How a 3 Wire Alternator Works

by Vee Enne

Alternators are devices that are responsible for charging a battery and keeping a car running. Alternators also help charge boat batteries and any other vehicle or machinery that runs off battery power. Vintage vehicles that have not been restored often have a one-wire alternator system. The most common type of alternator in newer model vehicles is the three-wire alternator.

An alternator works with the battery to supply electricity to components of a vehicle. The headlights, dashboard lights, radio and interior lights all rely on the alternator to keep the battery charged and the car operating. The alternator has a rotor that spins when the engine cranks. This rotor spins past wire coils causing a magnetic field. The magnetic field creates a current which feeds through the alternator charge the car's battery.

The three wire types in a three-wire alternator include the battery positive wire, the voltage sensing wire, and the ignition input wire. The battery positive wire connects to the starter. The voltage sensing wire connects to the battery, and the ignition wire connects from the alternator to the key switch. All of these wires pull power from the battery through the alternator to keep the electrical systems running and the car operating.

Newer vehicle models have so many different electrical components, that the three-wire alternator is a necessity to keep the components running smoothly. Alternators have an internal regulator that monitors the amount of volts going to the battery. Should the voltage raise or decrease drastically, the regulator will increase or decrease the output of the alternator to maintain a steady flow of voltage to the battery. Alternators with only one wire have an external regulator, which means that the regulator can be replaced if broken. In current alternator models, mechanics replace the entire alternator if the regulator malfunctions or wears out.

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