Class X2, Class Y Capacitors, and Snubber Networks

[Julesomega]

In a previous thread Which (UK) Class ? we were given a useful account of when and where to use Class X2, Class Y Capacitors, and Snubber Networks, but it seems a bit of a challenge to find where to buy the things. I've spent an hour trying to find a replacement for a Rifa X2 100nF which popped in a 70s stereo receiver, where it was wired across the primary of the mains tfmr using the full length of its axial leads. Unfortunately I started my search with CPC who have next to nothing. RS have a good range, but these components are not cheap and are on a long lead time so I ended up buying on eBay, where also there is next to nothing.

CPC only have two "class x2 suppression capacitors" which are in fact Rifa snubbers, 47nF with either 47 or 100 Ohms. They have 3 Vishay ceramic Class Y caps in 1, 2.2, or 4.7nF

RS have X2 Class from Kemet and Vishay:

KEMET PME271 series paper 250V ac with long leads: (1nF, 1.5nF, 2.2nF, 3.3nF, 33nF), 47nF stock No. 210-617 @ £1.80 ea in packs of 5, and most usefully 100nF stock No. 311-1074 @ £4.09 ea in packs of 5

Vishay F1772S series Polyester 310V ac are much cheaper but for long leads RS have only: 68nF stock No. 874-0793 @ £0.78 ea in packs of 10, and 470nF stock No. 874-0816 £2.05 ea in packs of 5

For Snubbers they have two "RC Network Capacitors". One is "RC Capacitor 100nF 120? Tolerance ±20% 250V ac" Stock No.672-7032 £2.48 ea "Our best size/performance series". The other is "XEB Surge Suppressor Unit 250 V Mains Protector" Stock No.672-7035, £3.90 ea - if you look at the datasheet you find it is 100nF + 120 Ohms, "Our best performance series"

They also have Class Y series from both mfrs.

I'd like to know what values are most useful for transient suppression at switch-on or switch-off?

I hope this may be of use to others who need to replace these capacitor types.

You can pull used axial X2 types from almost any scrap consumer unit with a switch-mode power supply, but these are invariably fitted on a PCB and the leads cropped off, making them useful only as replacements on SMPS, once you have checked that they haven't lost any of their capacitance.

[stevehertz]

Cricklewood do them for 25p. Ok, it's best to buy a bit of stuff while you're on as it will offset the postage cost.

https://www.cricklewoodelectronics.c...apacitors.html

[Philips210]

CPC have these https://cpc.farnell.com/epcos/b32922...vac/dp/CA07116 and also a Class X1 (440Vac) cap https://cpc.farnell.com/vishay/bfc23...40v/dp/CA06016

Regards,
Symon

[Philips210]

Re CPC stock. There seems to be a problem with their search engine and quite often gives few results when infact there are others available.

If you do a global search for say 100nF X2 or 0.1uF X2 it only returns the four from Rifa. Doing a local search within Capacitors returns more possibilities. As well as those I linked in post #3, there are also these: https://cpc.farnell.com/vishay/bfc23...?st=0.1uF%20x2 and these: https://cpc.farnell.com/vishay/bfc23...?st=0.1uF%20x2

Regards,
Symon

[Maarten]

RIFA PME series should be avoided as the paper plague. Just use MKT or MKP X and Y types.

[Julesomega]

Maarten - I only want 20 years operation Won't a RIFA PME last that long?

Thanks for all the recommendations, but they are all for through-hole PCB mounting and won't reach across transformer terminals. Reichelt have a PHE820 type that might stretch. Maybe the PHE820 series is more reliable.

I'm still puzzled about the range of values on offer: my failed item uses, like the DAC90 about 20 years earlier, 100nF, so why are we seeing values like 1nF and 4.7µF? Maybe large SMPS use that sort of value.

I had been assuming that KEMET was a brand, but it looks more like a technology.

