What do relay numbers mean

To learn more please read our cookie policy. Why Use a Relay? Why Use a Relay in a Car? A relay is an electrically operated switch. They commonly use an electromagnet coil to operate their internal mechanical switching mechanism contacts. When a relay contact is open, this will switch power ON for a circuit when the coil is activated. The example relay diagrams below show how a relay works.

Why use a Relay? Relays allow a low current circuit to control one or more higher current circuits. Relays provide these benefits; 1. Thinner cables can be used to connect the control switch to the relay thereby saving weight, space and cost. Relays allow power to be routed to a device over the shortest distance, thereby reducing voltage loss. Heavy gauge cable only needs to be used to connect a power source via the relay to the device.

There are several benefits of using a relay in a car. Firstly using a relay means the switching circuit does not require a high current rated switch or cable which reduces cost and weight. Secondly, relays can be positioned anywhere in the vehicle to provide efficient power transfer to the electrical accessory you are controlling.

Relays are perfect for controlling many circuits in a car like headlights, electric motors, heater etc. How to Understand the Electrical Specifications of a Relay Basic relays feature electrical ratings for both the coil and the internal switching contacts. Live it. This is overwhelmingly the most common kind of relay found in a car. In it, the switch inside the relay has not just one position, but two—current can flow to one of two terminals at a time.

When the relay is energized, 87 and 87a change places—87 is disconnected from 30, and 87a is connected to Below are two of the relays in my BMW 3. On the relay on the right, you can see the little schematic drawn on the side of it, which looks remarkably like my hand-drawn diagram showing the coil of the electromagnet with terminals 86 and 85, and the switch with terminals 30 and All DIN relays should have the terminal numbers on the bottom.

On mine, you can see the labels for terminal 87 at the top and 30 on the left. Surprisingly, although the numbering of DIN relays is standardized, the terminal locations on DIN relays are not completely standardized. Terminals 87, 85, and, on a changeover relay, 87a, are I believe always in the same place, but terminals 30 and 86 can switch places with each other.

For this reason, you need to be very careful rummaging through the spare parts box to find a relay if one of yours has died, or accepting one from a well-meaning passer-by.

You can swap them the other way, however—a relay with a resistor or a quenching diode can generally take the place of one without them. They are rectangular in section and narrower than a mini relay with a slightly different pin layout, and are typically available in 'make and break' and 'changeover' configurations, with and without suppression diodes. There are other relay designs that are used for some more complex applications in vehicle systems.

They are still based upon the principle of switching higher current circuits using smaller current circuits but often combine this with electronics to perform special functions: Some examples are:.

These more complex relays can have up to 9 pins of various sizes. This increase in the number of terminals over the standard 4 or 5 in more simple relays is often necessary because additional connections can be required for the in-built electronics e. This simple circuit uses the power feed to the headlight main beam bulb as the trigger to energise a relay.

The high current circuit in this relay feeds power to the driving light bulb, so every time headlight main beam is selected, the coil is energised and the driving lights operate. Note: It is important that the new power feed to the driving lights is fused appropriately see our Knowledge Centr e fusing guide. Tip: It is a good idea to use a separate relay for the left and right hand driving lights and have them switched independently from the left and right hand main beams.

This way, if a relay on one side fails the driving light on the other side will still work. Adding a buzzer that warns when you've left your headlights on. This circuit is designed to alert you that you've left your lights on by activating a buzzer when you open the driver's door.

If the headlights are on and the driver's door is opened, the door switch will complete the coil circuit which will complete the high current circuit to the warning buzzer. A warning light could easily be added in parallel to, or used instead of, the buzzer. Also connects in parallel to terminal This is a clever little circuit involving two relays and a momentary switch and is more a of a 'logic' circuit than one used to switch a high current with a low current.

Once the ignition key is in the IGN position, you press and release the momentary switch and then turn the key to the START position and fire the engine as normal. This has the effect of keeping the coil energised after the button is released note that whilst the button is pressed there is 0V between terminals 86 and Terminal 87 also sends power to the coil of Relay 2 which enables the starter motor solenoid connection, ready for when the key is turned to the START position.

When the ignition is turned off the power to the coil of Relay 1 is cut which cuts the power to the coil in Relay 2 and breaks the starter motor solenoid circuit, so the engine cannot be started again without going through the above routine. The momentary switch can be mounted out of sight and acts a simple starter inhibit security device.

This supply also feeds the other side of the momentary switch. Need some hints, tips or guidance on 12V electrics? Visit our Knowledge Centre for a wealth of useful information. Watch our YouTube "how to" guides here.

We accept telephone orders Call Relay Guide Overview What is a relay? Why might I want to use a relay? There are several reasons why you might want or need to use a relay: Switching a high current circuit using a lower current circuit This is the most common reason and useful where an in-line switch or the existing circuit does not have the capacity to handle the current required.

Cost saving High current capacity wiring and switches cost more than lower current capacity versions, so by using relays the requirement for the more expensive components is minimised. Activating more than one circuit from a single input You can use a single input from one part of an electrical system e. All Rights Reserved. Company Reg no. Business Hours: Mon - Fri 9am - 5pm.