I'm not even sure how to search for this, so I'll just ask. How do you make a relay DISENGAGE when 12v is applied? For example... lets use a "light". I want the "light" to be on when the car is off. When the car is on/ignition is applied, I want the light off. Can this be done with relays or any other electrical equip? Thanks again.

 

OK, for relays have 4 terminals.

2 terminals for which you apply a voltage to energise the coil to make the other two terminals connect. Usually the other 2 terminals are Common and N.O. (Normally Open).

Some relays have 5 terminals. The fuel replay pump for a TPI motor has five. Again 2 terminals for the coil. The other terminals will be labelled N.O., N.C. and comm for common. The N.O. is Normally Open and N.C. is Normally Closed. Now this is in reference to common terminal and the coil is in its resting state, off. The N.C. switch will be connected to the Common Terminal, the N.O. will be an Open Circuit.

By applying the voltage to the coil, the relay then switches. The Common will now be connected to the N.O. terminal and the N.C. will become Open Circuit from the common.

So after waffling on, basically what you want to do is the following.

1. Connect one side of the coil to ground. The other to a ignition switched source so that when the ignition is one, the coil will get its power.

2. Connect the common terminal to one side of your light bulb and the other side of the bulb to earth.

3. Connect the N.C. (Normally Closed) terminal to a permanent 12 volt source. One that is not effected by the ignition being on or off.

This way when your ignition is off, power will flow through and your globe will light up. When you switch your ignition on, the coil is energised and the circuit is opened, extingushing the light.

Sorry for the crapping on but I hope it helps you.

Cheers,
Col.

P.S. Love the pic of the A-10 Warthog in the background!!

 

Nice explanation on the NC relay contacts.

There's also a way without using a relay, provided that the draw from the light will be minimal (i.e. you use an LED). Let me know if this is your case and would like to know more.

Hope this helps.
Lou

 

Thanks for the help guys. Its for an electric motor, so it will have heavy draw. I just used the light as an example. I completely forgot about the N.C. relays! thanks again!

thanks for the compliment, I figured a Firebird and a Warbird would go well in a picture!

 

Are you planning on making an automatic window closer to raise the window when you switch the car off?

 

no. I made my own nitrous bottle opener. At the moment, I am just using a window switch to open and close the bottle. But what I want to do is just flip a switch and have it open, instead of holding it down for those seconds it takes to open the bottle. Its very minuscule but I'd rather be shifting in those few seconds than holding down a windo button...

 

Good old NO2. Personally, I'm a big fan of CH3NO2.

 

yeah but I don't think I can get Nitromethane at Chevron