Wiring electric fan - relay or no

Discussion in 'Electrical Systems' started by MadMike, Feb 8, 2010.

  1. MadMike

    MadMike Administrator Staff Member

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    I haven't put power to my car yet, so I need a sanity check here

    I have an electric fan. (flex-a-lite 210). dual fan.

    I have a terminal block on my car - the horn relay. Has a stud on it which is a junction block for power. A bunch of heavy guage wires run off to other items to put power to them. I assume this is hot at all times (essentially battery power).

    I have the provided fan controller. There's 2 ways to activate this:
    1 prong gets battery power (my plan is from the horn relay)
    &
    The trigger can either be 12V switched -
    or battery power.

    Here's my question.
    If I come off the 12V switched source, I would probably want to run a relay?
    OR - per the instructions... if I run another wire from the horn relay and have the trigger hot all the time, I don't need a relay. The Tstat control will break the circuit and leave the fan off - unless the car is hot or I activate the fan via an auxilliary switch.

    Apparently method 1 (which would require a relay, but the fan instructions don't mention it) - only allows the fan to run if/when the key is ON.

    Method 2 - the way I'm leaning is to have the fan hot all the time. This way I can turn the fan on and cool the car when the things shut off.

    So summary - I don't need the fan relay if I go with method 2?
     
  2. mrdragster1970

    mrdragster1970 Veteran Member Lifetime Gold Member

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    .

    I know my stuff are racecars and have no keys for switched power.
    I like relays with a fused battery power for fans, especially dual fans.
    I just try to separate circuits as much as possible.


    .
     
  3. Aceshigh

    Aceshigh Veteran Member Lifetime Gold Member

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    I just did this and while I'm not the wiring God, I'll take a stab at it.
    If your switched source isn't built to carry the draw needed, yes.
    So if it's just a small gauge "Signal" wire, yes a relay is needed.

    I've got the SPAL PWM V2 fan controller.
    So there's the instructions on mine if you want to read them.

    I think running a relay keeps the big draw from going THROUGH your
    controller and therefore would extend the life of it possibly unless it
    specifically says to do so. Mine came with a resetable circuit breaker too.

    A $5 relay VS a $125 fan controller.......I'm putting a relay in. ;)
     
    Last edited: Feb 8, 2010
  4. Javelin3o4

    Javelin3o4 Veteran Member Lifetime Gold Member

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  5. yobin67

    yobin67 Veteran Member

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    Wire your fan with a relay,and a 2 position switch.Mine is wired this way.Position 1 is basically automatic.When the temp gets to 180,the fan comes on.Position 2 of the switch bypasses the temp sending unit and goes straight to the relay. I did it this way to cool off in the pits,and for testing the fans.Works great for me.I use relays on anything that draws more then a few amps..
     
  6. Aceshigh

    Aceshigh Veteran Member Lifetime Gold Member

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    Yep, IIRC switch 2 "Override" was the A/C turning on the fans
    regardless of temp used in most vehicles.

    A/C bypass switch or whatever.
     
  7. Tonimus

    Tonimus Veteran Member

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    Relays are your friend. I like relays because it keeps all the heavier gauge wire out of the passenger compartment.
     
  8. Knuckle Dragger

    Knuckle Dragger Mayor of Simpleton Staff Member Lifetime Gold Member

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    I've always wondered what the benefit is to run the fan when the engine is off. All you are doing is cooling the fluid in the radiator. If the temp sensor is in the head, or anywhere besides the radiator, couldn't you run the fans long enough to drain the battery?

    I'd go route 1. I like everything possible shut off when the key is off.
     
  9. mrdragster1970

    mrdragster1970 Veteran Member Lifetime Gold Member

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    Like I mentioned, for a racecar, you will 99.999% of the time want it on a dedicated circuit for cool down.
    No problems draining the battery, since they are plugged in after each pass.
    You only cycle the water 10-20 seconds at a time, so the starting over & over was probably a bigger drain??

    For a hot rod, it's nice, but not critical. I've been out beating on a street car, and when you just shut it off after,
    the heat will climb substantially from the heat soak. A couple of times after being on the highway for a couple hours,
    it would puke out after stopping. I remember one car that I had upgraded a little was fine when moving and running.
    The problem was you could not shut it off hot. I had to let it idle and spray the rad with water.
    I never did figure out why it ran so close to the edge like that??


    .
     
    Last edited: Feb 9, 2010
  10. MadMike

    MadMike Administrator Staff Member

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    I have the above mentioned relay too. (actually, painless 30130)

    Do I have the controller trigger the relay?

    So I wire the controller as normal, with the exception of:
    Rather than have the controller output 12V to the fan - it goes to the yellow trigger wire on the relay.

    I have 3 wires on the relay:
    12V hot
    12v input
    12v output to fan

    So rather than trigger the relay from a switch as it expects, the controller is actually the switch?
     

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