Failing Schaffner IEC Inlet Filters

[dinkydi]

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

[Sean Williams]

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.

Factually incorrect for the UK - we have fuses fitted in all plugs - Ideally in the majority of these items they will be rated at no more than 5A (well, apart from ones that have been changed to 13A.....)

Really a non issue for us in the UK.

Cheers
Sean

[dominicbeesley]

Oh, I dunno, I've made some ruddy good fires with 5 amps!

However, that damage doesn't look consistent with the usual Rifa Madness! I've had a good half a dozen or so go and they just make a stink but I've never had one fail S/C, at least not to the point of blowing a 3A fuse which is what all my BBC Micros have had in them.

Also, a point to note, is that I have a good number of things plugged into a UPS using IEC male to female leads...no idea what the UPS is rated at but assume it will pass more than a few amps as it has 3 big computers plugged into it!

Peter, did these failures cause any collateral damage either in their respective machine or to the mains wiring, outlet or plug?

D

[Wellington]

Originally Posted by Sean Williams

Really a non issue for us in the UK.

Possibly - but anything featuring photos of stuff that has exploded (or at least melted violently) is always interesting. And there seemed significant UK interest in the Solartron thread to which Peter posted a link.

I enjoyed your post, Peter!

[Sean Williams]

Oh, certainly interesting, but not something that is usual in the UK - Things that have died a violent death are good to see, reminds us all just how unreliable these modern things can be!

[cmjones01]

Originally Posted by dinkydi

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.

What evidence have we that it actually drew hundreds of amps when failing? The whole point of X2 capacitors is that they fail safely when they fail. Yes, the failure may involve fizzing, popping, clouds of acrid smoke and a few sparks, but that doesn't mean it's drawing uncontrolled amounts of current. Indeed, like many people here, I've seen a fair few of these things fail and in most cases that I've seen the equipment with the faulty filter capacitor has continued working normally with not so much as a blown 3A plug fuse.

Chris

[dinkydi]

Hi Sean,

My post is written from a designer's viewpoint. A fuse fitted in a plug is not an "equipment fuse".

A designer must cover all contingencies. Even if equipment is destined for Britain, it cannot be assumed that equipment will always be used with some given fused plug. The equipment has an IEC input which allows the user to choose any of a considerable number of different power cords. Also, you cannot say with absolute certainty that equipment will forever stay in a given country.

This means that, to be safe, equipment should be designed on the assumption that there is no plug fuse.

I am aware that substantial numbers of Schaffner mains filters have and will continue to fail in the UK.



Hi Dominic,

My experience of Rifa mains capacitors is that damage is by no means consistent, although your experience may well be different. How is this seeming contradiction resolved?

Cellulose materials such as paper are hygroscopic. They have a continuing propensity to absorb water. As a result, the paper dielectric of a Rifa mains capacitor gradually absorbs moisture and swells, cracking the epoxy coat which has poor tensile strength. If equipment is used on a regular basis, the amount of moisture that can have been absorbed by a Rifa since last use is small and may only affect a small part of its dielectric. If the capacitor fails in this situation, detonation is contained and the short-circuit current may be limited.

On the other hand, if equipment is poorly stored (in a garage with climatic extremes, for example) and is left there unused for say 5 years, the moisture continues building up to a high level throughout the dielectric. If the equipment is suddenly brought out of storage and powered up, and the Rifa fails in this situation, the detonation is extreme. The capacitor fails as a whole and the severe short circuit allows very substantial current flow.

This explanation fits the observations of many posters and my own experience.

Peter

[QQVO6/40]

Ref Rifa “X2” capacitors.
Peter “Dinkidi”.
I have to agree with you fully. Only on Monday this week we had an incident at home here with a “Clipsal” branded portable RCD double 15A GPO (general purpose outlet) units. These units have been very popular here in Australia for the protection of tradesmen and other portable appliance users.

