NC button to supply +12V to solenoid

Question

I've got a normally closed momentary push button switch that I would like to make behave as normally open.

E.g. I press the button and 12 V is supplied to the solenoid. I understand that it would be easy to do with the NO push button switch but I've got a very specific push button that I'd like to use and it happens to be NC.

Can this be done? How?

Answer 1

Connect the pushbutton to drive a relay coil. Then connect the relay's NC and common primary contacts where you would normally connect the NO push button terminals. Note that the relay coil will always consume power when not pushed though...The idle current will be whatever the relay's coil current is which could be some tens of milliamps.

^{simulate this circuit – Schematic created using CircuitLab}

Below is the method @Sunnyskyguy is talking about. It's what I would use because it is lower power when idle. But you may not want to if you are a beginner since it is more difficult to understand and use since you can't just drop it in wherever a NO pusbutton would go without considering what surrounds the pushbutton. The relay circuit can be inserted anywhere a NO pushbutton might go, but the transistor circuit requires the emitter/source pin of the NPN/NMOS to be connected to ground (i.e. the NO pusbutton must hve been connected to ground on one end).

The diode is there to protect the transistor from the voltage spike generated by the solenoid's inductance when current is interrupted through it during turn off. The relay circuit benefits from this too but it is mandatory for the transistor since it is more sensitive to damage than the relay.

^{simulate this circuit}