The working of Dynamo electric machine or motor, described in U.S. Patent No. 390,415, follows the basic principle of electromagnetic energy conversion, but Tesla’s design makes that process smoother and more efficient. When electric current flows through the field coils wound around the pole pieces, it magnetizes them alternately as north and south poles. These poles create a strong, well-defined magnetic field across the air gap where the armature is place.

As the armature (the rotating part mounted on the shaft) turns within this magnetic field, its conductors either cut through magnetic lines of force (when used as a generator) or experience magnetic forces that cause rotation (when used as a motor). In generator mode, mechanical rotation produces an electric current in the armature windings. In motor mode, supplied electric current interacts with the magnetic field to produce torque. The same machine can therefore work as either a motor or a generator, depending on how energy is supplied.

A key part of the working is how the magnetic circuit is completed. Tesla designed the frame so the magnetic flux flows through solid iron side bars connecting the pole pieces. This reduces magnetic losses and improves efficiency. Importantly, the shaft bearings are positioned at magnetically neutral points, meaning the rotating armature is not pulled unevenly by the magnetic field. This results in smoother rotation, less vibration, and reduced mechanical wear.