Simple Way to Make a Time Delay Relay?

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Forum Name: Relays
Forum Discription: Relay Diagrams, SPDT Relays, SPST Relays, DPDT Relays, Latching Relays, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=124243
Printed Date: May 09, 2025 at 8:42 AM

Topic: Simple Way to Make a Time Delay Relay?

Posted By: southface
Subject: Simple Way to Make a Time Delay Relay?
Date Posted: November 02, 2010 at 7:16 AM

Sorry if I'm posting something that someone else has answered. I really did check and could not find anything!

I'm looking to build a simple circuit that will activate a relay but with a short time delay. I understand this means I need a normally-open, timed-closed relay, or a simple circuit that can act like one.

It will use 12V DC on the coil. I'd like the relay to be normally open and only close after about half a second of continuous charge/current on the coil contacts. I understand it may be possible to do this by simply using a capacitor and a resistor with a standard 12V relay. Is there anyone who has details who can help, for example:

- how do I wire the capacitor and resistor to the relay?

- what sizes do I need?

Thanks

Paul

Replies:

Posted By: i am an idiot
Date Posted: November 02, 2010 at 5:27 PM

Do you have any capacitors available? If so, what values do you have?

Posted By: southface
Date Posted: November 03, 2010 at 12:22 AM

I don't, but I am willing to go and buy the value I need.

Posted By: rock61992
Date Posted: January 16, 2011 at 3:58 PM

I need the exact same thing, but i also need it to delay in shutting off for about half a second as well. I guess its just getting a capacitor to discharge onto the coil after the trigger current is off but i have no idea how to wire it or if i would need diodes in certain spots. Any advice or a wiring diagram would be much appreciated, Thank you.

For clarity...

I need a relay to contol the timing of another circuit with about a half second delay going on and off.

Posted By: oldspark
Date Posted: January 16, 2011 at 6:50 PM

You can't do BOTH using simple Rs & Cs and diodes. (Not without using several relays....)

IMO these tings are better done by circuitry anyhow - ie, semiconductors, chips etc.

Posted By: hotwaterwizard
Date Posted: February 16, 2011 at 12:38 AM

What you want is called an On Delay. There are several ways to do this.

posted_image

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John DeRosa (Hotwaterwizard)
Stockton California
When in doubt, try it out !

Posted By: oldspark
Date Posted: February 16, 2011 at 12:58 AM

PEDantic: In the last fig, #85 & #86 should be swapped...
(Convention is #85 is -ve or GND; #86 is +ve.)
....but this only matters if the relay has an in-built spike-quenching diode.
(Which I hate for that polarity reason - I prefer to wire such diodes in the socket/harness so I can use ANY relay (suppressed or not).

And IMHO as usual - hotwaterwizard so often supplies a great collection of circuits or circuit ideas. (Well worth waiting for!)

Now - a simpler FET delay....????

Posted By: hotwaterwizard
Date Posted: February 17, 2011 at 9:56 PM

https://www.bowdenshobbycircuits.info/page2.htm#relay_i.gif

posted_image

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John DeRosa (Hotwaterwizard)
Stockton California
When in doubt, try it out !