rifa input caps - Page 1
Forum section: electronics / projects

author: m3vuv
author_rank: Super Contributor
timestamp: March 10, 2022, 08:16:44 pm
content: are these needed for a device/appliance to work or just to complie to emc regs?.

author: Benta
author_rank: Super Contributor
timestamp: March 10, 2022, 08:23:13 pm
content: Originally there to damp switch arcing.My feeling is, that a lot of times they're just there "for tradition".

author: SHTechnics
author_rank: Regular Contributor
timestamp: March 10, 2022, 09:31:28 pm
content: The X and Y caps are for limiting the RFI. Watch out for old broken Rifa caps, they tend to blow.

author: floobydust
author_rank: Super Contributor
timestamp: March 10, 2022, 09:53:41 pm
content: If they're old, just outright replace them.They can usually be found in mains EMI filters, but also across switches or in snubber networks.The part does do a few things, so simply pulling them can cause unexpected problems. If they are before a fuse, that is big trouble.Because they usually affect EMC test results, there is some fear about using a different part (EMC re-test needed) so they persist to be used.I don't know why their metallized-paper is a selling feature. As if they have magical EMI properties. PME271's are still for sale to this day.

author: Gyro
author_rank: Super Contributor
timestamp: March 10, 2022, 09:57:13 pm
content: Quote from: floobydust on March 10, 2022, 09:53:41 pmHigher dV/dt specs than MKP.... When/if it matters.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 10, 2022, 10:28:37 pm
content: Well, what kind of appliance? Either way, it's a matter of suppressing interference, and perhaps increasing contact life where applicable. Do you mind having more noise around? Would others (neighboring radio users)?Would you saw off the muffler or catalytic converter of your car?Tim

author: Gyro
author_rank: Super Contributor
timestamp: March 10, 2022, 10:36:00 pm
content: Quote from: T3sl4co1l on March 10, 2022, 10:28:37 pmI don't know about over there, but here, there are quite a few nasty characters who will come and saw your Cat off for you in the wee small hours, like it or not!

author: pqass
author_rank: Super Contributor
timestamp: March 10, 2022, 10:53:10 pm
content: Quote from: SHTechnics on March 10, 2022, 09:31:28 pmThey blow up real good!

author: floobydust
author_rank: Super Contributor
timestamp: March 10, 2022, 11:22:28 pm
content: I find Rifa clear epoxy fails with age, it cracks. From new, unused old ones I had, it's like the core (wrapped part) grows larger, pillows out and cracks the epoxy. Or, the epoxy is shrinking with age.It could also be a mains transient taking them out but they are supposedly almost 3kV tested (once, when new) for 250VAC rated parts. After a few decades...With a stolen catalytic converter, there are mechanics here that just plumb in a bypass pipe so you don't need to spend big money replacing it. We don't have vehicle emissions testing here.Note the ECU is fully aware of this - vehicles with two O2sensors (before and after cat) model the cat and expect to see the delay and thermal mass as well- or it sets a trouble code and the Check Engine light turns on.People that think removing a part has no consequences, well it's there for a reason or two or three.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 11, 2022, 03:31:07 am
content: Quote from: Gyro on March 10, 2022, 10:36:00 pmI mean... the "would you really do X?" setup is usually meant as a statement, but it could honestly be a plain old question these days...Say, how big a sack of Rifas do I need to bring to get five bucks at the scrapyard?...Tim

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 11, 2022, 03:43:43 am
content: Quote from: floobydust on March 10, 2022, 11:22:28 pmOr, say, removing the EGR valve, because, obviously, all those emissions controls bollocks are sapping the raw unfettered power of my engine!Which I guess the equivalent would be, removing the snubber on an SMPS perhaps; but that's as likely to cause destruction, just due to simple overvoltage. Which, if it survives, then maybe it does increase efficiency slightly, at the expense of emissions. (Note: as far as I've heard, EGR actually improves efficiency on modern engines, so it is actually just that ridiculous and self-spiteful to remove it. It was just the early ones they whined and moaned about having to tack on emissions controls, in the 70s, resulting in gutless and wasteful designs.)Alas, engines are vastly more complicated machines than almost anything electronic, short of an actual CPU, so this isn't really much of a comparison. The muffler at least is fair, as it mostly is just acoustic "EMC" filtering (which, still, that's aside from the resonant ones that do affect engine operation).Tim

author: Haenk
author_rank: Super Contributor
timestamp: March 11, 2022, 10:18:41 am
content: Quote from: pqass on March 10, 2022, 10:53:10 pmOne down (up), couple more to go

