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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.
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:
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.