AC Generator vs. DC Generator: Key Differences Explained

This article explores the fundamental differences between AC (Alternating Current) and DC (Direct Current) generators. Both types of generators, regardless of size, rely on the principle of magnetic induction.

In DC generators, the armature is always the rotor. However, in AC generators (alternators), the armature can be either the rotor or the stator.

AC Generator

An AC generator is a machine that converts mechanical energy into AC electrical energy.

It operates based on the principle of electromagnetic induction: “Whenever a conductor cuts magnetic lines of force, an electromotive force (EMF) is induced in it.”

Figure 1: AC Generator Types

As shown in Figure 1, there are two main types of AC generators:

1. Rotating Armature Alternator: The armature rotates within a stationary magnetic field.
2. Rotating Field Alternator: The magnetic field rotates around a stationary armature.

The generated AC voltage from the alternator is supplied to the external circuit via slip rings and brushes.

DC Generator (Dynamo)

A DC generator, also known as a dynamo, converts mechanical energy into DC electrical energy.

The EMF generated by the dynamo is supplied to an external circuit in the form of DC voltage using a commutator and brushes.

Dynamo efficiency is calculated as follows:

Dynamo efficiency = (Output electrical power / Input mechanical power) x 100%

Figure 2: DC Generator

An elementary generator consists of a single coil rotating in a magnetic field, producing AC voltage. A basic DC generator is created by replacing the slip rings of the elementary generator with a two-piece commutator. This converts the output voltage to pulsating DC voltage, as depicted in Figure 2.

Using a multiple coil armature decreases ripple and increases the output voltage of the DC generator.

Comparison Table: AC Generator vs. DC Generator

The following table highlights the key differences between AC and DC generators: