Plastic Cap Capacitors

To: tesla-at-poodle.pupman-dot-com
Subject: Plastic Cap Capacitors
From: Tesla List <tesla-at-stic-dot-net>
Date: Sun, 20 Apr 1997 16:19:30 -0500
Approved: tesla-at-stic-dot-net
Subject:       Plastic Cap Capacitors
       Date:   Sun, 20 Apr 1997 10:24:04 -0700
       From:   Bert Hickman <bert.hickman-at-aquila-dot-com>
Organization:  Stoneridge Engineering
         To:   tesla-at-poodle.pupman-dot-com


All,

David Flinn came over last night to show me his smaller coil powered
from a pair of open frame Actown neons. The tank cap he used was a small
rectangular plastic-cased capacitor from Plastic Capacitors, rated at
7500 VAC, and the coil was powered by some really sharp-looking band new
Actown open-frame 7.5 KV 30 MA transformers, each with a single
epoxy-encapsulated secondary winding. Both ends of the secondary winding
were isolated from the transformer core. The unit used a set of six 1
1/4" x 6" water-filled copper pipes as spark gaps, with a total gap
setting of about 0.100". The secondary was a short (20"?) 6.5" diameter
coil, and the primary was short (2" high, 12" diameter) helical coil
wound from 6 or 8 gauge THHN house wire. The entire assembly was mounted
on an oak base - all in all a very nice looking small coil!! 

David also brought over a larger .01 uF 15 KV Cap from Plastic
Capacitors in order that we could do a "stress test" in my larger
system. Plastic Capacitors rates their units similarly to Condensor
Products (CP) - Input RMS for Tesla Coil use - and this particular unit
costs about $180. Plastic Capacitors uses a number of internal and
external construction techniques that differ from CP in order to get a
pulse cap which, they claim, is more robust. The case appears to be
fabricated from a phenolic material and is rectangular in shape, roughly
1.5" x 4" x 12". The unit is filled with silicone capacitor oil, and its
construction apparently permits thermal expansion without excessive
internal pressure build-up. Polypropylene film is used as the
dielectric.  

The last commercial capacitor we tried on this system was a CP 0.025 uF
20 KV CP cap that Don Froula brought over last October. This particular
unit failed, fairly explosively, blowing off one end and physically
ejecting oil and one of the internal capaitor rolls. A subsequent
failure-mode analysis by CP indicated that this unit was part of a batch
which had a manufacturing defect, prompting a recall of the batch of 25
that were purchased by many in this group last year. This particular
unit failed only at about 80% power input to a pair of 15 KV 60 MA,
using 13 gaps (7 static, 6 vacuum), at about 400 mils of total gap
spacing. 

In last night's runs, we disconnected one of the two 0.01 uF home-made
flat-plate caps and connected the little .01 uf 15 KV Plastic Capacitors
unit in parallel with the remaining flat-plate cap. The system tune was
left untouched. We then started running at successively higher gap
settings and power levels, finally going to full power (18 total gaps -
0.54") and 140 VAC input. Coil output and performance was the same, or
perhaps somewhat better, with white-hot streamers and solid, loud, 60+"
ground hits. Maximum runtimes were kept to about 30 seconds. 

Results:
The little cap took a lickin' and kept on tickin'(!) with absolutely no
evidence of internal heating or any other abnormal behavior. The next
trial will use two of these units in in parallel. I've got to admit that
I was favorably impressed! We'll keep the group posted on any future
runs with these units. Chuck Curran sounds like he is getting very close
to firing up his new coil using a much larger 0.05 uF 30 KV Plastic
Capacitor unit in larger 15" system... hope it works as well as this
little unit seemed to on mine!

Safe coilin' to you!

-- Bert H --