What comes into your mind when you hear the term “relay?” To most of us, we assume it is something that receives and passes over an object. In most electric circuits, relays act as switches.
A typical relay is a closed electrical circuit that is used to switch electric currents from one circuit to another. It’s an important and useful part of many everyday electrical systems, including the home circuits and vehicle’s electrical systems.
Let’s assume that you already know about PCBs or printed circuit boards. Our focus is one of the key components-PCB relays.
This article will discuss the basics of PCB relays, how they work, how to choose the right relay for your projects, and how to wire one together. We’ll also look at some of the most common PCB relay usages for electronics hobbyists, commercial electronics projects, and designers.
- 1 What is a PCB relay?
- 2 How do PCB relays work?
- 3 PCB Relay Types
- 4 Other classifications of PCB Relays
- 5 Electromechanical features of PCB relays
- 6 PCB relay design considerations
- 7 How do you test a PCB relay?
- 8 Precautions for mounting PCB relays
- 9 Where can I buy PCB relays?
What is a PCB relay?
A PCB relay is an electromechanical device used to switch an electrical circuit on or off. It consists of a coil of wire wrapped around a ferrous core, which is magnetized by electricity. The core, in turn, moves two metal contacts that can be used to complete or break an electrical circuit.
The physical structure of a PCB relay is fairly simple: it’s basically a switch with two metal contacts and a coil of wire wrapped around an iron core. The contacts are mechanically actuated by the movement of the magnetized core when current flows through the coil.
There are many different types of PCB relays available, each designed for specific applications. So if you are looking for a particular type, you will need to know what type you need before choosing one. Many types of PCB relays are available on the market, from common ones such as DPDT (double pole double throw) to special types such as FET (field effect transistor) PCB relay.
There are also PCB relays that can be used for switching AC voltages, DC voltages, and even very high voltage power supplies. The most common types of PCB relay are the mechanical type – these use a physical switch to complete or break the circuit.
How do PCB relays work?
The PCB relay consists of a coil of wire, an iron core, and two metal contacts. When the coil is energized with electricity, it creates a magnetic field that attracts the core. This results in the closing of the contacts.
Conversely, when the current stops flowing through the coil, the magnetic field disappears, and the core moves away from the contacts; this causes them to open again.
PCB Relay Types
Are PCB relays all the same? Of course not. These relays come in different forms and designs, even though all are designed to perform the same functions.
Here are the types of PCB relay you should know:
PCB Relay with a Mechanical Switch (SPDT)
This type of PCB relay uses a metal switch to complete or break the circuit. These are also called “momentary” relays because they do not remain in their “on” or “off” position after they have completed the switching action.
This type is ideal for switching low-voltage AC and DC applications and low-power motor control circuits. The SPDT PCB relay is the most common type used in automotive applications. It has two pairs of contacts, and each pair can be used independently or simultaneously by simply wiring them to different poles on a switch or other device.
PCB Relay with a Solid-state Switch (SPST)
These relays contain an electrically operated switch rather than a mechanical one. The solid-state relay is used to control AC or DC circuits. It is sometimes referred to as a “latching” relay because the contacts remain in their on or off position after completing the switching action.
An SPST PCB relay can be used to replace mechanical switches, limit switches, and other devices that require an electrical switch. A solid-state relay may be either unipolar or bipolar; the latter also has three pairs of contacts instead of two.
PCB Relay with a Reed Switch (DPST)
A reed switch is actually just a form of solid-state switch that contains two thin metal reeds instead of contacts. These are positioned between the poles on a magnetic core. They are held in place by electromagnetic attraction when power is applied to the device.
When power is removed from the relay, the reeds will spring back to their original position and open the circuit. This PCB relay is used in situations where a low current and/or a high degree of safety is required.
PCB Relay with Magnetic Contacts (SPDT)
This type of PCB relay has two sets of contacts that are controlled by a magnetic core. It is used to control AC or DC circuits and can be either unipolar or bipolar. When power is applied to the device, the magnetic field will attract the armature to one set of contacts; when power is removed, the armature will return to its original position and make contact with the other set of contacts.
The latter type of PCB relay may also contain a reed switch that allows it to provide switching action without requiring any power at all. This type of PCB relay can be used to replace mechanical switches, limit switches, and other devices that require an electrical switch.
Other classifications of PCB Relays
In addition to the above types, we also have other classification parameters for the PCB relays. These classes include the following:
-High-voltage PCB relays: The relays under this category are designed for high-voltage applications. These relays are used in high-voltage AC and DC applications like industrial, commercial, and automotive.
-Thermal-efficient relays: These are used in applications characterized by high temperature.
Electromechanical features of PCB relays
To better understand what PCB relays are, let’s highlight some of their key electrical and mechanical characteristics.
