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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 2nd Oct 2012, 9:24 am   #101
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Default Re: Beware Rifa Class X Capacitors!

Common features that these Rifa and Wima caps share are the paper dielectric and epoxy encapsulation. I suspect that paper is used as the dielectric to provide the "self healing" property i.e. when an area of dielectric material is stressed, it effectively burns away both itself and the capacitor foils in that area leaving an open circuit.

It's well known to most on the forum that paper dielectric capacitors tend to be inherently unreliable. Forum member GMB's experiments here

https://www.vintage-radio.net/forum/...d.php?p=293402

imply that leakage in paper capacitors may be caused by a combination of water ingress and some internal chemical processes.

Rifa and Wima's encapsulation does not appear to be capable of preventing leakage happening eventually, either the encapsulation is faulty and allows water ingress or some internal process causes the capacitor to become leaky, to swell and crack the encapsulation.

Perhaps we just need to assume that paper dielectric capacitors are likely to fail eventually, regardless of who makes them and the safety marks that they may carry.

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Old 2nd Oct 2012, 11:29 am   #102
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Default Re: Beware Rifa Class X Capacitors!

The resin is not perfectly water proof or air tight.
I would guess that ingress would be something like 10 years per mm or something like that.
I used to visit an old guy whom worked in a factory that made parts for aircraft.
His veg was grown in raised beds held together with sections of composite material that would have been used for aircraft floors.
These used to soak up water and swell.
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Old 11th Oct 2012, 3:18 pm   #103
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Default Re: Beware Rifa Class X Capacitors!

If I remember rightly, there was a thread about these caps losing their capacitance due to perforation of the foil electrodes caused be minute self-healing failures, on here about 2-3 years ago.
I think Rifa had the finger pointed at them for exibiting that fault more than most other common makes, too.
Incidentally, when putting a low wattage low value resistor in series as a 'fuse' for the capacitor due consideration must be made for the fact that under fault conditions full mains voltage will appear across the resistor after it goes o/c, and a type which will not arc and burst into flames must be chosen, or better still, a proper fusible resistor with a ceramic body.
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Old 4th Nov 2013, 1:51 pm   #104
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Default Re: Beware Rifa Class X Capacitors!

Just had one of tese parts fail. It was in a Danfoss oil boiler control unit, used as a dropper capacitor to develop a 39 volt supply without a transformer. Made an awful stink, and took various other parts of the unit out when it went. The disgusting brown oily deposite generated took alot of cleaning out. It had a resistor is series with it, which I found in two one legged pieces. Most difficult to find was the 39V zener which had been cooked enough that it had become a 12V zener. The inspection sticker indicated 1991, so it had done 22 years.

All back working now, thank goodness.
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Old 4th Nov 2013, 2:08 pm   #105
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Default Re: Beware Rifa Class X Capacitors!

Yes the smell is horrible, as is the "white" smoke, and the tarry gunge that comes out of them can make a real mess.

Replace any "Rifa" capacitor on sight!
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Old 1st Jul 2015, 10:59 pm   #106
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Default Re: Beware Rifa Class X Capacitors!

One of the things that pushes these over the edge is damp, but another is heat. I wonder how many rifa's will fail over this heatwave. I've had my first today in a ceiling-fan controller
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Old 3rd Jul 2015, 9:59 pm   #107
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Default Re: Beware Rifa Class X Capacitors!

Even in the fairly short time I've been taking things apart, I've found lots of these in power supplies. All kinds of ages, type of device and manufacturer. What they all seem to have in common though is lots of hairline cracks in the cases. The majority still appear to work, but I don't trust them when they're covered in cracks. I've been replacing them with WIMA MP3 X2. Are these less likely to crack and explode when they're old? I don't know. They look quite similar.
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Old 4th Jul 2015, 9:01 am   #108
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Default Re: Beware Rifa Class X Capacitors!

The clue is in the "MP" in the part number. This indicates that your Wima capacitors are of metallised paper construction, just like the Rifa and other Wima types referred to in this thread. I would assume that they will fail eventually.


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Old 4th Jul 2015, 2:30 pm   #109
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Default Re: Beware Rifa Class X Capacitors!

Quote:
Originally Posted by jjl View Post
would assume that they will fail eventually.
I expect so too, as I believe that the self healing properties are damaging over time to the capacitance. What I don't know is how well the plastic case holds up over time on these compared to the RIFA ones.
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Old 6th Jul 2015, 3:52 pm   #110
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Default Re: Beware Rifa Class X Capacitors!

Self healing also happens in polypropylene capacitors, but possibly slower and in a less destructive way (graceful degradation). The quality of the casing seems to me only a small factor in the faillure mode of impregnated paper capacitors (I have definitely seen older MP3s fail in a very similar manner). I would stronlgy advise to use MKP replacements.
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Old 7th Aug 2015, 2:45 am   #111
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Default Re: Beware Rifa Class X Capacitors!

