The Kynix Blog - Relays

A Relay is an electrically operated switch. It allows a low-power signal (like one from a microcontroller or dashboard switch) to control a high-power circuit (like an electric motor, headlights, or industrial machinery). In essence, it provides complete electrical isolation between the control system (input loop) and the controlled system (output loop).Used extensively in automotive systems, industrial automation, and modern Smart Home setups, the relay acts as an "automatic switch." It uses a small current to control a much larger one, offering crucial benefits like automatic adjustment, safety protection, and circuit conversion.As of 2025, while Solid State Relays (SSRs) are gaining popularity for their silence and longevity, the traditional electromechanical relay remains the industry standard for high-current and cost-effective switching. This guide covers how to wire these essential components effectively.Ⅰ Electrical Relay Structure & BasicsFigure 1. Electrical Relay StructureTo understand how to wire a relay, you must first understand its internal architecture:Core Components: A relay consists of four primary parts: the coil, the magnetic circuit (core/yoke), the spring, and the contacts.The Coil: When energized, the coil generates an electromagnetic field. This attraction pulls the armature, changing the state of the contacts.Magnetic Circuit: Comprising an iron core, choke, and armature, this establishes the path for magnetic flux.Air Gap: This is the critical distance between the armature and the core. When the coil is off, the gap is at its maximum (contacts in initial state). When on, the gap closes (contacts switched).The Spring: Provides the resetting force. When the coil is de-energized, the spring pushes the armature back to its original position.Contacts: These execute the control. They are divided into Normally Closed (NC) and Normally Open (NO).Energized: NC opens, NO closes.De-energized: Contacts reset to initial state.Common Types of Relays:Voltage Relays: High coil turns, thin wire. Connected in parallel with the load. (Most common).Current Relays: Few turns, thick wire. Connected in series with the load.Intermediate Relays: Used for signal transmission and controlling multiple secondary circuits.Ⅱ How Do Relays Work?An electromechanical relay is a switch operated by an electromagnet. When the coil receives current, the magnetic force pulls the "Common" (COM) contact arm from the "Normally Closed" (NC) position to the "Normally Open" (NO) position. When power is cut, a spring snaps it back.In short: When a specific input (voltage, current, temperature) hits a set value, the relay changes the state of the output circuit to control or protect the system.Example Analysis: Controlling a LightFigure 2. 8 Pin Relay Wiring ConnectionFigure 3. Relay Controls One LightWiring Logic:To control a lamp using a relay, the power circuit is wired through the relay's contacts. The Neutral wire connects directly to the lamp. The Live (Hot) wire connects to the relay's Normally Open (NO) contact. When the relay is triggered, the circuit closes, and the light turns on.Figure 4. Relay Controls Two Lights (Toggle)Dual Light Setup: By using both NC and NO contacts, you can toggle between two loads. When the coil is OFF, the NC light is ON. When the coil is ON, the NC light turns OFF and the NO light turns ON.Ⅲ Relay Wiring with Different Pins3.1 3-Pin RelayWhat is a 3-Pin Relay?These are commonly found in automotive applications as Flasher Units (for turn signals) or simplified horn relays. They work on electromechanical or thermal principles to cycle power on and off.How to Wire a 3-Pin Relay:Figure 5. 3-Pin Relay Wiring DiagramStandard configuration for a horn or load:Pin 1 (Load): Connected to the device (e.g., horn).Pin 2 (Battery/Power): Connected to the 12V power source (Common).Pin 3 (Switch/Coil): Connected to the button (e.g., steering wheel button).3.2 4-Pin Relay (SPST)What is a 4-Pin Relay?The 4-pin relay is the most common Single Pole Single Throw (SPST) relay used in automotive and general electronics to switch a single circuit on or off.How to Wire a 4-Pin Relay:Figure 6. 4-Pin Relay Wiring DiagramPins 85 & 86 (Coil): These control the magnet. Connect one to ground and the other to your switch (+12V).Pin 30 (Common): Connected to the high-power source (Battery +).Pin 87 (Normally Open): Connected to the load (Fan, Light, Motor).When the coil (85/86) is energized, Pin 30 connects to Pin 87.Figure 7. Standard 12V 40A 4-Pin RelayFigure 8. Coil Pins (85 & 86)Figure 9. Contact Pins (30 & 87)3.3 5-Pin Relay (SPDT)What is a 5-Pin Relay?This is a Single Pole Double Throw (SPDT) relay. It allows you to switch power between two circuits (e.g., High Beam vs. Low Beam) or simply use the "Normally Closed" feature.How to Wire a 5-Pin Relay:Figure 10. 5-Pin Relay Wiring DiagramPins 85 & 86: Coil (Control).Pin 30: Common (Power In).Pin 87a: Normally Closed (Power flows here when relay is OFF).Pin 87: Normally Open (Power flows here when relay is ON).3.4 6-Pin RelayWhat is a 6-Pin Relay?A 6-pin relay often functions similarly to a 5-pin but includes an extra terminal for internal bridging or specific DPDT signal configurations. In some automotive wiper relays, the extra pin handles parking logic.Wiring Overview:Figure 11. 6-Pin Relay Wiring DiagramTypically, two pins act as the coil, and the remaining four form two pairs of switching contacts (or one complex changeover). Always check the specific datasheet, as 6-pin configurations vary more than standard 4/5-pin types.3.5 8-Pin Relay (DPDT)What is an 8-Pin Relay?This is usually a Double Pole Double Throw (DPDT) relay. It effectively houses two 5-pin relays inside one shell, controlled by a single coil. It is ideal for reversing polarity on motors.How to Wire an 8-Pin Relay:Figure 12. 8-Pin Relay Wiring DiagramPins 2 & 7: Coil terminals (Power these to activate).Pins 1 & 8: Common terminals (COM).Pins 3 & 6: Normally Open (NO).Pins 4 & 5: Normally Closed (NC).3.6 Intermediate (Auxiliary) RelayWhat is an Intermediate Relay?Often used in industrial control panels (DIN Rail mounted), these relays transmit signals to control multiple larger contactors or actuators simultaneously. They are the backbone of classical automation logic.Wiring and Safety (Flyback Diodes):Figure 13. Intermediate Relay Wiring DiagramStandard industrial numbering (IEC):13 & 14: Coil (A1/A2).Contacts: Arranged in groups (e.g., 5-6-7-8 as NC, 9-10-11-12 as NO).⚠️ 2025 Safety Tip: When using intermediate relays with DC currents, always install a Freewheeling (Flyback) Diode across the coil (Reverse biased: Cathode to Positive). When the coil turns off, the collapsing magnetic field creates a high-voltage spike (back EMF) that can destroy sensitive control electronics (like PLCs or Arduino boards).Ⅳ FAQ: Relay Wiring in 20251. What is the difference between a Solid State Relay (SSR) and a Mechanical Relay?Mechanical relays use moving parts (magnets/contacts) and make a "click" sound. They are cheaper and handle high surge currents well. SSRs use semiconductors (light/optical isolation), have no moving parts, are silent, and last much longer, but they generate heat and are generally more expensive.2. What do the numbers on a standard automotive relay mean?These are DIN standard numbers: 30: Common (Main Power Input) 85: Coil Ground 86: Coil Positive (Trigger) 87: Normally Open (Output when ON) 87a: Normally Closed (Output when OFF)3. Does a Smart Home relay switch require a Neutral wire?Yes. Unlike older mechanical switches that just cut the Live line, most modern 2025 Smart Relays (WiFi/Zigbee) need a Neutral wire to power their internal WiFi chip so they can stay connected even when the light is off.4. What happens if I wire Pins 85 and 86 backwards?On a standard mechanical relay without a diode, nothing happens—it will still work because the coil is not polarized. However, if the relay has a built-in suppression diode (common in modern cars), wiring it backwards will cause a dead short and blow your fuse.5. What is an SPDT Relay?SPDT stands for Single Pole Double Throw. It has one input (Common) and two outputs (NC and NO). It can route power to Circuit A when off, and switch to Circuit B when on.6. Can I use a 12V relay on a 24V circuit?No. You must match the Coil Voltage to your control system (e.g., 12V car vs. 24V truck). However, the contacts (switch part) can often handle higher voltages than the coil. Always check the rating printed on the case.