-High voltage capacity: PCB relays are designed to work with high voltage, up to 1,000 volts for some models. This is mainly due to the high current capacity of relays.
-Overcurrent: In most applications, the relay will be used to switch a low current circuit like lighting or air conditioners. However, overcurrent protection is important in such applications to avoid short circuits and other possible problems due to overcurrent.
-Timer delay: The timer delay feature is usually found on relay models with a manual reset button or with the option to set time delays from 3 seconds up to 24 hours, depending on the model you buy. This helps you avoid unwanted switching when there is no power supply. It also helps protect your equipment from damage due to an unexpected power outage or interruption in supply.
-Frequency protection: Most relays have built-in frequency detection circuits that prevent them from being switched at excessive speeds. This helps protect your equipment from damage caused by the relay’s excessive switching of high voltage circuits.
-Differential protection: A PCB relay is designed to trigger in case two parts of the circuit have different currents or even voltages. If one of the parts of the circuit exceeds its rated capacity, it will trigger the relay to open and close at a very fast rate to protect your equipment.
-Overload protection: Overload protection is a very common feature found on most relays that can help protect your equipment from damage caused by excessive current. In most cases, an overload protection circuit is built into the relay, and it can detect a drop in current and trigger the relay to close.
-Thermal sensitivity: PCB relays are designed to detect temperature changes in the circuit. They will trip once the temperature shoots up beyond the rated capacity.
PCB relay design considerations
The following are the basic considerations for designing PCB relays:
-The PCB relay design should be kept as simple as possible.
-PCB relays should be designed by considering the circuit to which it is connected.
-PCB relays should be designed with the minimum number of contacts that are required in the circuit.
-The PCB relay design should consider the voltage and current ratings of the circuit to which it is connected.
-The PCB relay design should reflect the need and requirement of operating at a particular temperature range.
PCB relays can be used in any type of application like industrial, commercial, automotive, etc., so PCB relay design must always consider all these applications while designing PCB relay.
If you are planning to buy PCB relays, the manufacturer will collect all those details to use them for designing the right relays for your application.
How do you test a PCB relay?
Now that you have bought the PCB relay, how do I know it is working?
You will have to test it. To test, ensure that you identify all the key components of the PCB. These are contacts, poles, coil, and terminals.
Once you know the physiques, you can get various tools for doing the test. An ammeter will be an important tool to help you do the test.
Here are the steps to follow when testing PCB relays:
-First, connect the ammeter to the terminal connected to the load.
-Then, connect the ammeter to a point on the PCB and connect it to the load.
-Next, you will have to check whether there is a voltage drop between terminals and where you have connected it. If there is no voltage drop, you are good to go. If there is a voltage drop, you need to check what caused that voltage drop and fix it accordingly.
-If you are using an AC mains power supply for testing PCB relays, make sure that it has been tested for correct polarity before testing PCB relays.
-If your ammeter has an adjustable scale from 0 VDC up to 20 VDC (milliamp scale), you can use this scale while doing your test. You can also use an ohmmeter with low resistance mode to test PCB relays.
-If you are using a DC mains power supply for testing PCB relays, you can check whether there is a voltage drop between terminals and where you have connected it.
-Before taking the test result, make sure that the load is not connected to the circuit or switch itself.
Precautions for mounting PCB relays
After buying a PCB relay, you will wish to correctly secure it to the PCB. However, this may not be an easy task. If not done carefully, you may end up causing some damage to the relay and even to the PCB.
Various precautionary measures can help you do the mounting safely. Here are some of these precautions;
-Gently push the PCB relay in place and make it fit. Make sure that the pins of the PCB relay are not bent or damaged.
-Ensure that the PCB has the right holes to support the mounting of the PCB relay. If the holes are not properly fabricated, you may damage the PCB.
-Ensure that the mounting hole of the PCB relay has been drilled in a way that it can be properly fitted with screws. If screws have been used incorrectly or if they have been damaged, you may cause damage to it.
-Ensure that all the components on both sides of the PCB relay are properly connected to their respective terminals. If any of these components are not connected properly, you may cause damage to it.
-Make sure that relays and other components do not touch each other or contact each other for a long time, as this might lead to a short circuit and cause damage to them.
-Always use soft cloths while handling relays and other components because hard materials such as metal tools will lead to breakage of delicate parts.
Where can I buy PCB relays?
You can buy PCB relays from online shops and hardware stores. The prices of these relays vary depending on the material used to make them and the product’s specifications.
You can also buy PCB relays in specialized institutes or stores. PCB relays are very expensive in these places.
If you wish to have a custom-made PCB relay, you can go to the PCB manufacturer and give your specifications. The manufacturer will design the exact PCB relay that you want.
And in case you want to find the right PCB relay manufacturer in China, we can link. ICRFQ as a trusted sourcing agent in China, we have contacts of the best PCB manufacturers.
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