When there is a change in magnetic flux linkage through a conducting loop, an emf is developed as per the Faraday’s Law of Electromagnetic Induction. Generators use Electromagnetic Induction to convert mechanical energy into electrical energy. In an AC, or alternating current, Generator, the electrical current periodically reverses its direction. With a DC, or direct current, Generator, the current flows only in one direction.
The major difference between an AC Generator and a DC Generator is that the DC Generator requires a mechanism to provide a DC output. This can be done mechanically with a commutator or electronically with a rectifier. Internally, all generators produce an alternating voltage.
There are several other primary differences between AC and DC generators. Some of them are listed below.
- Both AC and DC generators produce currents using electromagnetic induction. In AC generators, the coil through which the current flows is fixed, and the magnet is moving. The magnet’s north and south poles cause the current to flow in opposite directions, producing alternating current.With DC generators, the coil through which the current flows rotates in a fixed field. The two ends of the coil attach to a commutator, different halves of a single, rotating split ring. Metal brushes connect these split rings to an external circuit. The commutator balances the charges leaving and returning to the generator, resulting in a current that does not change direction.
- All generators require a magnetic field. The field can be provided by permanent magnets or by a DC current that the generator produces itself. If the generator produces its own magnetic field, it can be initially put into operation using residual magnetism or by initially generating the field with an external power source. The only type of generator that uses a type of AC field excitation is an induction generator, essentially an induction motor operating as a generator.
- The rotating parts in AC Generator is the low current high resistivity rotor (the iron core with little copper wire winding). So it is safe even in high speed. Rotating parts in a DC generator is heavy and with high current, limiting its maximum speed.
- AC and DC generators serve different purposes. In home appliances we typically use AC generators to power small motors and common electrical appliances. These include vacuum cleaners, food mixers, juicers and electrical fixtures. DC generators are used to power very large electric motors such as those needed for subway systems. Moreover, DC generators provide a reliable and efficient energy supply that can charge banks of batteries used for mobile and off-grid uses.
- Currently, the majority of generators are the AC type, because the DC units have brushes that require periodic replacement. Although the electrical systems in many autos had DC generators before the 1960s, lower-maintenance AC units replaced DC generators. Key to this advance was the introduction of the reliable solid-state diode, an inexpensive electronic component that converts AC to DC.