Generators are machines that are capable of generating electrical current by converting mechanical energy into electrical energy via electromagnetic induction. There are two types of generators, namely, AC generator and DC generator. The former is called AC generator because it produces an alternating current which is a type of electrical current that reverses direction sinusoidally. While the latter is called DC generator because it produces direct current which is a type electrical current that flows steadily in one direction. Though these two types of generators generate electric current through electromagnetic induction, they differ in many aspects especially in their designs, mechanisms and uses.
Different in designs and mechanisms
AC generators come with fixed coils through which current flow. The magnet normally moves. The north and south pole of the magnet make the current to flow in an opposite direction. On the other hand, the coil in DC generators is not fixed rather it rotates in a fixed field as the current flows through it. Each of these types of generators has an armature coil and slip rings known as the commutator. The commutator is made from metal. The type of current produced by any of them depends on the nature of the connection between the armature and the outside circuit. In other words the difference in the type of current produced by these generators is caused by the difference in the manner in which their armatures are connected to their external circuits. An AC generator has two metal rings; each end of the armature coil is connected to a separate commutator making it possible for the commutators and the armature coil to rotate simultaneously. Each commutator moves against its brush made from carbon. The brush of the AC generator does not move. The outside circuit as well as the end of the armature is also connected to the same brush. In other words, the two ends of the armature are connected to one end of the external circuit. The currents flowing from the metal slip rings are transferred to brushes.
The external circuit gets the current from the brushes. The electromotive force induced in the armature as well as the rate with which the coil cuts through the magnetic field is at the highest level whenever the armature is at 90 degrees to the magnetic field. However, the induced electromotive force and the rate at with which the coil is moving through the magnetic force come to zero level whenever the direction of the magnetic field and the rotating field are at parallel to each other. In a complete revolution of the armature, the induced current rises to the maximum points and falls to the zero point twice in opposite direction. This explains the generation and distribution of the alternating current to the external circuit.
The DC and AC generators work on the same electromagnetic principles. The difference lies in the manner of the collection and transfer of the induced electromotive force to the outside circuit. The difference is because of the difference in the way in which the armature and external circuit are connected. DC generators come with one commutator rather than two as in AC generators. This single slip ring is made up of 2 semicircular metal rings insulated from each other. Each of the armature ends is connected to one half of a single commutator instead of 2 individual commutators. This makes it possible for the current in the armature to reverse direction anytime the armature rotates half a turn. The induced current rises to its highest point and falls back to zero again when the armature rotates to 180 degrees between the magnetic poles. The brushes that bear against the slip ring collects and transfer the current to the external circuit. The direction of the current reverses in the same way with alternators. However, as this happens, each part of the insulated metal slip ring comes in contact with the opposite brush. This makes it possible for the current to continue to flow in the same direction from the brushes to the external circuit.
Another difference between these two types of generator is seen in their output voltage. The output voltage produced by AC generators also known as alternators varies in time and amplitude. In some places like America, Japan and Europe, the normal frequency for alternators is 60 Hz. The output voltage produced by the DC generators does not vary in time and amplitude. It is steady. The reason a DC generator does not produce AC output is because the voltage comes from the commutator ring.
Difference in uses
AC and DC generators are not usually use to power the same type of devices. Household electrical appliances and small motors are normally powered with alternating current generators. Examples of appliances that can be powered with AC generators include food mixers, juicers, vacuum cleaners, electrical fixtures and the likes. On the other hand, large electric motors like the ones used in the subway systems are powered with DC generators. Batteries used for off-grids are charged with direct current generators because they are capable of providing efficient and reliable energy supply.