In this article, we will present you a comprehensive introduction to solid state relay, covers from its definition, characteristics, structure, pros and cons, and some problems you might encounter with during using SSR and so on. Catalog I. What is a Solid State Relay? 1.1 Brief Introduction 1.2 Structure of Solid State Relay 1.3 Characteristics of Solid State Relay 1.4 Difference Between Solid State Relay & Normal   Relay II. Pros and Cons of Solid State Relay III. Common Problems of Solid State Relays IV. Maintenance Method of Solid State Relay V. Application of Solid State Relay FAQ I. What is a Solid State Relay? 1.1 Brief Introduction The solid state relay (SSR) is a non-contact switch composed of microelectronic circuits, discrete electronic devices, and power electronic power devices. It is a component of a full electronic circuit combination. It depends on the electromagnetic and optical characteristics of semiconductor devices and electronic components. Its isolation and relay switching functions.   This video tells briefly what solid state relay is. Compared with the traditional electromagnetic relay, the solid-state relay is a relay without machinery and no moving parts, but has essentially the same functions as the electromagnetic relay.   Solid state relays are widely used in industrial automation control, such as electric furnace heating systems, familiar control machinery, remote control machinery, motors, solenoid valves and signal lights, flashers, stage lighting control systems, medical equipment, photocopiers, washing machines, fire protection systems, etc. It works reliably, has no contact, no spark, long life, no noise, no electromagnetic interference, fast switching speed, and achieves the purpose of directly driving a large current load with a tiny control signal. 1.2 Structure of Solid State Relay The solid state relay is composed of three parts: input circuit, isolation (coupling) and output circuit.   1. Input circuit: According to the different types of input voltage, the input circuit can be divided into three types: DC input circuit, AC input circuit and AC/DC input circuit. Some input control circuits are also compatible with TTL/CMOS, positive and negative logic control and inverting functions, and can be easily connected with TTL and MOS logic circuits.   For a control signal with a fixed control voltage, a resistive input circuit is used. The control current is guaranteed to be greater than 5mA. For the control signal with a large variation range (such as 3~32V), a constant current circuit is used to ensure reliable operation of the current greater than 5mA within the entire voltage variation range.   2. Isolation and coupling The input and output circuits of solid state relays can be isolated and coupled in two ways: photoelectric coupling and transformer coupling: photoelectric coupling usually uses photodiodes-phototransistors, photodiodes-bidirectional light-controlled silicon controlled thyristors, photovoltaic cells, to achieve control side and load side Isolation control; high-frequency transformer coupling is a self-excited high-frequency signal generated by the input control signal is coupled to the secondary, detected and rectified, and processed by a logic circuit to form a drive signal.   3. Output circuit The power switch of the SSR is directly connected to the power supply and the load side to realize the on-off switching of the load power supply. Mainly use high-power transistors, unidirectional thyristors (or SCR), bidirectional thyristors (Triac), power field effect transistors (MOSFET), and insulated gate bipolar transistors (IGBT).   The output circuit of solid state relay can also be divided into DC output circuit, AC output circuit and AC/DC output circuit. According to the load type, it can be divided into DC solid state relay and AC solid state relay. Bipolar devices or power FETs can be used for DC output, and two thyristors or one bidirectional thyristor are usually used for AC output. The AC solid-state relays can be divided into single-phase AC solid-state relays and three-phase AC solid-state relays. AC solid-state relays can be divided into random AC solid-state relays and zero-crossing AC solid-state relays according to the timing of turn-on and turn-off. 1.3 Characteristics of Solid State Relay The solid state relay is a non-contact electronic switch with isolation function, and there are no mechanical contact parts during the switching process. Therefore, in addition to the same functions as electromagnetic relays, solid state relays also have logic circuit compatibility, vibration resistance and mechanical shock resistance, unlimited installation location, and good moisture, mildew and corrosion resistance. It also has excellent performance in explosion protection and prevention of ozone pollution. It also has the characteristics of low input power, high sensitivity, low control power, good electromagnetic compatibility, low noise and high operating frequency.   (1) The SSR has no internal mechanical parts, and the structure adopts a fully sealed method of perfusion. Therefore, the SSR has the advantages of vibration resistance, corrosion resistance, long life and high reliability, and its switch life is up to 10.1 million times; (2) Low noise: AC SSR adopts zero-crossing trigger technology, so the voltage rise rate dv/dt and current rise rate di/dt value are effectively reduced on the line, so that the SSR has minimal interference to the mains during long-term operation; (3) Its switching time is short, about 10ms, which can be used in higher frequency occasions; (4) It adopts photoelectric isolation between its input circuit and output circuit, and the insulation voltage is above 2500V; (5) Its input power consumption is very low, compatible with TTL and COMS circuits; (6) Its output terminal has a protection circuit; (7) Strong load capacity. 1.4 Difference Between Solid State Relay & Normal Relay Ordinary relays are generally composed of relay coils and static and dynamic contacts. The movable contact is actuated by the electromagnetic attraction force of the relay coil to realize the connection and disconnection of the circuit. So there is mechanical movement. When the current reaches a certain level, the contacts will spark. Ordinary relays are cheap and simple in structure, but sparks and mechanical movements during operation will have a certain impact on its life.   The advantages of ordinary relays are: simple drive, good isolation, and good short-term overload tolerance. The disadvantages of ordinary relays are: large size (heavy), slow response speed (up to ms level), and large power consumption to drive the relay.   The comparison between traditional relays and solid-state relays, as there are many types involved, the following is a comparison between electromagnetic relays and corresponding solid-state relays to illustrate their differences:   1. Structural difference: Electromagnetic relays work by using the suction force generated by the circuit in the input circuit between the electromagnet core and the armature; solid-state relays use electronic components to perform their functions without mechanical moving components, and the input and output are isolated.   2. Difference in working mode: Electromagnetic relay uses the principle of electromagnetic induction to control the on-off of the circuit through the power of electromagnet. Therefore, when DC is used to connect the coil, the contacts can pass AC and DC; solid state relays rely on the electrical, magnetic and optical characteristics of semiconductor devices and electronic components to complete their isolation and relay switching functions. Therefore, they are divided into DC input-AC output type and DC Input-branch output type, AC input-AC output type, AC input-DC output type.   3. Differences in working status: Electromagnetic relays make use of the suction force generated between the armature to make and break the circuit. Therefore, the action response is slow, noisy, and life is limited; solid state relays have fast response, operate without noise, and have a long life.   4. Operating environment: In the influence of temperature, humidity, atmospheric pressure (altitude), sand and dust pollution, chemical gas and electromagnetic interference, electromagnetic relays are generally inferior to solid state relays.   5. Electrical performance difference: Compared with the corresponding solid-state relay, the electromagnetic relay is simple to drive, but has large power consumption, good isolation, good short-term overload tolerance, and is not as good as the latter in high-current and high-power situations. And when controlling the circuit with frequent action, the life of the electromagnetic relay is not as long as the latter.   In short, traditional relays and solid state relays have their own advantages. The latter is more and more popular because of its reliable operation, no contacts, no sparks, long life, no noise, no electromagnetic interference, and fast switching speed.   II. Pros and Cons of Solid State Relay Pros: (1) Long life and high reliability: SSR has no mechanical parts and solid components to complete the contact function. Because there are no moving parts, it can work in a high impact and vibration environment. Because of the components that make up the solid state relay The inherent characteristics determine the long life and high reliability of solid state relays.   (2) High sensitivity, low control power, and good electromagnetic compatibility: The solid state relay has a wide input voltage range and low drive power, and is compatible with most logic integrated circuits without the need for buffers or drivers.   (3) Fast switching: Because solid-state relays use solid-state devices, the switching speed can range from a few milliseconds to several microseconds.   (4) Electromagnetic interference: The solid state relay has no input "coil", no arc ignition and rebound, thus reducing electromagnetic interference. Most AC output solid state relays are a zero-voltage switch, which is turned on at zero voltage and turned off at zero current, reducing the sudden interruption of the current waveform, thereby reducing the switching transient effect.   Cons: (1) After the solid state relay is turned on, the tube voltage drop is large, and the forward voltage drop of the thyristor or two-phase thyristor can reach 1~2V, and the saturation voltage drop of the high-power transistor is also between 1~2V. Generally, the on-resistance of the power FET is also larger than the contact resistance of the mechanical contacts.   (2) The semiconductor device can still have a leakage current of several microamperes to several milliamperes after it is turned off, so ideal electrical isolation cannot be achieved.   (3) Due to the large pressure drop of the tube, the power consumption and heat generation after the turn-on are also large, the volume of the high-power solid-state relay is much larger than the electromagnetic relay of the same capacity, and the cost is also higher.   (4) The temperature characteristics of electronic components and electronic circuits have poor anti-interference ability and poor radiation resistance. If effective measures are not taken, the working reliability of solid state relays will be reduced.   (5) Solid state relays are more sensitive to overload and must be protected by fast fuse or RC damping circuit. The load of the solid state relay is obviously related to the ambient temperature. As the temperature rises, the load capacity will drop rapidly. III. Common Problems of Solid State Relays When the solid state relay is open and there is voltage at the load terminal, there will be a certain amount of leakage current at the output terminal. Care should be taken to prevent electric shock when using or designing. When solid state relays fail to be replaced, products with the same original model or technical parameters should be used as much as possible to match the original application circuit to ensure the reliable operation of the system. Among all, overheat, overcurrent and overvoltage are always the common problems you might encounter when using a solid state relay.   overheat When the SSR is turned on, the component will withstand the dissipation power of P=V (tube pressure drop) × I (load), where the effective value of V and the effective value of I are the effective values of the saturation voltage drop and the operating current, respectively.   The load capacity of the solid state relay is greatly affected by the ambient temperature and its own temperature rise. It must be based on the actual working environment conditions and strictly refer to the allowable case temperature rise (75°C) at the rated working current. Reasonably select the size of the radiator or reduce the current for use. During installation and use, ensure that it has good heat dissipation conditions, otherwise it will cause loss of control due to overheating, and even cause product damage.   