delay relays

Printed From: the12volt.com
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=118672
Printed Date: May 15, 2025 at 2:58 PM

Topic: delay relays

Posted By: icearrow6
Subject: delay relays
Date Posted: December 20, 2009 at 3:00 AM

Hiya Fellas:
I want to set up a couple of relays that will allow me to delay the output of each relay by changing the ground resistor size.
I think i'll just trial and error to figure out the exact time i want between the outputs. Its for a sequential lighting project that i have in mind.
I just want the opinion of the relay experts here if my simple schematic here is correct.
posted_image

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Replies:

Posted By: howie ll
Date Posted: December 20, 2009 at 6:52 AM

Look at this item on relays on this site, you will find you need caps as well, and the resistor/cap combination varies the time delay.

Posted By: i am an idiot
Date Posted: December 20, 2009 at 8:13 AM

Howie has been paying attention and taking notes, hasn't he? I still have not found the diagram that I know is on this site somewhere. Depending on the amount of delay you want the capacitor and resistor will both affect the time. Larger capacitor = more delay. Higher value resistor will also increase the delay time. 47 ohm 2 watt resistor and a 4700 mic capactior may be a good starting point. You can parallel capacitors to increase the value. 4700 + 2200 = 6900

https://www.the12volt.com/installbay/forum_posts.asp?tid=113479&KW=delay+relay&tpn=1#548122

Posted By: icearrow6
Date Posted: December 20, 2009 at 11:47 AM

Thx for the info.
Howiee the relay diagrams that i could find were only to provide a temporary pulse using the mention cap/resistor setup.
I did look around for about 30 mins, but couldn't find it, :/

So delay the trigger via cap / resistor. GOT IT!

Iam could you tell me why supplying constant 12v+ to the relay coil and adding resistance to the (-) won't delay the relay coil?

THX again guys.

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Posted By: howie ll
Date Posted: December 20, 2009 at 11:54 AM

Your right they will only work for about 30secs. I found a UK manufacturer who made them to run computers, games etc. but I'm damned if I remember them! I think Google will have to be your friend!

Posted By: i am an idiot
Date Posted: December 20, 2009 at 12:13 PM

The resistor will only add resistance to the circuit. It just won't delay it. The delay comes in when the line has to charge the capacitor through the resistor. The cap will not charge instantly. That is the only simple way I know of to delay the turn on of a relay.

Posted By: oldspark
Date Posted: December 20, 2009 at 4:30 PM

It depends on how long the delay is.
Because solenoids are a relatively high current, large capacitors may be required.

For long delays, a smaller RC combination feeding a transistor of FET (or a "smaller" relay) is usually used.
Alternatively delay circuits using counter or 555-time chips (IC) are common.