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Re: Blown Rolled Cap

tesla-at-grendel.objinc-dot-com On Wed, 27 Mar 1996 11:01:57 +0700, you
wrote:

>>From richard.quick-at-slug-dot-org Wed Mar 27 01:23 MST 1996
>>Received: from uustar.starnet-dot-net (root-at-uustar.starnet-dot-net [199.217.253.12]) by uucp-1.csn-dot-net (8.6.12/8.6.12) with SMTP id AAA07554 for <tesla-at-grendel.objinc-dot-com>; Wed, 27 Mar 1996 00:44:18 -0700
>From: richard.quick-at-slug-dot-org (Richard Quick)
>Subject: Re: Blown Rolled Cap
>Date: Wed, 27 Mar 1996 01:11:00 GMT
>To: tesla-at-grendel.objinc-dot-com
>
>Quoting jim.fosse-at-bdt-dot-com (Jim Fosse):
>
>> I just took apart my first blown cap. 1 layer of 0.060" 
>> polyethylene. Identical failure!  Both look as if a sharp point
>> on the edge of one of the plates punched thru the dielectric. 
>> Both holes were 1.5' to 2' in from the inside of the roll.
>
>> I had sanded and smoothed both cap's plates and used my fingers
>> as roughness gages.
>
>Having done this more than a few times on different capacitor
>designs I can tell you the sharp raised points were most likely
>not there when the capacitor failed. It is the energy released at
>the instant of failure that distorts the plates; frequently you
>will find holes blown clear through the plate, but if there was
>insuffient energy to completely hole the plate, a sharp rasied
>point will often be formed in the plate during the failure.
>
I was just replying to Jim Watsons post on the blown neon about an arc
striking his primary when I realized that I had been doing the same
thing last month.

BINGO!

I had just retuned my system with my second cap, I started getting
2.5' to 3' arcs to a) my primary, I hadn't put in a strike rail and b)
TO THE TERMINALS of my cap!

I rebuild my support system to move the caps below the coil, put in a
strike rail above the primary, but by this time it was to late, I had
already weakened the cap, and it only ran for a few minutes before the
dielectric failed. It would not suprise me to see my neon fail in the
next run.

	Wiser, but poorer

	jim