Trystan Casey
Relays are electrically operated switches that can be used to control high-power devices such as motors, heaters, and lamps. They are commonly used in consumer electronic devices, industrial machinery, control panels, and automotive systems. When designing a circuit, it is important to consider the type of relay required, such as a 4-pin or 5-pin relay, and the mounting and positioning of the relay to ensure its protection. Connecting a relay involves identifying the pinouts, which may not always be marked, and understanding the switching action of the relay coil. By energizing the coil, a magnetic field is generated, causing the movement of the armature and the subsequent connection or disconnection of the circuit.
| Characteristics | Values |
|---|---|
| Relay Type | Electromagnetic, Thermal, Timer, Flasher, MOSFET, Bipolar Junction Transistor (BJT), ISO Mini, 4-Pin, 5-Pin |
| Relay Function | Turns on/off high-power devices with small signals |
| Relay Composition | Coil, Core, Armature, Return Spring, Moving Contact, Fixed Contact |
| Coil Composition | Copper coil around an iron core (the electromagnet) |
| Coil Function | Generates a magnetic field when an electrical current passes through |
| Armature Function | Moves when the coil is energised, completing the circuit |
| Return Spring Function | Provides a restoring force when the coil is de-energised |
| Moving Contact Function | Moves with the armature, making or breaking contact with fixed contacts |
| Fixed Contact Function | Normally Closed (NC) when the relay is not energised |
| Relay Coil Terminal Polarity | None unless the relay coil is protected by a diode |
| Relay Applications | Consumer electronic devices, industrial machinery, control panels, medical and scientific equipment, communications equipment, transportation |
| Relay Mounting | Away from transformers, semiconductors, or other devices that generate heat |
| Relay Design | Protects relays from shock or vibration |
| Relay Terminal Widths | 6.3mm, 2.8mm, 4.8mm, 9.5mm |
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What You'll Learn
Identifying relay pinouts
Relays are an essential component of modern electrical systems, allowing a low-current circuit to control one or more higher-current circuits. They are used in a variety of applications, from automobiles to home automation systems.
Understanding Relay Basics
Firstly, it's important to understand the basic components of a relay. A relay consists of a coil and a spring-loaded contact that can move across a pivoted axis. The coil is wound around an iron core, creating an electromagnet when a current is passed through it. This electromagnetic field attracts a nearby spring-loaded metal pole, switching the contacts. These contacts are the relay's terminals or pinouts.
Identifying Relay Types
Relays come in different configurations, so pin identification varies depending on the type. Common relay types include:
- 4-pin relays: Used to control a single circuit. They have two pins for controlling the coil (85 and 86) and two pins for switching power (30 and 87).
- 5-pin relays: Used to switch power between two circuits. They also have two pins for coil control (85 and 86) and three pins for switching power between two circuits (30, 87, and 87A).
Identifying Pinouts with a Meter
If your relay does not have marked pinouts, you can use a meter to identify them:
- Connect the meter probes to any two pins on the relay.
- Look for pins indicating resistance (between 100 and 500 Ohms) on the meter display. These are the coil pinouts.
- Repeat the process with the remaining terminals until you find two pins showing continuity. These are the N/C (Normally Closed) and the pole of the relay.
- Identify the single terminal forming a triangular configuration with the previously identified pins. This is typically the relay pole.
- The remaining pin is the N/O (Normally Open) contact.
Relay Diagrams and Markings
Relays often have diagrams and markings that can help identify pinouts:
- Relay diagrams: These use standard symbols for the coil, contacts, and other components. Learning these symbols can make it easier to interpret the diagram and identify pinouts.
- Relay markings: Relays usually have voltage and current ratings, terminal numbers, and other specifications marked on the body. These markings assist in identifying the pinouts and their functions.
Common Relay Pinouts
- Coil Pins: Used to energize the relay coil.
- Contact Pins: Connect the relay to the load and control circuits.
- Common Pin (COM): The common connection for the switch.
- Normally Open Pin (NO): Connects to the common pin when the relay is energized.
- Normally Closed Pin (NC): Connects to the common pin when the relay is de-energized.
Remember to exercise caution when working with electrical circuits, and ensure you have a good understanding of relay functionality before proceeding.
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Connecting a relay to a PCB
Electromagnetic relays, for instance, receive an electric signal and convert it into the mechanical action of a switch, opening and closing the circuit. When mounting electromagnetic relays to a PCB, it is essential to determine whether the relay is unsealed, sealed, or a flux-protection type. Unsealed relays require manual soldering and cannot withstand immersion cleaning, so the terminals must be separated from the PCB surface, and the contacts positioned away from the base. Sealed and flux-protection relays, on the other hand, prevent flux and cleaning solvents from entering the housing. Flux-protection relays direct solder onto the PCB but also cannot withstand immersion cleaning.
Solid-state relays (SSR) offer advantages such as long service life, no contact bounce or arching, zero-crossing capability, low power input, and high resistance to shock and vibration. They can switch much faster than PCB power relays due to the absence of moving parts.
Reed relays feature a pair of magnetic strips sealed within a glass tube, and they act as an actuator and contact blade during switching. Thermal relays, connected in series with a motor, have two terminals and switch contacts when the ambient temperature rises above a certain limit, protecting the motor or device from overload.
When connecting a relay to a PCB, it is important to ensure optimized connections for consistent performance. This includes minimizing contacts for efficiency and cost-effectiveness, matching voltage and current ratings, and optimizing the operational temperature range.
