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Connect electric fan to coil terminal

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robert_ellison

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I just installed an electric fan and ran the hot wire to a fuse block on the right side of the car. The closest source of power for the fan is the 2nd hot terminal on the coil ( white wire terminal). If I connect the power to this 2nd terminal will this create problems?

The benefits are:

I am close to the coil and wont have to run a wire all the way across the firewall to the main fuse block.

The coil is switched as will be the fan so it provides an on/off controlled by the key.
 
I think you are probably OK if the current draw of the fan isn't too high. The wire from the ignition switch supplies electricity to a bunch of things like the fuel pump, overdrive solenoid, wiper motor, heater motor, turn signals, gauges, etc. If the wire isn't getting warm with most of this stuff on, you are probably OK. Better way is to measure the current draw and check that it isn't over the rating of the gauge of wire from the ignition switch. I've never seen an Ampere rating for the switch. Maybe someone else has this info.
 
I would not recommend adding a fan to the ignition circuit. Most likely it will draw too much current for that circuit. Also, a fan may introduce electrical noise into the ignition circuit.
.....
A better choice would be to add another wire to the starter solenoid ( on same terminal as the battery cable ) to feed the fan. You could also use the same additional circuit to supply the power for headlight relays if you chose to add them later.
Other's opinions may vary but I would not recommend using the coil wire to power anything other than the coil.

Ed
 
robert_ellison said:
If I connect the power to this 2nd terminal will this create problems?
Click to expand...

In addiition to the obvious current draw down on the coil and reducing the high voltage of the coil to the plugs, some fans, especially brushless, induce what is called a Back EMF on to the power line when the power is turned off.

In other words, when the power is switched ON, the fan acts as a motor (to cool the engine).

When the power is switched OFF, the fan spools down to a stop. While the fan is unwinding, the fan acts as a generator and a voltage is created and induced into the power line. In your case, because the power line also goes to the coil, you may NOT be able to get the car to stop untill the fan unwinds.

If you really want to do this, install a diode in the power line to the fan so that any generated back EMF will not keep your car running.

Run a separate wire to s different power line that is NOT on the coil or install a switch between the fan and the coil wire so that you can turn the fan off before you turn the car off.

Remember also, at highway speeds you may not need or want an electric fan anyway.

Tim
 
Thank you for the replies.

The idea of connecting to the battery terminal on the solenoid is not workable as there is power to that terminal even with the switch off.

So... if I can't connect to the solenoid or the coil is my only option to run a wire all the way to the fuse block and connect to the switched relay? (ugh!)
 
If I understand you right, you have a relay energising the fan? That's why you have a "hot wire" to a fuse block?
If so, I don't see anything wrong in energising the relay from the coil terminal. In fact, this is a pretty normal way of doing things for other ignition-switch controlled relays for fuel pumps and the like. You'll get no feedback from the fan motor at all.
 
Well , to clear up a misunderstanding, I have a wire from the + side of the fan to a fuse block specifically added to fuse this fan (which requires a 25Amp fuse).

I now need to run a wire somewhere to draw current to the fuse block to activate the fan.

I'd rather not have to run all the way across the firewall to the main fuse block to get power but the coil, & the solenoid battery connection are out.

so...
what's left?
 
I assume you have converted to negative ground or else your fan will run backwards if you connect the plus side to the negative hot wire on a positive ground system. If you still have a positive ground system you could hook the ground to plus side of the fan if you have electrically isolated the fan from the chassis. But I have no alternative to your choices of using the coil as a hot source or running a wire to the fuse block. Your car, you decide.
 
Robert--

Consider getting your power from a source that is NOT switched by the ignition so that you can, if you choose, run the fan with the engine off. This would allow you more flexibility and you would be able to cool down the engine after a particularly tough bout with traffic, etc. The Hayden fan on my car is loud enough so that I could not possibly walk away from the car with it running unless I chose to do so.
 
Some interesting thoughts here. Since the resistance of the wiring is very low there really shouldn't be an appreciable effect on coil voltage as long as the ignition wire isn't overloaded. A simple check would be to measure coil voltage with the fan on and off. If there isn't much difference, say about 0.1 Volt, I still think you won't have a problem. Have you noticed any change in operation?
 
The resistance of the wiring (unless VERY high) is not an issue in play here.

The issue is that the coil probably pulls about 2.5 amps and the fan probably pulls 25 amps. 10 times as much.

Remember that here you have two resistors (one is 10x the other) in parallel. Given a finite voltage/current input (through the fuse), the needs of the fan will GREATLY overpower the needs of the coil and suck most of the available current.

With the fan ON, I would expect to see a 2-3 volt drop across the coil as compared to the fan OFF. IF you have a resistance wire or a ballast resistor between the Ign. switch and the coil/fan, I would expect to see a 3-5 volt drop across the coil (the higher of the two resistors).

Remember, the voltage output of the coil (to the plugs) is directly relational to the voltage input to the coil. If you lower the input by 25%, you lower the output by 25%.

Personally, I would save myself any further trouble shooting and just run a separate fused wire from the main power buss and install a thermo-switch with a manual On and manual Off override switch to control the fan.

Remember also what I mentioned above about back EMF.

HERE is a discussion about it that popped up today on from a Classic Mustang forum. I am NOT a part of this discussion.

Tim
 
Hello robert ellison,

I hope this doesn't open up another can of worms but why do you need an electric fan?.

Is there something I missed here.

Best regards,

bundyrum.
 
well, in order to provide better cooling for a hot engine. It's been so long since I've driven the car that I don't recall everything but as I remember it got pretty hot at idle/stop signs etc.

There have been many recommendations for use of electric fans or improved airflow fans so I decided, as I'm not concerned about originality, to upgrade where it's reasonable to do so.

Of course I know I'm a bit obsessive but it works for me,

Thanks everyone for the useful information on this subject.
 
Robert, I had an overheating problem that was caused by much of the radiator being plugged up with clay-like plugs of rusty mud. I tried a bigger fan, but it didn't do much good. I ended up solving the problem with a re-cored radiator.
 
If you are going to install the fan, the power supply for the fan should be run through a relay ,with the 30 terminal hooked up to a conveniently heavy supply ,possibly to the live side of your solenoid and through a fuse,and the switch side of the relay could be hooked up to the hot wire of the coil as the current draw for the switch side of the relay is very small.But it will be running all the time-surely you will need to be able to switch the fan on and off?otherwise you run the risk of the engine not getting up to running temp,the switch should go in the feed to the 85 or 86 terminal of the relay.You could also put a thermal switch in (as with kenlowe type fan)to have automatic cut in at certain temp and an overide switch to manually put the fan on
 
Hello robert ellison,

Regarding TimK's answer I couldn't have said it better myself.

I had exactly the same thing with my BN7 and solved it with a re-cored radiator with 5 rows of tubes rather than the original 3 rows.

I've never had any problems since except in the cooler months I remove the fan blades so the water can get hot. otherwise it runs at about 160deg.

Best regards,

bundyrum.
 
Robert -

You fan should be attached, via a relay, to the green wires in your fuse box. The white wires to the coil are not fused and therefore very dangerous to take a lead off of.

The green wires works best because when you shut your motor off, you don't want your fan to keep running. If you attach the power (through a relay) to the green wires coming out of your your fuse box, you'll have switched power that is fused. Best set up.

For a road map for what all he wiring colors mean, go here:

https://www.mgexperience.net/article/lucas-colours.html

Best,

Alan
 
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