How well do you understand the general purpose relay and its application? Our today’s guide introduces this popular electrical device. Let’s start by defining the relay before exploring its various types and applications.
What is a General Purpose Relay?
A general purpose relay is a type of relay designed to work in a broad range of applications. It contrasts with special-purpose relays, which can only operate in specific settings.
In other words, it’s a multipurpose device that works in most standard electrical circuits. The relay is usually a standalone type or built-in. It can also be a mechanical or electronic type.
The relay’s casing is sometimes transparent case, allowing a view of the coil and other parts. Rugged types feature more robust bodies with only connection contacts and terminals.
What Does a General Purpose Relay Do?
A general purpose relay is mainly designed for switching external electrical load on or off depending on the desired function. It helps regulate operations involving electricity, water, and gas.
The relay uses a small excitation current to control circuits that connect to it. The load circuit has a higher output than the trigger circuit, enabling the device to utilize sensor or microcontroller inputs.
That way, the slight change in the primary produces a more significant change in the output, generating a desired function in electrical equipment or control systems.
Areas where you can use the product include homes, commercial places, and industrial settings. Its design allows many installation options, from wired to simple plug-ins.
Resource: https://www.youtube.com/watch?v=cunddFiQzrk
How Does a General Purpose Relay Work?
A small electrical impulse current from the primary circuit goes into its coil. The switching component in the relay responds to this current, moving to close contacts that connect to the moving part.
Sometimes, the relay uses electronic switching components instead of physical parts. These operate more silently than mechanical switching but are more expensive and less rugged.
The device also works with normally open (NO) or normally closed (NC) application needs. “Normally open” configurations maintain open circuits before switching, while the “normally closed” types operate oppositely.
Resource: https://www.youtube.com/watch?v=dAOBHUrw10k
Types of General Purpose Relays
General relays mechanical or solid-state types. The two variants differ in the parts they use to switch loads but their application remains identical. Here is more about them, including their benefits and drawbacks.
Mechanical Type
The mechanical type moves physical components using electromagnetic force. It typically features a coil around a magnetic core and a movable armature. Current flowing through the coil generates a magnetic field.
The field moves the armature which, in turn, opens or closes a set of contacts. Manufacturers usually rate the coil for specific voltages.
The electromagnetic relay’s simple design makes it a cost-effective solution in many situations. However, its moving parts are more prone to wear. This wear decreases their lifespan in high-frequency uses.
Solid State Type
Solid state types use semiconductors for the ON/OFF function. They replace the electromagnetic and moving parts of mechanical relays, making the device more compact and quieter.
Electronic switching also offers better control features and fast action. They also consume less power, making them crucial where efficiency is critical.
The SS types of relays have their drawbacks despite offering several advantages. For instance, they cost more making them less viable in simpler operations.
Key Specifications of a General Purpose Relay
A device has various specifications. Buyers must understand these features when selecting the product. They include the following, depending on whether the device is mechanical or solid-state/electronic.
- Voltage Rating — the switching voltage is the maximum the relay can withstand across its contacts, while coil voltage is the highest level required to energize it.
- Current Rating — the maximum current it can sustain during switching without damage.
- Power consumption — the amount of power the device consumes when current is applied to the coil.
- Temperature Range — the temperature within which the device can operate safely.
- Contact Form — options include NO, NC, SPDT, DPDT, etc.
- Response Time — the time it takes the device to switch the load circuit on/off upon activation
- Contact Resistance — the combined resistance of the contacts and armature, terminals, etc.
- Coil Resistance – the resistance measured at the coil contacts, usually expressed against a specific temperature level.
- Life Cycle — the estimated number of cycles it can undergo in its lifetime.
- Mounting Method — the choices include DIN rail, PCB-mounted, or socket/plug-in.
Resource: https://www.youtube.com/watch?v=zGlWCBoQSyo
What is a General Purpose Relay Used For?
