X and Y capacitor replacement--RIFA, etc.

[bdunham7]

Is there any reason that I can't use this product to replace old rectangular X and Y caps such as the exploding RIFAs, etc?

https://www.mouser.com/pdfdocs/KEM_C1068_X1_400VAC_Y2_400VACR21.pdf

[David Hess]

Yes, X1 capacitors can replace X2 capacitors and Y1 capacitors can replace Y2 capacitors.  X1/Y1 have a higher safety rating than X2/Y2.  Ceramic X and Y parts will work fine as replacements for common film and/or paper X and Y capacitors.

Also, Y capacitors can replace X capacitors but not the reverse.  The difference is that Y capacitors are tested to fail open instead of shorted.  X capacitors are permitted to short because being connected line-to-line, they present no danger.  But typically Y capacitors are much lower value than X capacitors.

[pigrew]

I generally replace them with film capacitors of the same dimensions+value. Film capacitors are sold as "self-healing" whereas ceramics are not. Film usually has better (more constant) capacitance versus temperature and voltage, so generates less line harmonics, too. It's likely 90% just marketing to differentiate them in line filter applications. As long as you get the proper X or Y rating, you should be safe.

EDIT: kinda replying to Electro Detective's post: probably sticking with the same type of dielectric (metalized film) is a good idea since switching to ceramic has a chance of creating EMI issues due to the vastly different properties of the ceramic dielectrics.

[Electro Detective]

Less thinking and legal dramas if you put in exactly what was in there, be it a RIFA or better equivalent

They don't care much for electronics speak in courtrooms,
just to stitch anyone suspected of 'interfering/modifying' electrical equipment that went smoke for unrelated reasons

[EHT]

Here is an article from RIFA explaining some details. I did look into this a while ago when I replaced a bunch of these and it seems the metallised paper types (like RIFA) are superior due to the self-healing of damage caused by transients. I wonder if they have improved the resin which they are potted in over the years. I think those about to fail can be seen from cracks appearing in the resin, which seems to happen to all of them at about 15-20 years old. In this case, perhaps the failure does not depend on how many hours the equipment has been plugged in, just how old it is.

I notice the X & Y caps are always put on the line-side of AC power switches,presumably to make sure that there is no transient spike on the AC power lead at the point when the AC switch is turned off. The result is many of these X, Y caps are operating 24/7...

[bd139]

I usually replace RIFAs with new RIFA capacitors. They have a different epoxy now and are quality controlled by Kemet. Still replace them every 10 years or so. Most of the reason they explode is because the kit is old and they have well passed their design life. The original capacitors do have a design flaw but they certainly were not expected to be in operation now.

For ref I've had 4 explode on me and replaced at least 20 of the damn things. They're just a thing you have to watch out for.

They also turn up in interesting places. My mother's food blender from the 1980s exploded a few months back. RIFA! My Henry hoover exploded about a year back. RIFA! They're everywhere.

[tooki]

Do they actually have a different epoxy?? I’ve seen nothing to indicate this.

Given that these things fail even when not in use — the local mom-and-pop electronics shop has Rifas on the shelf that are already crazing — I’d be leery to put them in anything, given the availability of alternatives.

[bd139]

Almost certainly different. The package dimensions are slightly different and the colour is different since Kemet took over.

The ones in your local shop are probably quite old and from an earlier batch.

If you think the alternatives are better, I've had a Chinese one go woosh within 6 months of it being installed.

I have about 15 of the things left so I'm tempted to go and hang one off one of my hanging basket hangers in the garden on a cable tie for a couple of years and see what happens. Nothing like extremes of temperature and moisture to see what happens.