Relay

When working on projects that involve different components, managing powerful workloads can be challenging. For example, an electric motor or lighting lamps require high current and voltage levels that cannot be controlled directly by a controller, except for low-power LED lights. Direct control could lead to damaging the controller in case of short circuits or sudden power surges.

To solve this problem, relays are an excellent choice as they can control loads by closing the contact needed based on the commands from the controller. If the controller can operate with low voltages like 5 or 3.3 volts, the switched load can be much more powerful, up to 220V AC.

If you're dealing with an electric motor, it's better to use a separate motor controller. But if you only need to turn on the engine without adjusting the speed or soft start, you can use a relay. The simplest relay is an electro-mechanical relay with a reed switch. It mechanically closes the contact through which the main load applies under the influence of a logical signal. The advantage of such relays is that they're cheap and versatile. It doesn't matter whether direct or alternating current flows through it when the contact is mechanically closed. However, it has some disadvantages, such as clicking sounds when triggered and limitations in performance and service life due to mechanical parts. If you don't need to switch the load multiple times per second and don't require the relay to serve for years, this option is optimal.

If a mechanical relay is not suitable, solid-state relays can be used. Unlike mechanical relays, they have no moving parts and switching occurs using semiconductor components like thyristors or transistors. These relays are compact, silent, and have a long service life and switching speed. However, they're sensitive to overloads, even short-term excesses of the transmitted current and voltage, and have a small additional resistance in the closed state.

Several other specific types of relays, such as photovoltaic and induction relays, are available. But if the project requirements don't need them, you're unlikely to use them.

The choice of relay depends on the load that needs to be controlled and the level of the control signal. Electro-mechanical relays can be controlled by a 5V logic signal, so they can be connected directly to the controller outputs. More powerful relays can be controlled by a voltage of 12V and higher. In such cases, you may need to install an additional amplifying transistor or make a chain of several relays.

Relays are one of the easiest electrical circuit components to learn. They're essential in any practical application that manages real loads.