RIFA Madness - Identifying RIFA Capacitors - Page 1
Forum section: electronics / testgear

author: Kinkless Tetrode
author_rank: Regular Contributor
timestamp: September 03, 2019, 11:18:06 am
content: I recently got a new old HP 5334B Universal Counter. When I opened it up to run some performance tests on it, I found what looks like a few of the infamous pyrotechnic RIFA capacitors. I don't see any explicit RIFA name marked on the caps, so I'd like to confirm that these are the RIFA caps that are ripe to explode at any moment. Their translucent plastic cases are crackled and look ready to blow. Attached are photos of them.I'm going to replace them, so can anyone suggest the appropriate replacement capacitors? A quick search gives:Murata 2200pF 250V Radial Ceramic Cap, Digikey part no. 490-9513-1-NDMurata 0.1uF 250V X7R Radial, DigiKey part no. 490-9240-1-NDThe 2200pF should be a Y rated and the 0.1uF should be an X2 rated capacitor, but I'm not entirely sure if they are the right ones. Any comments are welcome.

author: Yansi
author_rank: Super Contributor
timestamp: September 03, 2019, 11:24:17 am
content: https://www.digikey.cz/products/en?keywords=490-9240-1-NDJeesus crist... sticking this to mains? You sure what ya doin' there? That would become a hell of a bang. (the ceramic cap is rated only 250V DC!)If you know, those caps shall be X2 and Y rated, why selecting those obviously that aren't, not even good enough with its rated voltage?The other Y cap is fine, but not a fitting replacement (original one was a foil type). Probably just cosmetic detail, but when ordering specifically, why not shop for correct ones?//EDIT: Just a simple search of "100n X2" brings you where you should be:https://www.digikey.cz/products/en/capacitors/film-capacitors/62?k=x2%20100n//EDIT2: Here for the other cap:https://www.digikey.cz/products/en/capacitors/film-capacitors/62?k=2200p%20y2

author: Kinkless Tetrode
author_rank: Regular Contributor
timestamp: September 03, 2019, 11:29:56 am
content: Right, these Murata caps came up in the DigiKey search as X and Y rated caps, but the ratings are not explicitly stated in the description, though I could, but haven't yet, read the datasheet on them. So, there are more suitable choices, I presume?

author: Yansi
author_rank: Super Contributor
timestamp: September 03, 2019, 11:30:50 am
content: I have edited my post to include links to suitable ones.

author: Ringmodulator
author_rank: Regular Contributor
timestamp: September 12, 2019, 06:47:03 pm
content: Hi,these caps are mains connected!The X and Y designations are very important for safety of the unit.Seehttps://en.wikipedia.org/wiki/Capacitor_types#Class_X_and_Class_Y_capacitorsNever use generic caps for this, even if the voltage seems right. X7R has nothing to do with that.Choosing the wrong type of cap may have lethal consequences.They must be specified for mains use and RFI suppression.

author: Kinkless Tetrode
author_rank: Regular Contributor
timestamp: September 12, 2019, 10:13:34 pm
content: Thanks for the information. No need for undue concern, I had no intention of using the exact capacitors from the original post, those merely popped up in the quick initial search and they did not say that they where X and Y rated, so I just asked. Nobody was able to suggest an appropriate replacement and they wouldn’t have fit the board anyway.Turns out a proper search for these capacitors should include the term “safety capacitor”. Then the appropriate items appeared in the search.Just including 'X' or 'Y' will not be effective, being that 'X' and 'Y' could be just a part of the name for the capacitor and not at all what we are looking for. We must explicitly include the term "safety" in the search.The tricky part of the search is finding replacements that have the proper lead spacing dimensions so that they will properly fit the PCB. Got to read those data sheets carefully. That was the hardest part of the search.I have replaced the original RIFAs with these X2 and Y2 line filtering capacitors.https://www.mouser.com/datasheet/2/440/e_WIMA_MP_3-X2-1139937.pdfhttps://www.mouser.com/datasheet/2/440/e_WIMA_MP_3-Y2_3R-Y2-1375650.pdfThese WIMAs are suitable replacements for the RIFA pyro-caps and they even have identical safety certification symbols as on the originals. Now I don’t have to worry about fireworks at power up.The original RIFA models also came up in the search, under the KEMET brand, look the same, and still appear to be sold, but no way would I consider using them. I guess KEMET believes that the RIFA reputation is not tarnished enough to make the slightest changes to the packaging of the infamous product.

author: dom0
author_rank: Super Contributor
timestamp: September 13, 2019, 01:15:43 pm
content: Quote from: Kinkless Tetrode on September 03, 2019, 11:18:06 amI don't think them being RIFA or not has much to do with their combustive abilities, since metal-paper capacitors from KEMET and others of similar vintage will also show cracks and thus the associated moisture ingress. I had some of these in my 3478A, for example.

author: Kinkless Tetrode
author_rank: Regular Contributor
timestamp: September 13, 2019, 04:03:54 pm
content: Quote from: dom0 on September 13, 2019, 01:15:43 pmYes, that is likely to be closer to reality. I think my seeing photos of the destruction that it can cause triggers an overreaction to RIFAs on my part. The fact that they are still being sold decades later shows that someone is still buying and using them.

author: wraper
author_rank: Unknown
timestamp: September 13, 2019, 04:14:57 pm
content: Quote from: dom0 on September 13, 2019, 01:15:43 pmIt has everything to do with Rifa. No other widely available cap cracks and explodes so often. 20 years old Rifa PME = guaranteed cracks. And KEMET literally is RIFA but newer (acquired in 2008), so you mentioning it just proves the point. If there are cracks they just did not have enough time or energy available to explode. Explosion usually happens when equipment was no powered for long time or it was powered from 230V after staying at 110V. Most likely being under voltage causes moisture to evaporate.

author: dom0
author_rank: Super Contributor
timestamp: September 14, 2019, 03:56:28 pm
content: Oh interesting, I didn't know KEMET and RIFA are literally the same. Personally I replace them with WIMA MP3-X/Y2 which look pretty much the same, or WIMA MKP-X/Y2 (which look exactly like regular WIMA foil caps), but I never really saw cracked cases on any WIMA capacitor ever. So I guess they are better after all.