Generally speaking, under 10A, an instrument base plate with good heat dissipation conditions can be used, and a product with a rated working current above 10A should be equipped with a radiator.   Below 30A, use natural air cooling. When the continuous load current is greater than 30A, the instrument fan must be used for forced air cooling. Products above 100A should be equipped with a radiator and a fan for forced cooling.   When installing, pay attention to the good contact between the bottom of the relay and the radiator, and consider applying a proper amount of thermal grease to achieve the best heat dissipation effect.   For example, when the relay is working at high temperature for a long time (40℃~80℃), the user can consider derating according to the curve data of the maximum output current and ambient temperature provided by the manufacturer to ensure normal operation.   Reasons for overheating of solid state relays: When the solid state relay is working normally, there is a certain power loss on its internal chip. This power loss is mainly determined by the product of the output voltage drop of the solid state relay and the load current, and is consumed in the form of heat.   Therefore, the quality of heat dissipation directly affects the reliability of the solid state relay, and the excellent thermal design can avoid failure and damage caused by poor heat dissipation.   Overcurrent and overvoltage When the relay is in use, the internal output thyristor of the SSR solid state relay will be permanently damaged due to overcurrent and load short circuit. You can consider adding a fast fuse and an air switch to the control loop for protection (the product output protection should be selected when selecting the relay, built-in Varistor absorption circuit and RC buffer can absorb surge voltage and improve dv/dt tolerance).   Fast fuse and air switch are general overcurrent protection methods. Fast fuse can be selected according to 1.2 times of rated working current, generally small capacity fuse can be used. Pay special attention to load short circuit, which is the main cause of damage to SSR products.   For inductive and capacitive loads, in addition to the internal RC circuit protection, it is recommended to use a varistor in parallel at the output as a combined protection. The area of the metal zinc oxide varistor (MOV) determines the absorption power, and the thickness determines the protection voltage value.   For AC 220V SSR, select MYH12-430V varistor; 380V select MYH12-750V varistor; for larger capacity motor transformer, select MYH20 or MYH2024 varistor with large current capacity. The selection principle is to use 500V-600V varistors for 220V, and 800V-900V varistors for 380V. IV. Maintenance Method of Solid State Relay 1. When selecting solid state relays used on printed circuit boards with low current specifications, since the lead terminals are made of high thermal conductivity materials, the soldering should be carried out under the conditions of a temperature less than 250℃ and a time less than 10S. If the surrounding temperature is considered, If necessary, derating can be considered. Generally, the load current should be controlled within 1/2 of the rated value.   2. Selection of solid state relays for various load surge characteristics   The controlled load will generate a large inrush current at the moment of switching on. Because the heat is too late to dissipate, it is likely to damage the SSR's internal thyristor.   Therefore, the user should analyze the surge characteristics of the controlled load when selecting the relay, and then select the relay. The relay can withstand this surge current under the premise of ensuring steady-state operation. When selecting, refer to the derating factor of various loads in Table 2 (at normal temperature).   If the selected relay needs to work in the occasions with more frequent work, high life and reliability requirements, it should be multiplied by 0.6 on the basis of Table 2 to ensure reliable work.   Generally, follow the above principles when selecting, and when low voltage requires low signal distortion, you can choose a DC solid-state relay that uses a field effect tube as an output device; for example, for AC resistive loads and most inductive loads, you can choose a zero-crossing relay. Extend the life of loads and relays, and also reduce their own radio frequency interference. For phase output control, random solid state relays should be used.   3. The influence of ambient temperature   The load capacity of solid state relays is greatly affected by the ambient temperature and its own temperature rise. During installation and use, ensure that it has good heat dissipation conditions. Products with a rated operating current of more than 10A should be equipped with a radiator, and products with a rated operating current of more than 100A should be equipped with a radiator. Equipped with a radiator and a fan for forced cooling. When installing, pay attention to the good contact between the bottom of the relay and the radiator, and consider applying a proper amount of thermal grease to achieve the best heat dissipation effect.   For example, when the relay is working at high temperature for a long time (40℃~80℃), the user can consider derating according to the curve data of the maximum output current and ambient temperature provided by the manufacturer to ensure normal operation.   4. Overcurrent and overvoltage protection measures   When the relay is used, the internal output thyristor of the SSR solid-state relay will be permanently damaged due to overcurrent and load short-circuit. Consider adding a fast fuse and air switch to the control loop to protect it (the product output protection should be selected when choosing the relay, built-in Varistor absorption circuit and RC buffer can absorb surge voltage and improve dv/dt tolerance); RC absorption circuit and varistor (MOV) can also be connected in parallel at the output of the relay to achieve output protection. The selection principle is to use 500V-600V varistors for 220V, and 800V-900V varistors for 380V.   5. Relay input circuit signal   When in use, when the input voltage is too high or the input current is too large and exceeds its specified rated parameters, consider connecting a voltage divider resistor in series at the input end or a shunt resistor in parallel at the input port, so that the input signal does not exceed its rated parameters value.   6. In specific use, the control signal and load power supply should be stable, and the fluctuation should not be greater than 10%. Otherwise, voltage stabilization measures should be taken.   7. Keep away from electromagnetic interference and radio frequency interference sources during installation and use to prevent the relay from malfunctioning and out of control.   8. When the solid state relay is open circuit and there is voltage at the load terminal, there will be a certain amount of leakage current at the output terminal. Pay attention to it when using or designing.   9. When the solid state relay is replaced by failure, try to choose the product with the same original model or technical parameters to match the original application circuit to ensure the reliable operation of the system. V. Application of Solid State Relay The dedicated solid-state relay can have short-circuit protection, overload protection and overheat protection functions, and the combination logic solidification package can realize the intelligent module required by the user, which can be directly used in the control system.   Solid state relays have been widely used in: (1) Computer peripheral interface equipment, constant temperature system, temperature adjustment, electric furnace heating control, motor control, numerical control machinery, remote control system, industrial automation device; (2) Signal light, dimming, flasher, lighting stage lighting control system; (3) Instruments, medical equipment, photocopiers, automatic washing machines; (4) Automatic fire-fighting, security systems, as well as the switch of power capacitors for power factor compensation of the power grid, etc. In addition, solid state relays are widely used in chemical, coal, and other occasions that require explosion-proof, moisture-proof, and corrosion-proof. FAQ 1. What is solid state relay and how it works? A solid state relay (SSR) is an electronic switching device that switches on or off when an external voltage (AC or DC) is applied across its control terminals. It serves the same function as an electromechanical relay, but has no moving parts and therefore results in a longer operational lifetime. 2. What is the difference between a relay and a solid state relay? The main difference between solid state relays and general relays is that there is no movable contacts in solid state relay (SSR). In general, solid state relays are quite similar to the mechanical relays that have movable contacts. ... SSR provide high-speed, high-frequency switching operations. 3. How fast is a solid state relay? The SSR output is activated immediately after applying control voltage. Consequently, this relay can turn on anywhere along the AC sinusoidal voltage curve. Response times can typically be as low as 1 ms. The SSR is particularly suitable in application where a fast response time is desired, such as solenoids or coils. 4. Do solid state relays get hot? All solid state relays develop heat as a result of a forward voltage drop through the junction of the output device. Beyond a point, heat will cause a lowering (or derating) of the load current that can be handled by the SSR. ... Loads greater than 4 Amps will require heat sinks. 5. What causes solid state relay failure? What are the main causes and solutions of the Solid-state Relays (SSR)'s failures? If an inrush current exceeds the rated making current of the SSR due to the high inrush current of loads such as motors and lamps, SSR output elements are damaged. Consider using an SSR with a higher capacity. 6. Can a solid state relay switch DC? Solid state relays can be designed to switch both AC or DC currents by using an SCR, TRIAC, or switching transistor output instead of the usual mechanical normally-open (NO) contacts. 7. How do you test a solid state relay with a multimeter? Using Multimeter:  1. Set the multimeter in continuity test mode. 2. Place the probes of the multimeter on the coil terminals. 3. If the multimeter beeps (or show any sign of continuity), the coil is electrically closed (good). 4. If the multimeter does not beep, the coil is open & damaged. The relay needs to be replaced. 8. How reliable are solid state relays? Solid-state relays are the preferred choice for system reliability because they have no moving parts or contacts. Over time, the plating on the contacts inside EMRs can erode. This erosion can cause the contacts to weld shut; therefore they no longer open/close properly, and the relay has to be replaced. 9. Is a solid state relay a transistor? Solid-State Relay: A sort of hybrid between a conventional relay and a transistor, these relays switch a load using an LED activated by the control circuitry. The LED activates a light-activated MOSFET that controls the load. 10. How do I know if my solid state relay is bad? Solid-state relays should be checked with an ohmmeter across the normally open (N.O.) terminals when control power is off. The relays should be open, switched to OL, and closed (0.2 , the internal resistance of the ohmmeter) when control power is applied. 11. How do I choose a solid state relay? When selecting a Solid State Relay, consider: Current rating, as a general rule consider using the relay at no more than 70% of its rated current. Electrical environment,. i(In harsh electrical environments, consider a relay with an line voltage rating above the application line voltage.) 12. Do solid state relays need a diode? 2 Answers. The control side of solid state relays is usually just a LED, sometimes two LEDs back to back, and sometimes with integrated resistor. ... If the relay is on the same board as whatever is driving it, then no inductive kickback diode is needed. It's no different than driving any other on-board LED. 13. Do solid state relays leak voltage? Solid State relays have leakage. If you want to repeatedly switch something on / off, use them. But when you want the SSR to be fully off, say after pressing an off switch, a mechanical relay should be across the load to take it off the SSR. ... The SSR control is attached to the atmega328 through a 200ohm resistor.

