An alternator is a machine that converts mechanical energy to electrical energy by outputting alternating current (AC). It has different power factor characteristics depending on the load and produces a voltage-current relationship curve. Alternators are used as electric generators in power grids, to charge batteries and power electrical systems in automobiles, provide electricity to traction motors in diesel-electric locomotives, for yachts needing saltwater adaptability, and for radio transmission through high frequency variable reluctance alternators.