Through the coupling of commutator machines, self-excited alternating power can be spontaneously generated with no external electrical exc<tations. Standard frequencydomain analysis is applied to the various equivalent circuits for each configuration. Conventional series and shunt self-excited generators are shout to have a single pole in the right-half s plane, indicating growing exponential solutions, whereas coupled generators are shown to have a pair of complex conjugate poles in the right-half s plane, indicating over&able modes, which oscillate as they grow, resulting in. self-excited two-phase alternating power generation. Because of this interesting result, the analysis is extended to consider N-coupled generators which shows the existence of many over&able modes, resulting in multi-frequency, multi-phase power generation. The existence of electromechanical alternating self-excitation is demonstrated with the periodic speed reversals of a separately excited d.c. motor, which has its armature in series with the field and armature windings of a generator. Experimental results are presented w?Gch indicate that the linear circuit representation is appropriate for the onset and early time interval of these self-excited machines. The magnetic saturation characteristic limits the exponential growth so that a steady state results. These devices are of use in low-frequency, high-power applications, as well as serving as a model for other spontaneous mechanisma in nature.