Warm hints: The word in this article is about 2500 words and reading time is about 12 minutes.   This paper mainly introduces that how to use a solid state relay to drive a thermostat.    As we all known,relay is an electrical control device, an electrical appliance that makes the predetermined step change in the electrical output circuit when the input (excitation) changes reach the required requirements. Catalog   I. Solid State Relay Basics 1.1    What is solid state relay 1.2    Solid state relay working principle 1.3    Solid state relay appliances II. Thermostat Basics 2.1    What is thermostat 2.2     Types of thermostat 2.3    Features of thermostat 2.4    Applications of thermostat III. Drive Thermostat by Using Solid State Relay 3.1    Power thermostat 3.2    Case of driving thermostat FAQ   I. Solid State Relay Basics   1.1 What is Solid State Relay   A solid-state relay(SSR) is a contactless switch consisting of microelectronic circuits, discrete electronic devices and power electronic power devices. The isolation between the control end and the load side is realized by isolation devices. The input of the solid-state relay is controlled by a tiny control signal to directly drive the large current load.   SSR takes advantage of the switching characteristics of electronic components, such as switch triode, bidirectional thyristor and other semiconductor devices, to achieve the purpose of connecting and disconnecting the circuits without contact and sparkless, and therefore is also called "contactless switch".    A solid-state relay is a four-terminal active device, of which two terminals are input control terminal, and the other ends are output controlled ends. It has both amplification and isolation function. It is suitable for driving high power switching actuator, which is more reliable than electromagnetic relay and has no contact, long life, fast speed and interference to the outside. Because of its small size, it has been widely used.   1.2  Solid State Relay Working Principle   SSR can be divided into two types: AC type and DC type according to the use occasions.    They can switch loads on AC or DC power supply, and they can not be mixed. The following is an example of the AC type SSR as an example of its working principle. The following diagram is a block diagram of its working principle. The components in the diagram constitute the main body of the AC SSR. From the whole, SSR has only two inputs (A and B) and two output terminals (C and D), and is a four-terminal device.   Working principle block diagram of solid state relay   When a certain control signal is added to the A and B, the "switch" and "break" between the two ends of C and D can be controlled and the function of "switch" can be realized. The function of the coupling circuit is to provide a channel between the input/output terminal of the control signal input from the A and B ends, but it disconnects the input and output terminals of the SSR in the electrical circuit.    In order to prevent the effect of the output end on the input end, the coupling circuit used the "optical coupler", which is sensitive, responsive, and high in the input/output insulation (voltage resistance) level; because the input terminal load is a light-emitting diode, this makes the input end of the SSR easily matched with the input signal level. When used, it can be directly connected to the output interface of the computer, that is, the logical level control of "1" and "0".    The function of the trigger circuit is to generate the required trigger signal, drive the switch circuit 4, but because the switch circuit does not add the special control circuit, it will produce the radio frequency interference and pollute the power grid such as the high order harmonic or the peak, so the zero-crossing control circuit is set up. The "zero crossings" means that when the control signal is added and the AC voltage is over zero, the SSR is a passing state, and when the control signal is broken, the SSR is to wait for the junction point (zero potential) of the positive half of the alternating current and the negative half of the half-week (zero potential), and the SSR is broken.    This design can prevent high-order harmonic interference and pollution to the power grid. The absorption circuit is designed to prevent the shock and interference (or even misoperation) of the peak, surge (voltage) transmitted from the power supply to the bidirectional thyristor in the switch device, usually using an "R-C" series absorption circuit or a nonlinear resistor (varistor).   1.3  Solid State Relay Appliances   The special solid-state relay can have the function of short circuit protection, overload protection and overheating protection. With the combined logic curing package, the intelligent module can be realized by the user. It is directly used in the control system.   Solid-state relay has been widely used in computer peripheral interface equipment, thermostat system, temperature regulating, electric furnace heating control, motor control, CNC machine, remote control system, industrial automation device, signal light, light adjustment, scintillator, lighting stage lighting control system, instruments, medical instruments, duplicator, automatic laundry. Machine, automatic fire protection, security system, and power capacitor switching switch as power factor compensation for the power grid, and so on, in addition to the chemical, coal mine, explosion-proof, anti-corrosion, corrosion prevention and so on. The logical curing encapsulation can realize the intelligent modules that users need and is directly used in the control system.     II. Thermostat Basics   2.1  What is Thermostat   The thermostat is a device that directly or indirectly controls one or more hot and cold Yuanlai to maintain the desired temperature. In order to achieve this function, a thermostat must have a sensitive element and a converter. The sensitive element can measure the change of temperature and produce the function required for the converter. The converter converts the function from the sensing element to the proper control of the device that changes the temperature. Thermostat 2.2 Types of Thermostat The types of the thermostat are generally the following: （1）Insert thermostat is installed on the pipe and sensitive element is inserted into the pipeline. （2）Immerse sensitive elements immersed in liquid in pipes or containers to control liquids. （3）Surface sensitive elements installed on the surface of pipes or similar surfaces.   2.3  Features of Thermostat This thermostat pressure gauge setting range (5~35 C) This thermostat measurement accuracy: plus or minus 1 DEG C The thermostat. Size: 86 x 86 (mm) Power supply: AC220V thermostat. This thermostat using ultra-thin design, electrical interface It has a large LCD screen with an LCD thermostat (backlight green, Lan Beiguang) You can display the thermostat in international language (Chinese + English) The thermostat has the function of automatic and manual. This thermostat for refrigeration heating and ventilation three working modes This thermostat high low-speed automatic selection Thermostat timing shutdown function. This thermostat control fan coil end of the fan, water valve, air valve You can also set the password on the thermostat setting temperature and wind speed according to the requirements of users.   Features of thermostat 2.4  Applications of Thermostat   The most common use of the thermostat is to control the room temperature.   Typical uses include: control the gas valve; control the fuel furnace regulator; control the electric heating regulator; control the refrigeration compressor; control the gate regulator.   A room temperature regulator can be used to provide a variety of control functions, such as heating control, heating - cooling control, day and night control (at night at lower temperatures), multistage control, primary or multistage heating, primary or multistage cooling, or multistage heating and cooling control.       III. Drive Thermostat by Using Solid State Relay   3.1  Power Thermostat   There are two kinds of power supply for the thermostat: battery and 24VAC power.    The thermostat needs battery power to run without interruption. It is very important that these batteries consume as low energy as possible, but even if you minimize the power consumption, the users are still inconvenient because the battery needs to be replaced from time to time. In order to reduce the replacement frequency, you can use a 24 VAC power supply. When the C line in the system is not available, the bridge rectifier shown in Figure 1 can convert the AC (AC) voltage to a DC (DC) voltage by the load. Single thermostat signal relay connection with HVAC load   3.2  Case of Driving Thermostat When the HVAC load (compressor, fan, gas valve, etc.) is turned off, the contact of the signal relay is broken. When the contacts are open, the terminals of the rectifier bridge see the voltage of the HVAC transformer is 24VAC, and convert the AC power to DC power, as mentioned earlier. The resulting DC voltage is used to drive the thermostat or subcircuit.   During the HVAC load conduction, the contacts of the signal relay are closed. When the contact is closed, the voltage across the bridge terminal is reduced to zero. This eliminates the need to use 24VAC as a power supply, so the thermostat battery power must be controlled. The range of current required for operating electromechanical relays ranges from tens to hundreds of Ma, which can have a significant impact on battery life.   If there is a way to drive a relay without using a thermostat battery, what will happen? Battery life will increase and replacement frequency will be further reduced. One way is to turn on the relay and charge the control system briefly during the HVAC load conduction (signal relay contact closure).  Compared with the turn off time of the power relay, the time required during charging is very short, which can stimulate the power relay and its corresponding load. Unfortunately, electromechanical (signal) relays are not likely to achieve this goal due to their switching speed limits. The time taken by the contact to the desired location is in milliseconds and will interrupt the HVAC load.   Fortunately, a device can achieve the appropriate switching speed: solid-state relay (SSR). SSR is a semiconductor repeater based on a thyristor or power transistor to perform on / off control.   This recharge method requires a dual MOSFET SSR because it can turn off MOSFET based SSR when necessary. Besides, body diodes of each MOSFET can assist in 24VAC rectification. A full-wave rectifier bridge is built with two diode MOSFET diodes, as shown below.   A power supply for SSR in a HVAC system The following figure shows the rectified waveform corresponding to the color coded diode in the above figure. The voltage ripple of the final waveform can be eliminated by connecting a suitable capacitor to the output of the rectifier bridge. Then, you can reduce the DC voltage of the control system to the desired voltage. Full wave rectifying waveform The use of SSR enables the HVAC system to fully supply the thermostat and reduce the power utilization rate of the battery. When SSR closes, the HV1 and HV2 pipelines will see the full 24VAC voltage and provide a constant 33VDC voltage at the output of the rectifier bridge. When SSR is connected, it may still be circulated through a short-time on/off state to recharge the power supply capacitor. This design can greatly reduce the energy requirements of the thermostat battery and reduce the battery replacement frequency.   FAQ   1. What is solid state relay and how it works? A solid state relay (SSR) is an electronic switching device that switches on or off when an external voltage (AC or DC) is applied across its control terminals. It serves the same function as an electromechanical relay, but has no moving parts and therefore results in a longer operational lifetime.   2. What is the difference between a relay and a solid state relay? The main difference between solid state relays and general relays is that there is no movable contacts in solid state relay (SSR). In general, solid state relays are quite similar to the mechanical relays that have movable contacts. ... SSR provide high-speed, high-frequency switching operations.   3. How fast is a solid state relay? The SSR output is activated immediately after applying control voltage. Consequently, this relay can turn on anywhere along the AC sinusoidal voltage curve. Response times can typically be as low as 1 ms. The SSR is particularly suitable in application where a fast response time is desired, such as solenoids or coils.   4. Do solid state relays get hot? All solid state relays develop heat as a result of a forward voltage drop through the junction of the output device. Beyond a point, heat will cause a lowering (or derating) of the load current that can be handled by the SSR. ... Loads greater than 4 Amps will require heat sinks.   5. What causes solid state relay failure? What are the main causes and solutions of the Solid-state Relays (SSR)'s failures? If an inrush current exceeds the rated making current of the SSR due to the high inrush current of loads such as motors and lamps, SSR output elements are damaged. Consider using an SSR with a higher capacity.   6. Can a solid state relay switch DC? Solid state relays can be designed to switch both AC or DC currents by using an SCR, TRIAC, or switching transistor output instead of the usual mechanical normally-open (NO) contacts.   7. How do you test a solid state relay with a multimeter? Using Multimeter:  1. Set the multimeter in continuity test mode. 2. Place the probes of the multimeter on the coil terminals. 