As mentioned by some colleagues in this forum, some thermal effects due to altitude are caused by reduced air density, which decreases the heath dissipation through convection. The percentage of heath dissipation by convection depends of the construction of each power supply (I don't believe most of the manufacturers are able to provide a number there). For terrestrial application, the convection being the dominant path, anything above 50% can be a good guess. By determining the density of the air at a given altitude versus "normal operating level" it can be determined the impact on convection, and ultimately the derating of the PS. To be noted that: forced air, or natural convection cooling processes are not affected the same way; PS' working in uncontrolled environments at high altitude can be affected by low ambient temperatures. And as a final note, sometimes the experiment is the fastest, easiest way.
Alexandru Guidea CAE Inc. Canada (my opinion and only mine) -----Original Message----- From: Carmen.Filimon [mailto:carmen.fili...@leitch.com] Sent: Friday, January 04, 2002 11:28 AM To: EMC Forum Subject: SMPS Derating reqs for Altitude range of 5000-10000ft 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. ------------------------------------------- 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.
