I am trying to use a push button switch to send 120VAC for a certain amount of time after it has been pressed. I want it to only be pressed once, and not have to be held in the closed position. Is there some sort of timer/timed relay I could use to accomplish this?
There are industrial timing relays that can do this, in addition to the pneumatic ones that Majenko mentioned. From the outside, they appear to work similarly to traditional relays, except that there's a (usually programmable) delay between the "coil" receiving power and the contacts moving. Here's one possible way to wire one:
- When you push the button, the load and both coils get power. The normal relay closes immediately and maintains power when the button is released.
- The timer relay does nothing for the programmed time. When it finally moves, it removes the normal relay's ability to hold the circuit on, and so everything resets.
You can buy buttons that do exactly that. They are often pneumatic, holding themselves in until enough air has leaked in to release them. They're used for lighting stair wells, etc.
Alternatively a 555 timer in monostable mode driving a relay, or a small microcontroller doing the same job (easier to make configurable and get more precise times).
You can also get various DIN and panel mount timer relays that do this.
Purely as an example:
This may not be exactly what you are after but you can generally get various timer schemes or multifunction units in various voltage ranges.