CD 942 failure - Found it!!

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

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