What prevents heat generation in magnets?
What prevents heat generation in magnets?
(OP)
It appears that my motor is generating heat in the magnet or the rotor yoke. Under what conditions does rotor heating occur? What advice do you have for reducing it?
Thanks.
Thanks.





RE: What prevents heat generation in magnets?
1. Voltage harmonic distortion causing voltages of higher frequency that causes higher Eddy Currents and Magnetization losses.
2. Lower voltage at the motor terminals. This causes higher currents flowing through the windings which heats up motor iron.
3. Higher voltage at the motor terminals which causes the higher magnetization current thus higher magnetization losses.
RE: What prevents heat generation in magnets?
RE: What prevents heat generation in magnets?
What type of motor is it?
RE: What prevents heat generation in magnets?
This is a four pole high speed (30 krpm) brushless dc motor. The motor uses a high strength extruded neo magnet. The rotor is 17-4 stainless.
Thanks.
RE: What prevents heat generation in magnets?
1. Gordon R. Slemon "Magnetoelectric Devices Transducers, Transponders, Transformers, and Machines," John Wiley and Sons, Inc., 1966,
Section 2.2 Eddy Currents.
Equation 2.37 on page 124 indicates:
p=[(c x w x B)**2]/(24 x ro)
p is average Eddy Current Power Loss in Watt/(cubic meter)
c is lamination thickness
w is angular frequency = 2 x pi x f
B is maximum flux density
ro is the resistivity of material (notice that the high resistivity of material is reducing Eddy Current Losses)
RE: What prevents heat generation in magnets?
Assuming constant flux density somewhere near saturation of core steel, the voltage induced around a loop within the core (not interrupted by lamination boundary) will be proportional to the perpendicular area through which the flux flows. V = d/dt(B*A)
jbartos' expression I believe will estimate the heating associated with a section of core formed in a long thin lamination of area length * c, c<< length. I think I can derive that result P ~ c^2 as follows:
Rloop ~ 2*length+2*c ~ 2*length.
I ~ V / R ~ A / length ~ (length*c)/length ~ C.
P ~ I^2*R ~ c^2
RE: What prevents heat generation in magnets?
1. reduce the slot opening size
2. adjust the pwm frequency
3. adjust the pwm harmonic response
3. laminate the magnet
4. laminate the rotor yoke
5. reduce the pole count
Can you think of other things I should consider? Do you think that skewing the lamination stack would help?
RE: What prevents heat generation in magnets?
One more to add to your list - neodymium magnets have higher resistivity than samarium cobalt.