How to Understand and Use a Relay in Electronic Circuits

If you are intending to switch heavy electrical loads through an electronic control circuit, you would need the help of a relay unit. Whether it’s for flashing a lamp, for switching AC motor or for other similar operations, relays are 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 pin outs and learn regarding relay operations. Let’s begin the discussion.

Understanding Relay Mechanism

A relay mechanism basically consists of a coil and a spring loaded contact which is free to move across a pivoted axis.

The contact is hinged in such a way that when its not operated it connects with one of the terminals of the device called the N/C contact (Normally/Closed). Conversely when the contact is operated it disconnects itself from the N/C terminal and joins itself with a second terminal called the N/O contact (Normally/Closed). During it’s operations it switches from N/C to N/O alternately depending upon the activation 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 giving rise to the above situations.

The above movable spring loaded contact inherently forms the main central switching lead or the pin out of the relay. 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 contact in response to the coil activations.

The terminals of the coils also become the major pin outs of the relay.

Therefore in all we have 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 ad How to Use 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 use them 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 above three contacts may be further confirmed by powering the relay coil with the specified voltage.



A Typical Chinese Make Relay Pin Outs

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