Re: CD 942 failure - Found it!!

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Erik Byng" <ebyng-at-knox.edu> 

Terry:

Sharp detective work.  Would it be possible to see a less magnified version
of that so I can pinpoint roughly were in the cap we're talking about?  I
haven't dissected one of the CD caps myself yet, so I'm at a bit of a loss
to say with any precision where you've seen this.

Best,
Erik.
----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: "John Richardson" <jprich-at-up-dot-net>; <tesla-at-pupman-dot-com>
Sent: Monday, March 08, 2004 7:08 PM
Subject: CD 942 failure - Found it!!


 > Original poster: Terry Fritz <teslalist-at-twfpowerelectronics-dot-com>
 >
 > Hi John and All,
 >
 > It's a peak current failure.
 >
 > Our new failure mode...
 >
 > Although the CD942 caps have solid metal plates that never blow
 > out.  Apparently, the floating metalized layer can.
 >
 > http://hot-streamer-dot-com/temp/JohnRcap.jpg
 >
 > http://hot-streamer-dot-com/temp/JohnRcap2.jpg
 >
 > The entire area between the electrodes has bad current stress failure
areas
 > much like a fuse.  About 1/4 of it is blown clear.  There does not seem to
 > be any RMS heat melting, but the peak currents probably are twice what the
 > cap is rated at:
 >
 > http://www.cornell-dubilier-dot-com/film/9422000.htm
 >
 > maybe 860 amps per cap or a total of 2600Amps peak in the four
 > strings!!  John mentions that the primary and such get very hot!!  What I
 > don't know is why the high currents?  People use one string with 12/30,
two
 > with 12/60 without trouble.  So it would seem John's coil is drawing
 > unusual very high peak currents.  But I don't know why.
 >
 > Cheers,
 >
 > Terry
 >