Electrical Wiring for electric fan

Discussion in 'Classic Mustang Specific Tech' started by highhorseb, Feb 28, 2013.


  1. highhorseb

    highhorseb Founding Member

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    I have a 66 coupe and need some advice on a power source for my electric fan. I am currently using the solenoid but the problem is when stopping for a few minutes (gas station) and trying to hot start the fan kicks on and quickly drains the battery. In turn the car will not start..big PITA and embarrassing to need a jump. I know I could wire a switch inline but I'm afraid I'd forget to turn it on and overheat. I'd prefer to power the fan with another lead that is only hot when the car is running but do not know where that could be (stock wiring). Any help is appreciated!
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  2. madspeed

    madspeed Colonel Mustard Mod Dude Founding Member

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    DCControl.com
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  3. highhorseb

    highhorseb Founding Member

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    Nothing there that solves my problem. The fan is already on a temp sensor. Even if it's variable with temp I will still have the same issue with hot starts.
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  4. madspeed

    madspeed Colonel Mustard Mod Dude Founding Member

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    Every controller that DC makes have a "soft start" feature built in. Another problem is that it sounds like you have it wired direct to a power source. Any relays in there?
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  5. highhorseb

    highhorseb Founding Member

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    I would still need a source wire so it would recognize the vehicle was starting (which is what I lack now). I have the power to the batt+, circuit braker to relay (which has the thermoswitch & switched source). My switched source is on the solenoid and thats where the problem is. Every time the key is turned on during a hot start the fan is active. I thought there was a source on the alt I could use that would only be activated while the vehicle is running but I'm not certain if thats true or not.
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  6. SHEDRED

    SHEDRED New Member

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    U should b using the solenoid for main power and ur switched power should b on an ignition on curcuit. Turning the key on should power up fan but it would only come on when ur thermostatic switch says go. Through the relay the load will go directly from battery to fan and the relay is switched on by turning key from off position. Alot of electric fans r used in vehicles that just dont need them. The stock fan and shroud off the pully or using a clutch fan r very reliable and dont suck up that much gas. I doubt u would see a mileage improvement and very little power differences unless ur tuning high rpm. If no high rpm, I recommend stock type fan and shroud all day.
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  7. highhorseb

    highhorseb Founding Member

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    It's a 410W putting out around 450RWHP, so I'm quite certain the electric fan is a good idea. I didn't put an electric fan in for gas mileage.

    Actually the power is supposed to come off the battery as I have it set up. The reason for the thread is to find an iginition circuit that is only active in a running situation rather than activated during "on" and "start".


    I know, this is how it currently works. The problem is when hot starting the battery is drained by both the starter and fan drawing too much amperage at the same time.

    I guess the only way to correct this is with a switch.
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  8. 95PGTTech

    95PGTTech Member

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    No - you need the power coming off the battery to a relay (power side) then going out of the relay to the fan.
    You need a +12V ignition only source coming to the trigger side of the same relay, then ground its sister terminal.

    When key is on, it completes the circuit inside the relay and allows full battery voltage to the fan.
    The relay would need to be fused and rated for the amperage you expect the fan to pull.
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  9. SHEDRED

    SHEDRED New Member

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    Its sounds like your down a cell in your battery or your battery is too small. Or your charging system isn't working correctly. Are your battery cables the right gauge for your set up? Ground is the most important. Heat soak can cause the resistance to shoot right up to a no start situation under a load from you fan (s). Should just be a couple minutes. Then you restart and the fan comes right on. You dont mention battery voltages, and I would check it before start, during cranking, @ idle, and when your in that situation. Something else is wrong besides your signal wire to solenoid from relay. All keyed ignition cicuits are "on" and active when key is on whether car is running or not. The start function is only momentary and won't affect that voltage sensing wire. Maybe your starter is just too taxed and is pulling mad amps. Is it a gear reduction? That wire that turns on the relay can be on any keyed circuit so that is not the problem unless you miss wired the relay. Your thermostat switch is your switch so im not underatanding why you would put in another switch if you think you will forget to turn it on. Just trying to help.
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  10. highhorseb

    highhorseb Founding Member

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    Batt +, circuit breaker, relay is already set up properly. I'm almost certain there is a lead that is only on during running conditions and for the life of me can't remember or find that information.
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  11. highhorseb

    highhorseb Founding Member

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    Battery new, charging system @13.5v, starter is 87-93 foxbody, new and works fine.

    Example;

    Thermoswitch is 180*, I stop for gas. Car is at 185* when attempting to start. So when key goes to "on" position fan runs and the car will briefly crank but not enought to start before killing the battery. If I unplug the fan prior to hot starting I have no issues. An inline switch inside the car would kill the fan solving my issue in a round about way-not the way I'd prefer to do it since I could forget to turn it back on (very doubtful but could happen). I'd prefer to find a signaling source (which I beleive does exist underhood) that would only operate while the car is running.
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  12. SHEDRED

    SHEDRED New Member

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    gotcha. I suppose it doesnt start hard regularly and it starts immediately with the dreaded jump start. I would check for a continual voltage drain in your system somewhere else. Try disconnecting positive cable and measure voltage between positive disconnected cable and positive terminal with key off then try with key on and see what your votage drop is. It shouldnt be much more than a volt but depends on electrical accessories. Hope the solution comes sooner than later.
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  13. 95PGTTech

    95PGTTech Member

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    Am I understanding this correctly that the fan is wired through the relay to only come on in the key RUN position? If this is correct, when you're at the gas station you need to take the key out of the RUN position and put it in the ACC position if you want to use radio/windows/etc and not kill it. If the fan relay is wired to come on any time it's +12v battery, that's a problem and needs to be triggered by the +12v RUN signal.
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  14. horseballz

    horseballz Member

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    Use another relay, inline that is normally closed (on) and open (off) when seeing trigger voltage. You can then trigger it from:
    A-The wire from ignition switch that goes to "S" terminal of solenoid that only sees power when switch is in "start" position. Downside is another small load on the 40-ish year old switch/wiring
    B-"I" terminal of solenoid that also only sees power in start mode, intended for providing a full 12v to the coil during start-up
    C-Starter terminal of solenoid.
    This setup would still allow, of course, the fan to run as the key switch passes through "run" position, but will not provide any power to the fan while starter is actually cranking. Another option and/or addition to this would be to wire in a several to 20 second delay timer of some sort into the trigger side of your existing relay.
    Just A Couple Thoughts,
    Gene
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  15. blown65

    blown65 Founding Member

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    Something else is up cause just your fan running for a short time should not stop you from starting your car. Mine was setup to run the fan in the pits to cool it off with the electric water pump also. Even after sitting like that for 10-15 minutes it would start right back up. That is on a 14-1 compression motor BTW.

    Check your voltage when your trying to start at the battery and also at the starter, if the voltage drop is too much you will have a problem with the cable or connection being an issue.
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