emergency fail safe relay/warning light.
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=131883
Printed Date: May 04, 2024 at 9:10 AM
Topic: emergency fail safe relay/warning light.
Posted By: chaddaddy
Subject: emergency fail safe relay/warning light.
Date Posted: July 25, 2012 at 11:18 AM
I am doing an electric cooling fan in my truck. I bought some good relays but i want to be 100% safe. I want to set up a fail safe system. If any of the three relays powering the fan fail, I want an LED light to come on.
Fan info: the fan is a 2 speed motor that has three wires. Ground, Power 1 (low speed), Power 2 (low speed) If you energize power 1&2 at the same time = high speed.
Relay 1 SPDT (Air conditioning triggered): 30:12V, 86:air conditioner ON trigger, 85:ground, 87:Power 1. 87a:empty
Relay 2 SPDT (185 degree thermostat triggered): 30:12V, 86:Thermostat 1 trigger, 85:ground, 87:Power 2. 87a:empty
Relay 3 Dual make SPST (200 degree thermostat triggered): 30:12V, 86:Thermostat 2 trigger, 85:ground, 87:Power 1, 87b:Power 2
So my question is, how do I wire 1 LED/light bulb to come on if ANY of the three relays fail?
Replies:
Posted By: howie ll
Date Posted: July 26, 2012 at 10:33 AM
Ignition to plus side of LEDs (4) negs to relay 1 and 2 87 3 87 and 87a.
In practice, if the relays are fitted in such a way as to be heat and moisture protected e.g. from Raw Components in the UK relay boxes, they will be the LAST part to fail.
-------------
Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.
Posted By: chaddaddy
Date Posted: July 26, 2012 at 12:06 PM
Okay. So the + side of the LED to ignition? Then the light will be on whenever the relay is closed? Wouldn't I use my 12V source from the 86's? So when 12V is to 86, if 87 does NOT have 12V, light. But that doesn't work either. 87 wont be grounded, just at rest? And what happens when the relays are working perfect and 86 and 87 both have 12v, will that damage the LED?
Posted By: howie ll
Date Posted: July 26, 2012 at 12:18 PM
OK, next idea + side to 86, - side to 87 on 1 & 2 and 87 and 87a on 3.
Then the LEDs will only come on if fans are actuated and they are working, or use dual colour LEDs and run the extra ground to the outputs then you will have say green for working and red for fail.
No you won't damage the LEDs if you're worried blocking diodes.
-------------
Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.
Posted By: chaddaddy
Date Posted: July 26, 2012 at 12:31 PM
Okay i'll give that a try.
Posted By: howie ll
Date Posted: July 26, 2012 at 1:12 PM
Just a thought:- failsafe.bmp
Completely over the top!
Blue status you're getting power, totally uneccessary!
Green OK.
Red failure.
Just a thought, if you're not using 12V LEDs remember resisters are required. ------------- Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.
Posted By: hotwaterwizard
Date Posted: August 05, 2012 at 11:12 AM
Don't forget the voltage dropping resistors on the LED's
------------- John DeRosa (Hotwaterwizard)
Stockton California
When in doubt, try it out !
Posted By: howie ll
Date Posted: August 05, 2012 at 11:22 AM
I took that as a given or test. If the OP doesn't know that he/she shouldn't be doing this, just like on the Car Security and Convenience section I say DMM rather than Digital Multimeter. If they don't know what DMM means.....
I had a poster awhile back, explained about diodes on aux outputs towards relays, didn't listen then posted a plaintive request for any other ways to lock their vehicle as the outputs were fried.
-------------
Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.
Posted By: hotwaterwizard
Date Posted: August 05, 2012 at 11:28 AM
I try to tell everything in as simple terms as possible .
The K.I.S.S. Method always works best.
Remember : You can't fix stupid. ------------- John DeRosa (Hotwaterwizard)
Stockton California
When in doubt, try it out !
Posted By: howie ll
Date Posted: August 05, 2012 at 11:45 AM
If they don't listen the first time I bloody well give up!
I've been demoted twice from Platinum for calling people fools.
-------------
Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.
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