An equivalent electrical circuit, characterized by the minimum coil sections number necessary to analyze the commutation in a universal motor, is discovered. The model parameters are also determined: in particular, the self and mutual inductance coefficients and the electromotive force induced in the coil sections (taking into account the magnetic saturation), the brush-commutator voltage drop, the electric arc. By means of a numerical solution of the equivalent circuit, the current waveforms are analyzed; the comparison between the computed and measured waveforms of the brush-commutator voltage drops allows to verify the model.