First Coil - No Sparks

From:  Bert Hickman [SMTP:bert.hickman-at-aquila-dot-com]
Sent:  Wednesday, June 10, 1998 6:31 AM
To:  Tesla List
Subject:  Re: First Coil - No Sparks

Tesla List wrote:
> ----------
> From:  djQuecke [SMTP:djQuecke-at-worldnet.att-dot-net]
> Sent:  Monday, June 08, 1998 8:07 PM
> To:  Tesla List
> Subject:  First Coil - No Sparks
> I just completed my first coil yesterday but I'm not getting any discharge.
> 4.3" x 21.625" secondary - 22awg - 10 coats laq before winding then 15 more
> coats.  Ground via 10' flat braided cable to 10' of #4 stranded to 8' ground
> rod.
> Started with slight overcouple.  Moved incrementally up to 1/4" above first
> primary turn (no affect).
> 19"x4" toroid - Foil tape over foil over dryer duct and pizza pans.  Tried
> 4" - 8" above final turn on secondary.
> 1/4" copper tube primary, spaced 1/4" 15 turns total - tried tap at several
> spot on turns 14 and 15.  15 degree rise. Just over an inch between first
> turn and secondary.
> 15kv 30ma NST
> NST protection -
>     A 500ohm/65w resistor from each NST lead
>     1000pf ceramic caps across resistors
>     3.5mh coil on each leg (one coil showed "minor" shorting so I removed
> both from circuit without affect)
> Safety gap - across NST (actually more like two gaps, one from each leg to
> ground)
> I set gaps so they just barely didn't fire with NST alone.  During runs, gap
> would go off almost non-stop, I adjusted so that it didn't go off, no change
> on output, readjusted so it goes off intermittently (once every 2 or 3
> seconds)
> Main gap - RQ static 6"x9x2" (8 gaps total) tested at 7 gaps in use)
> Caps - 4 Oil filled poly each rated around 5300pf, 7500v, wired 2 pair in
> series then the 2 pair are paralleled.  Value tested at 5240pf on a decent
> LC digital meter.
> Power controlled by 10a variac.
> There appears to be a great voltage increase if intensity of safety gap
> discharge is a correct indicator.  Main spark gap is firing and appears to
> be doing what I expected.
> All settings have resulted in zero output.  I had hope to be ballpark close
> and adjust from there but apparently, I'm not even on the field yet.
> Thoughts?
> Thanks,
> dj


I "went through the numbers" on your system - it looks like the
secondary's loaded resonant frequency is around 300 kHz, and your
primary inductance is about 82 uH. With a tank cap of 5240 pf, you're
out of tune between turns 14 and 15 (243 - 263 kHz). You should be
closer to 300 kHz between 12 and 13 turns. 

Try putting a small object in the top outer surface of the toroid to
stimulate breakout and then adjust the tune for maximum spark. Then
remove the "breakout aid" and let 'er rip. 

BTW, the voltage rise you're seeing in the primary circuit is very real.
Your NST and tank cap are sized so that you are resonantly charging at
60 Hz. Don't open your main or safety gaps too far - this condition is
quite hard on NST's because you're running with higher secondary
recharge currents and with an increased risk of overvolting the NST.

Good luck, and safe coilin' to you!

-- Bert --