A selenium rectifier is a type of rectifier that uses selenium, a chemical element that is not a metal, as a semiconductor for electrical conductivity. For a certain period of time, the selenium rectifier enjoyed popularity as perhaps the most widely used rectifier. Silicon rectifiers eventually took over this title.
As early as the late 19th century, metal rectifiers were used to convert alternate current (AC) to direct current (DC). This process, known as rectification, was done to point electricity to one fixed direction, which DC offers, as opposed to AC, which reverses directions. The device uses a piece of metal as its semiconductor for its electrical conductivity. This means that such a component has to possess the ability to conduct an electric current, which is not as good as an conductor, but better than an insulator. The most common type of metal rectifiers included copper oxide and vacuum tube rectifiers.
Starting in the 1930s, some companies began manufacturing rectifiers using selenium, a chemical element that is actually not a metal. Usually, they are made to resemble stacks of thin round or square plates, which are then plated with aluminum or steel. The selenium rectifier rose to prominence when vacuum tube rectifiers failed to provide the sufficient amount of amperes of electrical current needed to charge the batteries on automobiles.
A notable advantage of the selenium rectifier was the ability of the user to stack more plates to increase the device's voltage endurance. Additionally, unlike vacuum tube rectifiers, they did not require a warm-up period, as they were capable of providing instant operation. Far from restricted to automobile batteries, selenium rectifiers were used for electronic devices as diverse as radios, televisions and photocopiers.
Use of the selenium rectifier reached its apex during the mid-1940s and mid-1970s, when they were commonly employed for radios and TVs. By this time, they had replaced DC generators. Before the advent of the selenium rectifier, DC generators were the only semiconductors used in battery charger applications that required high amounts of electrical current.
By the end of the 20th century, however, selenium rectifiers had been overtaken by silicon rectifiers, or silicone diodes. These devices were actually available in the mid-1950s, but it was not until the 1960s that they began to establish their dominance. These devices perform at higher voltages than selenium rectifiers, and are also less expensive and more reliable. The selenium rectifier, however, is still manufactured today as a replacement device.