author: CaptDon
author_rank: Super Contributor
timestamp: March 12, 2022, 02:44:42 pm
content: Fortunately here in 120vac land they tend to live a longer life even when compromised with cracks and such. Most of the ones I have removed here in the states were 250VAC rated. What do they use in 240vac land? Seems I have seen some rated at 320VAC on 'dual voltage' supplies. That isn't much margin, especially if you live in a rural area with lots of switching transients and huge EMP from nearby lightning strikes. My friend lived way out in a wooded area and during lightning storms you could hear arcing from the receptacles to the metal boxes they were housed in. You could often see in a darkened room the bluish flash lighting up the white or ivory colored wall plate. He never seemed worried. Well, strangeness of all strangeness, during a hospital stay his house burned to the ground. There was no evidence of arson or vandalism, anything worth stealing was still present in the ashes. It was surmised that lightning caused a smoldering fire that may have lasted a day or so until windows broke from the heat and allowed a raging fire to burn it to the ground. His house had stone walls so thick you could sit in the window sills!!

author: rfdes
author_rank: Regular Contributor
timestamp: April 20, 2022, 02:39:37 pm
content: Hi - I've been reading up on this 'RIFA' topic and see that old RIFA begin to crack and fail. I am in the process of replacing some in a '95 vintage test equipment and see that Kemet capacitor still sell the RIFA PME271M style caps. My question to the group is whether the capacitor design has improved over time where the plastic crazing has been resolved or are they (Kemet) still using the same design ?In short, should I stray away from new RIFAs?ThanksJim

author: Gyro
author_rank: Super Contributor
timestamp: April 20, 2022, 05:58:59 pm
content: Quote from: rfdes on April 20, 2022, 02:39:37 pmYou'd hope, wouldn't you. Unfortunately you'll probably need to wait 20 years or so to get a definitive answer. It's pretty much a time related phenomenon, unless they're stored really badly. They're still epoxy, but whether it's thesameepoxy, I don't know.

author: wraper
author_rank: Unknown
timestamp: April 20, 2022, 06:08:31 pm
content: Quote from: rfdes on April 20, 2022, 02:39:37 pmAFAIK they probably did not improve. I've seen reports of mid 2000's caps failing. And personally have seen them shorting in mains filters in equipment made around 2003-2008. By that time the issue was already well known. I would use PP caps instead. I don't see a single reason you would want to keep using those paper capacitors.

author: rfdes
author_rank: Regular Contributor
timestamp: April 20, 2022, 11:40:13 pm
content: Thanks for the advise. My only real issue is finding a PP cap that will properly fit the circuit board layout as the lead spacing is 20.3mm. I'll be able to take whatever I can find and force it to fit.Take care

author: wraper
author_rank: Unknown
timestamp: April 21, 2022, 06:58:16 am
content: QuoteWithout knowing capacitance, it does not say anything. If you cannot find PP cap in proper size, then use polyester. They are available in smaller sizes.

author: rfdes
author_rank: Regular Contributor
timestamp: April 21, 2022, 05:14:44 pm
content: Quote from: wraper on April 21, 2022, 06:58:16 amHi -Well the original cap was a Kemet RIFA PME series at 220n/250VAC. The lead spacing is 20.3mm and I have struggled to find something close enough to drop in. I ended up buying a 15mm lead spacing PP part and will squeeze it into the spot.

author: floobydust
author_rank: Super Contributor
timestamp: April 21, 2022, 07:46:37 pm
content: Long ago I'd fired off an email to Kemet (Yageo) with pics and mention of the proven hazards of the component - wondering why they still make the Rifa PME271. Didn't hear a peep, no response. Somebody must still be buying and using them.Nearest standard lead spacing is 15mm or 22.5mm and some have longer leads so you can stuff that in. There's many X, Y safety capsavailable.

author: SHTechnics
author_rank: Regular Contributor
timestamp: April 25, 2022, 07:21:47 pm
content: The RIFA (now acquired by Kemet) caps are still in production to replace them among others in homologated equipment mostly for government, science institutions. The caps are also self-healing and have a better resin than before.

author: free_electron
author_rank: Super Contributor
timestamp: April 25, 2022, 07:34:56 pm
content: ahh. The old Pifa capacitors. also use in Paffner (Schaffner) input filters.

author: madires
author_rank: Super Contributor
timestamp: April 25, 2022, 07:43:03 pm
content: Last week I took an old Cisco PIX firewall from early 2000s apart and found two lovely RIFA caps in the PSU. Cracked of course. Two bangs for your bucks.