Rifa capacitors again - Page 1
Forum section: electronics / general

author: TimFox
author_rank: Super Contributor
timestamp: February 06, 2022, 05:43:17 pm
content: There have been many posts here about Rifa safety capacitors (usually class X, I believe) that have failed in commercial equipment, either discrete components or included in mains-input line filter modules.I own some test equipment from the era in question (such as -hp-), but have yet to suffer this problem (knock on wood).In the US, of course, my capacitors have been exposed to only 120 V, but the equipment is designed to apply either 120 or 240 V to the components in question, depending on country.Obviously, the stress on an individual capacitor is worse at 240 V than at 120 V.In the actual experience of the members here, is this problem much more prevalent in 240 V countries?

author: mawyatt
author_rank: Super Contributor
timestamp: February 06, 2022, 05:48:26 pm
content: For US use (120VAC), had one explode in a 2400 series Tek scope. Also noted the other Rifa caps in old HP and Tek equipment are cracked, mostly the larger values.Best

author: andy2000
author_rank: Frequent Contributor
timestamp: February 06, 2022, 09:05:12 pm
content: I've had two go off on me, just after powering on a long disused piece of equipment.I always replace them when I see them, but I have a lot of equipment that probably still has them since I haven't checked everything I own. I've never had one fail in something that's used regularly. It's possible that frequent use helps prevent them from absorbing moisture.

author: m k
author_rank: Super Contributor
timestamp: February 07, 2022, 09:39:19 am
content: Don't know about Rifa or Class-X but impression of Class-Y was that they are leaking.(from 240V and 90's computer stuff)Maybe Class-X stuff were better or local approval was tighter.

author: jonpaul
author_rank: Super Contributor
timestamp: February 07, 2022, 12:17:31 pm
content: Class Y are designed for CM noisette surpression, a maximum leaking current within safety limit at 240V usually 2200 or 4700 pF. Never seen one fail, low stress.The X caps are 470 nf, line to line have a continous AC current. They are the failure proneMany other 1970s stacked or wrapped foil caps have such issues.The Schaeffer EMI line filters and filtered IEC receptacles contain those caps.Jon

author: m k
author_rank: Super Contributor
timestamp: February 07, 2022, 07:23:19 pm
content: Failing Hi-Pot test was the cause of impression, usually passed with lower test voltage.Back then accepted devices still had those round FI stickers, that I can't find from google.(CE covers it now)Filtered IEC was also many times a bit different from what google shows now.Maybe I had wrong words since no lumps in heat-shrink tubes where present.It was time when far east stated filling homes with computers and local electrical safety certification was leaving behind.

author: thm_w
author_rank: Super Contributor
timestamp: February 07, 2022, 10:02:17 pm
content: They fail just sitting on the shelf:https://old.reddit.com/r/TheAmpHour/comments/s4vbbg/4yo_rifa_caps_cracking/

author: m k
author_rank: Super Contributor
timestamp: February 09, 2022, 11:24:24 am
content: (just in case)I'm not proposing that Rifa is a good catch.

author: Vovk_Z
author_rank: Super Contributor
timestamp: February 13, 2022, 04:35:42 am
content: I have Tec 2465 bought from the USA. It was bought about 10 years ago. I have to say that it worked fine several years here in Ukraine, and only then later started to show noise on a screen, so I had to take it apart and have a look. X2 Rifa caps were all cracked in a power supply, so I had to replace them all. I can only guess how damaged they were when it arrived here.

author: David Hess
author_rank: Super Contributor
timestamp: February 16, 2022, 02:51:59 am
content: Quote from: TimFox on February 06, 2022, 05:43:17 pmThey will destructively fail sooner at higher voltage.

author: mawyatt
author_rank: Super Contributor
timestamp: February 16, 2022, 03:47:06 am
content: Quote from: Vovk_Z on February 13, 2022, 04:35:42 amConsider changing all the electrolytic caps in the power supply. These are noted to fail, we had a few that were leaking in our two 2465 scopes, and most of the removed caps were undervalued.Best,

author: TerraHertz
author_rank: Super Contributor
timestamp: February 17, 2022, 07:47:25 am
content: Quote from: TimFox on February 06, 2022, 05:43:17 pmWell how would anyone know? Individuals experience failure rates in either 120V or 240V countries where they live, so lacking any kind of statistical comparison study, who knows.All I can say is that pretty much every time I import some bit of gear from USA, that has always run on 120V, and I switch it to 240V in Australia then power it on without first replacing all the RIFA mains caps, there will be a stinky explosion very soon. And this still happens because sometimes they are hidden inside metal can mains EMI filters.