Brian Glad someone else considers multiple faults - IMHO, lack of testing under such conditions can be a major failing in some internal evaluation programmes because managers say :- if it is not called up by the standard then don't do it because we can't afford it. OTOH, it is also possible that problems like these could occur due to issues relating to outsourcing of components and sub-assemblies to third parties where you have relatively poor control of the components used and the way they are assembled. That, together with the continual pressure on suppliers to reduce costs, could lead to "cost reductions" and the use of components which will last the warrantee period and not much longer. This is a known problem in consumer electronics units like TV's and satellite receivers, where the capacitors in PSUs often have insufficient temperature specs - some product ranges and reknowned for it and one of the biggest sellers in the satellite receiver business are PSU repair kits with higher rated capacitors!. When they fail in those items then the results are normally benign because there is relatively more space around the components and the chassis are often partially or totally metal for screening reasons. However, in the laptop market, the PSU's and battery compartments are much smaller and less well ventilated and cooled - and the units are often used in less than favourable locations and of which the test conditions in some standards are not representative. BTW: one of the reasons that some laptop batteries - particularly the older NiCads - can explode is because the cells "gas" and produce hydrogen which is then ejected from each cell via the safety vent. If this gas builds up, and there is some sort of spark then there can be an explosion. The effect gets more pronounced as the cells get older - one major manufacturer (which I obviously cannot name!) firstly told my then-mployer that hydrogen release would never occur, and then some years later admitted that 50% of cells gas during their lifetimes. This was after we had a sealed multicelled 24V battery explode when being used because the battery designers had not taken extra precautions to prevent sparks inside the casing because they had been assured that there was no possibility of the hydrogen building up! It was also notable that the battery casing itself had a pressure operated safety vent, but the hydrogen pressure was apparently not sufficient to open it and release the gas! Murphy strikes again John Allen ERA Technology Ltd.
From: Brian O'Connell [mailto:[email protected]] Sent: 03 September 2004 15:22 To: [email protected] Subject: tests beyond PS Std requirements Good People I am in the process of re-writing Type Test procedure and test condition requirements for the company's compliance lab. My principle objective is to not only represent the intent of the applicable safety standard, but to formalize multiple fault tests; that I currently perform, but are never included in the TCF or CB report, and are thus part of "engineering notes." Some inspiration is from stupid stuff like this: http://www.theregister.co.uk/2003/01/17/dell_laptop_named_in_sa/ http://www.theregister.co.uk/2004/09/03/ibm_recalls_adapaters/ http://www.theregister.co.uk/2001/10/05/compaq_recalls_fiery_laptop_adapters/ Other inspiration comes from talking to customers and performing RMA analysis of abused units. While I have a decent understanding of the basic performance and construction requirements required by safety standards, I am not certain that some of my multiple fault test conditions are not (somewhat) contrived. Any ideas that are derived from "real-world" experience? Another (stupid) question: How did these units, mentioned in the above URLs, ever pass the most basic abnormal/SFC Type Tests in 950 or 65-based standards? Thanks much in advance. luck, Brian _____________________________________________________________________ This e-mail has been scanned for viruses by MCI's Internet Managed Scanning Services - powered by MessageLabs. For further information visit http://www.mci.com ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/listserv/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Ron Pickard: [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: http://www.ieeecommunities.org/emc-pstc ********************************************************************** Copyright ERA Technology Ltd. 2004. (www.era.co.uk). All rights reserved. The information supplied in this Commercial Communication should be treated in confidence. No liability whatsoever is accepted for any loss or damage suffered as a result of accessing this message or any attachments. ********************************************************************** _____________________________________________________________________ This e-mail has been scanned for viruses by MCI's Internet Managed Scanning Services - powered by MessageLabs. For further information visit http://www.mci.com ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/listserv/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Ron Pickard: [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: http://www.ieeecommunities.org/emc-pstc
