PSU Caps

pixelphoto · 14th July 2012, 01:10 AM

There are two (2) large rectangular caps at the ac inlet. They are labeled as such; 0.1uF 250V~X2. What does the X2 mean? Yeah I know, stupid question, but I'm at least looking for a intelligent answer. What would I replace them with. Would a WIMA MPK 10 0.1uF 250V work?

PChi · 14th July 2012, 08:27 AM

It's a mains safety / fire hazard rating. X2 capacitors are designed to be connected across the AC mains (between Live and Neutral, not ground) and can survive voltage transients and must never cause a fire.
The WIMA MPK 10 0.1uF 250V will work (depending on mains peak voltage) but might fail with voltage transients and isn't guaranteed to never catch fire. I don’t know what the regulations are in the USA but UL is likely to mandate something similar.

marce · 14th July 2012, 08:56 AM

If you change them for a non X2 capacitor you wilol break probably all the electrical saftey regulations, UL especialy. Plus put people at risk of fire. In fact to replace them with non X2 capacitors would be an act of stupidity IMO, it is safety.

DF96 · 14th July 2012, 10:44 AM

250V~ means AC voltage rating. 250V means DC rating. You should use an X2 cap, as the others have said. Failing that, use a 1000V DC cap but I don't advise it. For continuous AC stress the DC rating needs to be considerably higher than the peak AC voltage.

So to answer your specific question, a WIMA MPK 10 0.1uF 250V would not work and a loud bang is the most likely outcome. Google will help you learn about X2 caps. One final question: why do you want to change the caps anyway? Are you attempting an 'upgrade'?

indianajo · 07:42 PM

Yeah, film caps don't fail often. Electrolytic caps are the ones that go in 10-20 years based on the calender. X2 caps are for sale at farnell.com (newark.com) and mouser.com. If a lightning strike took out yours, then buy some more of the same rating of whatever brand is in stock. The caps at the mains inlet aren't sonically significant anyway.
If you've ever had a PCAT power supply go out, they have two of them in every one. Lots of other useful devices at the input like MOS surge suppressors and anti static chokes, worth cutting up for the parts and an education in lightning control, too.
Wikipedia has a nice writeup on x2 and y1 etc caps. Older equipment had 1000 VAC caps in these positions, but different vendors have lied on their specs. Sleazeball CEO's that buy a good name and use it to sell trash can't lie for long to UL, they check every year or two.

Elvee · 14th July 2012, 07:58 PM

Quote:

Originally Posted by pixelphoto

There are two (2) large rectangular caps at the ac inlet. They are labeled as such; 0.1uF 250V~X2. What does the X2 mean? Yeah I know, stupid question, but I'm at least looking for a intelligent answer. What would I replace them with. Would a WIMA MPK 10 0.1uF 250V work?

X2 is a slightly relaxed version of X capacitors, which is sufficient to pass most certification tests, and is therefore almost universally used for economical and regulatory reasons.
If you want an upgrade (why???), the only solution is X1, the unadulterated version of across-the-line capacitors, but it might be difficult to source.

pixelphoto · 15th July 2012, 12:19 AM

Thank you all for your response and edification. Rest assured I have know intention of replacing the mentioned caps with those of lesser specs. My question was meant to bring forth your intelligent responses. And you did. So now I may safely replace the aging caps on some PSU boards. Including the X2 caps with X2 caps of same or higher specs.

Thanks much,
Marvin
(pixelphoto)

14th July 2012, 01:10 AM	#1
pixelphoto diyAudio Member Join Date: Jun 2010	PSU Caps There are two (2) large rectangular caps at the ac inlet. They are labeled as such; 0.1uF 250V~X2. What does the X2 mean? Yeah I know, stupid question, but I'm at least looking for a intelligent answer. What would I replace them with. Would a WIMA MPK 10 0.1uF 250V work?

14th July 2012, 07:37 PM	#5
indianajo diyAudio Member Join Date: Jan 2010 Location: Jeffersonville, Indiana USA	Yeah, film caps don't fail often. Electrolytic caps are the ones that go in 10-20 years based on the calender. X2 caps are for sale at farnell.com (newark.com) and mouser.com. If a lightning strike took out yours, then buy some more of the same rating of whatever brand is in stock. The caps at the mains inlet aren't sonically significant anyway. If you've ever had a PCAT power supply go out, they have two of them in every one. Lots of other useful devices at the input like MOS surge suppressors and anti static chokes, worth cutting up for the parts and an education in lightning control, too. Wikipedia has a nice writeup on x2 and y1 etc caps. Older equipment had 1000 VAC caps in these positions, but different vendors have lied on their specs. Sleazeball CEO's that buy a good name and use it to sell trash can't lie for long to UL, they check every year or two. __________________ Dynakit ST70, ST120, PAS2,Hammond H182(2 ea),H112,A100,10-82TC,Peavey CS800S,1.3K, SP2-XT's, T-300 HF Proj's, Steinway console, Herald RA88a mixer, Wurlitzer 4500, 4300 Last edited by indianajo; 14th July 2012 at 07:42 PM.

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14th July 2012, 08:27 AM	#2
PChi diyAudio Member Join Date: Jan 2012 Location: Staines, UK	It's a mains safety / fire hazard rating. X2 capacitors are designed to be connected across the AC mains (between Live and Neutral, not ground) and can survive voltage transients and must never cause a fire. The WIMA MPK 10 0.1uF 250V will work (depending on mains peak voltage) but might fail with voltage transients and isn't guaranteed to never catch fire. I don’t know what the regulations are in the USA but UL is likely to mandate something similar.

14th July 2012, 08:56 AM	#3
marce diyAudio Member Join Date: Jun 2007 Location: Blackburn, Lancs	If you change them for a non X2 capacitor you wilol break probably all the electrical saftey regulations, UL especialy. Plus put people at risk of fire. In fact to replace them with non X2 capacitors would be an act of stupidity IMO, it is safety.

14th July 2012, 10:44 AM	#4
DF96 diyAudio Member Join Date: May 2007	250V~ means AC voltage rating. 250V means DC rating. You should use an X2 cap, as the others have said. Failing that, use a 1000V DC cap but I don't advise it. For continuous AC stress the DC rating needs to be considerably higher than the peak AC voltage. So to answer your specific question, a WIMA MPK 10 0.1uF 250V would not work and a loud bang is the most likely outcome. Google will help you learn about X2 caps. One final question: why do you want to change the caps anyway? Are you attempting an 'upgrade'?

15th July 2012, 12:19 AM	#7
pixelphoto diyAudio Member Join Date: Jun 2010	Thank you all for your response and edification. Rest assured I have know intention of replacing the mentioned caps with those of lesser specs. My question was meant to bring forth your intelligent responses. And you did. So now I may safely replace the aging caps on some PSU boards. Including the X2 caps with X2 caps of same or higher specs. Thanks much, Marvin (pixelphoto)