Automotive Relays
Common Relay Pin Configuration (Bosch-type) Overview Relays are widely used in electrical applications where one circuit is to be energized or turned "on" by the presence of a voltage, provided by another circuit. An example of this is when an automotive radio sends out a triggering voltage to turn on an external amplifier or activate a motorized antenna. Anywhere a switch can go in a circuit, a relay can replace it, (as long as there is a triggering voltage available to activate it). The "switch" in a relay is more often called a solenoid. A solenoids is like a piston that pushes outward when energized with electricity. This push mechanically trips the switch in the relay, completing circuit and allowing the switched voltage output. A relay can be triggered with an electrical pulse as small as 150 milliamps. The switched output can be as high as 30 or 40 amps.   Relay energized Relay at rest |
The terminals of a relay are defined as follows:
- 30 is the common or input voltage (or ground) to be switched.
- 87a is the normally closed connection (can be used as a switched voltage output when the relay is at rest). (This terminal offers no voltage when the relay is energized.)
- 87 is the normally open connection (switched voltage output when the relay is energized).
- 85 is connected to the ground of the triggering voltage.
- 86 is connected to the positive 12V of the triggering voltage.
Note: in many cases, the connection of pins 85
and 86 can be interchangeable, but NOT if there is a diode wired across the coil.
Below are several common examples of how relays are commonly used:
This information provided as an option to those who wish to use it. It is recommended only to those who have some familiarity with such practices and/or audio electronics in general. You are responsible for any damages sustained from mishandling of products or incorrect interpretation of this information.