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Relay Logic

This page demonstrates several simple ways to wire a relay for various applications.  Click each of the photos below to enlarge.

The COM (Common) connection of a relay is the part of the relay that moves.  When a relay is off, the COMMON is connected to the NC (Normally Closed).  The NO (Normally Open) connection of the relay is not connected until the relay turns on.  When the relay turns on, the COMMON move from NC to NO.  Mechanical relays create a Clicking sound that indicates movement o the COMMON terminal.  Not all relays have a Normally Closed Connection.  For instance, 30A relays (as offered on our web site) do not have a Normally Closed connection.  We do not currently offer Solid State relays with a Normally Closed connection.  It is possible to use Two relays to create a Normally Closed condition.

Sample 1

This sample demonstrates how a relay can be used to activate a light bulb.  When the relay turns on, the light comes on.  Only one power wire is switched with this sample using the COM (common) and NO (normally open) connections of a relay.

Sample 2

This sample demonstrates how a relay can be used to turn a light bulb OFF.  When the relay turns off, the light will be ON.  Only one power wire is switched in this sample using the COM (common) and NC (normally closed) connections of a relay.

Sample 3

This sample demonstrates how two activated relays are required to activate a light bulb.  This is the same as a Logic AND function because Relay 1 AND Relay 2 MUST be on to activate the light.

Sample 4

This sample demonstrates how three activated lights are required to activate a light bulb.  This is the same as a Logic AND function because Relay 1 AND Relay 2 AND Relay 3 MUST be on to activate the light.

Sample 5

This sample demonstrates the AND/OR function.  The Light Bulb will be activated if Relay 1 AND Relay 2 are ON OR if Relay 3 is ON.  This sample is perfect for applications that may require a Logical condition of 2 relays PLUS an Override feature.  For instance:  Relay 1 is a Night/Day Sensor, Relay 2 is a Moisture Sensor.  If its Dark AND the soil is Dry, Relays 1 and 2 can activate a Pump.  If you want to override these conditions with a KeyFob, Relay 3 may be used.

Sample 6

This sample demonstrates how either relay can be used to activate a light.  In this sample, only one activated relay is required to activate the light.  If both relays are activated, the light will be on.

Sample 7

This sample demonstrates how a 3-way light switch can be used to activate a light.  A 3-way light switch is often found in your house where two light switches can be used to activate a single light.  This sample is exactly the same as a 3-way light switch, the only difference being each physical switch is replaced by a relay.  Operationally, it works the same way.  Each relay activation will cause the light to toggle.  Switching two relays at one time is like flipping 2 switches at once....with the same result.  This sample is particularly useful since you can replace one relay (as shown in the diagram) with a physical light switch.  This will allow a computer/Reactor to control a light as well as manual operation of a light.  Properly used, this can be one of the most valuable diagrams we offer on this page.

Sample 8

This sample demonstrates how to control the direction of a DC motor using 2 relays.  Braking is accomplished by connecting both motor terminals to a common power connection (Faraday's Law).  The capacitors shown may not be required for small motors, but if you experience problems with relays shutting themselves off, the induction suppression capacitor will be required.  The .1uF capacitor helps suppress electronic noise if the battery were to be used by sensitive devices (such as radios/amplifiers).