Original poster: "Barton B. Anderson" <bartb@xxxxxxxxxxxxxxxx> Hi Leo,Thanks for sending lots of details. I'm hoping the cap size was a typo. Did you mean .022uF? If so, I recommend using only 1. Then tap to 17 turns on the primary to a ballpark tune (do you have 17 turns?). If you designed for .044uF, then maybe only 13 or 14 turns? Even .044uF is to large to charge adequately (bps is ideally non-existent). In any event, if the cap is really as large as indicated, it's time to build an MMC! (Because your breaking out 8" sparks, I assumed the cap value was a typo).
If MMC caps are needed, contact Dr. Resonance. It would only take 30 caps to hit .02uF. 2 strings of 15 caps. Each string is .01uF. Put those 2 strings in parallel to achieve .02uF. You will still need quite a few primary turns to tune the coil. Because the primary has 1/2" spacing the primary is going to end up very large. To reduce the primary size, you need a larger cap size which leads me to this: Leave the .044uF as is and get a 2nd transformer of the same specs and parallel the two NST's for double the current.
Large coils tend to want relatively large caps sizes due to the geometry of the primary wound to practical dimensions. This in turn drives a coiler to use a transformer with enough current to charge the beast.
Take care, Bart Tesla list wrote:
Original poster: "Hajdrowski, Leo T." <leo.hajdrowski@xxxxxxx> Hi All, One quick question. I just finished helping my son build a coil: 15 kv, 60 ma nst with full wave rectification Secondary 10.5" x 30" #22GA wire Primary 3/8" 10 turns copper tubing flat coil - 1/2" spacing between winds 1" spacing between primary and secondary First windings of secondary approximately 1" above primary. Stationary spark gap with 1/4" spacing 20 amp variac 30" dia. Torroid (2) .22uf 90KV capacitors in parallel (They came from an X-Ray machine and are about 4" dia. X 18" long). We only get about an 8" spark and no corona.....it doesn't appear to be high frequency, more like a step-up xfmr. Is too much capacitance bad? Thanks...Leo