A small electric motor needs nothing more than a battery, a switch, and a thin 24 gauge wire. The motor draws at most a half amp of electricity, which will easily pass through the thin wire. However, a much larger motor will draw more amps, and therefore will need a larger wire. Think of people in a hallway. If too many people try to get through at the same time, the hallway gets clogged. And if they stay there for a while, because they are moving more slowly, the hall will heat up from everyone’s body heat.
The same is true for electricity. If too much electricity tries to go through a wire that is too small, the electricity backs up, and the wire heats up. As a result, the larger the motor needed for an application, the larger the wire is needed. Larger switches are needed with larger wires to handle the added power needed to run a bigger motor. In order to run a large, complex piece of machinery, several motors, large switches, and less flexible larger wires are needed.
All of this becomes too big and unwieldy to be very useful. By using relays, small wires and small switches can be used to turn the circuits on and off. Relays help make control boxes a more manageable size and the cabling going between the control box and the motors easier to work with.
FAQs
A relay is an electromagnetic switch operated by a relatively small electric current that can turn on or off a much larger electric current. The heart of a relay is an electromagnet (a coil of wire that becomes a temporary magnet when electricity flows through it).
What are the two main parts of an electromagnetic relay? ›
An electromagnetic relay primarily consists of two essential components: the contacts and the electromagnet. The contacts function similarly to a traditional mechanical switch. When the relay is activated, the electromagnet generates a magnetic field, causing the contacts to close and complete the circuit.
What is a relay switch? ›
A relay is an electrically operated switch. It consists of a set of input terminals for a single or multiple control signals, and a set of operating contact terminals. The switch may have any number of contacts in multiple contact forms, such as make contacts, break contacts, or combinations thereof.
Why do we need relays? ›
The primary purpose of a relay is to protect the electrical system from too high of a voltage or current, allowing the safe operation of any equipment it connects to. They're commonly found in a variety of applications, from commercial and industrial uses to home and consumer products.
What does 30 85 86 87 mean on a relay? ›
85 will be used to ground your relay, while 86 will be connected to the switchable power. 87 and 87a will be connected to your controlled accessories that you wish to turn on and off with your relay. 30 will then be the pin connected to your battery power.
How to tell if a relay switch is bad? ›
To test this, leave your multimeter on the ohms setting and measure the resistance between the switch pins. On a four-pin relay, these are typically labeled 87 and 30. You should see no resistance at all between these pins. If you do, that means that the pins are stuck closed and the relay is bad.
What does a relay do for dummies? ›
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 an open contact when the relay is not energized. When a relay contact is Normally Closed (NC), there is a closed contact when the relay is not energized.
Why use a relay instead of a fuse? ›
Fuse vs Relay: Comparison
Fuses prevent electric circuits from being damaged by melting the metal wire when excessive current passes through it. Relays prevent electric circuits from damage by mechanically opening or closing the switch contacts when high or low voltage passes through them.
What are the three basic functions of a relay? ›
It is actually an "automatic switch" that uses a smaller current to control a larger current. Relay plays the role of automatic adjustment, safety protection, and conversion circuit in the circuit.
Do you need a relay if you have a switch? ›
If you need to activate a heavy load, high current device using a small, light load switch – you will need a Power Relay!
Relays are used where it is necessary to control a circuit by a low-power signal (with complete electrical isolation between control and controlled circuits), or where several circuits must be controlled by one signal.
How long can a relay stay on? ›
Explanation: Continuous energization may cause the coil, which uses polyurethane copper wire, to generate heat. Since a single wire generally has a heat-resistant life of 40,000 hours, the life will be approximately 5 years when a rated voltage is applied and used in a standard environment.
How much current does it take to activate a relay? ›
A broadly accepted rule of thumb is 60% to 80% of the rated voltage but this depends on the relay's sensitivity, as evident from my tests.
How much current does a relay switch draw? ›
Typically, a relay coil draws a small current, usually in the range of 100 to 200 milliamps (mA). This current is necessary to generate the magnetic field that activates the relay switch.
What is the minimum current for a relay? ›
There are several relays used across this range of controllers and to ensure good low current operation, the minimum or wetting current should be 1milliamp at 5volts or greater. Wetting current is the minimum electric current needing to flow through a contact to break through the surface film resistance of a contact.
When a small current is used in a relay? ›
When a small current or voltage is applied to the coil of the relay, it creates a magnetic field which either attracts or repels a metal switch, thus opening or closing the circuit. The main advantage of using a relay is that it allows a low power signal to control a much larger power signal.