3. If the multimeter beeps (or show any sign of continuity), the coil is electrically closed (good). 4. If the multimeter does not beep, the coil is open & damaged. The relay needs to be replaced.   8. How reliable are solid state relays? Solid-state relays are the preferred choice for system reliability because they have no moving parts or contacts. Over time, the plating on the contacts inside EMRs can erode. This erosion can cause the contacts to weld shut; therefore they no longer open/close properly, and the relay has to be replaced.   9. Is a solid state relay a transistor? Solid-State Relay: A sort of hybrid between a conventional relay and a transistor, these relays switch a load using an LED activated by the control circuitry. The LED activates a light-activated MOSFET that controls the load.   10. How do I know if my solid state relay is bad? Solid-state relays should be checked with an ohmmeter across the normally open (N.O.) terminals when control power is off. The relays should be open, switched to OL, and closed (0.2 , the internal resistance of the ohmmeter) when control power is applied.   11. How do I choose a solid state relay? When selecting a Solid State Relay, consider: Current rating, as a general rule consider using the relay at no more than 70% of its rated current. Electrical environment,. i(In harsh electrical environments, consider a relay with an line voltage rating above the application line voltage.)   12. Do solid state relays need a diode? 2 Answers. The control side of solid state relays is usually just a LED, sometimes two LEDs back to back, and sometimes with integrated resistor. ... If the relay is on the same board as whatever is driving it, then no inductive kickback diode is needed. It's no different than driving any other on-board LED.   13. Do solid state relays leak voltage? Solid State relays have leakage. If you want to repeatedly switch something on / off, use them. But when you want the SSR to be fully off, say after pressing an off switch, a mechanical relay should be across the load to take it off the SSR. ... The SSR control is attached to the atmega328 through a 200ohm resistor.   Relevant information about "How  to Drive Thermostat by Using Solid State Relay " About the article "How  to Drive Thermostat by Using Solid State Relay", If you have better ideas, don't hesitate to write your thoughts in the following comment area. You also can find more articles about electronic semiconductor through Google search engine, or refer to the following related articles.   Making a Arduino Variable Timer Relay Comprehensive Introduction of the Time Delay Relays

SummarySome electornic or electrical appliances needs time limited power supply,or usage of some devices are depends on limitted time.To automate electrical devices depends on time simple and robust solution given based on arduino.Today let's make a arduino variable time relay together.By using this arduino variable timer relay we can control high voltage electrical appliances or electronic devices.Now let me share the process. To indicate the time duration and status 16×2 LCD display is included in this design, once the program uploaded to the Arduino then it can work independent with some external battery power source. Connection DiagramConstruction and Working In this project arduino uno board is used to control SPDT (Single pole double throw) Relay and 16 x 2 character LCD indicates the time duration status. Digital pins D2 to D7 are connected to the LCD display. VR1 varible resistor helps to control the contrast of LCD display, Transistor Q1 BC547 reacts as a Switching device and controls the power supply to the Relay coil depends on arduino output. There are three push buttons are placed to set different time durations, S1 Switch makes the count start, S2 changes the Hours and S3 changes the Minutes of time duration. Output signal from the Arduino is taken from D8 pin and it drives the Relay through transistor. After making the connection, upload the following arduino sketch and pretest the operation with real timer clock.Note:- Candle with extreme care if you using High voltage supply at the Relay end. Arduino Code #include <LiquidCrystal.h>LiquidCrystal lcd(7,6,5,4,3,2);const int set = 9;int hours=10;int start=11; int relay=8;int b=0,h=0,t=0;int buttonState = 0; int lastButtonState = 0; void setup() {    pinMode(set,INPUT);  pinMode(hours,INPUT);  pinMode(relay,OUTPUT);  pinMode(start,INPUT);  lcd.begin(16,2);  lcd.setCursor(0,0);  lcd.print("Adjustable Timer");  }int timer( int b,int h){         if(b<=9)           {            lcd.setCursor(3,1);            lcd.print(0);            lcd.setCursor(4,1);            lcd.print(b);          }     else{lcd.setCursor(3,1);lcd.print(b);}         lcd.setCursor(2,1);         lcd.print(":");     if(h<=9)           {            lcd.setCursor(0,1);            lcd.print(0);            lcd.setCursor(1,1);            lcd.print(h);          }     else{lcd.setCursor(0,1);lcd.print(h);}    }void loop()       {           buttonState = digitalRead(set);                         if (buttonState != lastButtonState)       {                 if(buttonState == HIGH)         {                       lcd.clear();           lcd.print("Set time in min:");                      ++b;           timer(b,h);                                   }                   lastButtonState = buttonState;          }       if (digitalRead(hours)== HIGH)          {              lcd.clear();              lcd.print("Set time in hours");              ++h;              timer(b,h);              while(digitalRead(hours)==HIGH);                                    }             if(digitalRead(start)==HIGH)          {             lcd.clear();             t=((h*60)+(b))*1000;             lcd.print("Timer is set for");             timer(b,h);             digitalWrite(relay,HIGH);             delay(t);             digitalWrite(relay,LOW);             while(digitalRead(start) == HIGH );                                   }                        } Have you make it successfully?  

In this article, we will provide you the basic information of relay: what is a relay? What types of relays are there? What are their characteristics? How to maintain the common faults of the relay? With these questions, let us find the answers in the article together.     Catalog     I. What is a Relay?     1.1 Electrical Symbol     1.2 Contact Form     1.3 Functions of Relay II. Relay Classification III. Main Types of Relay IV. How to Test a Relay V. Influencing Factors of Relay Reliability VI. Maintenance of Common Faults of Relay VII. Example Explanation: Delay Relays FAQ   I. What is a Relay? This video will explain what is a relay, and how does a relay works with basic information about construction and different types of relay.   Relay is a kind of electric control device. When the change of input quantity (excitation quantity) reaches the prescribed requirement, the controlled quantity will be changed step by step in the electric output circuit. It has an interactive relationship between the control system (also known as the input loop) and the controlled system (also known as the output loop). Usually used in an automatic control circuit, it is a kind of automatic switch which uses a small current to control the operation of a large current. Therefore, it can play the role of automatic regulation, safety protection, conversion circuit, and so on.   1.1 Electrical Symbol A relay is composed of two parts: coil and contact group, the graphic symbol of the relay in a circuit diagram also includes two parts: a box for coil and a set of contact symbols for contact combination. When the contact circuit is relatively simple, the contact group is often drawn directly on one side of the circle frame, which is called centralized representation.   Relay coils are represented by a rectangular symbol in the circuit, and if the relay has two coils, draw two side-by-side boxes. The contacts of relays are represented in two ways: one is to draw them directly on the side of the box, which is more intuitive. The other is to draw each contact point into its own control circuit according to the need for circuit connection. Usually, the contact of the same relay is marked with the same text symbol, and the contact group is numbered to show the difference.   1.2 Contact Form There are three basic forms of contact for relays: 1. The two contacts are disconnected when power off, and the two contacts are closed when power on.   2. The two contacts are closed when power off and the two contacts are disconnected when the power on.    3. The contact group has three contact points, that is, a moving contact in the middle and a static contact in the upper and lower parts of the contact group, respectively. When the coil is power-off, the dynamic contact is disconnected from one of the static contacts and connected with the other. After the coil is power-on, the dynamic contact moves, the connecting contacts state is opposite to the power-off state to achieve the purpose of conversion. Such contact groups are called switching contacts.      1.3 Functions of Relay Relay is an automatic switching element with an isolation function. It is widely used in remote control, telemetry, communication, automatic control, electromechanical integration, and power electronic equipment. It is one of the most important control components.   The relay generally has induction parts (input section) that can reflect a certain input variable (such as current, voltage, power, impedance, frequency, temperature, pressure, speed, light, etc.); an executing part (output section) capable of realizing power-on and power-off state of the controlled circuit. Between the input port and the output port of the relay, there is also an intermediate mechanism (driving section) for coupling the input, the function processing, and the driving of the output.   As a control element, relays generally have the following functions:   1) Expand the control range: for example, when the control signal of the multi-contact relay reaches a certain value, the multi-circuit can be switched on and off at the same time according to the different connecting forms of the contact group.   2) Amplification: a very small volume can control a large power circuit, such as sensitive relays, intermediate relays, etc.   3) Synthesis signal: when a plurality of control signals input multiple winding relays in the prescribed form, a predetermined control effect can be achieved by comparing and synthesizing.   4) Automatic, remote control, monitoring: relays on the automatic device, together with other electrical appliances, can form a program control circuit to achieve automatic operation.   II. Relay Classification   1. According to the working principle or structural characteristics of relays: 1) Electromagnetic relay: an electrical relay that is driven by the suction of an input circuit between an electromagnet core and an armature. 2) Solid relay: a relay in which electronic components perform their functions without mechanical movement, and the input and output are isolated. 3) Temperature relay: a relay that operates when the external temperature reaches a certain value. 4) Reed relay: a relay operates by a reed that is sealed in a tube and has a dual action caused by the electricity action on the reed and the armature. 5) Time relay: When the input signal is added or removed, the output part needs to be delayed or limited to a specified time to close off. 6) High-frequency relay: a relay used for switching a high frequency, a radio frequency circuit which had a minimum loss. 7) Polarization relay: a relay driven by magnetic field synthesis caused by a polarized magnetic field and a controlled current acting through the magnetic field generated by the control coil. The direction of the operating relay depends on the direction of the current flowing through the control coil. 8) Other types of relay: optical relay, sound relay, thermal relay, instrument relay, Hall effect relay, differential relay, etc.   2. According to shape size of relays: 1)miniature relay  2)subminiature relay 3)small miniature relay Note: for sealed or enclosed relays, the size is the maximum of the three vertical dimensions of the relay body, excluding the dimensions of mounting, leading end, rib pressing, edge pressing, flanging, and sealing solder joint.   3. According to the load of the relays: 1) micro power relay 2) small power relay 3) medium power relay 4) high power relay    4. According to the protective characteristics of relays: 1) sealed relay  2) enclosed relay 3) unenclosed/ open relay   5. According to the principle of action: 1) electromagnetic type 2) induction type 3) rectifier type 4) electronic type 5) dig type   6. According to the physical quantity of the reaction: 1) current relay 2) voltage relay 3) power relay 4) impedance relay  5) frequency relay 6) gas relay   7. According to the role of relays in the protection circuit: 1) starting relay  2) measuring relay  3) time relay 4) auxiliary/intermediate relay 5) signal relay 6) exit relay    III. Main Types of Relay   1) electromagnetic relay As long as a certain voltage is added at both ends of the coil, a certain current will flow through the coil, producing an electromagnetic effect, and the armature will contact the iron core under the action of electromagnetic force attraction, thus driving the armature dynamic contact and static contact (normally open contact) suction. When the coil is powered off, the electromagnetic suction also disappears, and the armature will return to its original position in the reaction force of the spring and release the dynamic contact from the original static contact (normally closed contact). In this way to achieve the purpose of switching on and off. In addition, it can be distinguished the "normal open and closed contacts of the relay.   