Relays are electrical or electronic devices that are part of the control system for wired installations used, among others, in in industry, construction, in systems of the so-called smart houses and in water and sewage systems. It is a popular element of control systems, for example in control cabinets, machines, control panels, operator systems and other control systems. Relays are used, for example, for time control of heating, lighting, signaling, ventilation, air conditioning, alarm system, as well as blinds and roller blinds, garage door or fire protection system. They are most often used in public buildings, on production lines, as well as in single-family houses.
The task of the relay, after meeting the appropriate input conditions, is to cause a specific state change in one or several (or even more) output circuits. This element reacts to a change of the selected input physical quantity (e.g. voltage, current, fluid pressure, temperature) in such a way that after exceeding a certain value, the output signal changes abruptly (usually it means that it goes from "on" to off or vice versa).
The el12 offer in the RELAYS category includes the following types of these devices:
- electromagnetic relay (the most popular industrial relay),
- priority relay (used, among others, in a situation where at least two high-power receivers are connected to the current circuit, which can work independently, and their simultaneous operation would trigger the current protection),
- 1-phase voltage relay (used to control the voltage value in a single-phase network in order to protect the receiver against voltage increase or decrease beyond the set values),
- bistable relay (including a time switch and voltage-free) - this device is also called an impulse relay, which is a control element that generates an impulse to the lighting system. As a result of the impulse, the lighting is switched on or off, depending on the construction and application of the relay,
- 3-phase voltage relay (used to control the voltage value in the 3-phase network in order to protect the receiver against voltage increase or decrease beyond the set minimum and maximum value),
- resistance relay with a probe - the model offered by el12.pl is used to protect electrical devices (e.g. motors) against a dangerous increase in temperature. Temperature measurement is carried out by external temperature sensors that can be connected in series. An increase in the temperature on the sensor beyond the safe value causes the output relay to operate. The sensor is galvanically isolated from the mains by an internal isolation transformer.
In this category, in the el.12 online store, you can also find the APM-10 universal automatic phase switch, which is used to power a single-phase industrial or household installation 230 V / 50 Hz from a three-phase 4-wire network in order to ensure uninterrupted power supply of a single-phase electrical installation and its protection against unacceptable voltage fluctuations in the network. Depending on the presence and quality of voltage on the phases, the device automatically selects the phase with the best parameters and switches a single-phase load of any power to it.
How do relays work?
The primary task of relays is to open and close an electrical circuit. Thanks to this, the relay can affect the operation of other devices in a given control system, i.e. it can turn them on or off.
The other most common options are:
- switch-on delay,
- shutdown delay,
- cyclic activation,
- cyclic switching off and impulsing.
Relays (in more advanced installations) can also send information about a failure in the system or, for example, an intruder detected in a building. These devices can also cause activation of external devices (e.g. lighting system, heating solenoid valve and others).
Importantly, with the right connection, you can create a system in which many elements control the same relay.
Construction and principle of operation of electromagnetic relays
The electromagnetic relay consists of an electric coil (with a large number of turns wound on a metal core), which is responsible for generating the electromagnetic field, contacts, a pusher and a moving contact.
Due to the fact that the coil is not electrically connected to the contact (galvanic separation is used), the control voltage of the coil may be different from the voltage applied to the contact. As a result, e.g. a smart home controller can control relays using one low voltage of 12 V. This means that the relays will switch on lighting or devices powered by different voltages, e.g. a 12 V light bulb in the bathroom, as well as a 24 V LED strip or a lamp in the living room for 230 V.
Applying the supply voltage to the coil causes the switching of contacts, thanks to which the current flows through the appropriate installation (after applying the appropriate voltage to the coil of the relay, it will create a magnetic field capable of attracting the pusher, which pushes the movable contact, which causes the relay to override). When no voltage is applied to the coil, the contacts return to their initial state.
Time relays, in addition to the coil with contacts (depending on the type of relay), are additionally equipped with an electronic system that performs various functions depending on time. The standard relay activates its executive contact immediately after applying voltage to the coil, while the time relay with delayed operation activates the contact after 5 seconds.
Timing relays differ from ordinary relays, for example, in the number of terminals, because they have an additional control input, which is used when the time function is more complicated. Such elements are used, for example, in the lighting of staircases, where many buttons are used (e.g. several on each floor of the building). The device works so that when any button is pressed, the light stays on for a minute. Through the buttons, the information goes to the time relay, which, from the moment of pressing the button, supplies the relay coil with voltage for 60 seconds. As a result of the operation of the coil, the relay contact changes position and supplies voltage to the lamp (regardless of which of the many buttons will be pressed).
The second distinguishing element of this solution is the signaling diode. Ordinary relays only indicate the position of its contacts. Time relays additionally inform about the status of the timer module. Usually, a flashing LED means that the time is counting down according to the set function. If the diode is constantly on, then the function is performed and the executive contacts are switched on.
For time relays, knobs are also characteristic, which, apart from setting the time, additionally allow you to select the function that this relay performs.
Relays vs. contactors - what's the difference?
The electromagnetic relay in terms of construction and operation is very similar to the contactor, because both operate on the same principle - by switching on, they transmit the signal. However, the difference lies in the application, because contactors are designed to connect main circuits, and relays - auxiliary ones. In addition to the main contacts, the contactors may have several auxiliary contacts for signaling or interlocking. Contactors are used to switch devices such as electric motors.
Relays, on the other hand, are used, for example, to provide control signals to (or from) PLC (programmable logic controller).
Contactors are usually larger than relays. They have a larger electromagnet and are adapted to withstand higher current overloads, both on the coil and on the contacts.