How Relays Work
FREE COURSE!! Learn the basics of relays to understand the main parts, the different types as well as how they work along with worked examples.
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What is Relay?
- A relay is an electrically operated switch.
- two versions
- traditionally, Use an electromagnet to mechanically operate the switch
- newly, Use electronics such as solid-state relays
Why Do We Use Them
- Relays are used where it is necessary to control a circuit using a low-power signal, or where several circuits must be controlled by one signal
- Relays ensure complete electrical isolation between the controlling and controlled circuits
Main Parts of a Relay
- Primary and Secondary
- Primary Circuit
- Control signal to operate the relay
- Gennerally connected to a low voltage DC supply
- Electromagnetic coil generates a magnetic field when current passes through it
- Armature
- At the end of the electromagnet we find the armature
- This is a small component which is pivoted
- When the electromagnet energises it attracts the armature
- When the electromagnet is deenergised, the armature returns to its original position
- Secondary
- Contain the load which needs to be switched and controlled
How an Electromechanical Relay Works
- normally open
- No electricity flows in the secondary circuit, the load is therefore off
- When a current is passed through the Primary Circuit, a magnetic field is induced in the electromagnet
- This magnetic field attracts the armature and pulls the moveable contactor until it touches the terminals of the secondary circuit
- This completes the circuit and provides electricity to the load
- normally closed
- The secondary circuit is normally complete and so the load in on
- When a current passed through the primary circuit, the electromagnetic field causes the armature to push away which disconnects the contactor and breaks the circuit
- This cuts the supply of electricity to the load
How solid state relays work (SSR)
- Unlike electromechanical relays, it has no moving parts
- Use the electrical and optical properties of solid-state semiconductors to perform its input and output isolation as well as swtiching functions
- Primary side
- LED light instead of an electromagnet
- The LED provides optical coupling by shining a beam of light across a gap and into the receiver of an adjacent photo sensitive transistor
- Control the operation of this type by simply turning the LED on and off
- Phototransistor acts something like an insulator and doesn't allow current to flow, unless it is exposed to light
https://www.galco.com/comp/prod/relay.htm
How Relays Work | Relay diagrams, relay definitions and relay types
Relays are switches that open and close circuits electromechanically or electronically. Relays control one electrical circuit by opening and closing contacts in another circuit. As relay diagrams show, when a relay contact is normally open (NO), there is a
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