Note: The static contact in the broken state when the coil is powered off is known as the "normal open-contact"; the static contact in the on-state is called the "normal closed-contact". Relays generally have two circuits, a low-voltage control circuit, and a high-voltage working circuit.   2) solid-state relay  A solid-state relay is a kind of four-terminal device with two connection terminals as input and the other two as output. In the middle, an isolation device is used to realize the electrical isolation of the input and output.   Solid-state relays can be divided into AC type and DC type according to the type of load power supply. According to the switch, type can be divided into normal open type and normally closed type. According to the isolation type, it can be divided into hybrid type, transformer isolation type, and photoelectric isolation type, and the photoelectric isolation type is the most.   3) thermal reed relay A thermal reed relay is a new type of thermosensitive switch which uses thermosensitive magnetic material to detect and control temperature. It consists of a temperature-sensitive magnetic ring, constant magnetic ring, reed tube, heat conduction mounting sheet, a plastic substrate, and other accessories. Thermal reed relays do not use coil excitation but are driven by magnetic forces generated by constant magnetic rings. In addition, whether the constant magnetic ring can provide magnetic force to drive the reed tube is determined by the temperature control characteristic of the temperature sensing magnetic ring.     4) reed relay Reed relay is a kind of coil sensing device, which uses a coil to produce a magnetic field to drive a magnetic reed tube. In addition, the characteristics of reed relays include small size, lightweight, fast reaction speed, short jump time, and so on.   When a whole piece of ferromagnetic metal or other conductive material is close to it, turn on or turn off the circuit. Reed relay consists of a permanent magnet and a reed tube. Both of them fixed to a bracket without magnetism or magnetic conduction. Take the line of the permanent magnet's north-south pole as the axis, which should be coincident or basically coincident with the axis of the reed. From far to near, adjust the distance between the permanent magnet and the reed tube, and fix the position of the magnet when it happens to move (turning off for normally open reed tube and turning on for normally closed reed tube). At this point, when there's a whole piece of magnetic material, and when the iron plate is close to the magnet and the reed tube at the same time, the reed tube will move again and return to the state without magnetic field action; when the iron plate leaves, the spring tube will move in the opposite direction. The reed relay has a strong structure, sealed contact, and high durability. It can be used as a position limiting switch for mechanical equipment, and can also be used to detect whether iron doors, windows, etc.    5) optical relay An optical relay is a semiconductor relay used in AC/ DC, refers to the integration of light-emitting and light-receiving devices. The input side and the output side are electrically insulated, but the signal can be transmitted through the optical. Its characteristics are semi-permanent, micro-current, high impedance, insulating, voltage-resistance, ultra-small, optical-transmission, contact-free, and so on.   It is mainly used in measuring equipment, communication equipment, security equipment, medical equipment, and so on. 6) time relay Time relay is a kind of control apparatus that uses electromagnetic principle or mechanical principle to realize time delay control. There are many kinds of it, such as air damping type, power-driven type, and electronic type.   Air damping time relay is often used in AC circuit, which uses the principle of air throttling through orifice compensation to obtain delay action. It consists of an electromagnetic system, delay mechanism, and contact. Time relay can be divided into two types: power-on delay type and power-off delay type.   The time delay range of the air-damping time relay is large (0.4~60s and 0.4~180s). Its structure is simple, and its accuracy is low. When the coil is electrified (voltage specification is ac380v, ac220v or dc220v, dc24v, etc.), the armature and bracket are attracted by the iron core and moved down instantly, so that the instantaneous action contact is turned on or off, and meanwhile, the piston rod and lever cannot fall with the armature at the same time, because the upper end of the rod is attached to the rubber film in the air chamber, and when the rod begins to move downward under the action of the released spring, the rubber film falls downward. Air becomes thin in the upper air chamber and the damping piston rod drops slowly. After a certain period of time, the piston rod drops to a certain position, then pushes the delay contact action through the lever, causing the dynamic break contact to break and the dynamic close contact turned off. From the coil to the delay contact to complete the action, this time is the delay time of the relay. The delay time can be changed by adjusting the size of the air chamber inlet hole. After the suction coil is powered off, the relay is restored by the action of the recovery spring, and the air was ejected quickly through the vent hole. 7) auxiliary relay a. characteristics of auxiliary relay:   The relay is composed of several high-quality sealed small relays with low coil voltage, which is damp-proof, dust-proof, non-breaking, high reliability, and overcomes the shortcomings of the electromagnetic auxiliary relay wire which is too thin and easy to break. Low power consumption, low-temperature rise, no need to attach high-power resistance, easy installation and connection, large capacity of a relay contact, long working life, easy to observe on the spot, and so on. The delay only needs to be adjusted by the dial switch on the panel, the delay precision is high, and the delay range can be set freely in 0.02S~ 5.00S.   Purpose of intermediate relay: auxiliary relay is used in various protection and automatic control lines to increase the number of contacts and the capacity of contacts in the protection and control loop.   b. classification of auxiliary relays:   static auxiliary relay   delay auxiliary relay   electromagnetic auxiliary relay   elevator auxiliary relay   rail auxiliary relay   c. auxiliary relay principle   When the coil is electrified, the moving iron core is absorbed under the action of the electromagnetic force, and the moving contact action is driven so that the normally closed contact is separated and the normally open contact is closed. When the coil is powered off and the moving iron core drives the dynamic contact to reset under the action of the spring. The working principle of the relay is that when a certain input (such as voltage, current, temperature, velocity, pressure, etc.) reaches a predetermined value, it operates. In order to change the working state of the control circuit, so as to achieve the established purpose of control or protection. In this process, the relay mainly plays a role in the transmission of the signal.   d. function of the auxiliary relay   The general circuit is often divided into two parts of the main circuit and a control circuit. The relay is mainly used for a control circuit, and the contactor is mainly used for the main circuit. Through the relay, using one control signal can control the other one or several signals, and the control of starting, stopping, linkage, and so on. The main control object is a contactor, the contact of the contactor is relatively large, and the carrying capacity is strong, but the control of weak current too strong electricity can be realized through the contactor, and a control object is an electric appliance.   1. Replace small contactor   The contact of the auxiliary relay has a certain load capacity. When the load capacity is small, it can be used instead of the small contractor, such as the electric shutter and the control of some small appliances. This advantage is that not only can play the purpose of control, but also can save space so that the electrical control part of the more refined.   2. Increase the number of contacts   This is the most common use of auxiliary relays, for example, in a circuit control system where a contact needs to control multiple contactors or other components, adding an auxiliary relay to the line.   3. Increase contact capacity   We know that although the contact capacity of the auxiliary relay is not very large, it also has a certain capacity with load, and the current required for its drive is very small. Therefore, the auxiliary relay can be used to expand the contact capacity. For example, it is not possible to use induction switches directly and the output of the transistor to control the heavy load of electrical components. In fact, the auxiliary relay is used in the control line, and the other load is controlled by the auxiliary relay to enlarge the control capacity.   4. Convert pin type   In the industrial control circuit, it is often necessary to use the normally closed contact of the contactor to achieve the control purpose. However, the normally closed contacts carried by the contractor are not enough to achieve the control task. At this time, an auxiliary relay can be parallel to the original contactor coil, and the corresponding components can be controlled by the normally closed contact of the auxiliary relay, and the contact type can be transformed to achieve the desired control purpose.   5. As a switch In some control circuits, intermediate relays are often used to turn on and off some electrical components, such as automatic demagnetization circuits common in color televisions or displays, and transistor controls the on and off of intermediate relays, which are controlled by the opening and closing of their contacts, such as color televisions or displays. So as to control the demagnetization coil on-off action.   6. Switching voltage   7. Eliminating interference in the circuit   8. Power direction relay   An electrical appliance that causes the controlled output circuit to be switched on or off when the input (such as voltage, current, temperature, etc.) reaches a specified value. It can be divided into two categories of electrical volume (such as current, voltage, frequency, power, etc.) relay and non-electrical volume (such as temperature, pressure, speed, etc.) relay. It has the advantages of fast movement, stable work, long service life, small volume, and so on. Widely used in power protection, automation, motion, remote control, measurement, and communication devices.       Common Types   1. overcurrent relay The overcurrent relay is a relay that operates from the current beyond its set value and can be used as a system line and overload protection. The most commonly used is an induction type overcurrent relay, which is opposite to the rotating disk of aluminum or copper by an electromagnet. The rotating disc is rotated by means of the electromagnetic induction principle so as to achieve the protective effect.   action principles:   The inductive overcurrent relay uses the secondary current of the current transformer to generate a magnetic field in the relay to cause the disk to rotate, but the current flowing through the relay must be greater than the current value of a certain current to rotate.   2. overvoltage relay  Overvoltage relay, its main purpose is that when the abnormal voltage of the system rises to more than 120% rating, the overvoltage relay operates so that the circuit breaker can jump off and protect the electric equipment from damage. The construction and operation principle of induction overvoltage relay are similar to those of overcurrent relay, except the main loop.   3. under voltage relay The under voltage relay is constructed in the same way as the overvoltage relay, except that the inner contact and the turntable turn immediately when the voltage is applied.   4. ground overvoltage relay The grounding overvoltage relay has the same structure as the overvoltage relay, and uses a three-phase three-wire non-grounding system, and is connected to the earthing transformer with an open triangle earthing to detect zero-phase voltage.   5. grounding overcurrent relay Grounding overcurrent relay, abbreviated as GCR, is a kind of high-voltage line earthing protection relay.   Main uses:   1) grounding overcurrent protection of high resistance grounding system.   2) grounding protection of generator stator winding.   3) layer short circuit protection of phase-separated generator.   4) overheat protection of grounding transformer.   6. selective grounding relay Selective grounding relay, also called directional grounding relay, is used in non-grounding systems to protect distribution lines. In addition, it can also be used in overhead lines and cable systems.   Selective grounding relay: if a zero-phase sequence current is detected by a grounding voltage transformer when a line is grounded, the selective grounding relay can accurately detect the fault line and alert it and disconnect it according to the requirement. And then continue to send electricity to the normal operating line.   7. free-phase relay In the three-phase line, phase-failure relay or phase-failure protection relay will burn out the single-phase operation of the motor if it does not cut off the line immediately when there is a one-wire break in the power supply end and causes the single-phase.   