Basic relay setup

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=79945
Printed Date: April 30, 2024 at 8:01 PM

Topic: Basic relay setup

Posted By: pointjg
Subject: Basic relay setup
Date Posted: July 05, 2006 at 10:39 AM

Hey guys,

I am making a fan switch for a LT1 Trans Am, the fans need to be grounded to turn on, and I am using a SPST rocker switch with a LED, meaning I cant retain LED functionality by just using a ground as the power-in. So my idea is to use a relay to convert/reverse the polarity... the switch in the off position however connects 'ground' and 'acc', meaning in the off position it would be giving the relay a ground signal. Would this cause any problems? (Im pretty new to relay setups).

Here is my idea for the setup:
posted_image

When the computer turns on the fans automatically it will also send a ground signal back to the relay, what will happen then? Will the relay send a positive signal back to the switch? If so the switch would be in the off position, meaning it is connecting ground with the postive signal and they would arch.

This is why I want to use a diode, but should it be used between the switch and relay or the relay and car harness? What kind of diode should I be getting? 1 amp?

Thanks in advance.

Replies:

Posted By: pointjg
Date Posted: July 05, 2006 at 10:41 AM

Even though it should not make a difference, the car is a 1995 Pontiac Trans Am (LT1 - 5.7L).

Posted By: Hoptup32
Date Posted: July 05, 2006 at 8:02 PM

Your switch wiring is OK the way it is. Even with the rocker switch in the off position, the 'ground' to 'acc' path to the relay will not affect the relay in any way, since the relay is only activated by a "+" feed to terminal 86, as long as the relay is wired as you have it shown.

I don't think there' is a need for the diode either. Even if the computer sends a ground signal to the fans, if the rocker switch is off, then the ground path from the computer stops at relay terminal 87 and doesn't affect the relay. Even with the rocker switch on, when the computer sends a ground signal, the ground signal would branch to the fans and pass harmlessly thru the relay from terminal 87 to 30 as another secondary ground path.

Posted By: pointjg
Date Posted: July 06, 2006 at 5:33 AM

Thank you Hoptup32! Just the information I was looking for :)