Hi Glenn, Appreciate your response. but, I believe you raised two separate and equally valid points.
1. Insulation breakdown. 2. Some other safety hazard caused by heat. Understand your primary concern well. As far as the secondary point, the two of them fought it out and one had it one way, and the other had it another. I believe one of them (CSA) had some trouble with a product whereby a transformer had come loose. Not sure of the specifics of that situation, but I believe that was his resolution for it. Doug ---------- > From: Lesmeister, Glenn <[email protected]> > To: '[email protected]'; 'IEEE Product Safety Technical Committee -' <[email protected]> > Subject: RE: EN 60950 and component heating > Date: Wednesday, September 17, 1997 4:27 PM > > Doug, > > To answer your question of which is better: > > The primary concern should have been the temperature of the windings > to see if the insulation (between primary and secondary?) would have > exceeded the allowable limits and thus possibly break down. > > A (much lesser) secondary concern would have been the risk of a fire > starting either in the transformer or in other components due to the > heating of the transformer. > > Glenn Lesmeister > > > -----Original Message----- > From: [email protected] > [SMTP:[email protected]] > Sent: Tuesday, September 16, 1997 5:35 PM > To: IEEE Product Safety Technical Committee - > Subject: Re: EN 60950 and component heating > > Hi Kevin, > > I had a rather bad experience between UL and CSA in > the older days when there wasn't so much discussion > and agreement between them. I had set up an MOU > between them with UL as the test location. > > Went like this ... > > Switching power supply. Has a transformer. > Must do abnormals on it. UL does the abnormals. > Temp probe on the *windings* of the transformer. > > CSA said, "No way. Since the real concern is > the PCB flaming from over temps > from the transformer, we want the > probes on the *bobbin*." > > UL said, "No way. Since the real concern is > what generates the heat, we want the > the probes on the *windings*." > > To this day, I can't say absolutely which way > is the better. > > Guess I didn't help you much either. > > Regards, Doug > > > > From: Kevin Harris <[email protected]> > > To: EMC-PSTC (E-mail) <[email protected]> > > Subject: EN 60950 and component heating > > Date: Monday, September 15, 1997 6:14 PM > > > > Hello All, > > > > In testing some product for excessive temperatures I have come up > > against the following problem. Consider a diode (part of a bridge > > rectifier circuit) and the PCB underneath the component. If one > measures > > the temperature of the diode it does not come close to the > specification > > for the part. However if we place a thermocouple on the pad where > the > > diode is attached to the PCB and we consider that as a temperature > > measurement for the PCB material itself ,then the temperature > obtained > > is above the board manufacturers spec of 110 C (when we take into > > account our maximum permissible ambient temperature of 49 C). By > the by > > all this is NOT operator accessible if that makes any difference. > > > > Questions. > > > > 1. Is this a valid temperature measurement for the PCB? I'm of two > minds > > on this. It could said that I'm really measuring the diodes > temperature > > and not the PCB. On the other hand the diode pad does touch the PCB > . > > > > 2.Would it be more reasonable to measure the temperature in the > same > > neighborhood as the pad but make sure that the probe does not touch > the > > PCB pad? Would a notified body be of the same opinion? > > > > 3.If you feel that the first method is a valid measurement > technique > > then do you know of any ways to work around the problem? There are > many > > power devices that can easily and safely exceed a PCB material spec > of > > only 110 C. > > > > Thanks for your opinions! > > > > > > Best Regards, > > > > > > Kevin Harris > > > > email [email protected] > >
