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Delay for 24VAC

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Dallas90

New Member
I would appreciate any help or direction. I have been working on a project for the last few months but while I'm pretty handy, the last time I did any real electronic work was putting together a HeathKit in Jr High shop class (1974 or so).
My problem is that I'm trying to put together a physically small delay to work on a 24VAC circuit. At this point I don't think it needs to be that precise +/- 5 seconds would be fine, and I'm thinking 40 seconds delay is what I need although that might change to as low as 30 or as much as 60.
Upon power up I need the delay, then for power to flow to the coil of a 24Vac relay. Once on it needs to remain on until system power down.
I've looked at 555 timers but I'm trying to keep the size at a minimum so I don't want to use a transformer unless that is the best way to make it small.
Thanks in advance.
 

mneary

New Member
We need to know what you mean by small. A surface mount 555 is 3mm square. Maybe you could say what type of relay you're using; i.e. how much current does the coil draw at 24VAC?
 

Hero999

Banned
Is the relay coil AC too?

It'll probably work from DC but you'll need to reduce the voltage.

A 555 would work.

You'll need to run it from a rectifier and 12V voltage regulator. A relay with a 24VAC should work off 12V.
 

Dallas90

New Member
By small, I mean I'm trying to get 2 relays and timing control on a circuit board that is 1 and 1/2 by 3/4 inches and it's already obvious It's gonna be a tight fit. I could jump up in size on the board but it kind of defeats some of what I'm trying to do, so for now I'm trying to make it fit.
Yes the coil is 24vac. I can change that, but again for space considerations I was trying to keep everything common.
How small is the smallest 12v regulator (that has a reasonable price)?
Also, I assume that a 555 could be set up to a 40 sec. +/- 5 delay without too much additional equipment. From what I've seen it looks like I would need a couple of resistors. does that sound about right? Or am I missing something important?
Oh, and thanks again for the help. Even the questions are opening up eyes to other possibilities.
 

Dallas90

New Member
So I need a transformer to take the voltage down right? But how low do I need to take it so as not to smoke a 555?
Then I need to regulate it and rectify it before I even think about the 555.
I think I'm going to have to put all this on a different board.
 
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