Hello everyone. I thought I would post a little about my latest coil.
The primary is flat with 3/8" tubing with slots in the form to allow
tapping from below. The secondary is an upside down polypropylene
trash can that measures 14" diameter on the bottom and 13" diameter on
the top and wound with 18gauge magnet wire for 24-1/4" winding length.
Two toroids are being used, a corrugated drain pipe wrapped with tin
foil that measures 4"x33", and two flexible ducts taped end to end for
7"x 40". I am using two of the H&R transformers that are wired
anti-parallel for 10kV 300ma. Six sets of polypropylene caps, .013uF
each for .078uF or so total and a sync-gap. This isn't quite resonant
yet, but will soon be larger than resonant.
The first run was just to see that everything worked. There were
serious racing sparks and as I found out, several spots had burnt.
Some turns had to be removed on the bottom and the other spots had the
burnt insulation scraped off and were coated with model paint. Trying
again the next night, one of the repaired spots burnt again and three
turns had to be removed. But there was a ground strike before shutting
down that I later measured at 80". Or 3.2 times the winding length.
Pretty decent, but will have to get better :-)
I setup again tonight with the newly repaired secondary, freshly
soldered and re-painted. More racing sparks and some that jumped
straight down to the primary from the lower toroid. Since I have never
had these kinds of problems, I didn't really know what to do. I have
only run with crappy capacitors before that wouldn't let the power out
to the coil and these polypropylene caps are working great. I tried
raising the secondary some more to reduce the coupling. It was now
1-1/2" above the primary, but still had the racing sparks. The only
other thing I could think of was to lower the toroids some. Now the
racing sparks have been eliminated. But the spark length dropped,
probably from the reduced coupling. I'll try increasing the coupling
in a few days and see if the spark length comes back up.
So, any comments or suggestions? All welcomed.