Due to the complex shape and variable flux densities in the toothed cores of motors, characterization of their core losses has been difficult. Manufacturers' material specification sheets usually only refer to Epstein tests, using sinusoidally varying flux densities in simple geometries. In this paper, a more accurate and direct method for measuring core loss is presented. This method consists of a device for spinning the motor core in a magnetic field andthen measuring the spin speed and drag torque imposed on the core. This test was used to successfully characterize the core loss in a small DC brushless spindle motor. Among the parameters examined were the turning speed, maximum gap flux, lamination material, lamination thickness, and the effects of stress relief annealing. Mathematical models of the core loss were constructed for specific core geometries based upon an assumed form for the empirical data. Among the final results were that the actual core losses are higher than would have been predicted based upon conventional Epstein tests.
展开▼
