non-maggy coil
with an 8x36 toroid!
Yes, I had to re-tune because of the extra topload capacitance. This was
actually quite convenient. For one, it allows you to significantly increase
the topload without having to resort to a single, awkwardly large toroid.
Stacking toroids vertically seems to allow only minimal gains because they get
"lumped" electrostatically.
Sure, you decrease the Cprim/Csec ratio which theoretically lowers the
voltage gain. But at the same time, I've heard the larger Csec mitigates
harmonics, stores more charge before breakout, and increases the discharge current
during each bang.
With no other modifications other than adding the extra toroid and
retuning, I'd say the spark length increased 10-15%. It was noticeable, and
surprising. Maybe it was really due to lower losses in the SISG from a lower Fres
and lower primary current. All I know is that it definitely helped!
Not willing to leave well enough alone, I decided to move the primary
tap back to fewer turns, and increase the primary cap for more power. That's
how I ended up running .150 uF of primary cap, and blowing up another SISG
section. Maybe when I hook up the 12" coil and I can get the Fres way down, I'll
push it to .300 uF and see how long things last...
-Phil LaBudde
Center for the Advanced Study of Ballistic Improbabilities
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