Whats a Relay? was: Hella headlight question

[TBerk16 <TBerk16@aol.com>]

In a message dated 1/7/98 1:16:50 PM, you wrote:

>Can someone please explain this entire "relay" system thing (in relation to 
>the headlights).  I am no electrician.  I have learned quite a bit about my 
>car in the last couple of years, but the electrical end of it still has me 
>a little clueless.  Please be as specific or as general as you would like.
>
>John
>80 Scirocco S

OK, Here we go-

A relay is a switch. Like a remote control switch. Or a switch's switch.

Dictionary says:
An automatic or automechanical device that responds to small a current or
voltage change by activating switches or other devices in an electric circuit.
Unquote.

How that helps with higher wattage upgrades is- instead of running a lot of
amps through your standard, dash mounted switch, the relay takes its place and
handles a lot more powerful amperage than the original switch could take. When
you close that switch on the dash it completes a circuit from the battery-
altenator,  through the wiring, through the switch,  on thought the device in
question (headlights), and back around to a chassis ground. (And back through
the Battery, around and around )

If the lights, or what ever, draw/consume more power than the switch was built
to take, it can burn out. 

The relay sits in between the orig. switch and the load (lights) and protects
the switch ( and it's wiring) from too heavy an electrical current.

It' s like your switching is done by proxy or remote control. 

A simple relay has four connectors to it; one for the 'heavy' current to enter
and one for it to exit and continue on. The third is usually a ground for the
fourth trigger or switch. This trigger is usually where you'd connect your
dash mounted switch. 

The heavy duty part of the relay remains OPEN or unconnected until the trigger
get powered up, when you activate it. This trigger side of the relay is an
electomagnetic switch and  will close or connect together the Heavy Duty
circuit side of the relay, allowing the current to flow onward to the lights.

You might think of it as if your dash mounted switch is handling the increased
current with Oven Mitts to keep from getting burned.

A common example of the use of a relay is the starter motor. It is probably
the single highest amperage device in a car. Luckily it's only needed for
short periods. It is triggered by the turning of the Ignition switch. But if
all the power running through the starter was routed through the ignition the
switch  would catch fire, or would be designed a lot beefier. A Heavy Duty
relay handles the starter's current draw. 

Hope your still awake, and that this helps, I prob. could do a better job of
it with some pictures.
TBerk
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