Hi Brian, Pat offers some great advice with respect to filter stability and resulting ringing. This is not something normally tested using a transient generator, so should be examined.
I’d also like to add an observation. During the time I worked for HP/Agilent in their scopes division, we also started noticing in the late-1990s that power supplies had become the #1 field failure. We pretty much determined (maybe more of a guess at that point) that due to the variety of failures across different products and vendors, that it was most likely a reliability issue, rather than due strictly to over stress. In fact, in the mid-1970s, the NAVY had come to the same conclusion and had instituted similar reliability research on power supplies. Our environmental test engineer, Brian Dahl (the “other other Brian”), who was also an expert (a black belt) in reliability, instituted two major changes in our power supply vendor selection process: 1. HALT testing of all power supplies (as well as whole products) 2. Life Testing of all power supplies For those unfamiliar, HALT (highly accelerated life testing) is a combination of very fast changing temperature extremes (high to low and visa versa in 1-2 minutes) in combination with three-axis vibration. He would run HALT on samples of power supplies prior to our selecting a final vendor. Those supplies that passed the HALT were then subjected to long term life testing in a large walk-in temperature chamber. He’d take a sample of 10 to 20 power supplies from each potential vendor, place them under full resistive loads and cycle the temperature every 5 to 10 minutes for 1 to 2 months. After starting this program, field failures of power supplies dropped almost off the list. Here are some references that might be helpful: http://www.cui.com/catalog/resource/reliability-considerations <http://www.cui.com/catalog/resource/reliability-considerations> http://www.astrodynetdi.com/pdf/MTBF_and_Power_Supply_Reliability.pdf <http://www.astrodynetdi.com/pdf/MTBF_and_Power_Supply_Reliability.pdf> http://www.sre.org/pubs/Mil-Hdbk-338B.pdf <http://www.sre.org/pubs/Mil-Hdbk-338B.pdf> http://snebulos.mit.edu/projects/reference/MIL-STD/MIL-HDBK-217F-Notice2.pdf <http://snebulos.mit.edu/projects/reference/MIL-STD/MIL-HDBK-217F-Notice2.pdf> I might add that Brian was a nominee for EDN's “Test Engineer of the Year” back then. If anyone would like to pick his brain, he may be reached at brian_d...@keysight.com <mailto:brian_d...@keysight.com>. I’m copying him on this email. Cheers, Ken _______________________ I'm here to help you succeed! Feel free to call or email with any questions related to EMC or EMI troubleshooting - at no obligation. I'm always happy to help! Kenneth Wyatt Wyatt Technical Services LLC 56 Aspen Dr. Woodland Park, CO 80863 Phone: (719) 310-5418 Email Me! <mailto:k...@emc-seminars.com> | Web Site <http://www.emc-seminars.com/> | Blog <http://design-4-emc.com/> The EMC Blog (EDN) <http://www.edn.com/blog/The-EMC-Blog> Subscribe to Newsletter <http://www.emc-seminars.com/Newsletter/Newsletter.html> Connect with me on LinkedIn <http://www.linkedin.com/in/kennethwyatt> > On Sep 16, 2015, at 6:50 AM, Pat Lawler <plawl...@gmail.com> wrote: > > Hi Brian, > > - Have there been changes to the design of your system, specifically > the AC EMI filter? Increased inductor values, either by design or > vendor change (filter manufacturer, or type of core used in the > filter) could cause excessive ringing at the input of the power supply > at turn-on. > - Try putting high-voltage scope probes at the input of the power > supply to see the common and differential mode voltage at turn-on, or > during line surge testing at 200V levels. I had one case where the > filter caused ringing to 2x the applied voltage! > - Is your equipment installed differently now, either by installation > or removal of isolation transformers or grounding changes? > > I once had a customer claim that our power supplies no longer met the > IEC 61000-4-5 line surge requirement, and the equipment was resetting. > After many heated conference calls, they admitted the equipment was > actually a redesign, with the addition of a Wi-Fi module. Not knowing > what else to try, I asked if they disconnected the Wi-Fi module, > returning the system to it's previous design configuration. > It turns out the noise from the line surge test was being picked up by > the Wi-Fi module and getting conducted into the rest of the system. > > Pat > > On Tue, Sep 15, 2015 at 1:53 PM, Kunde, Brian <brian_ku...@lecotc.com> wrote: >> Our company’s Service Department provides monthly field repair reports to >> our R&D department who looks for patterns and high fallout of components. >> Over the last 6 to 12 months, we have noticed a high fallout of Power >> Supplies in the United States. However, we have not been able to find the >> reason for the fallout. The power supplies have all shown arc damage to the >> AC front end, signs of arcing and traces burned or vaporized, blown fuses, >> and shorted FETs and/or Rectifiers. These failures have occurred on several >> different locations, on different power supply models, different >> manufactures and on different instruments. Some instruments have been in >> service for years; some for only a few weeks before they fail. Some >> instruments even have surge suppression modules installed and though the >> power supplies fail the surge modules tested out fine. The failures did not >> occur during any known lightning storm or any other known transient. Very >> strange. >> >> >> >> Of those of you who read these emails, have you experienced an unusual >> increase in such field failures in the last year? >> >> >> >> Anyone have an idea of what might be causing this increase? >> >> >> >> We test our products and power supplies to the IEC 61000-4-4 and 4-5 fast >> transient and surge immunity tests. We actually test beyond what is required >> for CE in Europe (often to the limit of our test equipment which is 5kV) and >> we audit every family of products about once a year. We have performed >> additional testing of production power supplies of known models that have >> failed in the field yet no unusual problems have been found. We also >> perform radiated and conducted RF immunity tests, ESD, voltage dips and >> dropouts, frequency variation testing, and harmonic and inter-harmonic >> immunity tests with no discernable problems found. >> >> >> >> We have AC Line Analyzers running for months at several customer locations >> and have not detected any unusual transients or reason for the high fallout >> of power supplies. >> >> >> >> Two weeks ago we had a power supply blow in one of our own labs on an >> instrument that had been running for several years. Two R&D engineers were >> sent over to investigate. They changed out the power supply and verified the >> instrument was running properly. As they turned to walk out of the room, >> POW!!, the power supply in the instrument next to the one they just fixed >> blew up. A power line analyzer has been running ever since but not unusual >> transients have been detected, yet. >> >> >> >> Are we missing something? Is there additional transient tests that we are >> not performing that we should be? Is there something we should be looking >> for and are not? Has this last year been unusually bad for power grid >> problems, sun spots, alien transmissions, ?? >> >> >> >> We are stumped. Thanks for any advice and comments. >> >> >> >> The Other Brian >> >> >> >> >> >> >> >> ________________________________ >> >> LECO Corporation Notice: This communication may contain confidential >> information intended for the named recipient(s) only. If you received this >> by mistake, please destroy it and notify us of the error. Thank you. >> >> - >> ---------------------------------------------------------------- >> >> This message is from the IEEE Product Safety Engineering Society emc-pstc >> discussion list. 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To post a message to the list, send your e-mail to <emc-p...@ieee.org> 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://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <sdoug...@ieee.org> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher: <j.bac...@ieee.org> David Heald: <dhe...@gmail.com>
