Ken, Even though they may have a DC rating that exceeds the AC Peak of the line. There are more factors.
Line rated caps also have surge ratings, typically in the kV range. Derek mentioned the X an Y series and surge is one of the main attributes of this type. I once had an RF engineer conceive the idea of putting the generator's RF returns on the rectified DC bus. He used 1000 V mica caps of about 2200 pF. They did not survive the required IEC surge tests. If the caps you propose are for connection between mains and earth, they must carry an appropriate certification. There are some rugged component tests that certified caps must pass and many standard types are not adequate. There is a reason why line rated caps tend to be physically larger. Finally, from a purely engineering standpoint, a few caps are not AC rated because they have a high dissipation factor and may actually overheat. Doug Douglas E Powell Independent Compliance Consultant http://www.linkedin.com/in/dougp01 http://www.linkedin.com/in/dougp01 -----Original Message----- From: Derek Walton <[email protected]> Date: Fri, 31 Aug 2012 22:06:23 To: <[email protected]> Reply-To: Derek Walton <[email protected]> Subject: Re: [PSES] Capacitor rating for mains useage HI Ken, you don't say how small and it's relative you know :-) Any cap I suggest for across the line use I strongly recommend it has an X rating, a Y rating if it goes between power and earth. Is this what you were meaning? Cheers, Derek. -----Original Message----- From: Ken Javor <[email protected]> To: [email protected] <[email protected]> Sent: Fri, Aug 31, 2012 5:58 pm Subject: Capacitor rating for mains useage Forum members, Am trying to spec out some small value capacitors to be placed across unrectified mains potentials. These caps are rated at dc potentials way beyond the peak of the ac bus potential, but they carry no ac rating. What are the issues here? The cap should not breakdown at ac mains potential, so what information does an ac rating provide? Is it related to surge potentials that can appear on ac mains? Thank you and happy Labor Day to those members are the west side of the Pond. Ken Javor Phone: (256) 650-5261 - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]> - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]> - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]>
