Condenser Products capacitor performance
Subject: Condenser Products capacitor performance
From: Scott Myers <scotty-at-wesnet-dot-com>
Date: Tue, 06 Feb 1996 13:54:34 -0500
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After reading the following excerpt from a recent post, I thought I would give a report on the
first firing of my new .025 uF, 20 KV RMS commercial pulse discharge capacitors. The initial
tests were outstanding.
> ........I just finished blowing 2 caps in my TC primary last
> night. I'd found some surplus 0.015uF 6.5KV DC film caps for $.99 each. I
> bought 10, wired 9 in series/parallel to get 0.015uF at 19.5KV. I was
> running about 6KV into the primary of my TC so I figured that a 3:1 safety
> margin was ok. WRONG! Both times that I approached resonance, beautifull
> little sparks started showing thru the case of the caps......
> .....I'm still argueing with myself over wether to build a oil and
> film cap or to order one from Condenser Products.
> I can tell you though, don't was your time with doorknob caps and 14 gage
> primaries! 4" sparks vs. 12" with dc rated caps and 1/4 copper tubeing
> primary. I can't wait to see what length sparks I'll get with a real pulse
> rated cap.
Secondary - 6" diameter on acrylic form with 943 turns of 22 gauge wire
for a winding length of 26.5", sealed with epoxy
Primary - 13 turns of .25" copper tube on a 20 degree inverted conical section
Final Toroid - 28" diameter homemade with a 5" cross section
Spark gaps - 6 series copper pipes 3" long with vacuum motor quenching,
gapped at .0045"
Transformer power - Neons, 15,000 VAC with 90 mA total current (1.35 KVA)
Setup - It consisted of using a balance primary with the capacitors on opposite sides of the
secondary for a total capacitance of .0125 uF. The spark gaps were across the capacitors. I
took care to keep off-axis inductance to a minimum. There is less than 2' from each side of the
primary back to the spark gaps, including the length of the capacitor. A "standard" filter
arrangement was used, .0009 uF and 2.2 mH was used per leg of the transformer in the filter. A
safety gap was in place. The RF grounding system consists of (5) 10' x 5.8" copper clad rods
spaced 9' apart. They are connected to one another via 2.125" wide solid copper strap that has
been soldered to the tops of each rod and buried along with the rods. Another identical copper
strap is soldered to this and connects the base of the coil via a connecting plate on the
secondary, per RQ's design.
After making several runs with smaller toroids and trying different coupling heights, I have
gotten as much as 4.5' discharges to a ground point. The free-air streamers are about 4'. I am
tuned all the way out to the end of the 13 turns of the primary. I need to make a larger toroid
to see if this can be improved without the addition of more power. Based on my previous
experiences and others observations, the efficiency seems very high. It calculates out to 300 VA
per foot of spark. I suspect I am at or very near the maximum discharge length for this level of
input power. I was pleasantly surprized by the results of this preliminary set-up. I would
guess that I am approaching the level of diminishing returns on this size coil. I will add more
power at a later date, as I have to move some items in my garage to allow longer free air sparks.
After going to a larger toroid, I will need to either add more turns on the primary, or drop out
one of the capacitors. I will initially drop out a capacitor, as this is the easier thing to do.
I will no doubt lose some efficiency by doing this. I will post the results of both adding
turns and increasing capacitance. I will not be able to get to this experimentation for about a
week, as I have to leave on business.