emergency fail safe relay/warning light.

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chaddaddy

Copper - Posts: 55

Joined: January 21, 2011

Posted: July 25, 2012 at 11:18 AM / IP Logged

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?

howie ll

Pot Metal - Posts: 16,466

Joined: January 09, 2007

Location: United Kingdom

Posted: July 26, 2012 at 10:33 AM / IP Logged

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.

chaddaddy

Copper - Posts: 55

Joined: January 21, 2011

Posted: July 26, 2012 at 12:06 PM / IP Logged

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?

howie ll

Pot Metal - Posts: 16,466

Joined: January 09, 2007

Location: United Kingdom

Posted: July 26, 2012 at 12:18 PM / IP Logged

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.

chaddaddy

Copper - Posts: 55

Joined: January 21, 2011

Posted: July 26, 2012 at 12:31 PM / IP Logged

Okay i'll give that a try.

howie ll

Pot Metal - Posts: 16,466

Joined: January 09, 2007

Location: United Kingdom

Posted: July 26, 2012 at 1:12 PM / IP Logged

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.

hotwaterwizard

Silver - Posts: 1,350

Joined: December 11, 2003

Location: California, United States

Posted: August 05, 2012 at 11:12 AM / IP Logged

Don't forget the voltage dropping resistors on the LED's

emergency fail safe relay/warning light. -- posted image.

John DeRosa (Hotwaterwizard)

Stockton California

When in doubt, try it out !

Search for other posts by hotwaterwizard

howie ll

Pot Metal - Posts: 16,466

Joined: January 09, 2007

Location: United Kingdom

Posted: August 05, 2012 at 11:22 AM / IP Logged

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.

hotwaterwizard

Silver - Posts: 1,350

Joined: December 11, 2003

Location: California, United States

Posted: August 05, 2012 at 11:28 AM / IP Logged

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 !

howie ll

Pot Metal - Posts: 16,466

Joined: January 09, 2007

Location: United Kingdom

Posted: August 05, 2012 at 11:45 AM / IP Logged

If they don't listen the first time I bloody well give up!

I've been demoted twice from Platinum for calling people fools.

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emergency fail safe relay/warning light.

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