Twintastic first light

        Twintastic first light
        Thu, 3 Apr 1997 14:34:52 -0500
        "Robert W. Stephens" <rwstephens-at-headwaters-dot-com>


A while ago I mentioned that I was building a compact tandem Tesla 
coil system (my first).  Several weeks ago on a very wet/foggy saturday 
nite I had it sufficiently finished to put power to it for low power
up to about 3 kVA.

Fellow list members Jeffrey Wiggins and special long distance guest 
Kevin Conkey were in attendance for this exciting session of first 
light.  The coil absolutely refused to connect streamers between 
towers at first.  This was a puzzle to me because I was *sure* I had 
calculated the handedness and thus the phasing of all the coils 
correctly before winding them.  It seemed the more power I threw at 
the system, the more the streamers ignored each other in the common 
volume between towers.  Just for fun I reversed the drive connections 
to one of the primaries.  Bingo!  Now we were cooking.  I had in fact 
figured my handedness correctly, but has erred in the way I hooked 
the two primaries in series in the temporary lashup all over the lab 

The secondaries are each 36 inch wound length of #18 AWG 
Polythermaleze copper magnet wire wound on 10.5 inch diameter, 
5/16ths inch walled PVC pipe.  The secondaries are of identical wind and 
each measure 50 mH.  The prmaries are opposites, mirror images of each 
other employing 7 turns each of 5/16th inch soft copper refrigeration 
tubing in flat spirals.  The secondaries are embedded about a full 
inch into the flat spirals yielding a measured K factor of 0.18.  
With the new, large 10 inch cross section x 35 inch toroidal toploads
system tunes about 100 kHz at about 5 turns on each primary.  System 
cap is a 0.05 mfd.

For first light only 1/2 of the center tapped secondary, 9 kV worth 
of my 4.5 kVA oil filled transformer was used to limit the voltage to 
the 35,000 VDC rated pulse cap.  A safety gap was placed across this 
cap with a gap setting of 1.125 inches.  It fired often during some 
of the tests approaching 3 kVA.  Small toploads were installed being
25 inch by 3 inch smooth commercial rings spaced about 8 inches apart
creating a larger 'phantom' terminal.  My larger toroids planned for 
the system had not yet been fabricated and I was eager to plug the 
sucker in! : )

With a heavy fog swirling airborn water droplets outside the lab and 
relatively high humidity in the lab the system was powered up after a 
quick instrument tune employing about 3.5 turns on each primary.
Jeffrey assisted with a few low powered runs into bleeder points 
while we moved the primary taps around a bit attempting to find the
*sweet spot*.  Once found, merely 2500 VA 
input was making tremendous solid connecting streamers between the 
towers with a distance of 7 feet 9 inches between terminals, and no 
bleeder points.  This is a witnessed accomplishment also recorded on 
videotape by Kevin C.  This is my best power/distance Tesla coil
achiement to 

Since then I've finished the new bigger toploads and with a higher 
voltage capacitor have been able to wire in the full 18000 volts of 
the transformer.  Now at 7500 VA I am making a great show with the 
terminals spaced at 132 inches (yes 11 feet), all underneath a 10 ft 
4 in metal ceiling.  This successful, exciting twin system is going on 
permanent display in the 72 seat electricity theatre I'm now building at 

Check this out for yourself, two jpegs of 7.5 kVA operation at 132 inch 
terminal spacing are attached.  twin1rws.jpg is with smooth terminals.  
twin2rws.jpg is with very tiny pieces of adhesive aluminum foil tape 
stuck to the terminals with a corner lifted about 1/8th of an inch, 
just enough to help concentrate the streamers towards the opposite 
tower.  Although these pictures were taken with very low humidity in 
the lab, a condition which I consistently find gives me LESS 
performance per VA, some of the photos from the session show 
streamers from each tower reaching out as far as 8 feet to connect 
with stuff in the room.  That's about 2.7 times the individual 
resonator length.  I can't wait to push this sytem outdoors and turn 
it up to eleven! : )