Relays

What are relays? Relays are simple electromechanical switch composed of a “set of contacts” and an “electromagnet”. They’re found concealed in many types of devices. Actually, a number of the very first computers ever made utilized relays to implement the “Boolean Logic” gates, but that’s another story. Let’s concentrate on how relays work, as well as some of its applications.

Relay Construction

Although they may seem complex, relays are in fact simple devices. Basically, the main parts of each relay include four parts: the electromagnet, the armature, the spring, and the set of electrical contacts.

To present a much simpler picture of how these four parts in relays work; let’s take the case of a light bulb. A relay contains two separate and totally independent circuits. The first can be found at the bottom, and runs the electromagnet. When it is turned on, the electromagnet is switched on, attracting the armature. The armature acts like a switch for the second circuit. Thus, when the electromagnet is keyed up, the armature fulfills its second circuit so the bulb lights. Once the electromagnet is switched off, the spring hauls the armature away; therefore the second circuit isn’t complete.

Purchasing Relays

When you buy electrical relays, there are a number of factors that you usually have control of: first is the current and voltage needed to turn on the armature; second is the highest current and voltage that can power through the armature and its contacts; third is the number of armatures, usually 1 or 2; fourth is the number of armature contacts, usually 1 or 2; and fifth is whether the contact is NO (normally open) or NC (normally closed).

Relay Applications

Generally, the main aim of a relay is to utilize little amount of power in electromagnet to shift an armature, which is capable of switching much bigger power amount. For instance, you may wish to energize the electromagnet using 5V and 50-milliamps, whereas the armature can hold up 120V AC at 2-amps.

Relays are rather widespread in home appliances that need electronic controls to turn up something such as a light or motor. They’re also commonly applied in cars, where “12V supply voltage” implies that almost everything requires big power amount. In more modern vehicles, manufacturers have begun combining panels of automotive relays into the “fuse box” for easier maintenance. In areas where a big amount of voltage needs to be energized, relays are frequently cascaded. In cases like this, a “small relay” is required to run a bigger relay, and this second relay turns on the power to run the load.

In cars, they are basically very small devices present in custom installations. They can be used for turning on several amplifiers, door-lock actuators, motorization projects, running fans, and many other car audio devices. They typically feature a “mounting tab” and a standard “5-pin layout” that attaches to any type of “female spade terminals”.

One may also obtain an optional “relay wiring harness” that are separately available in the market. The primary connections or contacts are rated 30A maximum amps at 12VDC. The relays are powered with 9-15VDC that depends on the voltage, as well as an estimated “100mA” current draw.

“Single Pole Double Throw Relay” (SPDT) automotive relays are electromagnetic switches that contain a coil, one common terminal, one “normally closed” terminal, and one “normally open” terminal. SPDT relay coils are commonly used in cars as they draw very small amount of current.

Anytime one wants to switch on a device that draws extra current than what is provided by the component or switch, will need to utilize a relay. Relays serve as electrical switches that close and open, under the power of another electrical circuit.