on/off delay relays ??

[wsemajb]

I need to use 12 or 24vdc to activate a 120vac circuit. I have that down. I've found any number of 24vdc relays, reasonable amperage, very inexpensive.

The problem is I'd like to have an adjustable timer, ideally 15 seconds to three minutes (approx range) to activate "off delay". When the 24vdc circuit is opened, the 120vac will continue for the set time, and then shut off.

The following suits my needs with two exceptions. It's still pricey.. and it adjusts to less than two minutes on the outside range.
**broken link removed**

The signal I have available is 24vdc. There are a few ways to approach this. A 24vdc off delay timer (which I cannot locate in a web search) connected to a standard 24vdc 10amp (min) relay. Or a 12vdc relay (low amp) connected to a 120vac delay timer. I'm not sure which is the better option.

Another board advised that I just use a 12vdc relay and a 555timer IC. But by the time I got the pin connections figured out and located the right potentiometer, etc, etc, it might be more headache than forty two dollars worth.

Any advice???? Know a better source for any 24vdc relays w/delay off?
Thanks so much

 

[MadAlexis]

One way of doing it would be to use an RC network onto the base of a transistor. When the 24VDC falls way the cap slowly discharges. After a while the transistor will turn off. You would have to get your biasing correct though.

 

[gramo]

One way of doing it would be to use an RC network onto the base of a transistor. When the 24VDC falls way the cap slowly discharges. After a while the transistor will turn off. You would have to get your biasing correct though.

Would be a rather crude design, but might suit the ticket. The delay would be slightly different depending on temperature etc..

 

[BeeBop]

Another board advised that I just use a 12vdc relay and a 555timer IC. But by the time I got the pin connections figured out and located the right potentiometer, etc, etc, it might be more headache than forty two dollars worth.

Their advice is good. If you need just one, then the $42 is the best choice. If you need two or more, then go with the 555 timer solution.

 

[wsemajb]

Now I'm quite confused. I've found exactly what I'm looking for, and for less than twenty dollars. I'm all set. All of a sudden, I read the application pdf for the unit. The delay on break is supposed to keep whatever powered unit (pump, motor, lamp, etc) deenergized for a set period of time following the broken circuit. This is supposed to safeguard against unwanted cycling in case power is reapplied too soon after the break.

So if you set it for 120 seconds "delay on break", mains voltage will be cut for a guaranteed 120 seconds even if power is reapplied to the relay coil. EXACTLY the opposite of what I'm trying to accomplish. I'm almost certain that some of the data sheets for these "delay on break" relays describe the delay as MAINTAINING mains power for the set period of time. Is this a matter of some nomenclature I'm not yet aware of?

Anyone know the story here? This is kind of a electrical/electronic crossover question. Perhaps I need to ask at some sort of electrical trade forum. Can anyone recommend one? This is so frustrating. The sales/tech help at Digi-key is absolutely no help whatsoever. I really can't blame them. I should be able to describe exactly what I'm looking for, but for some reason, this application just seems to confuse.

 

[Leftyretro]

Now I'm quite confused. I've found exactly what I'm looking for, and for less than twenty dollars. I'm all set. All of a sudden, I read the application pdf for the unit. The delay on break is supposed to keep whatever powered unit (pump, motor, lamp, etc) deenergized for a set period of time following the broken circuit. This is supposed to safeguard against unwanted cycling in case power is reapplied too soon after the break.

So if you set it for 120 seconds "delay on break", mains voltage will be cut for a guaranteed 120 seconds even if power is reapplied to the relay coil. EXACTLY the opposite of what I'm trying to accomplish. I'm almost certain that some of the data sheets for these "delay on break" relays describe the delay as MAINTAINING mains power for the set period of time. Is this a matter of some nomenclature I'm not yet aware of?

Anyone know the story here? This is kind of a electrical/electronic crossover question. Perhaps I need to ask at some sort of electrical trade forum. Can anyone recommend one? This is so frustrating. The sales/tech help at Digi-key is absolutely no help whatsoever. I really can't blame them. I should be able to describe exactly what I'm looking for, but for some reason, this application just seems to confuse.

I think the terms used by the electrical world is delay-on and delay-off relays. You would probably get more useful advice from a electrical parts supplier Vs a general electronics parts supplier.

Lefty