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Old 13th Sep 2012, 5:06 pm   #1
dinkydi
Retired Dormant Member
 
Join Date: Feb 2011
Location: Sydney, Australia
Posts: 277
Default Failing Schaffner IEC Inlet Filters

Schaffner IEC Mains Inlet Filters of many types have a long history of premature failure. This has been noted in previous threads eg https://www.vintage-radio.net/forum/...ad.php?t=82160

The failure of these filters appears to be related to their age rather than hours of use. New old stock filters may fail in the first few weeks of operation.

If you are selecting a mains filter choose one with the highest possible reliability because it is in use whenever equipment is plugged in (if the equipment power switch is used rather than the wall-socket switch). That is, 24 hours a day.

In addition, if a mains filter fails with a short circuit there is no equipment fuse to isolate the problem (any equipment fuse is after the filter). The short circuit current is limited only by the mains circuit breaker. While this might be nominally specified as 16A, for example, the actual peak current that flows may be in excess of 100A.

Some time ago in a previous post I speculated that the Schaffner filter failures may occur because they employ Rifa mains capacitors. These are known to have poor reliability https://www.vintage-radio.net/forum/...ad.php?t=69128

So recently, when another Schaffner mains filter failed, drawing 100s of Amps limited only by a circuit breaker, I decided to open it to see if a Rifa was hiding as suspected.

The first photo shows the failed filter. Black burnt goo has oozed from all case gaps. The second photo shows that the case has been blown out by high internal pressure at failure. The third and fourth photos show the filter with the case stripped off.

When I dug the X2 capacitor out of the potting it was in pieces, however, these pieces were consistent with a Rifa capacitor - in particular, it had the same constructional elements, namely, gold-tinted epoxy potting. But the few pieces I was able to retrieve did not actually contain the brand name, so I am only 99% sure.

Assuming that the X2 capacitor was a Rifa, this means that the filter potting and metal housing did not significantly slow down the inbuilt premature-lifetime failure process of the Rifa. This is surprising because the mode of failure is generally agreed to be moisture absorption against which potting is a barrier.

Peter
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Last edited by dinkydi; 13th Sep 2012 at 5:17 pm.
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