[factory]

Kemet (now part of Yageo) took over RIFA madness, not all of them are the bad types, the ones to avoid with metallized paper dielectric start with "PM" & "PZ", these crack & adsorb moisture, then burn up. We also had some go open circuit a few years ago at work, they were only 5 years old at the time.

The sooner Yageo/Kemet discontinue these the better, which is probably unlikely if people keep buying this rubbish, unfortunately Kemet even make a surface mount version starting with "SMP", there may be others in this new series to avoid.



Also avoid Wima starting with "MP" these are also paper.

I've used ceramic X/Y types, where I couldn't find plastic dielectric types with long leads, Murata & Vishay have ceramics with long leads.

David

[Maarten]

Also, leads can be extended.

Originally Posted by Julesomega

Maarten - I only want 20 years operation Won't a RIFA PME last that long?

They might, they might not. It depends on the storage before use, the use itself (continuous use in a climate controlled dry environment is likely best, mechanical stress under intermittent use in a damp environment worst), maybe even the phase of the moon when they were manufactured... Who knows... It's just outdated rubbish, when they were "current" they were mediocre at best but had good marketing. One of the selling points was they don't cause fires, yet they do. They already did back in the 1980s when Philips banned them from their V2000 recorders.

Thanks for all the recommendations, but they are all for through-hole PCB mounting and won't reach across transformer terminals. Reichelt have a PHE820 type that might stretch. Maybe the PHE820 series is more reliable.

[...]

I had been assuming that KEMET was a brand, but it looks more like a technology.

Kemet is a brand, that inherited and kept making some extremely questionable product lines. Any PHE series is better because it uses polyester instead of paper as a dielectric, though at this point why even do business with them....

[Refugee]

Originally Posted by Maarten

They already did back in the 1980s when Philips banned them from their V2000 recorders.

My guess would be that they cause too much goo all over the tape path if they blow.

[TonyDuell]

I bought a Philips VR2220 portable V2000 recorder along with the companion VR2120 tuner unit last year. The latter certainly contans a RIFA metalised-paper 'smokebomb' capacitor which I will replace before applying mains.

But as the tuner/PSU is a separate unit, I guess it wouldn't do much damage to the tape path if it failed.

[stevehertz]

Originally Posted by Julesomega

Thanks for all the recommendations, but they are all for through-hole PCB mounting and won't reach across transformer terminals. .

Just extend the leads and if the joint offends you, just cover it with sleeving. Job done, 25p from Cricklewood.

[Maarten]

Originally Posted by Refugee

My guess would be that they cause too much goo all over the tape path if they blow.

They're in some kind of enclosre by the mains entry, I think. It was mentioned to me that the modification bulletin explicitly mentioned fire hazard, but I haven't seen the bulletin in person. Keep in mind this was within a year or 4 since they started using them in videorecorders, possibly less. To be fair, some factories, I think mainly Norrköping but possibly Krefeld, had already used them in TV sets for some years as well so maybe that played a role into the decision to stop using them. Last year, Marcel from marcelstvmuseum had a 1977 K11 set go up in flames, traceable to this type of capacitor.

Originally Posted by TonyDuell

I bought a Philips VR2220 portable V2000 recorder along with the companion VR2120 tuner unit last year. The latter certainly contans a RIFA metalised-paper 'smokebomb' capacitor which I will replace before applying mains.

But as the tuner/PSU is a separate unit, I guess it wouldn't do much damage to the tape path if it failed.

Those tuner units started production around the 3rd quarter of 1982 so it would make sense that at least some of them would contain a RIFA. They were exclusively made in Krefeld, so that might confirm my memory that TV sets from Krefeld also used a RIFA as mains suppressor.

Also, in those days the plastic cases might not have been very flame retardent (think of the K40 TV sets) so continuing to mount a capacitor that could possibly burn up, must have been a big no-no.

[Julesomega]

Originally Posted by stevehertz

Just extend the leads and if the joint offends you, just cover it with sleeving. Job done, 25p from Cricklewood.

Agreed; I have added a pack (AKA a lifetime's supply) of the 310V X2 type suggested by Symon to my latest order from CPC