I have quite a good workshop and my eldest son was going to do some work outside and as is usual here he grabbed the portable RCD unit along with the electric drill to do his job outside. As a correct procedure he plugged the RCD lead into the GPO in the workshop and switched the supply on. He then did what he should do and he pressed the test button on the rear of the RCD unit to test it’s operation before attempting to plug in the electric drill he was about to use. On pressing the test button, Quite a loud bang, his cry of pain, the workshop power went off, cloud of smoke with a distinct smell and all at once. I grabbed him and thrust his hand into water and then took him to the local hospital for burn treatment.
After making sure he was OK I returned to my workshop to investigate what had occurred with a supposed to be “top class piece of safety equipment”.

The 20Amp breaker in the circuit supply had tripped. The 50Amp 3 phase breaker in the workshop supply board had tripped and the 100Amp 3 phase breaker for the workshop supply in the main property supply board had tripped.

The case of the portable RCD unit was partially melted near a join in the case. Lots of carbon residue around the melted hole. I am guessing that my son was holding the unit in such a way that his hand was somewhere near this burnt hole when it failed. On opening the case of the RCD unit, it was a mess. Melted and burnt plastic. This unit uses an electrically operated solenoid to trip it’s circuit breaker. It has a small printed circuit board in the unit and it seems as if they use an integrated circuit to amplify the signal from the balanced core to sense when there is an imbalance in the incoming and outgoing current to the unit. On the PC board there is a quite large “Rifa” X2 cap. It seems as if this has failed and somehow created an arcing fault.
My son is ok as he had only a couple of hours in the hospital to see the doctor and to get some silver burn ointment along with having to put up with a sore hand for a while. His comment was along the lines of “this equipment is supposed to protect us from injury not to cause it”. I have to agree with him and in this regard I have informed our state government Workcover Inspector of the circumstances of the incident and they look likely to issue a workplace safety alert for these devices. This RCD device was used very often and it still had a catastrophic failure.
So in answer to someone’s comment about “Rifa” cap damage not being so bad I have to disagree. Especially after this last episode of “Rifa” cap failures along with the usual damaged sewing machines, washing machines and numerous other household appliances. I am well and truly sick of the damned things.
I have not yet experienced a Schaffner line filter failure yet but after Peter’s very kind warning I will be on the lookout for them for sure. Remove and execute with large hammer. Hihi.

[Radio Wrangler]

It's likely the burn was a result of a spray of vapourised copper. Very common when conductors and fuses do a rapid vanishing act. It certainly sonds like a very large fault current even if for a short time. Fuses and breakers all have current versus time curves and the short-time currents ar very large.

Glad he's fixable

David

[Refugee]

NOS ones fail in storage.
I found these two WYMA ones and one was split wide open.
The faulty one is the golden resin type and has quietly exploded in a draw while the other made with clear resin does not look quite so bad. I am going to keep it for testing when i have finished my cap tester that will have a maximum test voltage of 3KV and will work as a range extender for an AVO.
I have even added close ups of the leads. They are DNOS (duff new old stock).

[dinkydi]

Fuses and circuit breakers have a rating at which they can pass current on a continuous basis. However, currents that are orders-of-magnitude higher can be supplied in the short term.

In the investigation of sudden short-circuits on a supply line, when you have two or more breakers of different capacity in series supplying the load, you may find that a larger breaker trips but not a smaller. What does this tell you?

Plainly the fault current must have been in excess of the larger breaker, but also, at this current the larger breaker must have been faster than the smaller breaker. As David notes, the manufacturers supply current-versus-time characteristics for their breakers. (In general, breakers get faster with larger current.) The characteristics enable you to determine the minimum current at which the larger breaker is faster than the smaller one.

In a real case with a 20A and a 50A breaker in series with only the 50A tripping, examination of the characteristics shows that the minimum short-circuit current that could cause this situation is 300A. The actual short-circuit current must be greater than this. (For reference, note that the peak current in some "solid" short circuits may reach 1000A, though usually only for a limited time!)