The product has a wide range of applications, given its standard construction and varied ratings. Here, we review its most popular uses in homes, automobiles, communication, and industrial settings.
Household Appliances
The relay is an automation device in home lighting, air conditioning, and water treatment systems, among other needs. These applications often involve paring the relay with electronic controllers and sensors.
Automotive Systems
The relay is an invaluable device in the automotive industry. It controls electrical systems in vehicles, enabling their precise control. Systems that use the device include lighting, actuation components, and various motors.
Telecommunication Equipment
Telecommunication equipment uses the device to control various processes. The relays in this application operate in high-frequency circuits requiring fast switching, quiet operation, and several other features.
Industrial Machinery
The relay is often a sequencing device in industrial automation processes and I/O systems, enabling electronic controllers to automate procedures. It uses low-power inputs to control high-power loads.
For instance, it may use controller signals to switch a motor or solenoid valve. Many industrial robots also use the device, given its versatility and ease of use.
Factors to Consider When Choosing a General Purpose Relay
The relay is available in various configurations and ratings. This variation can present selection challenges. Buyers should consider the following when choosing the device for their projects.
Load Requirements
Different load types impact the relay’s performance and longevity. Ensure the model you choose matches your application’s voltage and current ratings. It helps you avoid failure or shortened product lifespan.
For instance, inductive loads cause current and voltage spikes. The relay must be able to handle that without getting damaged or wearing too quickly.
Size and Compatibility
Size and system compatibility are key features when selecting the device. For example, a miniature general purpose relay is suitable for compact devices and low-power settings.
Ensure the size matches the installation area of the electric system or equipment. The device is available in many dimensions, making its selection less challenging.
Environmental Conditions
Determine the operation environment or condition. Adverse situations include excessive heat, dust, humidity, and vibrations. Ensure you choose a model that can withstand the specific application conditions to prevent failure or durability issues.
Resource: https://www.youtube.com/watch?v=a_1zCZ1Xavs
How to Wire a General Purpose Relay
The device works like any other relay – using a small current to switch a larger circuit on or off or control components. It has contacts that connect to the signal source and load circuit. Here’s how to wire one correctly.
Materials and Tools
Gather all the tools and materials you need for the job depending on the relay’s type (wires, pliers, crimping tool, wire strippers, shrink tubing, and a digital multimeter for testing).
Wiring Diagram
Read the product’s wiring diagram. It provides a visual representation of the connections and circuits. The relay’s symbol is typically a triangle on the schematics, while the switch is a line with a break.
On the other hand, the load circuit is a light or motor symbol. Other visuals include solid lines for wires and lines with decreasing lengths for the ground connection.
Wiring Steps
First, determine whether the relay is a 4 or 5-pin type. Doing so will help you tell which terminals you have for connections. Follow the coil circuit and identify its pins.
The pins are usually labeled (30) for “common”, 85 and 86 for the coil circuit, and 87/ 87a for the load’s NO/NC contacts. Follow these steps to wire a 4-pin, normally open type.
- Identify if the pins are NO or NC.
- Connect pin 85 to the negative terminal of your power source (or ground).
- Connect pin 86 to the control circuit’s positive.
- Next, connect the load by wiring pin 30 to the power source positive.
- Connect pin 87 to the load’s positive terminal.
- Pin 87 connects to the power source positive in a normally closed configuration, while pin 30 connects to the load positive.
A 5-pin type has NO and NC contacts, making its application more flexible and versatile. Here is how to wire one.
- Connect pin 85 to the ground or power source negative.
- Connect pin 86 to the control circuit’s positive.
- Connect pin 30 to your power source.
- Connect pin 87 to the load’s positive for NO operation and 87A for NC function.
Conclusion
The general purpose relay is one of the most used devices in electrical equipment and systems. It has applications in home appliances, industrial operations, telecommunications, and car systems. The type of relay you choose must match its various requirements, such as voltage, current, and environmental protection.
