A relay is an electric switch that can be used in various electrical circuits. Generally, they are used in cars to control multiple circuits like headlights and electric motors. However, it can be difficult to find the right kind of relay that is suited to your car.
Relays are an essential part of any electrical system as they can switch many different circuits at the same time. They can be found in all sorts of places in a car and also on many other devices such as TVs, fridges, microwaves etc.
When an electrical signal is applied to the coil of a relay, a magnetic field is generated around it which pulls the hinged armature down onto the contact. This completes the ‘high’ current circuit between the terminals and switches the relay on. The spring then pulls the armature back into it’s ‘at rest’ position breaking the circuit between the terminals.
The coil of the relay is then wired to one side of the relay and the high current circuit to the other side. This can be done by either using heavy gauge cable or a special connector, such as an Isolator connector.
Most relays have two main contacts, each of which can switch off or on the circuit between them (and the coil). The switching pins include common, NC and NO.
A typical example of a relay is the car horn. These are made up of a copper coil and an iron core that is connected to a hinged armature.
To activate the horn, a button on the steering wheel is pressed which then applies electricity to the coil and the solenoid. This electricity then moves metal diaphragms that generate the sound of the horn.
The horn has a current draw of about 150-200mA. It is therefore important that the power supply is rated at at least this amount to prevent damage from over-current.
Wiring a four-pin relay is simple and you don’t need to be a technical person to do it. All you need is a good knowledge of the relay and the wiring connections.
Start by connecting the battery positive and negative poles to the coil terminals of the relay – these are called terminal 85 and 86. Then connect the switch terminal to the other end of the relay and then connect the component that you want to switch off or on to the second terminal 87.
Next, connect the fuse to the relay. This is an essential step in wiring a 4 pin relay as it will help you avoid over-currents and will protect the driving lights and the circuit from getting damaged by too much current.
Another thing to keep in mind is that a relay has a +12V coil so be sure to connect the correct voltage source upstream of the coil. This can be achieved by using a diode across the coil, which will absorb any high voltage spikes before they reach the equipment upstream of the relay.