Method for measuring and characterizing core loss in a motor

Because of the complex shape and variable flux densities of the toothed cor es of motors, characterization of their core losses has been difficult. Man ufacturers' material specification sheets usually refer only to Epstein tes ts, based on sinusoidally varying flux densities in simple geometries, Here , a more accurate and direct method for measuring core loss is presented, T he method spins the motor core in a magnetic field and then measures the sp in speed and drag torque imposed on the core. This test was used to success fully characterize the core loss in a small de brushless spindle motor. Amo ng the parameters examined were the turning speed, maximum gap Bur, laminat ion material, lamination thickness, and the effects of stress-relief anneal ing. Mathematical models of the core loss were constructed for specific cor e geometries based upon an assumed form for the empirical data. The actual core losses were higher than would have been predicted from conventional Ep stein tests.