How To Use A Relay?

How does a relay work?

Relays are switches that open and close circuits electromechanically or electronically.

Relays control one electrical circuit by opening and closing contacts in another circuit.

When a relay contact is Normally Closed (NC), there is a closed contact when the relay is not energized.

When would you use a relay?

Relays are often used in circuits to reduce the current that flows through the primary control switch. A relatively low amperage switch, timer, or sensor can be used to turn a much higher capacity relay on and off. Another primary use for relays is when upgrading to halogen headlights on an older car.

How do you control a relay?

When you activate the relay by applying an appropriate voltage to the control circuit, the electromagnetic coil in the relay activates and pulls the switch open, stopping any current flowing through the switched circuit.

How a relay is wired?

A relay is an electromagnetic switch operated by a relatively small electric current that can turn on or off a much larger electric current. The heart of a relay is an electromagnet (a coil of wire that becomes a temporary magnet when electricity flows through it).

How do you check if a relay is working?

Listen for a click when the relay is energized. Check the energized condition of the relay contacts. Use a digital multimeter (DMM) to test the resistance between each pole of the relay and the corresponding NC and NO contacts for that pole. All NC contacts should read infinite resistance to the corresponding pole.

What is the symbol for a relay?

A single pole switch is often denoted by the letters SP, and a double pole by DP. Relays can have one, two or more poles. Throw: The number of throws on an electrical switch is the number of positions that are available. For an electromechanical relay, there are normally only one or two throws.

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Why do relays fail?

In fact, the life of a relay is essentially determined by the life of its contacts. Degradation of contacts is caused from high in-rush currents, high- sustained currents, and from high voltage spikes. Relays can also fail due to poor contact alignment and open coils.

How many relays does a car have?

Two circuits (terminals 87 and 87a ) have a common terminal (30). When the relay is at rest 87a is connected to 30, and when the relay is energised 87 becomes connected to 30 (but never both at the same time).

Relay Guide.

Terminal/Pin number and size Connection
5 – 6.3mm Normally Open (NO)

4 more rows

Does a relay have to be grounded?

If the relay is in a metal housing, It may have only ONE pin for the coil. The second pin, or ground is the housing which must be mounted direct to chassis or otherwise grounded. If your relay is in a plastic housing it will have 2 pins for the coil, usually reversible.