I agree that creepage and clearance distances change. However, I'm not sure if you can answer that it is not a power issue. If the power supply depends on air for cooling; wouldn't the less dense air at higher altitudes be less effective at cooling the supply?
A rough guess (admittedly thought up as I'm typing this message) would be that the cooling effectiveness of air would vary proportionally with air density. A furthur stretch of that reasoning would lead me to believe that the power ratings of forced air cooled supplies would also vary with air density. It may not vary with one to one correspondence due to the fact that there are other cooling mechanisms such as radiative cooling which can occur without air. As altidude goes up, air density goes down. Wouldn't cooling effectiveness also go down leading to a slightly lower power rating for air cooled supplies? Chris Maxwell | Design Engineer - Optical Division email chris.maxw...@nettest.com | dir +1 315 266 5128 | fax +1 315 797 8024 NetTest | 6 Rhoads Drive, Utica, NY 13502 | USA web www.nettest.com | tel +1 315 797 4449 | > -----Original Message----- > From: Andrew Carson [SMTP:acar...@uk.xyratex.com] > Sent: Friday, January 04, 2002 12:59 PM > To: Carmen.Filimon > Cc: EMC Forum > Subject: Re: SMPS Derating reqs for Altitude range of > 5000-10000ft > > > Carmen > > If your power supply is approved to IEC60950, then normally it will be > approved upto 2000m. Above this altitude the > required creepage and clearance distances start to increase. It is an > electrical insulation issue, not a thermal > issue. > > "Carmen.Filimon" wrote: > > > Hi All > > > > I'm trying to find out what the specified operational > altitude > > range(s) is (are) for power supplies (particularly switching mode > ones). Do > > any of you know what that spec may be, and particularly what is the > rule for > > derating at altitude for thermal issues. Many manufacturers don't > specify a > > maximum altitude but instead design in enough thermal overhead to > > accommodate any reasonable terrestrial location. > > According to GR-63-CORE the operating range without derating is > 1800m above > > sea level. If derating is required above 1800m > > then the manufacturer must specify any additional requirements. Is > it a > > safety derating factor so that customers at 5000-10000ft don't smell > smoke? > > Do we have any recommendations for derating the operational > temperature / > > power consumption of power supplies as the operational altitude > increases? > > > > Any information or ideas you have would be appreciated. > > > > Regards, > > > > Carmen Filimon > > Leitch Canada > > > > > > > > > > ------------------------------------------- > > 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: > > majord...@ieee.org > > with the single line: > > unsubscribe emc-pstc > > > > For help, send mail to the list administrators: > > Michael Garretson: pstc_ad...@garretson.org > > Dave Heald davehe...@mediaone.net > > > > For policy questions, send mail to: > > Richard Nute: ri...@ieee.org > > Jim Bacher: j.bac...@ieee.org > > > > 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. > > -- > > Andrew Carson - Senior Compliance Engineer, Xyratex, UK > Phone: +44 (0)23 9249 6855 Fax: +44 (0)23 9249 6014 > > > > ------------------------------------------- > 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: > majord...@ieee.org > with the single line: > unsubscribe emc-pstc > > For help, send mail to the list administrators: > Michael Garretson: pstc_ad...@garretson.org > Dave Heald davehe...@mediaone.net > > For policy questions, send mail to: > Richard Nute: ri...@ieee.org > Jim Bacher: j.bac...@ieee.org > > 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. ------------------------------------------- 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson: pstc_ad...@garretson.org Dave Heald davehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org 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.
