Specifications

181
Car Audio Reference Guide
Relays
The ability to switch high current
electrical circuits using low current
control systems has made the use
of relays extremely popular. Relays
can also be used to perform rela-
tively elaborate processes - including conversion
from positive to negative pulsing, negative to
positive pulsing, momentary to constant pulsing,
retained accessory circuits and so forth. This sec-
tion will look at the basic connections on a relay
and some of the most basic circuits. A few min-
utes of searching on the Internet will reveal some
of the more complex circuits available.
Relay Connections
The most popular (and recommended) relays are
available from Bosch and Potter and Brumfeld.
These SPDT (Single Pole Double Throw) relays
can handle in excess of 20A of current while only
requiring 200mA (0.2 A) to energize the circuit.
This diagram shows the pin locations and labels
on the bottom of a relay.
Pin Function
30 Common Connection
87 Normally Open Connection
87a Normally Closed Connection
85 Coil
86 Coil
Relay Circuits
This circuit allows multiple loads to be switched
from a single relay. This is convenient for using a
single remote turn on wire from a source unit to
turn on multiple amplifiers.
The following circuit will take a positive input
(front a door trigger for example) and convert it to
a negative output.
The following circuit will take a negative trigger
(output from an alarm) and convert it to a positive
output (to drive a light or fan for example).