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point me to the correct 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=117148
Printed Date: May 10, 2025 at 2:37 PM


Topic: point me to the correct relays

Posted By: bradleys
Subject: point me to the correct relays
Date Posted: October 21, 2009 at 9:28 PM

I want to create a specific 12v circuit.

I have two power inputs.  Input 1 and Input 2, I need one power output.  Input 1 is a lead off the the main power, input 2 is a lead from the kill switch.  I want to add a warning bell that will indicate that main power is still on when the kill switch has been turned off.  I am looking for:

  • When Input 1 has power and Input 2 has no power - output should have power.
  • When input 1 has power and Input 2 has power - output should not have power.

Is there a relay or combination of relays that will help me do this?




Replies:

Posted By: i am an idiot
Date Posted: October 22, 2009 at 3:33 AM

That will be a piece of cake.  I will draw you  a diagram tonight.  It will require 2 relays.   Do you want a 5 second delay before it sounds the buzzer?  That will require a few more parts.





Posted By: bradleys
Date Posted: October 22, 2009 at 11:09 AM

A five second delay would be very cool.  Yes...

To answer your question: "Will input 2 ever be powered without input 1 being powered?"  NO





Posted By: i am an idiot
Date Posted: October 22, 2009 at 8:19 PM
I re-read your post and figured that out.  That is why I deleted the question.  I will have to work on the delay later.  The 2 relays to do exactly as you asked need to be wired as follows.  Input 1 to terminal 86 of relay 1.  85 of relay 1 is to be grounded.  Input 2 to terminal 86 of relay 2.  85 of relay 2 needs to be grounded.  Fused 12 volts to terminal 87 of relay 1.  Terminal 30 of relay 1 is to be connected to terminal 30 of relay 2.  87A of relay 2 is the positive output that powers your buzzer, beeper or whatever the audible device may be.




Posted By: bradleys
Date Posted: October 22, 2009 at 10:25 PM
Fantastic...  Do I need SPST relays with dual outputs (87 and 87A) or the SPDT relays?




Posted By: i am an idiot
Date Posted: October 23, 2009 at 5:54 AM
Relay 1 can be SPST. (87 terminals in 2 locations, or missing the middle 87A connection) Relay 2 has to be SPDT.  (87 and 87A)




Posted By: bradleys
Date Posted: October 26, 2009 at 11:01 AM

Thanks!  I picked up the Relay's and will wire them together for a quick test some evening this week.  YOU HAVE BEEN A HUGE HELP!

I really appreciate it...

Scott






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