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Electricity Explained: What Are Relays?

Electricity can be described as one of the most important discoveries in history. Defined as the transfer of an electric charge between two particles, it has been harnessed to power numerous things, from large machines to our portable device chargers. The significance of electricity in modern life is such that when a blackout occurs, you can expect life to grind to a halt until the power comes back on.

Most of our everyday interactions with electricity come in the form of what is known as an electric current, wherein electric charges move along a current that is typically conducted through wires. This current can either take the form of a Direct Current or Alternating Current (which is the more commonly used one). This is what enables electricity to reach our homes from power plants and power many of our devices.

However, in order to save energy needed to generate electricity, many machines use switches to open and close circuits. When a circuit is open, electricity cannot flow, and thus no power is generated. The most practical example of this is in our light switches; if lights are turned off, it means that no electricity is flowing to power the lights, while the reverse is true if lights are turned on.

While light switches are an example of manual switches, where one has to physically move the switch from the “on” to the “off” setting, technology today has enabled the action of turning a switch on or off to be eliminated, through what is known as a relay.

What is a relay?

A relay allows power to be allocated through a circuit without having to open and close the switch manually. Instead, a relay utilizes an electrical signal to operate the switch and direct the opening or closing of a circuit. Because of this, they were first heavily utilized in telegraphs, telephones, and early computers, as these all involved several circuits, and a relay allows all of these circuits to be controlled simultaneously.

The relay itself has evolved through the years, relying on different materials to be responsible for sending the signals that open and close switches. Two of the most common types of relays are the electromechanical relay and solid-state relays, each with its own performance advantages.

What is an electromechanical relay?

The electromechanical relay is the most traditional form of a relay, using an electromagnet to move a part which is responsible for opening and closing a switch. Because it requires a part to move, an electromechanical relay requires a higher amount of input power to operate. Due to the nature of its operation, it is also unsuitable for environments with volatile substances or powerful electromagnetic fields. However, an electromagnetic relay does not require much thermal management, thereby making it cheaper due to the savings on heat sinks and fans.

What is a solid-state relay?

Electrician fixing electric wires
The solid-state relay, on the other hand, does not require any moving parts, instead of generating an optical semiconductor signal from a low-power electrical signal. This semiconductor signal is what performs the switching functions of the relay.

This advancement in technology, while making solid-state relays more expensive, gives it a number of advantages compared to an electromechanical relay. These include minimal electrical noise and disturbance, lower power requirements, and suitability in a wide variety of environments. Hence, although the upfront cost of a solid-state relay is higher, in the long run, the advantages provided make a solid-state relay a more efficient option that yields better performance results.

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