![]() ![]() ![]() This is based on standard switch terminology. Make & break relays are also known as Single Pole Single Throw (SPST) and changeover relays as Single Pole Double Throw (SPDT). ![]() These have two contacts connected to a common terminal. ISO mini relays with two circuits, one of which is closed when the relay is at rest and the other which is closed when the relay is energised, have 5 pins on the body and are referred to as changeover relays. Normally Open relays are the more common type. If the contact is broken with the relay at rest then the relay is referred to as Normally Open (NO) and if the contact is closed with the relay at rest then the relay is referred to as Normally Closed (NC). The ISO mini relay we have looked at above has 4 pins (or terminals) on the body and is referred to as a make & break relay because there is one high current circuit and a contact that is either open or closed depending upon whether the relay is at rest or energised. The following simplified circuit diagram is often used to easily understand how a relay operates: The coil circuit simply switches the high current circuit on. Note: It is important to understand that the coil circuit and the current-carrying (or switched) circuit are electrically isolated from one another within the relay. So by applying or removing power to the coil (the low current circuit) we switch the high current circuit on or off. When voltage is removed from the coil terminal the spring pulls the armature back into it's 'at rest' position and breaks the circuit between the terminals. This completes the 'high' current circuit between the terminals and the relay is said to be energised. When the coil is supplied with voltage a magnetic field is generated around it which pulls the hinged armature down onto the contact. The coil and contact (or contacts) are then connected to various terminals on the outside of the relay body. The braided bonding strap provides a good electrical connection between the armature and yolk, rather than relying on contact between the armature pivot point alone. This is the relay in its de-energised state or 'at rest' with no voltage applied. One end of the armature is connected to a tension spring which pulls the other end of the armature up. This is what the inside of an ISO mini relay looks like:Ī copper coil around an iron core (the electromagnet) is held in a frame or 'yoke' from which an armature is hinged. Note: In this article we are going to focus on ISO mini or 'standard' relays which have a 1" cube body and are the most commonly used in vehicle electrical systems. Although these logical functions have now been superseded by electronic modules for OEM designs, it can still be useful, fun and often more cost effective to use relays to perform them for some after-market projects (particularly where you have a bespoke application). central locking output, manual switch etc.) to activate one or more relays that then complete one or more other circuits and so carry out multiple functions from one input signal.Įlectromagnetic relays can be put to some quite clever (and complex) applications when linked up to perform logical operations based on certain inputs (for example, latching a +12V output on and off from a momentary input, flashing alternative left and right lights etc.). You can use a single input from one part of an electrical system (e.g. Activating more than one circuit from a single input.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. For example, if you wanted to fit some high power work lights that come on with the headlights but there is a risk that they would exceed the capacity of the existing loom. 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. Switching a high current circuit using a lower current circuit.There are several reasons why you might want or need to use a relay: These are used extensively throughout vehicle electrical systems. Although there are various relay designs, the ones most commonly found in low voltage auto and marine applications are electro-mechanical relays that work by activating an electromagnet to pull a set of contacts to make or break a circuit. Taking care of the customer is Lutron’s first principle and our number one priority.A relay is essentially a switch that is operated electrically rather than mechanically.Whether you are looking to reduce energy costs, increase comfort, or manage light control solutions, Lutron products offer the flexibility you need with the energy savings you want.Ĭonnected lighting, shades, and hand-crafted controls that elevate everyday life. ![]()
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