What is relay?
A relay is an electrically controlled switch that has the ability to turn a circuit on or off. Depending on the application relays can do a number of things. Relays can be used as switches to turn things on and off, or as amplifiers to convert smaller currents into larger ones. They can also be used to control a circuit with a low power signal or when multiple circuits need to be controlled by a single signal.
There are two kinds of relays, electromagnetic and solid state. In this post, we will be focusing on electromagnetic relays and how they work.
Basic Parts of a relay
Armature– is a basic metal piece that is balanced on a pivot or a stand. It is considered the moving ‘arm’ of the relay. It makes or breaks the connection with the contacts connected to it.
Spring– is connected to one end of the armature and pushes the armature back into place if no current is passing through.
Electromagnet– is a metal wire wrapped around a metal core. The wire does not have magnetic property but can be converted into a magnet with the help of an electrical signal.
Yoke– is a small metal piece affixedon a core which attracts and holds the armature when the coil is energized.
Contacts– conductive material that exists within the device whose physical contact opens or closes a circuit
A break refers to the number of locations on a circuit that a switch can make or break the flow of current. In electromechanical relays, there can be single breaks and double breaks. A single break is usually used with low power devices while a double break is usually used with high power devices.
A pole refers to the number of circuits that relays can pass through a switch. A single pole contact carries current through one circuit, while a double can carry it through two.
A throw refers to the number of separate wiring paths. For example, a triple throw switch can be connected to one of three contacts instead of one.
How does it work?
In an electromechanical relay, a small circuit has the ability to switch a larger circuit on or off through contacts by using an electromagnet. When charged, the electromagnet creates a magnetic field that attracts the armature and closes the contacts. Some contacts come in different configurations depending on the use of the relay. A normally open (NO) relay’s contacts are open when there is no current passing through, while a normally closed (NC) relay’s contacts are closed when there is no current passing through.
There are many things to consider when choosing a relay for a project. Lifespan, operating environment, mechanical loads, size, and number and type of contacts are all important factors in choosing the right relay.
Pros and Cons of Electromagnetic relays
Fast operation and reset
More definitive ON/OFF
Simple and most reliable
Suffers the effects of age
No directional features
MRO Electric and Supply has an extensive inventory of relays in stock. Please call email sales@mroelectric or call us at 800-691-8511 for a quote.