# AC Generator VS DC Generator

In this article, we will discuss the similarities and difference of AC vs DC Generator in detail. Before that if you want to study the working of AC vs DC generator, kindly read the following article:

Working of DC Generator

How does AC Generator Works ?

Similarities:

Both machines operate due to the relative motion between a magnetic field and coil in order to produce electricity. Hence both AC and DC Generators generate electric current by the principle of Faraday’s law of electromagnetic induction.

Both of them converts mechanical energy into electrical energy. Moreover, both machines initially produce AC voltage.

##### Differences:

Definition:

AC Generator also known as alternator is a machine which converts mechanical energy into electrical energy in the form of alternating current (AC). DC Generator on the other hand converts mechanical energy into direct current (dc) electrical energy.

Direction of Current:

In case of AC Generator, electric current periodically reverses its direction due to which current produce at the output is alternating (AC). On the other hand, dc generator produces current which flows in only one direction.

Field Winding:

Field winding applies to that winding which produces main magnetic field in a machine. In case of DC generator, field winding is installed on the stator. On the other hand, field winding in AC Generator is placed on the rotor.

Armature Winding:

Armature winding applies to the winding where main voltage is induced in the machine. In the case of AC Generator, armature winding is provided on the stator. Armature winding in dc generator is placed on the rotor.

Operational Difference:

Since both machines works on the relative motion between a magnetic field and conducting coil (faraday’s law). In case of AC generator, the coil through which the current flows is stationary and magnetic field is rotating. In other words, armature of AC generator is stationary while electromagnet (field poles) are rotating.

On the other hand, armature of dc generator rotates while it has fixed electromagnets (constant electromagnetic field).

Constructional Difference:

The main constructional difference between two machines is in their output connections. As describe earlier, both machines initially produce AC voltage. In Alternator, induce voltage is directly supplied to the load by means of slip rings. DC generator on the other hand requires mechanism to provide a DC output. Hence ends of the armature coil is connected with commutator (also known as split rings) which converts AC voltage to DC voltage.(can be seen in below diagram)

Maintenance:

DC Generator consists of brushes and commutator which needs regular maintenance. Hence maintenance cost of dc generator is high.AC generator on the other hand doesn’t have such mechanism due to which maintenance cost of AC generator is low as compared to dc generator.

Size:

Size of AC generator is large as compared to dc generator since they are designed for producing large power.

Frequency:

Output voltage of AC generator varies both in amplitude and time. Hence the frequency of AC Generator is variable. DC Generator produces steady output voltage which doesn’t vary both in amplitude and time. Hence  frequency in case of of dc generator is zero.

Efficiency:

DC Generator uses commutator and brushes which doesn’t last longer and wear out very quickly. They need regular maintenance and also produce sparks. AC generator on the other hand have slip rings which makes contact with the brushes. However, the brushes in AC generator do not wear out quickly and they have no such losses due to which efficiency of AC Generator is high as compared to DC Generators.

Output Voltage:

AC generators generally designed for producing large power. They can produce large power( measured in terms of megawatts) with high output voltages. DC generator on the other hand generates very less voltage as compared to AC generators.

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