Automotive Relays
& Sensors
A relay is a simple
electromechanical switch made up of an electromagnet and a set of contacts.
Relays are found hidden in all sorts of devices. In fact, some of the
first computers ever built used relays to implement Boolean Relay Applications
In general, the point of a relay is to use a small amount of power in
the electromagnet -- coming, say, from a small dashboard switch or a
low-power electronic circuit -- to move an armature that is able to
switch a much larger amount of power.
For example, you
might want the electromagnet to energize using 5 volts and 50 milliamps
(250 milliwatts), while the armature can support 120V AC at 2 amps (240
watts). Relays are quite common in home appliances where there is an
electronic control turning on something like a motor or a light.
They are also common
in cars, where the 12V supply voltage means that just about everything
needs a large amount of current. In later model cars, manufacturers
have started combining relay panels into the fuse box to make maintenance
easier. For example, the six gray boxes in this photo of a Ford Windstar
fuse box are all relays: In places where a large amount of power needs
to be switched, relays are often cascaded.
In this case, a
small relay switches the power needed to drive a much larger relay,
and that second relay switches the power to drive the load.
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