How a Relay Works
If you are wondering how a relay works in order to switch heavy electrical loads through an electronic control circuit, you would need to learn the following article.
Whether it’s for flashing a lamp, for switching AC motor or for other similar operations, relays are the best in the business. However young electronic enthusiasts often become confused while assessing the pin outs of the relay and configuring them with a drive circuit inside the intended electronic circuit.
Whether it’s for flashing a lamp, for switching AC motor or for other similar operations, relays are the best in the business. However young electronic enthusiasts often become confused while assessing the pin outs of the relay and configuring them with a drive circuit inside the intended electronic circuit.
In this article we’ll study the basic rules that will help us to identify relay pinouts and learn regarding how a relay works in circuits. Let’s begin the discussion.
How a Relay Works
A relay mechanism basically consists of a coil and a spring loaded contact which is free to move across a pivoted axis.
The central pole is hinged or pivoted in such a way that when the relay is switched ON it connects with one of the side terminals of the device called the N/O contact (Normally Closed).
And the relay is switched OFF it disconnects itself from the N/O (Normally Open) terminal and joins itself with a second terminal called the N/C contact.
During such switch ON and switch OFF operations it switches from N/C to N/O alternately depending upon the power supply input states.
The above activation of the relay contact is done by energizing the coil inside the relay.
The coil of the relay which is wound over an iron core behaves like a strong electromagnet when a DC is passed through the coil.
When the coil is energized the generated electromagnetic field instantly pulls the nearby spring loaded contact or the pole giving rise to the above situations.
The above movable spring loaded pole inherently forms the main central switching lead and its end ts terminated as the pinout of this pole.
The other two contacts N/C and the N/P form the associated complementary pairs of relay terminals or the pin outs which alternately get connected and disconnected with the central relay pole in response to the coil activation.
These N/C and N/O contacts also have end terminations which move out of the relay box to form the relevant pinouts of the relay.
Thus we basically three contact pinouts for a relay, namely the pole, the N/C and the N/O.
The two additional pinouts are terminated with the coil of the relay
This basic relay is also called a SPDT type of relay meaning single pole double throw, since here we have a single central pole but two alternate side contacts in the form of N/O, N/C, hence the term SPDT.
Therefore in all we have 5 pinouts in an SPDT relay: the central movable or switching terminal, a pair of N/C and the N/O terminals and finally the two coil terminals which all together constitute a relays pin outs.
The central pole is hinged or pivoted in such a way that when the relay is switched ON it connects with one of the side terminals of the device called the N/O contact (Normally Closed).
And the relay is switched OFF it disconnects itself from the N/O (Normally Open) terminal and joins itself with a second terminal called the N/C contact.
During such switch ON and switch OFF operations it switches from N/C to N/O alternately depending upon the power supply input states.
The above activation of the relay contact is done by energizing the coil inside the relay.
The coil of the relay which is wound over an iron core behaves like a strong electromagnet when a DC is passed through the coil.
When the coil is energized the generated electromagnetic field instantly pulls the nearby spring loaded contact or the pole giving rise to the above situations.
The above movable spring loaded pole inherently forms the main central switching lead and its end ts terminated as the pinout of this pole.
The other two contacts N/C and the N/P form the associated complementary pairs of relay terminals or the pin outs which alternately get connected and disconnected with the central relay pole in response to the coil activation.
These N/C and N/O contacts also have end terminations which move out of the relay box to form the relevant pinouts of the relay.
Thus we basically three contact pinouts for a relay, namely the pole, the N/C and the N/O.
The two additional pinouts are terminated with the coil of the relay
This basic relay is also called a SPDT type of relay meaning single pole double throw, since here we have a single central pole but two alternate side contacts in the form of N/O, N/C, hence the term SPDT.
Therefore in all we have 5 pinouts in an SPDT relay: the central movable or switching terminal, a pair of N/C and the N/O terminals and finally the two coil terminals which all together constitute a relays pin outs.
How to identify Relay Pin Outs and Connect a Relay
Normally and unfortunately many relays don’t have there pin out marked, which makes it difficult for the new electronic enthusiasts to identify them and make these work for the intended applications.
The identification of a typical relays pin outs may be done in the following manner:
Firstly you would require finding out the coil pin outs of the relay. This is simply done by randomly connecting the prods of a multitester across the different terminals of the given relay.
The multitester needs to be fixed at the Ohms range preferable at the 1K range.
The coli pin outs can be confirmed the moment a relevant resistance value is indicated over the meter, the particular pin outs or the terminals may be marked appropriately.
Next, follow the same procedure of connecting the meter prods randomly to the remaining three terminals.
Out of the three terminals, identify the two terminals which show continuity across each other, it can be assumed that one of these terminals includes the N/C terminal, the other one should be the central moving common terminal and the third one which is not connected to the meter is the N/O terminal.
The geometry of the above three pin out will easily confirm and identify the central movable common terminal.
The single terminal which may be oriented somewhere in between the remaining two terminal making a triangular configuration should be the central common moving contact while the other two which may be placed parallel to each other should be the N/C and the N/O depending upon which gets connected to the central contact and under what conditions as explained in the previous section.
The single terminal which may be oriented somewhere in between the remaining two terminal making a triangular configuration should be the central common moving contact while the other two which may be placed parallel to each other should be the N/C and the N/O depending upon which gets connected to the central contact and under what conditions as explained in the previous section.
The above three contacts may be further confirmed by powering the relay coil with the specified voltage.
A Typical Chinese Make Relay Pin Outs
Source : http://www.homemade-circuits.com/2012/01/how-to-understand-and-use-relay-in.html
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