New primary test
From: Esondrmn-at-aol-dot-com [SMTP:Esondrmn-at-aol-dot-com]
Sent: Friday, May 29, 1998 11:43 AM
Subject: New primary test
Well, it finally quite raining here for a day and I got to do some testing
last night. The first objective was to compare the new flat primary
performance with the old 30 degree saucer shaped configuration. The bottom of
the new primary (3/8" tubing) is setting just even with the first turn on the
secondary. I had calculated that it should tune at turn 11.5 and the best
tune turned out to be 11 3/8 turns. The gap started firing at about 125 volts
on the primary at about 12 amps. The best performance was 56" sparks compared
to 52" for the old primary. This was with the old 3.3 ohm resistor stack
(oven elements) in series with the 5000 watt variac used as inductive ballast.
Primary voltage into the pole transformer was 190 volts at 25 amps.
Now I ran the same set up only using the new 2.4 ohm resistor bank in series
with the inductive ballast. Runs good, no cap safety gap firing (set at
1/2"). Let some smoke out of the new 5000 watt variac at 35 amps. This thing
is rated at 41 amps (new brushes too) and I was surprised to see smoke. It
did make a hard spot where it was sitting which I will need to sand down. I
moved the setting a little to make sure the brushes were sitting on a single
wire and not bridging two. Never happened again and did not seem to be
getting overly warm. Best performance was 59" sparks at 35 amps with 210
volts into the primary. I have the ability to drop the series resistance
still further but I think 35 amps is about max for my current set up. I may
try the higher voltage tap on the main Powerstat variac some day.
Basically, I am happy with the performance and am looking forward to adding
the other .025 mfd cap (thanks to Chip's generosity) in parallel with the
first one for a total of .05 mfd. Thanks to the suggestions of Bill Wysock, I
have at least got rid of the firing of the cap safety gap and seem to have the
primary circuit under control. This seems to be about all I am going to push
out of this 6" coil.
It does make me think that I did have a primary charging resonance condition
with the old set up. At the same power level that I used last night,
producing 56" sparks, I used to get 80" sparks. The sparks are hot now
especially when they hit something but not the same as the thick white bolts
that I used to get. I guess what you want is resonant charging and expensive
very high voltage caps that can stand up to it.
My toroid is 5" x 40". I probably need a larger radius toroid like maybe 10"
- larger ROC. Would this provide more hold off and thus higher voltage and