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Understanding Relays

Bulletin 3008

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Various types of automotive relays


This bulletin will explain common types of automotive relays, how they work and how to choose a relay to prevent possible damage to the circuit.


There are many types of relays but the most common found in automotive applications are electromechanical, solid state and hybrid which is a combination of the two.  A relay is an electronically operated switch used to control high current circuit applications with the use of a low current switched circuit. The number of controlled circuits or poles depends on the system in the vehicle the relay is controlling.


When the coil side or low current side is energized, a magnetic field is created in the coil winding which pulls the contact arm within the relay open or closed completing the circuit between the high current contacts.


The left image is a common diagram of an electromechanical relay.  Terminal location and operation are usually printed on the housing of most relays.  A “click” sound can be heard on this type of relay as the contact points make contact either by magnetizing or demagnetizing from the internal coil winding.


The image on the right is a comparison of an electromechanical and a solid-state relay.  The solid-state relay functions much faster and can last significantly longer due to non-contact internal components and less heat generated during operation.


Relay control circuits can be wired using battery ground or battery positive as its controlling circuit.  When wiring a relay make sure you use the correct relay amp rating for the high current circuit you are working on.  Using a relay not capable of carrying the circuits high current will cause the relay to overheat causing significant damage and possible fire. Also make sure that all circuits going through the relay are protected by a fuse.


For addition support contact the GoTech technical services team at 855-207-5630 M-F 7:30-6:00 CST for assistance.

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