How can a generator operate as a motor when electrical current is supplied to it?

It is a common misconception that generators and motors are entirely distinct devices; in fact, many direct-current (DC) machines are inherently reversible and can function as either a generator or a motor depending on the direction of power flow.1

When a DC generator is supplied with electrical current, it operates as a motor through the interaction of electromagnetic forces. Specifically, when current is introduced into the armature windings, it interacts with the magnetic field produced by the stator poles. This interaction creates a mechanical torque that accelerates the rotor.23

As the rotor begins to spin, it generates a voltage—often called back electromotive force—that opposes the source voltage. This process is the inverse of how a generator functions, where mechanical rotation is used to induce voltage in the coils. Because the fundamental principles of electromagnetic interaction are the same for both modes, the machine can effectively convert electrical energy into mechanical energy when powered, or mechanical energy into electrical energy when driven by an external prime mover.3124