Electromagnetic relay contains a solenoid coil, NO-NC contacts & mechanical spring mechanism. The electromagnetic relay work as an electromechanical switch which contains moving contacts. When solenoid get power supply, It becomes electromagnet & attracts the contacts.
At “normal state” When electromagnet is not energized, The contact remains at its normal state due to the mechanical pull of the spring. Common contact is connected to NC contact.
At “forced state” When electromagnet get energized. The contact get attracted towards the electromagnet which result contact changes its state. Common contact get connected to NO contact. When electromagnet get de-energized; contact get back to its normal state.
Schematic Diagram of Electromagnetic Relay
Explanation about the electromagneticrelay through the images have been presented next:
This electromagnetic relay is 14 pins relay. In which 2 pins are coil’s terminals while rest 12 terminals represents 4 relays. Since each relay contains 3 pins.
Views of 14 Pins Electromagnetic Relay from 4 angles
Pin Descriptions of 14 Pins Electromagnetic Relay
Energized & non-energized states of 14 pins electromagnetic relay is shown below :
Electromagnetic relay When coil is energized
Electromagnetic Relay When coil is not energized
Since, Electromagnetic relay contains a moving part which make it a slow speed switch & having a less operating life as compare with solid state relay.
In this post, we will explain the brief working of solid state relay along with its applications.
SOLID STATE RELAY
Solid State Relay by OZO INPUT 3-32VDC OUTPUT 24-60VDC/40Amps
In an image above, 4 terminals SSR been shown; having 2 terminals are Input while rest 2 terminals are contact terminals for output. Both Input & Output are DC.
(SSR= Solid State Relay)
Solid state relay is an electronic switch which does not contain any moving part like an electromagnetic relay does. Instead, it mainly contains semiconductor components.
SSR Generally contains 4 terminals in which 2 terminals are input terminals while rest 2 terminals are output terminals. When input supply is applied to SSR. Both the output terminals of SSR get connected.
As explained in the diagram below, An input supply triggers photoelectric component which produces light signals to trigger the drive circuit. Drive circuit further triggers the main switch component which results output terminals get connected.
The main switch component of SSR is three terminals semi-conductor component whose 2 contacts are output contacts WHILE a third contact is trigger contact. When a trigger supply get applied at third contact; output contacts get connected. This main switch component can be any of these- TRANSISTOR, MOSFET, TRIAC & THYRISTER.
SSR Working diagram
FEATURES OF SSR
High speed switching – Since this relay doesn’t contains any moving part which makes it high speed switch.
Unlimited number of operations – The only problem in SSR is heating due to the forward voltage drop in semiconductor element. If adequate heat removal is present then SSR works for long for unlimited number of operations.
Noise free operation – The electromagnetic relay contains mechanical moving contacts which produces noise while working but SSR are noise free.
No erosion effect – Due to the absence of moving part; Solid state relay doesn’t have any erosion effect
High Ampere range – SSR up to 150Amps are available.
APPLICATIONS OF SSR
load connected across SSR
In Temperature control Applications
Temperature controller is the device which monitors the temperature continuously with the help of temperature sensor. By connecting or disconnecting the heating or cooling element; it maintains the desired temperature.
Electronic temperature controller which produces soft signals; heavy loads can’t be directly controlled through it. Controllers connects heating/cooling element indirectly through contactor or auxiliary relay. SSR can be used in controlling the heating or cooling element In which controller first produces command to SSR & then SSR connects heating or cooling element.
Terminals for SSR connections in SELEC TC513 SSR supply 12VDC@30mA
SSR controlling Heating Element Output of Selec TC513x connected as a input to SSR Negative supply is directly connected with heater while positive supply to heater passes through SSR output
Use With Sensors
Sensors are machines, devices & gadgets which monitors physical quantities like temperature, pressure, flow, light, motion, weight, vibration & then produces an output in the form of electrical signal. Sensor is designed for particular physical quantity That’s why each sensor has unique working principal.
Mostly, Electrical signal produced by the sensors are soft in nature & meant for control circuits only. Heavy load output can’t be controlled through it, directly. With the help of SSR, heavy loads can be connected with sensors, indirectly.
Inductive Proximity Sensor controlling load through SSR
In Motor applications
SSR can easily control heavy inductive loads which makes it an easy choice for motor applications. SSR are available up to 150Amps.
In an image below, 2 SSR’s are used to control the forward & Reverse direction of single phase induction motor. As neutral is directly connected to the common node of both the windings while phase is given through the SSR’s. One SSR is connected for forward direction while another SSR is connected for Reverse direction. The choice of direction depend upon SSR input.
SSR Used for forward & Reverse control of single phase induction motor
Transformer Tap Selection
Transformer is the static electrical machine which transfer electrical energy from one circuit to another at same frequency. It can easily change the voltage magnitude; Step up Or step Down. Transformer has two sides primary & secondary. Both the sides of Transformer contains windings. By adjusting the number of turns on either windings, voltage can be varied.
Transformer contain heavy load current; It is quite difficult to adjust the Transformer winding directly. Here, we can use SSR for Transformer Tap selection. Taps are the nodes on the transformer windings which are brought of the transformer.
SSR Controlling Taps in Transformer
DRAWBACKS OF SSR
Due to forward voltage drop in SSR semiconductor component; excess heat get generated. To remove that heat; heat sink is required.
The combo of SSR & heat sink requires some special extra space & ventilation for heat removal.
Not possible to repair.
HEAT Sink fitted behind the SSR
CONCLUSION
Solid state relay is an electronic switch which does not contain any moving part like an electromagnetic relay does. Instead, it consist of semiconductor components.
In this relay, Input is completely isolated from the output.
