Temperature Coefficient
Temperature Coefficient
(OP)
When calculating permanent magnet electric motor performance, the variation of the magnet (temperature coefficient of Br) and the winding (temperature coefficient of Resistance) over a temperature range is factored in using the value of thermal resistance (at some ambient temperature) published for the motor assembly. The temperature coefficients published for magnet materials and winding materials is assumed to be linear over a certain temperature range. Does the thermal resistance vary with respect to the change in temperature? If so, how is this characterized?
See reference at this site:
ht tp://www.s pecamotor. com/en/cas e_brushles smotor.php
I feel that the thermal resistance should vary since the materials that make up this resistance (air, copper, steel, etc.) change properties with temperature.
See reference at this site:
ht
I feel that the thermal resistance should vary since the materials that make up this resistance (air, copper, steel, etc.) change properties with temperature.





RE: Temperature Coefficient
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RE: Temperature Coefficient
http://
(see attached spreadsheet), however I have to use the thermal resistance as reported by the data sheet. Am I looking for something like a Nusselt number (http://en.wikipedia.org/wiki/Nusselt_number) that takes into account the convective heat transfer coefficient and the conductive heat transfer coefficient? If so, can this be calculated from any published material properties? Does the thermal resistance change with temperature, and is it an issue to properly calculate the temperature rise of the motor?
RE: Temperature Coefficient
And yes, the convective coefficient can be calculated: http://www
This issue will be that you don't know the actual parameters used, but you should be able to scale the equations to follow the temperature behavior of the equations used.
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RE: Temperature Coefficient
Thanks.
Rth2, my mistake.
Would it be correct to say that you agree that the thermal resistance will change with temperature? And if so, do you feel (gut reaction) that it will influence the calculations enough to pursue? Typically the temperature rise that I'm reffering to is about 100C.
RE: Temperature Coefficient
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