- A rotating electric machine which is utilized to convert one DC voltage to a DC voltage of another value. It is a combination of an electric motor and DC generator, and usually has two armatures and a single field magnet.
- A rotating electric machine which is utilized to convert a DC voltage to an AC voltage, or vice versa. It usually has a single armature with two or more windings, and incorporates a commutator for DC operation, and slip rings for AC operation. Also called rotary converter, or synchronous inverter.