Had one release its magic smoke today! I was at my parents' house testing out a few games consoles on our old Salora TV when I heard a slight crackling followed by lots of smoke pouring out the bottom of the TV!

Luckily I was able to switch off at the mains fairly quickly, but the smoke smell filled the house and took about an hour to get rid of! And that was with all the doors and windows wide open! Mother was not at all impressed!

Anyway, I've attached a picture. I'm not sure what make it is as it doesn't look like the RIFA ones shown in this thread..but it sure did behave like one!
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Old 6th Apr 2016, 4:26 pm   #112
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Default Re: Beware Rifa Class X Capacitors!

Hello there,

I came across this thread while Googling so joined the website to add my twopenn'orth.

These Rifa Capacitors were fitted to thousands of Kenwood Chef Mixers in the 70s and 80s and they all fail eventually. I have been selling DIY repair kits containing polyester film replacements, for years now.

They are widely used in sewing machine foot pedals, Revox reel to reel tape recorders and Henry vacuum cleaners to name a few.

Paper film caps do have some advantages over the polyester types. One is they hold their capacitive value for longer than other types.
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Old 6th Apr 2016, 6:37 pm   #113
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Default Re: Beware Rifa Class X Capacitors!

At Christmas I cleaned and re-greased my wife's Chefette (it was making a noise due to the grease having dried out), and thought while I was at it, I may as well do for the same for my late mother's older identical model that we kept as a spare. My wife's one worked perfectly on reassembly, but I must have got some water on the RIFA of my mother's one when cleaning out the inside, as switching on after reassembly produced a bang and the usual cloud of noxious smoke. Checking my wife's one showed that the Rifa's case was badly crazed, so I replaced that one as well as a precaution.

In all fairness, both Chefettes must be more than 40 years old. I wonder if their modern equivalents will still be functioning 40 years down the line?

Last edited by emeritus; 6th Apr 2016 at 6:44 pm.
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Old 6th Apr 2016, 8:31 pm   #114
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Default Re: Beware Rifa Class X Capacitors!

The last one I changed at home was in a Japanese Hitachi tuner, luckily I had a look inside before powering it up!

In an item I repair regularly at work, Rifa X Capacitors of only a few years old have failed open circuit or low value.

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Old 6th Apr 2016, 8:46 pm   #115
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Default Re: Beware Rifa Class X Capacitors!

I've just been out to a 70kW ball mill (pottery thing) and the slip-ring motor controller was fitted with the things. That wasn't the fault BTW, the capacitors were fine and we worked out the board was 27 years old (it's in continuous use and was second hand when they bought it).
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Old 7th Apr 2016, 12:43 am   #116
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Default Re: Beware Rifa Class X Capacitors!

I actually had a camera to hand when one let go several years ago.
There is a photo in post #9 of this thread. It was lurking in a Henry vacuum cleaner.
https://www.vintage-radio.net/forum/...d.php?t=106958
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Old 7th Apr 2016, 3:38 am   #117
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Default Re: Beware Rifa Class X Capacitors!

In Australia there were similar capacitors labelled "AEE Miniprint". I've got no examples to show because I threw them all away after one blew up in my Gran's sewing machine. Same deal, smoke and a horrible stink of burning plastic. If there was ever a smell that said "poisonous", it's that!
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Old 7th Apr 2016, 8:36 am   #118
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Default Re: Beware Rifa Class X Capacitors!

These things are not so much interference suppressors as a different sort of hours meter with a man-machine interface which operates without the part needing to show outside the product's cabinet...

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Old 9th Apr 2016, 11:27 pm   #119
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Default Re: Beware Rifa Class X Capacitors!

Quote:
Originally Posted by Kevin Meneely View Post
Paper film caps do have some advantages over the polyester types. One is they hold their capacitive value for longer than other types.
That's exactly why polypropylene (MKP) is the dielectric of choice for X, Y and pulse capacitors, nowadays. The less robust ones still go open after some years under prolonged noisy or moist conditions though, but mostly they won't let out the magic smoke.

Last edited by Maarten; 9th Apr 2016 at 11:34 pm.
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Old 23rd Dec 2016, 1:49 am   #120
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Default Another RIFA X2 failure...

The other half spent the evening saying "I can smell gas". Had a walk around, couldn't find anything. Then about 7PM I noticed a loud hum coming from the bench. Couldn't identify which instrument it was so I powered everything up and pulled plugs until it stopped. About 30 seconds into this process, smoke started pouring out of the Philips PM3217 scope. Dived on the master socket and powered the whole bench down.

Windows open, a couple of hours to clear the air and a screwdriver poking later, this popped out:

Click image for larger version

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As you can see it made a right mess. At least these are nicely enclosed in the back of the scope in the PM3217's!

Annoyingly I thought I'd replaced this one. Clearly not!

So symptoms:

1. Warmth. Scope was quite hot.
2. Someone else moaning about a funny smell.
3. Surprise smokescreen.

Going to bed now grumpy. No scope fun for me for a week

Last edited by MrBungle; 23rd Dec 2016 at 1:56 am.
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