What is PCB Relay? Types and Working Principle Guide

Introduction

Want to switch a high-power device from a sensitive microcontroller? The PCB relay is just the component you need. It allows a small signal to safely toggle a much larger PCB relay circuit. This guide will explain what a PCB relay is and how to use one effectively.

What is PCB Relay?

So, what is PCB relay? It’s an electromechanical switch packaged in a compact form, ready to be mounted directly on your printed circuit board. You use a PCB mount relay to enable a low-power signal to control a distinct high-power circuit. This gives you galvanic isolation, a vital safety feature that electrically isolates your control and load circuits. Since they solder onto the board itself, they assist you in developing a more streamlined and space-saving design. With so many varieties out there, they are a dependable and efficient component for your projects.

PCB Relay Features

A PCB relay has some important features that will improve your designs. It is designed to switch currents and high voltages, so it’s ideal for PCB power relay designs. Most have protection features such as time delays or thermal cut-offs. Some types have purely electronic switching for high-speed applications.

• High-Voltage Switching: You can switch high voltages and currents, so these relays are ideal for heavy-duty power applications.
• Electronic Switching: Solid-state models utilize semiconductors, providing you with quiet, high-speed switching without moving parts.
• Time Delay: There are models that activates or turn off after a scheduled, or measured period of time has passed.
• Thermal Protection: There are relays that automatically trip if temperatures get too high, preventing your components from overheating.
• Frequency Monitoring: Dedicated relays can monitor AC frequency and trip if it moves out of a specified range.

How Does PCB Relay Work?

Essentially, an electromechanical relay for PCB is a simple electromagnetic switch. When you supply a control voltage to its coil, it produces a magnetic field. The magnetic force operates upon a metal lever, referred to as an armature. The armature movement actually opens or closes a group of electrical contacts, affecting the switching action for your PCB relay circuit.

This one simple act is what makes the relay so versatile. The PCB relay pinout allows you to connect to both the coil and switch contacts. You have Normally Open (NO) contacts, which complete a circuit when energizing the coil. You have Normally Closed (NC) contacts, which break a circuit when energizing the coil. You just solder these pins onto your board to control your device.

The following table shows a standardized way to determine electromagnetic relay terminals.

Relay PCB Types

A PCB relay can be classified according to its poles and throws that determine its internal switch setup. This indicates the number of individual circuits that the relay can handle by the number of poles. The number of throws will indicate the number of output connections a pole can switch between, helping you pick the right component.

SPST (Single Pole, Single Throw)

This is the most basic PCB relay, merely a simple, on-off switch of a single circuit. It is a single-pole (single input), single-throw (single output) device. In this type, you complete or break a single electrical path. The switch operates in such a way that, when you energize the coil, the switch closes, and your device is activated. It is perfect for simple control.

SPDT (Single Pole, Double Throw)

This relay selects one of two possible outputs on a single circuit input. It has one common terminal (the pole) and two output terminals (the throws). The common terminal (COM) is normally connected to the NC terminal by default. By switching the relay on, that connection is broken at the same time, switching the circuit to the normally open terminal.

DPST (Double Pole, Single Throw)

A DPST relay can be thought of as two SPST switches controlled by one control signal. It has two poles, which allow you to simultaneously control two completely separate circuits. It is single-throw, so all you can do is turn both circuits on or off simultaneously. It is helpful in changing both the live and the neutral of a power application.

Based on Operation Principle

You can also select a PCB relay based on its internal operation. This is a key component of any PCB relay selection since the principle decides the speed, lifespan, and best application scenario of the relay. From solid-state to mechanical, each has something special to offer for your particular circuit needs.

Electromagnetic Relays

This is the traditional electromechanical relay for PCB, combining mechanical and electrical components. With the application of power, a coil generates a magnetic field that physically moves a contact to switch a circuit. These relays can be used with both AC and DC control signals. For DC circuits, a freewheeling diode would usually be included to dissipate back EMF when the coil loses its energy. These are a robust and low-cost option.

Solid-State Relays

In discussions of relay types, SSRs have some important advantages. They utilize semiconductors such as optocouplers in place of moving parts to switch circuits. This provides for silent, extremely rapid switching and a considerably longer lifespan. Since they consume less control energy, they are very efficient. Their only disadvantage is that they experience a slight voltage drop that creates some waste heat.

Thermal Relays

You apply thermal relays particularly in temperature-related protection. Their fundamental element is the bimetallic strip which is formed of two metals with different rates of expansion. The strip bends as it heats up due to the current flow, and it may trip a switch when it becomes excessively hot. This is what makes them a perfect protection for electric motors and other devices that may suffer damage, as a result of overheating.

Hybrid Relays

As the name implies, a hybrid relay is the best of both worlds. It couples solid-state elements with electromagnetic components to achieve maximum performance. This design overcomes the shortcomings of each category, cutting down on contact arcing and minimizing wasted heat. You receive an extremely efficient relay with superior longevity and low power consumption, a very useful switching option.

