Alternator vs Generator Differences

Alternator vs Generator

When most people think of a generator, they think of either a portable or standby generator used for producing power in homes and businesses. On the other hand, an alternator brings up the idea of car battery charging. While both assumptions hold true, there is more to alternators and generators than where they are most used for nowadays.

Both alternators and generators produce electricity. However, the way they do it is the major difference. In alternators, the armature is stationary while the field system rotates. In generators, on the other hand, the armature rotates while the field system is stationary.

This is just one of the differences although it’s the major one since it determines how each one produces electricity. Both devices, however, are based on the Faraday law of electromagnetic induction. On this one, the alternator induces alternating current (AC) while the generator induces both alternating current (AC) and direct current (DC).

Comparing an Alternator & Generator-Differences

DefinitionA device that converts mechanical energy into alternating current (AC) energy power.A device that converts mechanical energy into alternating current (AC) and direct current (DC) electrical energy.
Magnetic fieldRotatingStationary
Current typeAlternating current (AC)Alternating current (AC) and direct current (DC)
Input supplyTakes from the stator.Takes from the rotor.
Output EMFAlternatingConstant
Charging dead batteryNoYes
RPM (rotations per minute)Wide rangeNarrow range
Power outputHigherLower
Power productionPower produced when neededAlways producing power
Magnetic fieldRotatingStationary
Brush efficiencyHighLower
Alternator vs Generator Comparison Table

Given these differences, it’s clear to see why generators are favored in producing power for homes and businesses while alternators are used mostly for charging batteries in vehicles.


An alternator is a device which turns mechanical energy into electrical energy as an alternating current (AC). A common example is the alternator of a car which uses the mechanical energy of the car to produce energy to charge the car’s battery.

Alternator pictures

The mechanical energy in the engine rotates a magnet which in turn creates an electric current of the alternating type (AC). This process can be turned on and off automatically since alternators can only come on to charge the battery when the battery is low and turn off when it’s fully charged.

This feature means that you only use the alternator when needed. Besides saving on energy production, it reduces the likelihood of the alternator failing due to wear and tear. If your car battery dies when the engine is running, it means the alternator is not working.

The downside to an alternator is that it can’t charge a battery when it’s completely dead. If you try that, it’ll likely lead to the damage of the battery and even a fire.


Higher power output

Alternators are smaller in size and with more robust parts compared to those of a generator. This allows them to spin faster with a lower risk of damage. The higher speed of rotation translates into more power over the same period of time. Even at lower speeds such as when the vehicle engine is simply idling, the alternator will produce enough power to use for all the electric equipment on the car without tapping into the battery power.

Less maintenance needed

While both generators and alternators have a system of rings and brushes used in the generation of electricity, they are of different designs. Alternators use solid rings while generators employ split rings. Given that the brushes brush against the rings, the solid rings in the alternators will last longer than those in the generator due to a lower rate of wear and tear. You’ll thus need less service for the alternator over its lifetime.

Smaller size and less weight

Generally, alternators are compact ways of producing electricity and that’s why they’re favored over generators in car engines. The fact that the engine has lots of parts means saving on space is important as well.

  • Only produce the require energy hence conserves energy.
  • Polarization not required.
  • When used on a larger scale, alternators are better than generators in producing large amounts of power which can also be stepped up and done easily by transformers since they only work with AC power.


  • Can’t charge a battery when it’s completely dead.
  • Can’t be used as a motor directly and efficiently.

These aspects make alternators special purpose power generators. While they’re highly efficient, they’re also limited in some ways that’s why they’re not found in as many places as generators.


A generator is a device which turns mechanical energy into electrical energy both as alternating current (AC) and direct current (DC). The generator has rotor coil made of coiled wires. These wires rotate causing electricity to build up inside the magnetic housing which doesn’t rotate like in the alternator.


Unlike alternators, generators are constantly producing electricity and will charge a battery when it’s completely dead.

An example of a generator is the standby and portable generator which gains its mechanical energy from the motions of the engine it has.


  • Can also be used as a motor by applying power to the shaft.
  • Always produces energy hence reliable.
  • Produces both AC and DC current.


  • Can be wasteful as it’s always producing energy even when it’s not needed.
  • Needs polarization to work.
  • Needs more maintenance than alternators.

Generators are popularly used in powering homes and businesses as they can produce both AC and DC power without many modifications.

Which is better and why?

Between the two, alternators are the better device at energy production owing to their efficiency. The fact also that they only produce energy when needed makes them better power generators than generators themselves.

If it is all about energy production, alternators would be the device of choice. However, generators have their own advantages which have made them the better option in homes and places of business.

Further Reading