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    1. #1
      Join Date
      Aug 2006
      Location
      KC
      Posts
      149

      fan relay and fuse shorts out

      I put on a autowire cooling fan relay on my cooling components fan. Over the years I have had connetions melt fuses burn up relays go bad the fan never has a problem but the relay takes alot of abuse. Any thoughts?

    2. #2
      Join Date
      Feb 2009
      Location
      muggy midwest
      Posts
      533
      Country Flag: United States
      It comes down to current load and resistance building heat which leads to a meltdown of sorts. As cooling fans clock more service hours, brushes/windings can draw more and more current which can tax your power supply source and related wiring. I'd do an amp draw test with a meter to see what it draws upon start up and after it's ran for about 10 minutes to see if it fluctuates. If the draw gets higher and higher, I'd replace the fan/motor. If it's somewhat high but stable, try upgrading to a larger relay with heavier gauge wiring.
      "...if at first you don't succeed, try again.
      If you still don't succeed, then quit-no sense being a damn fool about it..."
      -W.C. Fields

      HARNESSWORX
      (formerly gmachinz)

    3. #3
      Join Date
      Nov 2008
      Location
      So. Cal.
      Posts
      1,240
      Country Flag: United States
      Quote Originally Posted by H2Ogbodies View Post
      If the draw gets higher and higher, I'd replace the fan/motor. If it's somewhat high but stable, try upgrading to a larger relay with heavier gauge wiring.
      I think thats the best bet. Heavy gauge wire and a heavy duty relay. Even if the fan is say only spec-ed at pulling 30 amps the inrush currents to get her spinning can be alot higher. And as often as a cooling fan cycles you are gonna see alot of higher currents. If the fan is said to need 30amps I would use a 60 amp relay and number 8 wire. Think of it as a big pipe and heavy duty valve. The cost isnt that much. And to be honest, it will save the fan motor. Instead of bogging down every time it starts up, it will see a large supply of current (due to full batt voltage) and fire right up. The windings of the motor will stay cooler.

      Why cooler? Well, it will get more voltage and get it up to operating RPMs faster. When its started at a lower voltage it is acting like a higher resistance load. More resistance equals heat. Why is there less voltage? The smaller relay and wiring are resisters. They will drop (you could say use, but properly its resist. It will resist the voltage and use the current due to resistance) a certain amount of voltage, thats why they heat up and get cooked.

      If you wire it up with really over sized wiring and relay the voltage drop on them is less and the fan motor gets the full voltage for its windings or its resistive load. Thats where you want the voltage drop (resistance and use of current), at the fan motor, not the wiring.

      Kinda like this, etreames here. If you use 20 gauge wire, and a 10 amp relay for a circuit (fan) that will pull 30 amps the relay and wire are a major resistor. So if you have 12 volts starting out, the high resistance of the thin wire and small relay will be just like putting in a big resistor in line. They will heat up (current use) and they will drop the voltage to the fan (resistance). You may only get 10 or way less volts to the fan.

      Take it too really far extremes just to get the idea. Make the wire so small that it acts like a MASSIVE resistor. It will glow hot and use all the current. And the voltage dropped across the thin wire will be so great so the fan doesnt see any voltage, and wont pull any current. The fan needs voltage first, to pull the current, and the current will follow.

      The voltage is what pulls the current. Supply the fan with the full batt voltage (no voltage dropping resistors in the way like a small wire or small relay) and it will pull current that it was designed to.

      So you think, whats keeping the fan from over currenting? Pulling too much current. Well that would be the resistance within the fan itself. The resistance of the wires in the coil of the fan. The designers of the motor said we should have a nominal voltage of say 12-14 VDC because its a car. So its a simple matter of math to figure out they need to provide X amount of resistance in the motor windings (maybe add a resistor in series) to pull the needed current through the motor to have it spin at a certain RPM.



      Thats why if you increase the voltage on a DC motor it will spin faster, it will pull more current. Not so true with synchronous AC motors. LOL Nuther motor subject. But DC motors are simple. Feed them with a certain ammount of voltage and they will turn at a set RPM. Feed them with more voltage and they will spin faster with all other things being similar.

      SO... Long winded again. Point is. Supply the fan motor with full Batt voltage, dont drop some voltage off on thin wires or small relays and the entire system will be happy and cool. JR

      http://www.wiringproducts.com/contents/en-us/d36.html
      What I write is opinion, none of it is factual. 2010

      Even though I'm conscious it doesn't mean I'm coherent. 2011

      I'm getting better with age. Best thing about old age is I don't know any better. 2012




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