PCB Power Relay Diagram

You have to open a PCB power relay to learn more about it. Its inner structure includes some components that interact to switch power. The relay has various components that are essential to its functionality. The following diagram will help break down a typical hinged-type relay into its most fundamental components.

PCB Relay Basic Design Requirements

To have your PCB relay functioning effectively, you have to observe important requirements in design. Internal mechanics are sensitive, and care is needed during soldering and washing. A correctly planned PCB relay footprint and placement on the board will prevent common failures and ensure a longer lifespan

• Choose the Right PCB: Select a 1.6mm thick board, usually a glass or a paper epoxy board, for secure through-hole mounting.
• Prevent Interference: Place your relay at a distance that does not cause magnetic, and thermal interference with other heat generating components, semiconductors or transformers.
• Mount for Stability: Mount the relay in such a way that any anticipated shock and vibration forces act perpendicularly to the direction of armature movement.

Tips and Techniques for Mounting PCB Relay

Correctly mounting your PCB mount relay is the key to its functionality. Whether you use an automatic or manual procedure, your method provides a secure connection. Adhering to the right temperature and time guidelines for your PCB relay footprint avoids damaging its internal mechanics and the board.

Automatic (Flow) Soldering:

1. Control Solder Level: Adjust solder level in your machine with caution. You need to avoid solder overflowing onto the top side of the PCB.
2. Apply Heat Correctly: Solder the relay for about 6 seconds. Keep a temperature of 500°F (260°C) unless the datasheet of the relay specifies otherwise.

Manual (Hand) Soldering:

1. Prepare Your Iron: Use a 30W to 60W soldering iron. Ensure the tip is clean prior to starting.
2. Set the Temperature: Preheat your iron to approximately 662°F (350°C).
3. Solder Quickly: Use heat and solder on each pin for up to 3 seconds to prevent overheating the relay.
4. Cool and Clean: Let the board cool down completely. After it has cooled, clean away any flux residue.

Testing PCB Relay

You can easily check a PCB relay with a multimeter. This is done to verify that the internal contacts function as they should and that the coil is good. By testing the relay in both its unpowered and powered states, you can be sure it will work properly in your circuit.

1. Set Your Multimeter: Set your multimeter into continuity test mode.
2. Check NC Contact: With the relay not powered, measure for continuity across the Common (COM) and Normally Closed (NC) terminals. You should hear a beep.
3. Check NO Contact: Then, measure for continuity between the COM and Normally Open (NO) terminals. The multimeter will read an open circuit (no beep).
4. Energize the Coil: Supply the proper voltage (e.g., on a 12V PCB relay) to the coil terminals. You will hear a distinct “click” as the internal switch flips.
5. Re-check NO Contact: With the coil energized, recheck the COM and NO terminals. You now have continuity.
6. Re-check NC Contact: Check the COM and NC terminals. They should now indicate an open circuit.
7. Measure Coil Resistance: Disconnect the power and take a measurement across the two coil pins for resistance. Compare this reading with the value on the manufacturer’s datasheet to verify the coil is not damaged.

Applications of Electric Relays

The PCB relay is used in numerous electronic applications across several industries. It is versatile and is a first-choice component in switching and protection applications. From basic control circuits to complex industrial controls, relays provide reliable performance. They form the main component in the creation of a safe and effective electronic design.

• Controlling High-Power Circuits: A small signal of low voltage can be used to control a high voltage or current. This is the main purpose of a pcb power relay.
• Creating Time-Delay Functions: Time-delay functions can be used with specialized relays to either open or to close a circuit after a small amount of time has elapsed, excellent as a method of sequencing operations.
• Automating Safety and Protection: You may set up your pcb relay circuit to alert when errors occur, such as overcurrent. The relay automatically then isolates this faulty part in order to protect the system.
• Implementing Logic Functions: It is possible to build simple logic gates with several relays. This enables you to develop safety-critical logic towards your applications.

FAQs

What is a PCB Relay Kit?

A PCB relay kit gives you everything required to assemble a functional relay circuit. It consists of a custom PCB, the relay itself, and other components such as resistors and diodes. These kits are a perfect means for you to gain hands-on experience with assembling a circuit. You can try various designs and see precisely how a PCB relay circuit works.

How to Solder a Relay on a Circuit Board?

You can solder a PCB-mount relay manually or with an automated process on a circuit board. For automated flow soldering, you would normally apply around 260°C for six seconds. When you solder by hand, you can use a 30-60W iron at 350°C and heat for a mere three seconds. Always check the PCB relay footprint and datasheet first, as too much heat can burn the component.

How to Test a Circuit Board Relay?

You can simply check a relay with a multimeter in continuity mode. When the relay is not powered, you should find continuity across the COM and NC pins. After connecting the proper voltage to the coil, you should notice a “click.” Now, continuity should change to the COM and NO pins, indicating that the PCB relay is functioning as it should.

Conclusion

A PCB relay is an essential protective mechanism for your whole circuit. Although small, it provides the same strong switching as bigger relays, protecting your system from harm. You will have to take its particular mounting and design requirements into account to make sure your PCB operates the way it should and will from the beginning.

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