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| Electrical Relay |
A relay is just like a switch you uses at home. That light switch is a device that used as isolation between you and the and the current flowing unto the wire that could burn you up. A relay functions closely the same. It's an isolation device that is used to interface a low powered circuit to high powered outputs including AC and DC lighting, motors, heaters, appliances, and almost anything else that uses electricity.
A relay is an electrical switch that uses an electro-magnetic solenoid to control the position of a mechanical power contactor. A solenoid is similar to a motor because it uses a magnetic field to produce physical movement of the solenoid cylinder—but instead of spinning like a motor output shaft, the solenoid cylinder moves back and forth in a linear motion. Most relays are encased in a plastic or metal housing to keep the moving parts free from outside interference and dust.
There are two parts to a relay: the solenoid and the contactor, and each is electrically isolated from the other. These two parts can essentially be treated as separate (but related) parts of a circuit, because each has its own ratings. The solenoid inside a relay has an electrical coil with a magnetic plunger that provides the movement needed to flip the contactor switch on and off. The relay coil should have the coil resistance listed as well as the operating voltage so that you can calculate how much current it will consume when in use. The contactor in a relay is where the high-power signal is switched. The contactor switch also has a voltage and current rating that tells you how much power you can expect the relay to conduct before the contacts fail.
Relays are available in different operation types depending on applications. When buying a relay, one must consider the configuration of that particular relay (e.g. Single pole, Single throw; Single pole, Double throw; Double pole, single throw; Double pole, double throw).
Calculating current draw
To determine the amount To determine the amount of current that a relay draws, you must first determine the coil resistance by checking the relay datasheet. If this information is not available, you can measure the resistance with your multi-tester. With the coil resistance and the voltage rating of the relay, you can calculate the current it draws by Ohm's Law.
Relay Driving
Relay driving refers to interfacing your relay to from low powered device such as Logic IC's or Microcontrollers unto high powered outputs. Read about Relay Driving.
