how relay works ? Options

[jimkelly]

and can some describe how a relay works?

is it that HIGH AMPERAGE thru 85 and 86 operate a switch, and when switched send LOW AMPERAGE thru 30 and 87? what is 87A's purpose?

[jimkelly]

freakin ingenious.

since our cars are run from a 12v battery, how does current know to be high or low, simply by the diameter of the wire it passes thru, or the draw of the item being run?

I assume running a circuit with a relay is cheaper than running a circuit thru a switch that can handle more current because of the cost of a better switch and the cost of running more heavy wire throughout the car?

I think I am beigining to understand the purpose of a relay, visually.

thanks guys (IMG:style_emoticons/default/idea.gif)

i think image is correct?

[Spoke]

freakin ingenious.

since our cars are run from a 12v battery, how does current know to be high or low, simply by the diameter of the wire it passes thru, or the draw of the item being run?

I assume running a circuit with a relay is cheaper than running a circuit thru a switch that can handle more current because of the cost of a better switch and the cost of running more heavy wire throughout the car?

I think I am beigining to understand the purpose of a relay, visually.

thanks guys (IMG:style_emoticons/default/idea.gif)

The thickness of the wire is determined by the load. Heavy load needs thick wire; light load needs thinner wires.

Cost and practicality determine minimum wire size. For example running battery cable thick wires through the car would be very expensive and would not fit under the dash.

The current draw is determined by the type of load for example:
1) A side marker light might draw 1AMP and only needs a small diameter wire.
2) A headlamp might draw 5-10AMP will need a heavier wire.
3) A starter might draw 60-100AMP will need a real heavy wire.

You are correct about the relay. It allows a small switch to switch a large current.

Think about a 914 with 2 headlights, 2 heater fans, the ECU, and FP. Even a large switch couldn't turn all these on/off. Each is run by relays where the ignition switch turns on the relays and the relay contacts carry the high currents.