22.12.2021

What is a relay?
A Relay is an electromechanical or

electronic device through which a heavy load can be switched ON & OFF with a nominal

input of current & voltage. This article focuses on electro-mechanical relays used in

automotive applications.
How does a relay work?
The utility and function of a relay can be best understood by thinking of a

lever. A lever is inserted at a corner of a heavy load and by placing a wedge

(fulcrum) under the lever, the heavy load can be easily lifted by a small amount of

effort.
Similarly, a heavy electrical load drawing heavy current can be switched on & off

by applying a small amount of current through a coil(solenoid). What happens is this

- the coil gets magnetized with the current and attracts or repels a plunger(a rod

passed through the coil). The attracting or repelling of the plunger either connects

two switching contacts in the relay (also known as NO or Normally Open/Single

Throw/Form A) or separates them (NC or Normally Closed/Double Throw/Form C), as

required. As soon as the energisation of the coil is stopped, the main contacts go

back to their original position.
In automobile applications relays of different configurations with single or

multiple contacts are used for different applications.
Another important function of the

PCB Relay is quick switching off(0.05Sec Max.). The more time the contacts of a

switch take to break at full load, the more sparks will be generated due to

electromagnetic effect on contacts in a switched on state. Prolonged sparking will

mean more wear of the contact points and the danger of contacts melting and

generating a fire. International standards have very stringent relay specifications.

The endurance of a relay is generally specified in millions of switching operations.
How to Understand the Electrical Specifications of a Relay
Basic 5pins Car

Relays feature electrical ratings for both the coil and the internal switching

contacts. The coil voltage rating is the voltage required for the coil to operate

correctly. The switching circuit of the relay also features a voltage and ampere

rating. This is the maximum rating of the switch contacts and should NOT be exceeded.

Double throw relays often have 2 x switch electrical specifications. One for the

normally open terminal, the other for the normally closed terminal. ie. N/O: 35A at

14vdc, N/C: 20A at 14V
Relays are part of a car’s electrical system. Without them, electrical

components would not work. Several electrical devices in a car run off relays.
WHAT IS A RELAY?
As its name suggests, it relays current from the battery to the device. It may

seem superfluous as any device would still function if wired directly from the

battery. But there is a sound reason for using relays. A relay is essentially a

switch with an electromagnet inside. When energised, it triggers a lever to close the

contacts of a circuit.
HOW DOES IT WORK?
Let’s use the car horn as an example. When you press the steering-wheel boss to

activate the horn, a small current – less than 0.5 amps – is sent from the horn

switch to the Auto Relay. The

relay’s electromagnet then activates an internal switch, which bridges the main 12-

volt supply to the horn’s terminal. Most horns require at least 10 amps to work. If

it is a twin-horn set-up, you are looking at 20 amps at least. A relay’s switch

typically handles 30 to 40 amps.
WHAT’S THE ADVANTAGE OF A RELAY?
The horn button, therefore, does not need to be wired with high-current capacity

wires. Nor does the horn switch need to endure the tens of amperes to power the horn.

This way, over time, wear and tear is confined largely to the relay instead of the

wires. Relays are workhorses that are usually installed close to the fuse box. They

are easily removed. A horn relay typically costs about $5.
A Push Button Switch is a

type of switch which consists of a simple electric mechanism or air switch mechanism

to turn something on or off. Depending on model they could operate with momentary or

latching action function. The button itself is usually constructed of a strong

durable material such as metal or plastic. Push Button Switches come in a range of

shapes and sizes. We have a selection of push button switches here at Herga.
Push button switches are used throughout industrial and medical applications and

are also recognisable in everyday life. For uses within the Industrial sector, push

buttons are often part of a bigger system and are connected through a mechanical

linkage. This means that when a button is pressed it can cause another button to

release.

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