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Wiring Relay Outputs
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Number of connections on a relay can be confusing, and there are many ways
you can wire them up to give you different effects.
The Above picture shows the main connections the coil is where the control
signal to operate the relay gets connected and is covered in the wiring
relay coils section.
The number of remaining terminals vary depending on the number of poles the
relay has, normally for each pole there is three terminals a common (COM),
normally open (NO) and a normally closed (NC), this means that a dual pole
relay will have 6 terminals (often called an 8 pin relay (2 coil pins and 6
contacts), and a four pole will have 12 terminals (14 pin relay). Each pole
is a separate switch which operates a separate circuit.
When wiring, you normally always wire to the Common, and then wire to both
of the NC and NO contacts. When a relay is at rest without its coil energized
there is an electrical connection between the Common and the NC contact,
and no connection between Common and NO. This is reversed when the coils
are energized, simultaneously switching anything connected to NC off and
anything connected to NO gets switched ON.
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Examples
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Here are a couple of examples at the simplest level of relay use, a simple
make/break circuit.
firstly my fogger, now it would be possible to control this by turning the
mains on and off, but this isn’t a very good method since the fogger needs
mains power to maintain the heating element, however, the fogger has a
remote pendant input at the back, so by a little rewiring I can replace the
pendant with two wires going to the relay.
In this configuration (wired to NC) the fogger will remain on until I send
an output signal to turn it off.
Probably the most common example of a contact circuit is a doorbell, by
wiring my doorbell to the relay as shown (wired to NO) I can make it ring
when I send an output signal to its relay
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The example above shows the connection of a powered device to the relay,
this time a 24VDC power supply is connected to the common, and a 24VDC
motor to the NO, causing the motor to turn on when the relay is energized
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Often just turning a motor on and off is insufficient, sometimes you want
to dictate whether it goes forward or backwards, this can be accomplished
using a pair of relays as shown above
The First relay controls the power on/off, and the second relay controls
the direction, each relay is controlled by a separate output from the IO
board.
Notice how the NO output from relay 1 is connected to the common on 2, and
then notice how the NC and NO contacts switch the polarity to the motor and
reversing its direction.
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