Relays

What is an Electrical Relay?

Regardless of the industry you work in, chances are you’ve come across a relay at some point.

We’ve all heard the word “relay.” As kids, many of us played relay races; one person runs, then passes the baton/stick to the next person, who continues the race. The action is transferred from one person to another.

An electrical relay works on a very similar principle, with one important difference.

Instead of passing a baton, a relay transfers electrical control.

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How Does a Relay Work?

Let’s look at a practical example.

Imagine you own a truck and want to install a high-voltage accessory, such as powerful auxiliary lights or a winch. You’d like to control it using a switch inside the cab.

However, you don’t want a large, heavy-duty switch mounted on your dashboard. You’d prefer a small, standard switch that blends in with the interior.

This is where a relay comes into play.

You can connect a small switch to a relay located behind the scenes (usually closer to the battery or accessory). The relay is then connected directly to the high-voltage accessory.

When you press the small switch, it sends a low-current signal to the relay. The relay then closes its internal contacts, allowing high current to flow to the accessory. 

In simple terms:

• The switch controls the relay.
•  The relay controls the high-power device. 

 This allows a small, safe control circuit to operate a much larger electrical load.

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What Is Happening Inside the Relay?

Inside a basic relay, there are three main parts:

• A coil (a small electromagnet)
• Electrical contacts
• A metal arm

When a small current flows through the coil, it creates a magnetic field.

This magnetic field pulls the metal arm down, which closes the circuit (otherwise open).

When the circuit closes, electricity flows to the high-power device.

When you turn off the switch, the magnetic field disappears, and the circuit opens again.

It’s like an automatic on/off gate for electricity.

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What is a Pneumatic Relay?

While an electrical relay controls electricity, a pneumatic relay, on the other hand, works with air pressure. Instead of switching electrical current, it uses a small air pressure signal to control a larger air flow.

They both act as “middlemen,” but they control completely different things.