What Does a Relay actually do?

[jimmyj]

not sure what a relay actually does, does it step down current?

[E30Adam]

It's just an electrical switch.

[Turbo-Brown]

If you have a look at this diagram, the outer two contacts are the high current circuit, the inner two are the low current:



You, the user, switch current to the little box in the middle of the diagram. This is called a solenoid and when activated has a little element which moves.

So, you switch it on and the solenoid pulls the contact closed (the dotted line is the solenoid link)

This switches the high current circuit on.

They're used to let you switch high current circuits on without having to run high current wires into the car/behind the dashboard where they could cause fires etc. They also isolate you from potential shock from the high current

[Brianmoooore]

Very good description from turbobrown - except the last bit.
You are more likely to get a shock from a relay controling a circuit, than from the circuit itself.
If the circuit in question is a resistive circuit, like a headlamp, the highest voltage you will find in the circuit is 12V or so, and there is no danger whatsoever of getting a shock from this. It's voltage, not current that causes shocks.
if the circuit is controlled by a relay, as the supply to the relay coil is broken, the magnetic field around the solenoid coil collapses, and a high voltage spike is generated (similar principle used in the ignition coil) and this is quite capable of giving a shock.

[Project_E30]

Very good description from turbobrown - except the last bit.
You are more likely to get a shock from a relay controling a circuit, than from the circuit itself.
If the circuit in question is a resistive circuit, like a headlamp, the highest voltage you will find in the circuit is 12V or so, and there is no danger whatsoever of getting a shock from this. It's voltage, not current that causes shocks.
if the circuit is controlled by a relay, as the supply to the relay coil is broken, the magnetic field around the solenoid coil collapses, and a high voltage spike is generated (similar principle used in the ignition coil) and this is quite capable of giving a shock.

Remember its current that kills you not the voltage!

[Brianmoooore]

It's current that kills you, but you need a sufficiently high voltage to produce that current. It's the voltage you feel.

[Turbo-Brown]

Learn something new every day!