Hi Brian, Is the furnace type common to all the failed pieces of equipment? If not common, similar?
Reading on with interest James -----Original Message----- From: Kunde, Brian [mailto:[email protected]] Sent: 17 September 2015 14:37 To: [email protected] Subject: Re: [PSES] Unexplained High Fallout of Power Supplies Bob and all. Good question. Before I answer your questions, let me describe the typical architecture of the products that we make. Our instruments (laboratory equipment) are single phase 230VAC 50/60hz which powers two separate internal circuits; one being a relatively low current electronics powered by a purchased over-the-shelf 24Vdc power supply, and second, a high current furnace of some type; inductive, electrode, resistive heating elements, etc.. Because of the high overall current of the instruments, typically between 30A and 50A, the instrument is plugged into a high current branch circuit with a huge high current line filter. Internally, we usually have a smaller supplementary over-current protector (5, 10 or 15 amp) driving the lower current non-furnace electronics such as the dc power supply, cooling fans and blowers, etc.. The issues we are having are with these purchased power supplies blowing up. And because we pre-test power supplies and our finished products so extensively and we are not able to cause a power supply failure with the same damage pattern as we are seeing in the field, we believe that in the real world our products are seeing some kind of condition that we are not able to simulate in our EMC Lab. Identifying and understanding such conditions is our goal at this time. We use no additional inrush limiting other that what is built into the power supplies themselves. Other than a thermistor of some kind, how can the inrush be limited? We have also seen on several occasions in the field where a power supply will blow up in one instrument which causes the power supply in a nearby instrument to also fail. Two weeks ago we had an "event" occur right here at our own campus in our Application Lab where 40-50 instruments of different models and ages are being used daily to develop test methods. An instrument was power on but was not running an analysis (high current furnace wasn't running in what we call Standby-mode). BAM!! The 24Vdc power supply blew up. We sent two R&D engineers who have been working on our fallout problem in the field to investigate. They found the power supply had failed in the same way as those in the field. No other failed component in the instrument was found. The power supply was replaced and the instrument was once again functional. AS THE Engineers turned to walk back to their office, BAM!! The power supply blew up in the instrument installed NEXT to the one they just repaired. This second instrument is a different model with a different manufacturer of power supply. An AC Power Line monitor/analyzer was installed on the AC Mains circuit and has been c! hecked every morning since. No unusual transients or power dropouts have been detected. This lab area has surge protection, so again, we believe the problem is some kind of low voltage transient, voltage dropout, or waveform distortion that we have been unable to detect and simulate. Thanks to all. The Other Brian -----Original Message----- From: Bob LaFrance [mailto:[email protected]] Sent: Thursday, September 17, 2015 8:46 AM To: [email protected] Subject: Re: [PSES] Unexplained High Fallout of Power Supplies I am curious to what you are using for inrush limiting. Sorry if you already told us but I missed that. Regards, Bob LaFrance N9NEO Design Engineer Creare Inc. 16 Great Hollow Road Hanover, NH 603-640-2539 -----Original Message----- From: CR [mailto:[email protected]] Sent: Wednesday, September 16, 2015 2:56 PM To: [email protected] Subject: Re: [PSES] Unexplained High Fallout of Power Supplies On 9/15/2015 4:53 PM, Kunde, Brian wrote: > 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. Brian, The circumstances you describe -- arcing with no external transient seen -- point to an on-board occurrence, not an external one. I'd suspect (in no particular order and on little information -- heh) ) PWB material with insufficient dielectric withstand, and/or oscillation in a power FET due to its characteristics (or another device's) having changed enough to make the control loop unstable. You might have an oscillator the controller can't even detect. I'm on LinkedIn if you need help, eh? Cortland Richmond - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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Thank you. - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> 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 <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]> - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> 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 <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]>