8. percentage differential relay A percentage differential relay is used as the AC motor of the transformer. Alternator with differential protection and over-current protection relay used as the protection devices, and when abnormal current generated by external fault flows over protection equipment, if current on the transformer is unbalanced or inconsistent with the characteristics of the current transformer, in these cases, this phenomenon will extend several times and cause failure operation to the relay.     IV. How to Test a Relay Relay is the key device in the intelligent prepaid electric energy meter, the life of the relay determines the life of the meter to a certain extent, thus the performance of the relay is very important to the operation of the intelligent prepaid electric energy meter. There are many manufacturers of relays around the world. Their production scale is quite different, the technical level and performance parameters are very different. Therefore, the manufacturers of electric energy meters must have a set of perfect testing devices when detecting and selecting relays. To ensure the quality of the meter. At the same time, the national power grid has also strengthened the sampling detection of the relay performance parameters in the intelligent electric energy meter, which also needs the corresponding testing equipment to check the quality of the meter produced by different manufacturers. However, at present, relay testing equipment is not only a single test item, but detection process also can not be automated completely, the detection data needs manual processing and analysis, the detection results are random, artificial, and the detection efficiency is low, in addition, there is no guarantee of safety.   According to the test requirements of relay performance parameters, the test items can be divided into two categories: one is the test items without load current, such as operating value, contact resistance, service life; the other, test items with load current, such as contact voltage, electrical life, overload capacity.   1.Measuring coil resistance: the multimeter R×10Ω barrier can be used to measure the resistance value of the relay coil, so as to judge whether there is an open circuit phenomenon in the coil. The resistance value of the relay coil is closely related to its working voltage and current. And the service voltage and working current can be calculated by the resistance value of the coil.   2. Contact resistance measurement: using the resistance barrier of the multimeter, the resistance value of the normally closed contact and the moving point resistance should be 0, and the resistance value of the normally open contact and the moving point shall be infinitely large. From this, you can distinguish between the normally closed contact and the normally open contact.   3. Measure the pull-in voltage and current: using an adjustable voltage stabilizing power supply and ammeter, input a set of voltages to the relay, and connect the ammeter in the power supply circuit to monitor. Slowly raise the power supply voltage and note down the pull-in voltage and current when the relay absorbs sound. To be accurate, you can try a few more times and get the average value. Measurement of release voltage and discharge current: it is also like the above-mentioned connection test, when the relay suction, then gradually reduce the power supply voltage, when heard the relay again release sound, note the voltage and current at this time, in addition, you can also try more than a few times to get an average release voltage and current. Generally, the release voltage of the relay is about 10% of the pull-in voltage, and it will not work properly if the release voltage is too small (less than 1/ 10 of the pull-in voltage), which will affect the stability of the circuit and the device operation.   1. Understand the necessary conditions firstly.   1) The power supply voltage of the control circuit can provide the maximum current.  2) Voltage and current in the controlled circuit. 3) The requiring contacts on the controlled circuit. When the relay is selected, the power supply voltage of the general control circuit can be used as the basic factor for selection. The control circuit should provide sufficient working currently for the relay, otherwise, the relay absorption is unstable.   2. After consulting the relevant information to determine the applying conditions, you can find out the type and specification number of the relays required. If you already have a relay on hand, you can check whether it can be used against the data. Finally, consider whether the size is appropriate.   3. Pay attention to the volume of the apparatus. For general electrical appliances, consider the volume of the chassis and the layout of the circuit board installation. For small electrical appliances, such as toys, remote control devices should select ultra-small relay products.     The main test items are briefly described as follows:    (1) Operating value: The voltage required for relay action.    (2) Contact resistance: When electric contact closes, the resistance value between two contacts.   (3) Mechanical life: In the case of the mechanical part without damage, the relay switching times.   (4) Contact voltage: When the electric shock is closed, a certain load current is applied in the electric shock circuit, at this time, the voltage value between the contacts.    (5) Electric life: When the rated voltage is applied on both ends of the relay drive coil and the rated resistive load is applied in the contact circuit, the reliable operation times of the relay under the condition of duty cycle 1:4 less than 300 cycles per hour.    (6) Overload capacity: When the rated voltage is applied on both ends of the relay drive coil and 1.5 times rated load is applied in the contact circuit, the reliable operation times of the relay under the condition of (10 ±1) times/ minute (operation frequency). V. Influencing Factors of Relay Reliability   1.The influence of environment on relay reliability: the average fault interval time of relay working in GB and SF is the highest, reaching 820000h, while in the NU environment, it is only 60000h.   2.The effect of quality grade on relay reliability: the average failure interval of the A1 relay is 3660000h, while that of the C class relay is 110000, the difference between them is 33 times. It can be seen that the quality level of the relay has a great impact on its reliable performance.   3.The effect of the contact form on the reliability of relay: the contact form of the relay will also affect its reliability. The reliability of the single-throw relay is higher than that of the double-throw relay with the same number of tools, and the reliability decreases gradually with the increase of tool number, in addition, the reliability of a single-throw relay is higher than that of the double-throw relay with the same number of cutters. The average failure interval of a single-pole, single-throw relay is 5.5 times that of a four-pole double-throw relay.   4.The influence of structures on relay reliability: there are 24 types of relay structures, and all of them have an influence on the reliability of the relay.   5.Effect of temperature on the reliability of relay: the operating temperature range of the relay is between -25℃ and 70℃. With the increase of temperature, the average time between failures of the relay gradually decreases.   6.The effect of operating rate on relay reliability: with the increase of relay operating rate, the average fault interval time decreases exponentially. Therefore, if the designed circuit requires the relay to operate at a very high speed, it is necessary to carefully detect the relay in order to replace it in time for circuit maintenance.   7.The effect of the current ratio on the reliability of the relay: the so-called current ratio is the ratio of the operating load current of the relay to the rated load current. The current ratio has a great influence on the reliability of the relay, especially when the current ratio is greater than 0.1, the average fault interval time is rapidly reduced, and the current ratio is less than 0.1, the average fault interval time is basically unchanged, therefore, the load with a larger current rating is selected to reduce the current ratio when the circuit is designed because this ensures that the relay and even the entire circuit are not reduced in reliability due to the fluctuation of the operating current. VI. Maintenance of Common Faults of Relay   a. Maintenance of the sensing mechanism For electromagnetic (voltage, current, intermediate) relay, its sensing mechanism is the electromagnetic system. The fault of the electromagnetic system is mainly focused on the coil and the moving and static iron core.   1) coil fault Coil faults are usually caused by coil insulation damage; mechanical injuries form a turn-to-turn short circuit or grounding. Because the power supply voltage is too low, and dynamic, static core contact does not connect tightly, resulting in the current through the coil is too large, the coil heated to burn. The coil should be rewound during the repair. If the armature is not sucked after the coil is electrified, it may be that the wire connection of the coil is removed, so that the coil is short-circuited, therefore, the joint should be re-welded.   2) iron core fault The main fault of the iron core is that the armature can not be absorbed after the power on, which may be caused by the broken coil, having impurities between the moving and static iron core, and the low voltage of the power supply, thus repair should be differentiated. After the power on, the armature noise is big, this may be due to moving or static core contact surface is not smooth, or there is oil on the surface. During repair, the coil should be removed, filing or flattening the contact surface, and oil should be cleaned. Noise may be due to short-circuit or ring fracture, replacing new short-circuit ring to repair. After power loss, if the armature cannot be released immediately, possibly because the moving armature is stuck, the air gap of the iron core is too small, and the spring strain and the contact surface of the iron core have been polluted by oil. Taking maintenance should be differentiated according to the cause of the fault, or adjust the size of the air gap, or replace the springs, or use gasoline cleaning oil.   For the thermal relay, the sensing mechanism is the thermal component, and the common fault is that the thermal component burns out, or operation failures of the thermal element and does not operate.   (1) Thermal component burnout. This may be due to a short circuit on the load side or the high frequency of action of the thermal element. The thermal components should be replaced during maintenance and the setting value should be adjusted again. (2) Operation failure of thermal component. This may be due to the setting value is too small, the operation without overload, or the strong impact and vibration influence, make its action mechanism loosening and tripping. (3) No operation of thermal component. This may be due to the setting value is too small to lose the thermal element overload protection function. During maintenance, the setting current should be adjusted according to the overload working current.   b. Inspection and repair of executing parts Most relay actuators are contact systems. Through its "power on" and "power off" to complete a certain control function. Contact system faults generally caused by contact overheating, wear, melting soldering, and so on. The main reasons for contact overheating are insufficient capacity, insufficient contact pressure, surface oxidation or uncleanliness, etc. The main cause of wear is that the contact capacity is too small, the arc temperature is too high to cause contact metal oxidation, and so on. The main cause of contact melting soldering is that the arc temperature is too high, or the contact is seriously moved, and so on.   The order of maintenance of the contacts is as follows:   1) Open the outer cover and check the contact surface. 2) If the contact surface is oxidized, it is not necessary for the silver contact to be processed, and the oxide layer on the surface of the Cu contact may be lightly scraped with a file or a knife with a knife. 3) If the contact surface is not clean, clean it with gasoline or carbon tetrachloride. 4) If there is a burning trace on the surface of the contact, it is not necessary to repair the silver contact, and the copper contact should be repaired by a file or with a knife. Sand cloth or sandpaper is not allowed to be used for refurbishment, to avoid poor contact due to the residual stand. 5) Contact should be replaced if it welded. If the contact capacity is too small, replace the relay with a larger capacity. 6) If the contact pressure is insufficient, adjust the spring or replace the spring to increase the pressure, if the pressure is insufficient, the contact should be replaced.   c. Maintenance of intermediate part   1) In that air-type time relay, the intermediate part is mainly an airbag. The common faults are time delays. This may be because the airbag is not tight or air-leak, the action delay is shortened, and even the delay is not delayed; it is also possible that the air passage of the airbag is blocked so that the action delay is prolonged. In terms of repair, the former shall reassemble or replace the new airbag, and the latter should open the air chamber and remove the blockage. 2) For the speed relay, its rubberwood pendulum belongs to the intermediate part. If the motor can not stop braking during reverse braking, it is possible that the tilting rod of rubberwood is broken, and it should be replaced when overhauled.     