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Re: Cap Failure



In a message dated 96-10-12 21:09:59 EDT, you write:

<< 
 Cap Failure:
 ============
 Don Froula came over this evening to see my 10" coil in operation, and
 also to try out his Condenser Products 0.025 uF 20 KV capacitor that he
 had purchased as part of the last group buy, but had not had the
 opportunity to try out. After a number of extended experimental runs to
 demonstrate the coil, we hooked up Don's cap in place of the home-made
 caps. The primary tap was readjusted for the slightly higher cap value,
 the gap setting was reduced from 18 to 13 gaps (7 static, and 6 vacuum
 for about 0.40" total), and the coil run at varying power levels.
 Performance at this setting was quite good, with sparks easily reaching
 48" long. 
 
 Several brief runs were made at varying input power settings. Because of
 the smaller gap setting, gap saturation was occurring at higher input
 power levels, and the PPS rate was probably in the 360 - 420 range. The
 coil was shut down, and the capacitor checked for any signs of heating -
 none. During the next run, power was adjusted to about 80% (about 112
 volts) on the 15 KV 120 MA neon tansformer source, with good coil
 output, when after about 20 seconds one end of the capacitor was
 suddenly and explosively blown off with no prior warning. A loud "pop"
 and a yellowish colored flash were heard and seen, and capacitor oil was
 ejected in the immediate area.
 
 As Ed Sonderman had previously described, these capacitors consist of a
 number of identical rolled capacitors interconnected by soldered netal
 straps. The metal looks to be tin(?), and these straps are soldered to
 the end foil of the individual capacitor rolls as well as the capacitor
 end terminals. The individual cap rolls look to be about 4" in diameter
 and about 3-4" long, and are connected in series.
 
 The PVC area around the plastic endcap and terminal was fractured, and
 the endcap blown off with enough force that it apparently pulled off the
 soldered connection between the metal strap going from the end terminal
 to the end foil of the outermost capacitor roll. The last roll was
 physically ejected from the capacitor housing, but was still
 electrically attached via strapping to the next capacitor roll. 
 
 Under closer inspection, it was not obvious exactly what caused the cap
 to blow. However, this appears to be the third cap in the earlier group
 purchase that has failed in this manner, in this case at a relatively
 low power level (2.5 KVA). Don will post some pictures of the cap so
 that others can see the construction technique and failure mode. He's
 also going to contact Condenser Products to get a replacement, since it
 should be covered within the 1 year warranty period. 
 
 Thanks to previous posts on this conference, we were aware of the
 possibility of explosive failure, and had taken precautions to orient
 the cap so that it would do no damage if it blew (other than make an
 oily mess :^)). It appears that there may have been a problem with some
 of the CP capacitors in this lot, since I've not heard of any other
 similar CP failures in a while, and none outside of this lot... 
 
 Safe (and hopefully non-explosive) coilin to ya!
 
 -- Bert -- >>

Bert,

Sorry to hear about the cap failure.  It sounds exactly like the failure that
I experienced.  My cap that failed was not part of the first group purchase.
 I had ordered it individually about a year ago at this time.  It was not a
20kv cap.  It was rated at 15kv and I was using a 14,400 volt pig for a power
supply.  I am suprised to see a 20kv cap blow with a 15kv neon power supply.
 I calculate your input power to be 93%  (112 / 120) which would be only
about 1.7 KW.  I would certainly think the cap was defective.  Let us know if
C.P. honors the warranty.

Ed Sonderman