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An equivalent circuit of universal motors is developed, based on the design data. After representing the magnetomotive force distribution in the air gap, an analytical expression of the flux linkage of the armature winding coils is derived; this allows for the determination of the expressions of the speed and transformer EMFs induced in the armature winding and their representation by means of circuit parameters, as a function of the magnetic core saturation. The motor performances are computed, using the circuit parameters determined both analytically (by the design data) and by measurements. Some quantities are also compared with the ones obtained by finite-element analyses. Finally, the model is validated by experimental tests.