In electricity generation, an electric generator is a device that converts mechanical energy to electrical energy. A generator forces electric charge (usually carried by electrons) to flow through an external electrical circuit. It is analogous to a water pump, which causes water to flow (but does not create water). The source of mechanical energy may be a reciprocating or turbine steam engine, water falling through a turbine or waterwheel, an internal combustion engine, a wind turbine, a hand crank, compressed air or any other source of mechanical energy. Early 20th century alternator made in Budapest, Hungary, in the power generating hall of a hydroelectric station Early Ganz Generator in Zwevegem, West Flanders, Belgium The reverse conversion of electrical energy into mechanical energy is done by an electric motor, and motors and generators have many similarities. In fact many motors can be mechanically driven to generate electricity, and very frequently make acceptable generators.