I read in !emc-pstc that Chris Maxwell <[email protected]> wrote (in <[email protected]>) about 'Safety: Temperature Rise and Capacitor Clearance (EN 60950)', on Wed, 30 Jan 2002: > >I have a couple of questions regarding this standard: (I have the 1992 >version) > >First > >Table 16 specifies maximum temperature RISE for components, surfaces,... >What are the assumptions here? Are they assuming an ambient of room >temperature (25 deg C)? Which would mean that a rubber handle could >become as warm as 25 deg C + 50 deg C which is 85 deg C? This seems >high to me.
See 1.4.7 of your *out of date* edition. It's pretty hot but the thermal conductivity is low, so a burn is unlikely. > >This would be even worse under high temperature ambients. For instance, >our products are typically specified to operate in ambients up to 45 deg >C. In this ambient temperature, Table 16 would appear to allow an >absolute temperature of 45 deg C + 50 deg C for an absolute temperature >of 95 deg C!!!!! This seems high to me. Any thoughts? 1.4.7 indicates that you are expected to reduce the rise in such a case. > >Second > >I am planning on using high voltage hold-up capacitors in a high voltage >bus application (200VDC). The capacitors are aluminum electrolytic, >radial leaded, PCB mount with a safety vent. Nichicon The capacitors >will be the tallest components on a PCB within a metal chassis. The >metal cover going over them will be grounded. Do I need to leave a >clearance distance over the top of these capacitors for the safety vent >to operate? Do I need to leave a clearance between their top and the >grounded cover for dielectric withstand reasons? If the grounded cover >is within a few thousandths of an inch of the capacitor tops, do I need >to put some kind of mylar sheet in between insulate it from the >capacitors? (assuming that the cover could be bent to touch the >capacitors.) > Well, which way up are the caps? If you put the earthy end at the top, you don't have an electrical problem. BUT you do have a mechanical problem, not regarding safety but reliability. That cover WILL be pushed in to crush the caps. You need either more clearance or a pillar taller than the caps to prevent the lid caving in. THEN you need the Mylar, even if only to avoid spurious intermittent grounding. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk After swimming across the Hellespont, I felt like a Hero. PLEASE do NOT copy news posts to me by E-MAIL! ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson: [email protected] Dave Heald [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
