Good Day All.

I am in need of help and advice with designing a 24volt based time delay circuit.

I need the circuit to hold an output relay on all the time unto the circuit is triggered, then runs the pre-set time 1-5min, and then turns off the relay.

It will be triggered when the input is not longer powered by 24v, gone low.

Am i making any sence?

Thanks for your time.

Best Regards

 

When the power is lost to the 24v line, you want the relay to stay closed an additional 30-60 seconds (settable) before opening?

 

Sort of, i've just added a pic to the 1st post.

The circuit is always going to be powered by 24volts, the trigger is going to be connected to the 24 volt rail via a switch, when the feed from the switch is broken the circuit will run the pre-set time and then powering down the relay (opening the contacts).

I hope that makes more sence.

 

It would probably be better to trigger a 555 with the button press that will energize the relay for the set time then open it when done.

 

Hello,

The problem with the 555 is that it is limited to 15 Volts.
You will need some level adjustments to use the 555.

Greetings,
Bertus

 

Agreed. LM7815 will pull 15v off the 24v line for the 555.

 

Hello,

I would say use a 7812.
Then you can use a resistor voltage divider with two equal resistor for the trigger.
A mosfet for switching the relays can be connected to the output of the 555.
Do mind the gate resistor and the EMF diode.

Greetings,
Bertus

 

I had a feeling we would end up going down the 555 route.

From memory the NE555 has a max working voltage of 15/16volts, I don't want to run on the edge, so as bertus said I will use a 7812reg for the circuit supply.

Using a mosfet to drive the relay seems a little over kill, how about something smaller, like a 2N2222?

It's been about 10years since I last used a 555 chip.

As such can anyone help me out with a suitable schematic please?

This is as far as I have got

Best Regards.