Dynamo

A dynamo is an electrical generator that creates direct current using a commutator, and that uses self-powering electromagnets for its stator field rather than permanent magnets. Dynamos are self-starting, relying on the residual magnetic field left in the iron cores of their electromagnet field coils; if a dynamo had never been run before, it was common practice to use a separate battery to excite, or flash, the field of the electromagnets so it could self-start. Dynamos were the first practical electrical generators capable of delivering power for industry, and they became the foundation on which many later electric-power conversion devices were built, including the electric motor, the alternating-current alternator, and the rotary converter.