Introduction to Relays

A relay is best defined as a switch that is operated by an electromagnet.  A relay controller is a device that is used to control a bank of switches.  A relay controller works by turning on and off magnetic coils under logic control.  A computer controlled relay driver allows your computer to send simple commands to activate a switch or a group of switches.  Relays are ideally suited for controlling everything from lights and motors to telecommunication, audio, and video signals.

The boards at Relay Pros allow you to switch electrical equipment from a computer via Wired, Wireless or Network communications.  There are many advantages to using the different interfaces and we will look at these in future posts.

Relays typically have two or three connections: Common, Normally Open, and Normally Closed.   The Common is the part of the relay that actually makes a mechanical movement.  By default, many relays have their common (COM) lead connected to the normally closed lead (NC).  When the electromagnet is energized, the COM disconnects from the NC and reconnects to the Normally Open lead (NO).  When the relay is deactivated, the COM reconnects to the NC (see diagrams)
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Relay Types Available from Relay Pros

SPDT or Single Pole Double Throw Relays have three connections.  Common, Normally Open, and Normally Closed.  When the relay is off, the common is connected to the normally closed connection of the relay.  When the relay coil is energized, the Common swings over to the Normally Open Connection. Available in our 5, 10 and 20 amp versions.

SPST Single Single Single Throw Relays simply connect two wires together.  The COMMON is the moving part of the relay that comes in contact with the Normally Open when the coil to the relay is energized.  Available in our 30-Amp versions

DPDT Double Pole Double Throw Relays have a single coil with two arms that move at the same time.  There are two completely separate SPDT switch mechanisms inside a DPDT relay.  DPDT relays are most commonly used for signal switching applications, but can be found in high power switching applications.  Available in our 1, 3, and 5 amp versions starting with the 4-channel boards.