Since most of the ships generate A.C current from its alternator, it becomes essential to use a device, along with the transformer, that can convert this A.C current into D.C current for using equipment or circuit running on direct current. Rectifier is a circuit, which utilizes one or more semiconductor diodes to convert an alternating current into a pulsating direct current.

All electrical and electronic equipment or circuits on board ships play a vital role in the operation of ship’s m chin y systems. Equipment onboard vessels utilize alternating current, direct current or both depending upon the nature of operation. Some of the important circuits and setups are run through D.C current. Hence it is important to convert the generated A.C current in to D.C current and this process of conversion is known as rectification. Rectifiers are used for this purpose

Types of Rectifiers

Half wave rectifier:

Half wave rectifier consists of a single diode connected in series with the load resistor. During the positive half cycle of input voltage, the diode is forward biased and conducts for all voltages greater than its barrier potential.

During negative half of the cycle, the diode is reverse biased hence it does not conduct.

Full wave rectifier:

Full wave rectifier circuit allows unidirectional current to flow to the load during the entire input cycle. There are two types of single full wave rectifier:

·         Two diodes connected back-to-back using a center-tapped transformer.

·         Full wave bridge rectifier using four diodes connected in the form of bridge.

Bridge rectifier:

A single-phase bridge rectifier is used with four diodes connected in bridge with a noncenter tapped transformer.

Full wave rectifier has an advantage of converting both polarities of input A.C waveforms into D.C and therefore it is more efficient.

A three-phase rectifier circuit consists of six diodes, which are in pair of three, connected in series (anode to cathode).

It is commonly used in three phase circuits.

Applications onboard

Some of the uses of rectifiers on board ships are:

·         Used in marine electronic devices and circuits

·         Used for onboard battery charging from the ship supply

·         Used in detection of radio signals

·         Used in electroplating process

·         Used in ship construction for electrolyte refining of metals

·         Used in operation of D.C motor

·         Used in field excitation of three-phase alternator.