Fan start when stereo turned on
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=86456
Printed Date: July 04, 2025 at 4:09 AM
Topic: Fan start when stereo turned on
Posted By: agne
Subject: Fan start when stereo turned on
Date Posted: November 30, 2006 at 2:47 PM
Hi everyone, I'm trying to build a fansystem thats starts when I start my stereo. I have my amp built in a box and have fans that I want to start with the remote signal from the stereo. And if the fans for some reason doesnt starta I want a light to show that on my dashboard. I have bought a closed and a switched relay but dosent really know how to connect it all. Thanks in advance.
Replies:
Posted By: hotwaterwizard
Date Posted: November 30, 2006 at 8:53 PM
 ------------- John DeRosa (Hotwaterwizard)
Stockton California
When in doubt, try it out !
Posted By: agne
Date Posted: November 30, 2006 at 11:06 PM
Thanks now half of the idea I had works, fans etc starts when it gets signal on remote. Now to the other part of my problem. Im trying to get a light to show if the fans didn't start. I have tried to connect the diffret relays on various ways but can't seem to find the right way to do it. :S
Posted By: master5
Date Posted: December 01, 2006 at 1:56 AM
The indicator light is simple. connect one wire of a 12v light bulb to 30..the other to ground..if using an led make sure the anode (the longer leg on a raw LED or red on a wired led) is connected to +, which is again 30..and the other to ground. Make sure it is a 12v led (it will have a resistor) or you will need to add one. I would need the voltage/current spec of the led to recommend a value. However bear in mind the LED can only tell you if 12v is coming out of the relay..it will not let you know if the fan or its wiring connections develop a problem and is not operating. -------------
Posted By: agne
Date Posted: December 01, 2006 at 3:45 AM
I have a red lamp that is made for 12v however I'm kinda newbie at this and maybe I should just drop it. When I do as u posted above the light is on when the fans are I want it to be the other way around when the fans is off I want the light to be on and when the fans are on the light to be off. I'm trying to do this with to relays but cant get it to work.
Posted By: master5
Date Posted: December 01, 2006 at 7:09 AM
This circuit will do what you want..the reason 30 of the second relay will go to accessory (not ignition) is so the light will turn off when the key is off to save the battery. But when the system is on..the light will be off and when off light will be on
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Posted By: master5
Date Posted: December 01, 2006 at 7:16 AM
Actually...do it this way and you won't even need the 2nd relay... 
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Posted By: hotwaterwizard
Date Posted: December 01, 2006 at 11:11 AM
 ------------- John DeRosa (Hotwaterwizard)
Stockton California
When in doubt, try it out !
Posted By: hotwaterwizard
Date Posted: December 01, 2006 at 11:20 AM
 ------------- John DeRosa (Hotwaterwizard)
Stockton California
When in doubt, try it out !
Posted By: master5
Date Posted: December 01, 2006 at 2:01 PM
ah pretty slick there john..use the ground through the motor windings when off to turn the bulb on..impressive. Good Job !
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Posted By: hotwaterwizard
Date Posted: December 01, 2006 at 6:26 PM
This will also let you know the windings in the Motor are good as well.
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John DeRosa (Hotwaterwizard)
Stockton California
When in doubt, try it out !
Posted By: master5
Date Posted: December 01, 2006 at 6:54 PM
Excellent. John I was wondering since there will be some resistance through the windings, but we don't know how much..would it not be better to use a bulb with at least a 12v rating for longer potential bulb life? Of course we can't determine the brightness either way without knowing the resistance and ratings of the bulb but, if the resistance is very low I would fear sending too much volatge through a lower v rated bulb..you agree?
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Posted By: hotwaterwizard
Date Posted: December 01, 2006 at 7:24 PM
I have used this circuit in the past. The bulb never reaches full potential unless the windings are shorted. Larger than 8 volts is way too dim. A stereo indicator bulb from an old junk stereo works great. They are usually 8 volts. Remember the old Stereos with the Dial string and a Stereo Light?
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John DeRosa (Hotwaterwizard)
Stockton California
When in doubt, try it out !
Posted By: master5
Date Posted: December 01, 2006 at 7:32 PM
Ok cool..just checking, I would have no idea how to determine the voltage needed without knowing the dc resistance of the windings..but sounds to me like a perfect solution for him. -------------
Posted By: hotwaterwizard
Date Posted: December 01, 2006 at 7:34 PM
When in doubt ! Try it out ! ------------- John DeRosa (Hotwaterwizard)
Stockton California
When in doubt, try it out !
Posted By: master5
Date Posted: December 01, 2006 at 7:58 PM
couldn't agree more. I am moving and recently sold all my "junk" boxes so I don't have anything lying aroung presently. otherwise I would have taken measurments..tried different bulbs..just for the heck of it. whats the worse that can happen..a blown bulb in the name of science...very worth it.
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Posted By: agne
Date Posted: December 01, 2006 at 9:06 PM
Thanks so much for all the answers I'm kinda new at this and learnead alot from your diffrent thinking. Good support here :).
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