VII. Example Explanation: Delay Relays RF Cafe has said "Relays are a topic that never goes out of date even with the advent of fully solid state relays that use semiconductors in the conduction path,there are still many applications that only mechanical contacts can satisfy." in April 1967 electornics world. It is true that there are switching diode arrays that can handle very high powers,but they are typically expensive compare with relays. Today, let's talk about something about time-delay relays.     What is time delay relays? Time delay relays are simply control relays with a time delay built in. Their purpose is to control an event based on time. The difference between relays and time delay relays is when the output contacts open & close: on a control relay, it happens when voltage is applied and removed from the coil; on time delay relays, the contacts can open or close before or after some time delay. Time delay relays have an important influence in industrial contor logic circuits. There are some examples following:   Flashing light control (time on, time off): two time-delay relays are used in conjunction with one another to provide a constant-frequency on/off pulsing of contacts for sending intermittent power to a lamp. Motor soft-start delay control: Instead of starting large electric motors by switching full power from a dead stop condition, reduced voltage can be switched for a “softer” start and less inrush current. After a prescribed time delay (provided by a time-delay relay), full power is applied. Furnace safety purge control: Before a combustion-type furnace can be safely lit, the air fan must be run for a specified amount of time to “purge” the furnace chamber of any potentially flammable or explosive vapors. A time-delay relay provides the furnace control logic with this necessary time element.   How does time delay relay work? Time delay relays can provide simple, reliable, and economical control. Adjusting the delay time is often as simple as turning a knob. Providing time-delayed switching to start a motor, control a load, or affect a process, TDRs are typically used in industrial applications and OEM equipment. Additionally, they play an important role for targeted logic needs, such as in a small panel or in sub-panels. They have a variety of features and operating characteristics, such as compactness, economy, simplicity, and ease-of-use.Time delay relays not only can be available as plug-in devices but aslo as single-function,single-time-range devices traditionally.   All in all, with an on-delay timer, timing begins when voltage is applied. When the time has expired, the contacts close — and remain closed until voltage is removed from the coil.   Time delay relays circuit and working     See the above circuit diagram, time delay relay circuit contains an electromechanical relay and driver circuit, this circuit decides the time delay to give power supply to the electromechanical relay coil by the way to the load connected to the relay.   This circuit is divided into two sections. The first section is time delay elements such as voltage divider resistor series and two electrolytic capacitors. The second section is a relay with an indicator LED. Resistor R1, potentiometer, and R2 connected in series and across to the DC input supply, the output of the variable resistor (potentiometer) is connected to the C1 capacitor and reverse-biased Zener diode then C2 capacitor finally to the base of transistor SL100. 12V Relay is connected with the collector terminal of SL100 transistor and Bicolor LED terminal green is connected with the emitter of Q1 and terminal Red is connected across collector.   When the supply given to this circuit depends on the value of the Potentiometer small level voltage passed to C1 and it gets charged when its completed and above the cutoff limit of the Zener diode, Voltage passed to the C2 capacitor and it gets charge, finally the base-emitter voltage limit of Q1 transistor reached by the C2 then Q1 gets turn ON and Relay coil gets complete DC supply then Relay energized for to complete the above process it takes some time delay depends on Potentiometer value, C1-C2 charge time and Zener diode breakdown voltage hence we can achieve few seconds to few minutes time delay.   By changing the Potentiometer value or C1-C2 value we can achieve different time delay levels. We can use this circuit to turn ON or turn OFF some sensitive time delay required electrical applications.     How to select a delay relay? Selecting a relay, there are many factors that need to consider including data on thermal,motor-driven, pneumatic, RC, slugged, hydraulic, escapement, and solid-state types.   The fantastic growth of the field of automatic industrial control has increased the demand for new and more versatile devices to perform the basic electrical switching functions required. The use of time-delay relays has grown rapidly to keep pace with the demand for the basic function which they can perform: that of obtaining a predetermined delay from one switch operation to another.     (A) Delay on energization. (B) Delay on de-energization. Time-delay relays perform in a manner quite similar to a standard relay in that they have contacts that open and close when power is applied and removed from the input terminals. The basic difference is that a delay is incorporated into the contact opening or dosing. Time-delay relays are used in a wide range of applications: from determining how full your coffee cup will be when you put a dime in a vending machine, to shutting off the cutting oil on a milling machine. The most popular time-delay relay is the delay on operation, or de-energization, in which the normally open load switching contacts transfer at a predetermined time after power is applied to the input. The contacts drop out immediately upon the removal of the input power   Often a time delay on release, or de-energization, is required. In this case, the normally open load switching contacts operate immediately when the input power is applied and remain in this position as long as the input power remains "on". Upon removal of this power the timing begins, and after a predetermined delay, the contacts drop out. Several variations on these two basic timing modes are used, such as interval "on", automatic recycle, combined "on" and "off" timers, and sequence timers. Many of these can be made by simple connections of the two basic types.   FAQ   1. What is Relay and its uses? Relays are switches that open and close circuits electromechanically or electronically. Relays control one electrical circuit by opening and closing contacts in another circuit. ... In addition, relays are also widely used to switch starting coils, heating elements, pilot lights and audible alarms.   2. What is the relay device? Relay is an asynchronous, screen-free walkie talkie system that allows parents to stay in touch with their kids at the push of a button. Relay is a Republic Wireless product, and makes use of the carrier's cell phone network (via T-Mobile and Sprint).    3. What is Relay and its types? Relays are electrically operated switches. They are used to control a circuit by a separate low-power signal or to control several circuits with one signal. ... The three main types of relays are electromechanical, solid-state, and reed. This overload protection relay reacts to overheating.   4. What is the working principle of relay? Relay works on the principle of electromagnetic induction. When the electromagnet is applied with some current it induces a magnetic field around it. Above image shows working of the relay . A switch is used to apply DC current to the load.   5. Does relay important? Converting a small electrical input into a high-current output is no easy feat, but this task is necessary to efficiently operate a wide range of standard appliances and vehicles. Many circuits achieve these conversions through the use of relays, which are indispensable in all kinds of electronic equipment.   6. What are the 5 applications of relay? Applications of Relays in Electronic Circuits: Relay Drive by Means of a Transistor. Relay Drive by Means of SCR. Relay Drive from External Contacts. LED Series and Parallel Connections. Electronic Circuit Drive by Means of a Relay. Power Source Circuit. PC Board Design Considerations. 7. What is difference between relay and circuit breaker? The Relay is a switching and sensing device, but the Circuit breaker is an isolating or disconnecting device. Relays operate on low power input voltage. ... The Relay is used to control or select one among many circuits, whereas Circuit Breaker is one per circuit. Relay acts an electrical amplifier for discrete signal.   8. How fast can a relay switch? 5 to 15 ms. While the mechanical construction of electromechanical relays allows for much flexibility in switching capability, they have one important limitation: speed. When compared to other relays, electromechanical relays are relatively slow devices -- typical models can switch and settle in 5 to 15 ms.   9. Why do I need a relay for LED lights? Relays can be used to switch a low-current trigger to high current, switch a circuit on or off, reverse polarity, and much more. When adding LED lights, such as off-road light bars, driving/work lights, or other auxiliary lights to a vehicle, you must add a circuit to power the light adequately.   10. What is the major application of relays in our daily lives? The typical applications of electromechanical relays include motor control, automotive applications such as an electrical fuel pump, industrial applications where control of high voltages and currents is intended, controlling large power loads, and so on.   You May Also Like: Making a Arduino Variable Timer Relay How to Drive Thermostat by Using Solid State Relay Product Recommendation: CMRD6055 CB-1001B-70 G6K-2F-Y-TR DC24

The idea of home automation is not bounded to houses, the application area can be extended to security systems, auditoriums, function halls, Libraries etc. Home automation is just a catchy usage.Here, the medium for automation is not considered, only the switchboard connections are discussed. Every automation circuit finally has to control a relay through the port of the microcontroller. So, the circuit is similar up to the relay control, it slightly differs at the load terminals of the relay. Generally, NO and COM terminals of the relay are used for load control, here NC is also used. Basic Idea All the home automation circuits have a remote control feature, and it may be operated through Radio Frequency, Bluetooth, Infra-Red, GSM, Wi-Fi etc. But how to connect them to the existing switchboards, and what if the remote control is misplaced or if the circuit is malfunctioning? To avoid such disturbances in a practical scenario, it is better to have manual control as well similar to the switchboards. If the relays of home automation circuits are connected in series with the existing switches, they provide semi-manual control i.e., Turn OFF is possible, but to turn ON the load, the relay has to operate. So, this is not a suitable type of connection. Combining Two-Way switch and relay Two-way switches offer a solution to this. The relay is just similar to a two-way switch in terms of terminals i.e. both have three terminals like NC, COM, NO. Two-way switch connection for Staircase lighting actually gave this idea, but now, in this case, one manual switch and one electro-mechanical relay are used. Toggling any of them changes the ON/OFF state of the load. Actual wiring By using this, existing switchboards can be modified by replacing one-way switches with two-way switches. As already mentioned, the idea of home automation is not bounded to house, the application area can be extended to security systems, auditoriums, function halls, Libraries etc. Home automation is just a catchy usage.   In the above image, Phase wire is run through all the switches on the top terminal i.e. terminal 1 and these are again connected to NC terminal of all the relays. Common terminals of switches i.e. terminal 2 of the switches are connected to the COMMON terminal of respective relays. Terminal 3 of switches are connected to loads and again connected to NO terminal of relays. So, while modifying the existing one-way switchboard, the common phase is connected to terminal 1 of two-way switches and loads are connected to terminal 3 of two-way switches. In addition to this, three terminals of switches are connected to three terminals of relays as, Two-way switchRelay Terminal 1 ——- NC Terminal 2 –—– COM Terminal 3 ——- NO Now, the loads can be turned ON/OFF manually through switchboard as well as remotely. Suppose if manual operation is not used, then turn OFF all the switches, now this state is similar to One-way switchboard with all the switches in OFF state. All the loads can be operated remotely. Their status can be known from the remote device itself. Suppose, if automation circuit fails i.e., relays in OFF state, then loads can be operated manually similar to One-way switchboard. While using manual along with automated operation, in order to get the status of the loads, an additional circuit is required to read the ON/OFF state of the loads. This is generally required if the user is at a remote location like for a house, if the operator is at the office or on a journey, reading the load status is required. But it is not essential, when the user/operator is in sight of the loads, for example, ON/OFF status of the load is directly visible. Relay board can be placed below the switchboard in a separate enclosure along with the automation circuit. However, in typical situations and requirements, an opto-coupler based sensing circuit can be included in the circuit, if the status of loads is required. Ref: KY66-G3F-203SN DC5-24 KY66-CMRD6055 KY66-CKRA2420