Electronics question: cars

[daijobu]

I'm learning electronics along with my dd's using Charles Platt's excellent primer on the subject.  We are currently studying switches and relays.  Please help me to see if I understand correctly how these are used in a car's ignition.

 

When I turn the key in my ignition, I am effectively closing a momentarily ON switch (normally off, NO), sending a small amount of current to the relay.  Because the relay handles sending a greater electric current to the engine, it no longer needs a constant supply of electricity from the closed circuit of my key.  This is why (something I've been wondering about for years), when I release the key, it springs back to the OFF position, but the car continues to run. 

 

If this is true, then I have another question:  What is it about pulling the key out of the ignition that causes the car to turn off? 

 

I welcome all discussion about car ignitions, switches, relays, and even other electrical components (capacitors, resistors, etc.)  

[RootAnn]

When you take the key to 'on', it energizes the ignition circuit. (How this works exactly depends on the model & year of your car.) When you move the key to start, it sends current to the starter relay. The starter relay allows a large current to flow to the starter motor which will spin & start the vehicle engine. When you release the key (from start), it springs back to the 'on' position, de-energizing the starter relay and stopping the starter motor. At this point, the engine continues to run because the ignition circuit remains energizes with the ignition switch in 'run' or 'on.'

 

When you take the switch to off, it interrupts power to the ignition circuit, thereby shutting the car engine off. (Diesels are similar only different.)

 

(DH explained this to me & then I typed it up. If there are simplicities or mistakes, they are mine.)

[daijobu]

Thank you for this excellent explanation.  It really helps to have real-world examples of circuits in action.

 

And, yes, I did forget that the car actually turns off when you turn the switch to off, not when you remove the key, LOL!