relays for special application

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=121722
Printed Date: July 05, 2025 at 8:10 AM

Topic: relays for special application

Posted By: afg_capone
Subject: relays for special application
Date Posted: May 07, 2010 at 12:22 PM

okay, so i need some help with a project i'm doing. I have two switches that have a negative trigger and i have a relay that needs a constant negative to the coil. the idea is to have one of the switches turn the relay on and the other to turn the relay off. both switches are push button switches, so its a pulse. thanks for any help. its greatly appreciated

Replies:

Posted By: the12volt
Date Posted: May 07, 2010 at 12:40 PM

You'll need three SPDT relays. I'll draw a diagram and post it in a bit.

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Posted By: i am an idiot
Date Posted: May 07, 2010 at 12:42 PM

Do you have to have 2 switches? Or could you use the same switch to toggle between on and off?

Posted By: afg_capone
Date Posted: May 07, 2010 at 12:54 PM

thanks for the quick reply. i need to have the two switches because they are at different locations. both are pulsed ground but i need to make it so that one will turn on the relay and leaves it on until the other switch turns off the relay and leaves it off until the whole process is repeated. thanks a bunch guys

Posted By: the12volt
Date Posted: May 07, 2010 at 1:25 PM

Here ya go: https://www.the12volt.com/relays/relaydiagram61.html

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Posted By: syl20rochon
Date Posted: May 07, 2010 at 1:26 PM

Your push switch, are they normally opened or closed?

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Posted By: the12volt
Date Posted: May 07, 2010 at 1:30 PM

BTW, I just removed the diode initially shown on the coil of the left relay as it's really not needed, but it's still a good idea to place a diode correctly across each relay coil.

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Posted By: the12volt
Date Posted: May 07, 2010 at 1:31 PM

syl20rochon wrote:

Your push switch, are they normally opened or closed?

According to the OP's descriptions, they are normally open.

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Posted By: afg_capone
Date Posted: May 07, 2010 at 1:34 PM

thanks a bunch. after talking to my group members, we are debating on using one or two switches. how much different would it be to make it to one switch that pulses a negative output to the relays? the switches are normally open.

Posted By: the12volt
Date Posted: May 07, 2010 at 1:37 PM

https://www.the12volt.com/relays/relaydiagram23.html This is for a positive output. I'll draw a few more variations later and post them when I have the time.

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Posted By: afg_capone
Date Posted: May 07, 2010 at 6:43 PM

sounds good. i'll keep an eye out for those diagrams. thanks once again

Posted By: dustimizer
Date Posted: May 10, 2010 at 12:57 AM

This can be accomplished with your two switches, a diode and two relays.

Relay #1
85   Ground input from ON button
86   to 30 of relay #2
87A not used
30   Ground
87   negative output to load
Also connect a diode with stripe to 87 and other side of diode to 85. This will latch this relay on.

Relay #2
85   Ground input from OFF button
86   +12v
87A +12v
30   to 86 of relay #1
87   not used
This relay is used to interrupt the +12v supply to the coil on relay #1, which turns the circuit off.