Difference Between Alternators & Generators

By Scott Kratochvil

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Generators and alternators both convert mechanical energy from a car's engine into electrical energy. Generators were used until around 1970, when they were replaced by the alternator, which is used in cars today.

Electromagnetic Induction

Alternators and generators work through the process of electromagnetic induction. This means that a changing magnetic field, if applied to a coil of conductive wire, will produce a current. Conversely if a current is applied to a coil of wire, it will produce a magnetic field.


In automobiles, generators are connected by a pulley to the drive shaft. This pulley spins a coil of wire, called the armature, inside of a magnetic field. Electricity is created that can be used to power the car's electronics.


Alternators work in a similar way to generators. The main difference is that in an alternator the armature is static and the magnet is rotated to produce the current.

DC and AC Power

While generators produce a direct current (DC), alternators produce an alternating current (AC). This means that power generated by an alternator must be converted to DC before it can be used.


The amount of current produced by a generator depends on how fast the engine is running. Alternators have an easier time producing maximum current, since the heavier armature is fixed and the lighter magnet is rotated. Alternators can power most of a car's electronics, even if the engine is idling, which is the main reason they are used in automobiles today.