Electronic Components – Relays

Switches are an integral part of pretty much every sort of electronics build, and in instances where switches aren’t used you need something else to regulate and activate your circuit. In those instances you might want to use a relay. In essence, a relay is a switch, except instead of being activated manually by a switch, it’s instead activated by some sort of other stimulus making a relay more or less an automated switch. You can see pretty in depth how one works here. Relays are everywhere, and many of those places are things we never would consider and rarely think about. Since they’re switches they can often be used instead of a manual switch.

The relay began development in 1831 and was officially “invented” in 1835 by Joseph Henry. Henry’s relay was basically an electromagnet apparatus that used electricity to move a metal piece and subsequently open and close a circuit. The basic design has stayed more or less the same throughout the years, relays, except solid state relays which have no moving parts, basically make use of an electric magnet to move a metal armature to open and close a given circuit or multiple circuits. There are also springs and hinges which help the armature move and return to its original position. It’s incredibly simple, but endlessly useful and its inventor hadn’t even recognized its potential.

Strangely enough Henry’s primary interest was using it to entertain his students, probably as a cheap parlor trick using electricity to move the switch. Luckily the rest of the world saw the potential of the relay and quickly put the relay to good use. Samuel Morse (of the code fame) used the relay to help invent the telegraph and after telephones became a thing, relays were used in rotary dial phones, switchboards and early computers. Their use has of course grown from these early beginnings into practically any electronic device you can think of.

The main reason that relays caught on was due to the fact that a small amount of electricity could be used to activate the circuit and thereby allow a machine to function. Perfect examples of relays in use are motors, heaters, environmental controls, sprinkler systems/alarms, heated mirrors (and tons of other stuff in cars). In the case of a sprinkler system, the relay kicks in as the result of a timer or moisture sensor and turns the sprinklers on. With heated mirrors, the heat turns on or off at a certain temperature to ensure that the mirrors are free of ice and fog. With environmental controls, an electronic thermometer, at a certain temperature, activates an output circuit to power a cooling or heating fan. As you can see, relays are so basic that they can be applied to almost anything, even in Elenco Snap Circuits. Wherever you could need a switch, a relay might work instead.

Even though relays can be used in virtually any application, ensuring proper use in terms of Pole and Throw, as well as within the voltage and current parameters is quite important. Relays will usually be categorized like switches, so it’s a good idea to familiarize yourself with how switches open and close a circuit. The other part you want to pay attention to is current and voltage ratings which inform you how much of each the relay can handle. It goes without saying that if you exceed these ratings your circuit is going to blow up or become inoperable in some other way.

Despite how simple they are and their humble beginnings as a toy for a bored instructor, relays have become an invaluable piece in circuits of all kinds. You can find relays everywhere from cars, to HVAC systems, to sprinklers in landscaping and virtually anything you can think of. Here at EIO we sell many different relays, so we’d love to see what you’ve done with them!