7c. Relays and circuit example

Question 1

How does a relay’s work?

Define types and features

Answer 1

Brief explaination:
Relays are essentially an inductor (electromagnet) that activates or turns off, which moves a switch from normally closed or opened terminal to normally open or closed. A spring returns the common (switch) back to its orginally position.

Usually thats normally closed to open.

Types:
* SPDT = single pole double throw
* SPST = single pole single throw
* DPDT = double pole double throw
* DPST = double pole single throw

Question 2

Why isn’t a relay perfectly an inductor in reality?

Answer 2

there is resistance in it.

Relay coil has:
* inductance (from the windings of the coil)
* resistance (from the metal the coil is made of)

The switch also has contact resistance.

Question 3

what is the difference between these circuits functions?

Answer 3

For the top one, if a fault for the lamp develops then it will cause the circuit to stop working and the spotlight won’t either, assuming open-fault.

For the bottom one, if a fualt for the lamp develops then it will still work but the indicator lamp just fails. However, if its a short-cicuit fault then the circuit may damage itself with the battery and the lamp.

Question 4

What is the issue with this circuit when we suddenly open S2 after a while, What can we add to stop this issue?

Answer 4

Explaination:
* The current through an inductor cannot suddenly change
* A voltage large enough to drive a spark across the swtich will occur due to the inductor.
* High voltages like this can damage other circuit components as well as the switch (or switching transistors).

Solution:
* Add a flyback or snubber diode
* This allows the large voltage to circle round back to dissapade the stored energy by the resistance of the relay itself.