How to test electrical relay | methods of testing relay-multimeter

How to test relay? Methods for testing electric relay

A relay is defined as an electrically controlled device that opens and closes electrical contacts with the help of electromagnetic switching and performs ON and OFF operations of other devices in the electrical circuit. various methods are used to test relay like visual inspection, test with the multimeter

How to test electrical relay

To test electrical relay working or defective, the easiest way to test is to use a multimeter set it on ohmmeter settings, and measure the resistance of the relay coil.

In this article, we will learn how to test a relay using a multimeter by measuring the resistance of the relay coil and different Relay testing methods.

From obtaining the reading we can distinguish relay is in good condition or not.

Methods for finding relay conditions

Do a visual inspection of relays

Pla Relay 8 Pin Diagram
Pla Relay 8 Pin Diagram

Most of relay have a clear plastic transparent body containing coil and relay contacts.

From visual inspection, we can find Melton, blackening of contacts and this will help narrow down the issue.

‌Testing electrical relay coil using Digital Multimeter

PLA relay 8 circuit diagram connection details
PLA relay 8 circuit diagram
 

To test the relay coil using a multimeter put a multimeter on ohmmeter settings, and measure resistance between coil contact.

For that, we need a relay datasheet, in which all relay details are described. eg. its pin configuration like a number of pins, on which the pin relay coil is connected. NC and NO  pin.

Typically these data will be printed on the larger relay case.

If the measured value of relay coil resistance lies within the described range then the relay is in good condition. If the coil resistance shows very high or very low than the described value, the relay needs to be replaced.

For example, the relay coil may have a resistance of 520 ohms +_ 10% tolerance. then coil resistance must have resistance within 468-572 which indicates its good condition.

If it shows a difference than this value, then the relay is considered as not in good condition. and the relay needs to be replaced because we can’t repair the relay coil.

‌Testing other pins of the relay (NO  and NC)  contact

Pin diagram printed on the case of large size relay or also available in manufacture’s datasheet, some relay has one or more pin, like shown in the above image, it has 8 pins, and coil in between 2 and 7 pins.

Each pin has normally open NO and normally closed NC contact. The pin diagram indicates this contact.

Relay drawings will show each pole as either touching the pin indicating an NC contact or nontouching the pin indicates NO contact.

Testing normally closed NC contact

NC contact will show a 0 ohms result on the Digital multi-meter if the relay is in good condition otherwise shows a different value in ohms.

Testing normally open NO contact

NO contact will show high resistance in the range of Mega ohms, the digital multimeter will show OL (overload)

2 Comments

  1. Thanks for taking the time to discuss this, I feel strongly about it and love learning more on this topic. If possible, as you gain expertise, would you mind updating your blog with more information? It is extremely helpful for me. how to test a relay

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