first light - 2kW 4.5" coil - underperformance!

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jduva-at-baytechnologies-dot-net>

Hey everybody,
I have some specs to share with all of you for my latest coil, and the
results.

I looked around at what I had...a repotted a bad 12/60 that now calculates
to 12/184 when fed 141 V from my variac.  The core and windings were dropped
into a Tupperware container and insulated with melted petroleum jelly.  In
recent testing with a jacob's ladder, I was able to get the current draw
from the wall down to 7-8amps with one 30nf maxwell cap in series with one
of the HV leads from the NST.  With a 30nf cap in series with each leg, the
current draw dropped to, and below, 1 amp, as read by the panel mount
current meter.  The jacob's ladder output also increased from arcing a max
of 4" to a max of 7".  I decided to use this configuration in a tesla coil,
but wasn't sure of the new output with the caps in series.

The secondary is wound with 25" of 28-gauge heavy (double) build magnet
wire, with .75" extra form on the bottom, and .25" extra at the top.  It's
topped with a 1.75" x 6" toroid, a 3" x 13" AL ducting toroid, and a 4" x
17" AL ducting toroid, all stacked on top of each other.

The primary is wound with .25" copper tubing, spaced .5" apart
center-to-center (.25" air gap between turns).  Inner turn diameter is 6",
and there are 28 turns available.  If I remember correctly, it's tapped
somewhere around the 10th or 11th turn.

I'm using another 30nf maxwell cap as the tank cap, though I've also tried
60nf, and about 8 different 5.6nf increments from 17nf through 45nf.  So
far, the 30nf maxwell does the best.

The gap is a 1/6HP 120bps sync rotary with a total gap spacing of less than
.1", and all brass spark surfaces, all copper connections.

There's a pic of the circuit at
http://hot-streamer-dot-com/temp/experimental.gif

(Terry, correct me if I'm wrong?)


Once the tuning point is found, I've noticed that any tuning on points
farther out on the primary coil quickly diminishes output.  There will be
small brush sparks from a breakout point at 1 turn past the tuning point.
But tuning farther in on the primary has much more leeway.  One full turn
inward reduces output to half, then two full turns reduces it to brush
sparks, but still slightly larger than the outward tuning.  I wonder if
anybody has a theory on that?  All in all, my maximum output for this coil
has been 40", while drawing (again, according to the panel meter) ~1 amp.
The amp meter just twitches.

According to what I saw with the jacob's ladder, I'm guessing that this
isn't very efficient, but I'm still not too sure about the effect of adding
the two caps in series with the NST output, other than lowered current draw
from the wall.  If anybody sees any blatant inefficiencies on my part, let
me know! :)

And for those of you who are still reading (thanks!), I have notes on
performance without the two 30nf series caps on the NST.  
Mainly: Poor, poor performance.  The safety gaps still are right on the
brink of arcing over, the rotary gap didn't need any rough phase adjustment,
and I started with a 60nf cap bank.  Rough, sporadic arcing from the coil to
about half power, then the safety gaps start barking with any addition
power.  At about 65% power, they replace the spark gap completely, and the
arcs won't grow past 2.5'.  The current draw from the wall was pegging my
amp meter as well.  Perhaps the LTR cap was really sucking some juice?  I
got the same story with 30nf...safety gap firing all over the place.  I
thought the LTR would have helped keep the firing voltage a bit
lower...guess not.  I have no clue what's going on with just the straight
NST.  It's certainly not happy, and I certainly have no good idea why.
Well, that's the latest from the Annapolis apartment.  No complaints yet, no
fired, no smoky electronics.  Thanks for reading.
-Joe