In my experience of Schaffner filters tripping breakers and QQVO6/40's experience with Rifas, I think my estimate of "100s of Amps" is realistic. (By the way, QQVO6/40, at the risk of being called ghouls, Wellington and I would love to see photos of your unfortunate accident.)

Peter

[Refugee]

In my overview of this issue i have come to the conclusion that if the capacitor is in an encapsulated filter the swelling of the capacitor will not stop and that any metal shielding will be deformed.
If anyone finds an NOS encapsulated filter measure it and make sure it is not bulging before showing it power.
I have a hunch that the capacitor swells before the heat blows the melted resin out.
I would be interested to find out if this is true.

[matthewhouse]

Hello, I do hope your Son recovers soon, a couple of points:

Originally Posted by QQVO6/40

“Clipsal” -- have been very popular here in Australia -- “top class piece of safety equipment”.

I have never worked out why Australians love Clipsal so much, it seems to be used everywhere over there! Here, it is considered by many to be bottom of the barrel rubbish, certainly not top class. Do you not have any higher quality accessories? Is the Aus gear made better than the UK version? The style is certainly the same.

The stuff over here is getting poorer every year, even what was top quality a few years ago. The quality, and more important, safety of modern electrical equipment and accessories is often questionable, even the high priced items.

I'm sure I have a 20A chassis mount Schaffner filter in use home here, is this type affected too?
Edit: its a Roxburgh
Matty

[dinkydi]

Hi Matty,

I'm not sure about Aussies loving Clipsal. I think it's more about how aggressively Clipsal is marketed and the failure of quality products to survive in a modern marketplace that favours the cheap, irregardless of other considerations.

A wide range of Schaffner filter models is affected. I don't see enough 20A types to give you a specific meaningful answer, I'm afraid. I have used filters from Delta, TDK, and BIT without any issues.

Peter

[Radio Wrangler]

Amidst the cacophony of Rifa capacitors and Schaffner filter modules banging away in the distance, I think that leaves only Corcom filters with any semblance of reliability.... or does anyone know otherwise?

David

[Refugee]

I have found a list that contains some date code information and have dug the web link out for a share.
You will have to make sure that you have got something that can read .XLS files though.

http://www.google.co.uk/#hl=en&sclie...w=1212&bih=864

I have had another look at the two WYMA caps in my NOS draw a little more closely and even the one with clear resin is just starting to slowly explode.
I will have to keep an eye on it over time and see how long it takes to split open completely.
This is going to be like watching paint dry

[dinkydi]

Hi David,

There are a large number of manufacturers of potted filters and IEC types in particular. How they compare with respect to reliability - who would know? However, the only ones that I see fail are Schaffners.

Three brands that I have used without issue are given in my last post. Delta Electronics (Taiwan) is the darling of the computer industry for quality SMPS and have their own filter range. I don't need to say anything about the supreme quality of TDK (Japan) used by NEC. BIT (Korea) filters are favoured by some monitor manufacturers, Samtron, for example.

Peter

[dinkydi]

Hi Refugee,

Thanks for drawing our attention to the AVNET electronic component date-code identification spread sheets
http://www.avnet-logistics.eu/servic...ate-codes.html
These are a valuable resource for those interpreting the markings on older components.

I suspect that waiting for a paper-dielectric capacitor to swell up is slower that watching paint dry! No doubt it depends on the humidity, so Rifas may last longer in the desert.

Peter

[Refugee]

I have put it away and will check it every couple of months until i know how quickly the crack is opening then it can go in the bin.

[matthewhouse]

Originally Posted by Refugee

...then it can go in the bin.

Don't you want to connect it across the mains first, to check it really has turned faulty?

Are the current range of paper, class X resin encapsulated capacitors likely to go bad in the same way? The construction certainly looks similar, I have used a couple in the past to replace failed Rifa Caps, which I have replaced on sight for years now. And if this problem is so common why are they still being used in things like mains filters?


Matty