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Old 07-29-2012, 04:14 PM
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Cooling fan thermostat control and relay questions

I am also using a Derale adjustable thermostat fan controller but the two fans exceed the amperage rating so I need to know how to add two 30 amp relays that will control fans. I will use the Derale to9 turn the relays on but I am not sure of the wiring since the controller uses the negative wire to turn the unit on and off, anyone got a diagram to verify my wiring ???

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Old 07-29-2012, 04:20 PM
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Quote:
Originally Posted by badvibe View Post
I am also using a Derale adjustable thermostat fan controller but the two fans exceed the amperage rating so I need to know how to add two 30 amp relays that will control fans. I will use the Derale to9 turn the relays on but I am not sure of the wiring since the controller uses the negative wire to turn the unit on and off, anyone got a diagram to verify my wiring ???

Welcome to the site. If you go to the electrical form you should be able to find the information that you are looking for.
If not, am sure someone will answer your question or let you know where you can find out. This is a real helpful site with good people.
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Old 07-29-2012, 06:26 PM
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Hook a 14 gayge wire to each realy at the #85 terminal.Use a supply from a key on source.Hook the ground control wire from the derale control to the #86 terminal of the realys. The 85 and 86 control the coil of the relay which operates it.
The power switching part is the 87 and 87 a terminals. Use a heavy lwire, like a 12 gauge for each relay, hook it to the #30 terminal on each one. Be sure and use a spot that has a big postive connection and fuse the lead to the #30 terminal as well.
Use the #87 terminal to feed the fan motors the voltage. Simply ground the negative lead for the fan motors at a good spot , like under an existing ground terminal from the battery to the body.
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Old 07-29-2012, 07:06 PM
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This is a Derale adjustable unit from 150 to 250 model # 16749 with ac /manual override wire so the fans + wires are already hooked to to + 12 volts and the Derale controller has a red wire that is fused at 30 amps going to the negative wires of the fans but the fans pull to many amps so I wanted to somehow use the Derale controller red wire to energize two separate relays that are activated by switching to ground. I have wired normally open relays to show ground when energized in the past for transbrakes and such but cant remember the terminal configuration. Hope this helps explain what I am trying to accomplish instead of using a larger relay. dont know if the controller will stand it. It got pretty hot and burned up the 25 continuous relay and I opened the controller and it looks like it got pretty hot in there but it is still working. maybe a 100 amp solenoid would do the trick.. but I have relays and harnesses on hand.
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Old 07-29-2012, 07:07 PM
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See attached wiring diagram that should fit your situation.

vicrod
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File Type: pdf 2 fans 1 sensor .pdf (212.8 KB, 93 views)
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Old 07-30-2012, 11:21 AM
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Hey thanks for the diagram but that only works when your fans are not wire to 12V+ constant. I have used that configuration before and it works with a sensor that is preset however the Derale adjustable unit uses a sensor to send ground to the controller and then the controller uses a relay to turn the fans on by supplying ground to the negative wires of the fans thus leaving the option of adjusting the on / off temp. see the wiring diagram for this unit Thanks..http://static.summitracing.com/globa.../der-16749.pdf.
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