The type of relay selected depends on the specific requirements of the project. For example, solid-state relays are ideal for applications requiring long service life and shock resistance, while electromagnetic relays are suitable for projects where a mechanical switch is needed.
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Relay wiring diagrams
A relay is an electrically operated switch that can be used to control one or more circuits. They are commonly used in cars to control headlights, electric motors, heaters, etc. Relays can be identified by the number of pins they have, with 4-pin and 5-pin relays being the most common.
A 4-pin relay uses two pins (85 and 86) to control the coil and two pins (30 and 87) to switch power on a single circuit. There are two types of 4-pin relays: normally open and normally closed. A normally open relay will switch power on for a circuit when the coil is activated, while a normally closed relay will switch power off.
A 5-pin relay provides two pins (85 and 86) to control the coil and three pins (30, 87, and 87A) to switch power between two circuits. It has both normally open and normally closed connection pins. When the coil is activated, power will switch from the normally closed pin to the normally open pin.
- Connecting Additional Devices to the Remote Turn-On Wire: This diagram shows how to connect multiple devices to a single remote turn-on wire.
- Constant to Momentary Output with Negative Input/Negative Output: This diagram illustrates how to connect a constant power source to a momentary output using negative input and output voltages.
- Latched On/Off Output Using Two Momentary Negative Pulses with Negative Outputs: This diagram demonstrates how to create a latched output using two negative pulses, resulting in negative outputs.
- Basic Relay Diagram: This diagram shows the basic components of a relay, including the coil, core, armature, and contacts, and how they are connected in a circuit.
- Double-Pole, Double-Throw (DPDT) Relay Diagram: This diagram illustrates how a DPDT relay can control two separate circuits with two sets of contacts.
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Relay types and uses
Relays are electrically operated switches that can be used to turn on and off high-power devices with tiny electrical signals. They are commonly used in small electronic circuits and automotive applications.
There are several types of relays, each with its own unique characteristics and applications:
- Electromagnetic Relay (EMR): EMRs can be used with either an AC or DC power source, depending on the application. They are constructed using coils, which can create an electrical arc when separated, leading to increased contact resistance over time.
- Solid-State Relay (SSR): SSRs are composed of semiconductor components rather than mechanical elements. When a control signal is applied, an internal light-emitting diode (LED) illuminates, emitting infrared light.
- Electrothermal Relay: This type of relay uses a bimetallic strip, made of two metals with different thermal expansion coefficients. When current flows through the conductor, it generates heat, causing the strip to bend and close the contacts, activating the trip circuitry. Electrothermal relays are commonly used for electric motor protection.
- Sequencer Relay: These relays are designed to control the sequence of operations in various electrical devices or system components. They are often used in applications where precise timing and order of operations are critical, such as HVAC systems, to prevent power surges and ensure proper air circulation.
- Differential Relay: Differential relays are protective devices used in electrical power systems to detect faults within equipment, including transformers, generators, motors, and busbars.
- Distance Relay: This type of relay is used in electrical power systems, primarily for protecting transmission lines. It measures the impedance between the relay location and the fault on the line, allowing it to determine the approximate location of the fault and isolate the affected section.
- Latching or Bistable Relay: A latching relay is an electromechanical switch that can maintain its switching state even without continuous power applied to its coil, differentiating it from a standard relay.
Relays come in various configurations, including 4-pin and 5-pin designs, and they can control one or multiple circuits. The pins on a relay are typically marked with voltage, amperage, and a numbered diagram to indicate their function.
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Relay positioning
Relays are electromagnetic switches that can be used to control a variety of electrical circuits. They are commonly used in automotive applications to control multiple circuits with a single input, such as headlights, electric motors, and heaters, and indicators. Relays can also be used to protect various AC and DC equipment by controlling high-power devices with a small current signal.
When considering relay positioning, it is important to understand the two main types of relays: solid-state relays (SSRs) and electromechanical relays (EMRs). SSRs have control pins instead of coil pins, while EMRs use mechanical components that move in response to electromagnetic force. The choice between SSRs and EMRs depends on the specific application and design considerations.
In an electrical circuit, the relay is positioned between the power source and the load. The relay coil is connected to the power source, and when energised, it generates a magnetic field that activates the relay and completes the circuit. This allows electricity to flow through the relay and power the connected device.
The positioning of the relay in the circuit depends on the specific application and the number of circuits being controlled. In a simple circuit, the relay can be positioned before the load, with the power source connected to the relay coil and the load connected to the relay's output. In more complex applications, such as automotive systems, relays can be linked to perform logical operations and control multiple circuits.
When positioning a relay in an electrical circuit, it is important to consider the voltage and current ratings of the relay. The coil voltage rating is the voltage required for the coil to operate correctly, and it should not be exceeded. The switching circuit of the relay will also have a maximum voltage and ampere rating that must be considered when designing the circuit. Additionally, the physical size and shape of the relay may impact its positioning, especially in space-constrained applications.
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Frequently asked questions
A relay is an electrically operated switch that uses an electromagnet to operate a pair of movable contacts from an open position to a closed position.
Begin by connecting the meter probes to any two pins of the relay randomly until you find the pins that indicate some resistance on the meter display. These pins signify the coil pinouts of the relay. Next, connect the meter probes randomly to the remaining three terminals until you find two pins indicating continuity across them. These two pins are the N/C and the pole of the relay.
First, ensure that you have identified the pinouts of the relay. Then, connect the relay coil terminals to the circuit. If the relay coil is protected by a diode, the coil terminal wired to the diode's anode must be connected to negative. Finally, connect the relay to a power source to energize the coil and complete the circuit.
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