Dynamo

A dynamo is an electrical generator that produces direct current using a commutator, relying on self powering electromagnets for its stator field rather than permanent magnets. A dynamo starts itself using the small residual magnetic field left in the iron cores of those electromagnets, though a dynamo that had never been run before traditionally needed a separate battery to first excite the field. Dynamos were the first practical electrical generators able to deliver power for industry, and they underpinned later electric power devices including the electric motor, the alternating current alternator and the rotary converter.