How Do Relays Work And Change A System Automatic?

Relays and Solid State Relay
Relay and Solid State Relay
Basically relay is an electromechanical device or switch that is open or close by electrical current when flow through it. In a relay, a magnetic force relays the effect of one circuit (control-circuit) to other circuit (load-circuit). Relays work like a very simple remote control switch, which character helps to develop a basic ON or OFF basic logic, is the very fist step to change a system in automatic.

Relays are used in a wide variety of applications throughout industry, such in HVAC, Appliances, Security, Pool & Spa, Office Equipment, Telecommunications, Data-com, CP/OA, Office Automation, Process Control, Automotive, Energy Management Systems, Motor Drives/Controls, Appliance Controls, Industrial Control, Motors, Timers, Instrumentation, Test Equipment etc.
All relays actually contains basic two units- sensing unit, the electric coil and responsive unit, the switch contact. The coil is powered by AC (Alternating Current) or DC (Direct Current), when the applied current or voltage reached a pre-determined value then coil generate a magnetic field which cause a moving force to close the open contract and/or open the closed contract.

In simply, there is no electrical connection between control circuit and load circuit, they are electrically insulated each other; control circuit transfer signal to load circuit to operate in a pre-determined condition.


Types of Relays

Relays may be classified in different point of views- like construction of relays or purposes of relay using etc. As per relay construction, there are basic two types of relays- Electromechanical Relays and Solid State Relay. Electromechanical relays are constructed with mechanical moving parts, whereas solid state relays are the integrated electronic devices.

  1. Mechanical timer relay- use mechanical elements such as gears and springs or sometimes fluids to limit the movement (and time) something takes to change position.
  2. Solid-state timer relay- utilizes solid-state components such as SCRs , transistors, thyristors, and even other microelectronics to time something. These have the same function as the mechanical timers, but have no moving parts, making them last much longer when used properly.

For general purposes electromechanical relays used in huge, due to it’s low cost, multiple poles,suitable for large power, no heating issues, suitable for AC/DC system.

Solid state relays are used light signal to control the electronic devices. Advantages of solid state relays are small sizes, long life, moving parts less. But it can only accomplish single pole switching only.

For types of relays on the basis of  mechanism, functions and characteristics are as below-
General Purpose Relay;
Latching Relay;
Ratchet Relay;
Timer Relay;
Safety Relay;
Interlock Relay;
Polarized Relay;

High-frequency Relay;
Limit Relay;
Differential Relay;
High Sensitivity Relay;
High Speed Relay;
Current Relay;
Make-before-break Relay.
For more details about relay types, basis on using places and purposes, visit another complete post Lexis of Relays where described details. 

Relay Operations

Simple operation, the contacts of a relay switch when a voltage or current is applied to the relay coil. Electromechanical Relay operation actually determined by balancing the spring forces and attractive forces of the magnetic force generated in the relay coil.

Used Materials In Relays

 Relays normally used following material and their combination for contact, the ratio depends on the characteristic of load and sensitivity where it will be used.
Platinum, Gold, Silver, Cadmium Oxide, Nickel, Indium, Tin etc.

For magnetic materials, it’s important to consider improving electromagnet efficiency, high magnetic permeability & low-loss, stabilized and improved properties and no-oxidizing etc. and to do this soft iron, silicon steel, permalloy etc. are used.

Copper wires are used for relays winding and phenol resin, polyester resin, diallyl phthalate resin, polybutylene resin, polyacetal resin, polycarbonate resin, glass-reinforced materials are used as insulation materials.

polybutylene /terephthalate resin, polycarbonate resin and steel sheets are used for Relay Casing materials for transparent and hermit protection.

Pin Configuration Of Relays

Frequently used relays are 3 pin, 4 pin or 5 pin; all pin configurations are not same. The variation of relays pin configurations are shown in above figure.

Relay Checking Procedure


How Check Relay is in Good Condition: If you find a relay is not labeled, how you sure which pin go where? Then you must  need to carry out a continuity check and first identify the relay pins before use. An Ohm meter can use to check continuity.  For coil or control circuit you will find 50 to 70 ohm’s, and zero and infinity/ OL for closed and open circuit respectably. Unless otherwise, you will sure your relay is faulty.

How Check Relay is in Good Operation Condition: Using a battery power energized the relay coil or control circuit, you will hear click/ operating sound; also connect the battery +ve to one side of the load circuit then put the test light to other side and disconnect, repeat the test. You will find the test light ON and OFF, means the relay operating properly.

You also can carry out this relay operation condition check by a volt meter. Just put a volt meter instate of test light, meter will show the battery voltage, if it is in good condition.

Furthermore, you can carry out this test with an ohm meter. Just energized the relay coil or control circuit by battery power. Then check the load circuit with an ohm meter. The ohm meter reading will show zero if the contact is in closed, or it will show infinity/OL if contact is in open.

Finally we can say relay is just a device that can make or break a switch which is the primary condition to make a system automatic.

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