Difference between Alternator and Generator

Before studying the difference between alternator and generator, it is important to know about the working of alternator and generator in detail.

How does an Alternator works ?↗
Working of Generator in detail↗

By studying the operation of alternator and generator, we find some similarities in them like both machines operates on the principle of faraday’s law of electromagnetic induction. Both Alternator and Generator takes mechanical energy from the prime mover and converts it into electrical energy. However, there are some differences which we should need to know. Let discuss the difference between alternator and generator in various factors.


A machine which converts mechanical energy into AC electrical energy is known as Alternator. On the other hand, generator is a machine which converts mechanical energy into AC as well as DC electrical energy.

Comparison of Current:

Generator can generate both AC and DC current. However, alternator always induces only alternating current. That’s why the term alternator is used since it produces only AC current.

Input Supply:

Alternator gets input supply from the stator while generator takes input from the rotor.

Comparison of Armature and Magnetic Field Movement:

The main difference between alternator and generator comes in their way of operation. In case of alternator, armature is stationary while magnetic field is rotating. The revolving magnetic field spins inside the stationary armature coils of stator to induce electric current in the armature (Faraday’s law).

Difference between Alternator and Generator- Alternator

On the other hand, armature of generator (rotor) is rotatory while magnetic field is stationary. Armature conductors rotate in a steady magnetic field due to which emf is induced within the armature conductors by the faraday law of electromagnetic induction (Faraday’s law). Lets also look into faraday law to understand the above discussion.

Difference between Alternator and Generator- Generator

Faraday’s Law :

Faraday’s law states that whenever conductor is placed in a rotating magnetic field or conductor is moving in a constant magnetic field, emf gets induced across the conductor.  In other words, relative motion between a magnetic field and coil(conductor) induces an emf across the conductor. Actually, faraday law tells us about the state in which emf gets induced in the conductor or coil.

Usage Comparison:

Alternators are generally used in automobile industry for charging car batteries or they are used in producing small scale electricity. Generators on the other hand used to produce large scale electricity.

Comparison of Energy Conservation :

Alternator generates only the required amount of energy needed for the load. That’s why alternator is used in automobile industry for charging car batteries. Once battery of vehicle is charged, alternator stops supplying power. They provide stable charging due to which batteries in the car do not not die out. Hence we can say that alternator doesn’t waste energy. However, generator on the other hand uses all the energy that is being produced. Hence some amount of energy wastes in the case of generators.

Output Voltage :

The output voltage of generator is constant irrespective of the applied load. On the other hand, alternator generates variable voltage depending on the requirement of load.


Polarization of alternator is not required after installation. Generators on the other hand need to be polarized after installation (since dc generator has positive and negative polarity).

Size Comparison:

Alternators are generally smaller in size than generators. Smaller size makes it easy for the alternators to fit into smaller spaces. Generators on the other hand are quite large and requires large space.

Rotation Per Minute (RPM):

Alternator works efficiently at a wide range of RPM while RPM of generator is low.


Since generator uses split rings and the brushes rub against them. Hence brushes wear out and doesn’t last long. In case of alternator, armature is stationary and there is no friction. Hence brushes do not wear out and last longer than generators.

Rectifier :

Both machines induces AC voltage on its rotor. In order to convert alternating voltage into dc voltage, commutator is used in generator. Alternator on the other hand doesn’t have any such mechanical rectifier.


With having same rating of generator and alternator, Generators are less efficient that those of alternators. Actually, brushes and commutator in generators do not last longer and needs regular replacement. Generators also needed more regular maintenance than that of alternators.

Output :

The output (current) delivering capacity of alternator is much higher than that of generators.

That’s all. Hope this will helps you.

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