A relay is an electromechanical device that uses a coil (electro) to move switch contacts (mechanical). The coil can be energized with a small amount of current, while the switch contacts can be used for any number of applications, including switching a higher current, circuit isolation, or polarity reversal. A typical 12-volt relay requires a coil current of .150 Amps to energize. The relay contacts can switch currents up to 30 Amps, creating a power gain as high as 200 to 1. The main components of a relay are the coil, the spring, and the contacts. The configuration of these components determine how the relay is classified by the manufacturer, and how it is to be used by the installer.

Terminals 85 and 86 form the coil contacts. As current is passed through the coil, a magnetic field is produced, which actuates the switch contacts, causing terminals 30 and 87 to close. In order to pass current through the coil, 12 Volts must be applied to one side of the coil (terminal 86), while Ground is present on the other side (terminal 85). Although most relay manufacturers recommend that terminal 85 should be connected to Ground, and 86 should receive 12V, it is advisable to check the diagram for your specific relay type.

Terminals 30, 87A, and 87 form the contacts. When the relay is at rest, terminals 30 and 87A are connected. After the relay coil is energized, terminal 30 breaks its connection to 87A, and makes a connection to terminal 87. Knowing this action of the contacts allows you to apply the relay in various configurations to achieve the desired results.

• Common Types Of Relays

• Converting A Positive Trigger To A Higher Current Positive Output






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Converting A Positive Trigger To A Negative Output





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Converting A Negative Output To A Higher Potential Negative Output





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Converting A Negative Trigger To A Positive Output








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Types Of Starter Kill





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Five-Wire Rest At Ground Door Locks





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Using A SPST (Single Pole Single Throw) Dual Make Relay To Interface With Vehicles That Have Separate Left And Right Parking Light Circuits







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Using Relays To Add Actuators





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Adding Domelight Supervision To An Alarm That Doesn't Feature It

Latching Relays