I have used a Biddle 57J Energized Winding Resistance Meter. Connect the motor or transformer and you can take measurements while the device is powered.
Kevin ________________________________ From: John Woodgate <j...@woodjohn.uk> Sent: Tuesday, December 19, 2017 1:18:02 PM To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] Temp rise measurement I made a box with a double-pole, double-throw switch, an appliance toggle switch which is inherently break-before-make. This disconnects the supply and connects the ohmmeter in about 0.2 seconds. It takes longer to read off the resistance! John Woodgate OOO-Own Opinions Only J M Woodgate and Associates www.woodjohn.uk<http://www.woodjohn.uk> Rayleigh, Essex UK On 2017-12-19 17:55, Ted Eckert wrote: I’ve used the rise of resistance method without problems. The challenge is making the measurement before the windings cool off. The rise of resistance method can be more challenging when you have a small winding that doesn’t hold heat well. It is practically impossible to make the measurement the instance power is removed. You may want to record the resistance over time to see the winding cooling off, allowing you to extrapolate back to time zero. In a previous job, I had a product with a motorized impeller fan. The engineer from a NRTL asked me to use thermocouples. When I explained that the winding was spinning with the impeller, the engineer finally figured out that thermocouples wouldn’t work. It took 60 – 90 seconds to access the terminals on the winding from the time power was removed. I measured the resistance and recorded every 5 seconds to get enough information to extrapolate back to the time when power was removed. The windings were enclosed well enough that they were not getting much cooling from the moving air. As such, I did not expect that there was overshoot when power was removed and the fan stopped. Ted Eckert Microsoft Corporation The opinions expressed are my own and do not necessarily reflect those of my employer. From: John Woodgate [mailto:j...@woodjohn.uk] Sent: Tuesday, December 19, 2017 9:00 AM To: EMC-PSTC@LISTSERV.IEEE.ORG<mailto:EMC-PSTC@LISTSERV.IEEE.ORG> Subject: Re: [PSES] Temp rise measurement Yes, there is a much better method. It measures the average temperature of the whole winding, rather than the temperature at a particular spot. IEC 62368-1 incorrectly says that the thermocouple method measures the average temperature. You will find it explained in Annex E of IEC 60950-1. Incredibly, both IEC 60065 and IEC 62368-1 refer to the 'resistance method' without either detailing it or providing a cross reference. This is a serious omission. John Woodgate OOO-Own Opinions Only J M Woodgate and Associates www.woodjohn.uk<https://na01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.woodjohn.uk&data=02%7C01%7Cted.eckert%40microsoft.com%7Cab807d4d91914046799308d547020132%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C636492996306140994&sdata=3pJSgrFNNR2ypYnKwhCm4Yj4WBMWXEoLtvD1NJpqU9c%3D&reserved=0> Rayleigh, Essex UK On 2017-12-19 16:12, Scott Xe wrote: I will be conducting the temp rise measurements on windings of AC motors for electrical appliances such as washing machines, dishwashers, etc. It said the thermal couple method is commonly adopted for safety assessment. I can dismantle the windings and place the couples inside the windings using cyanoacrylate adhesive. However it may change the original shape of windings giving non representative measurement result. Is there any practically acceptable solution? Does the measurement result include the overshoot temperature after the power is cut? Thanks and regards, Scott - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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