Re: Capacitor Container Failure

To: tesla-at-pupman-dot-com
Subject: Re: Capacitor Container Failure
From: Robert Volk <smrtmny2-at-earthlink-dot-net> (by way of Terry Fritz <twf-at-verinet-dot-com>)
Date: Thu, 18 Mar 1999 18:18:12 -0700
Approved: twf-at-verinet-dot-com

Ross,
My rolled poly caps did same thing - on 2 out of 3. What I discovered
was that the end caps I used were bad. One of the caps was a heavy duty
cap from Home Depot - it had no problems. The 2 that failed were a
slightly translucent plastic ( not the solid, opaque type from Home
Depot). They were thinner than the heavy walled one as well. Every cap
made from this junk cracked on me after a few runs, top AND
bottom.UUUGGGHHH! I bought the JUNK END CAPS from Ace Hardware.... never
again.....

Hope this helps,
Bob Volk


> 
> The failure turned out to be a hairline crack in the side of the lower
> end cap.  The crack extends 1.5" vertically from the base.  It doesn't
> appear to go along the bottom of the endcap, but the paint may be
> obscuring it.  I am puzzled by this failure.  This doesn't seem to be a
> highly stressed area.  Being on the side, it is twice and thick as
> anywhere else and definitely didn't see the stresses during vacuum
> degassing that the bottom did.  My only guess is that the PVC cement
> softened it and somehow weakened it.  The coil (6" sec, 12KV, 120ma, 50"
> arcs)  has been run  5 times and the caps are only a couple of months
> old.
> 
> Has anyone ever seen a rolled LDPE cap with a PVC container fail in this
> manner before?  Is painting PVC considered a bad practice?  Are there
> some crazy PVC glue dynamics that I need to be aware of?