A Guide to Electrical Relays
Relays are useful electronic components that are present in many systems and equipment, allowing for remote, high voltage, and current switching. They are very beneficial for many electrical systems as they create the ability to control high voltages and currents with a much smaller voltage or current. They may also serve to protect, regulate, and monitor electrical systems depending on their type. In this blog, we will discuss relays and their functionality in more detail, as well as their various common types.
In general, an electrical relay is an electromagnetic switch that utilizes a small electric current to switch a larger current on or off. To achieve this, relays feature electromagnets, which are coils of wire that produce magnetic fields when electricity is induced. When the magnetic field is generated, it causes a contact to be attracted, thus activating the second circuit. When the relay loses power, the contact returns to its initial position by the force of an attached spring. When the spring returns the contact to its original position, the relay is then shut off. Depending on the need, relays may either be “normally open” or “normally closed”. In a normally closed circuit, the contact remains connected to permit current flow, and activating the electromagnet causes them to separate.
1. Solid-state Relays
Solid-state relays are switching devices that operate similarly to standard electronic relays, switching on or off when external voltage is applied. Typical solid-state relays consist of a sensor that responds to control signals, a solid-state switching apparatus to switch power to the load circuitry, and a coupling mechanism. Such relays can switch both AC and DC currents to a load, and they require no moving parts for operation.
2. Thermal Relays
A thermal relay is one that would be considered a protective relay, designed to open contacts if the ambient temperature exceeds a set limit. To achieve this operation, the thermal relay features a bimetallic strip that is heated by a heating coil as current is passed through the system. This causes it to bend, resulting in the contacts separating to open. As a protective device, a thermal relay may be used for overload protection for an electric motor.
3. Reed Relays
The reed relay type is one that utilizes its electromagnet to operate one or more reed switches. As the reed relay uses contacts that are manufactured from magnetic materials, the electromagnet can move contacts without the need for an armature. As compared to relays that have armature operation, the reed relay can switch much faster, as well as contains parts that are much smaller and lighter in weight. They also benefit from needing less power for their operation, and their contacts have lower capacitance. Reed relays are placed within a glass tube, protecting the contacts from corrosion and other damages. Dispute their limited current handling capacity, reed relays are reliable and tout long service lives. For their applications, reed relays are most efficient for dry switching applications.
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