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Where to wire a Pusher fan - BN1

Crowbar

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Hello all,

I'm planning on installing an electric "pusher" fan from Moss on my BN1. The unit has a thermostatic switch, but I was wondering where I should splice into the wiring harness for power...I'm new to Lucas wiring and am understandable anxious!

Any advice appreciated!

Best,

GC
 
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Use any terminal that is "always hot" so you can run the fan even if the ignition is off.

Though the unit you contemplate has a thermostatically controlled switch I recommend your using a regular SPDT switch in its place as there are times you may want to use the fan to get ahead of an issue--even before the temp rises to the preset point of the thermostatically controlled switch.

Use of a relay is a good thing. And a fuse.
 

Keoke

Great Pumpkin
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Connect the relay's primary power to "Any Terminal that is always hot".

Connect the switched relay power to the fan directly to the battery connection on the solenoid using an appropriately sized slow blow fuse.

:encouragement:'
 

vette

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Hi CG, The first thing that I would want to know is, how many amps does the fan use? I want to say that you definately must put this fan on a fuse, and I also think that you definately want it on its own individual, manual, on/off switch. Many fans that I have read about can pull some high amps but here's the rule, if the device does not pull more amps than the amp rating of the on/off switch you are going to use, then you don't need a relay. The switch can turn it on and off, you don't need to step it down , around or thru anything just let the single pole switch do what it is designed to do.
The next point is what are you going to hook it too? If this fan pulls some high amps such as 20 amps, then you don't want to hook it to just any wire on the Healey wiring harness because you will easily be exceeding the rating of that particular wire especially when combined with whatever else is on that wire. Most the wiring in a Healey is sized just right for what it was originally intended to supply, it has almost no capacity for additional amps. Just for conversation sake, if you over load a wire, it will at the very least run hot (fire hazzard), it will also cause a voltage drop out to the devise you are trying to supply, the lower voltage out at the devise will cause the devise to try to pull even more amps and the devise will be damaged.
So, as stated in an early post, the hot terminal of the battery wire at the starter solenoid is about the only location where the supply wire (large wire coming from the battery) is large enough to supply some relatively, extra, high amps for a device such as a cooling fan. I would use size number 12 stranded wire because it is rated at 20 amps. You will quickly notice that it is larger than most the wire in a Healey. You will have to crimp a large eye connector unto this wire to put it on the large terminal of the solenoid. Make sure you get it on the wire coming from the battery. Then you will have to immediately go to an In Line Fuse Holder. I can't think of any reason why you would need a slow blow fuse. If this thing decides it wants to pull more than the fused rating (a short in the circuit or an jammed fan blade) I believe I would want it to blow the fuse as fast as possible instead of sticking around long enough to create more heat in the circuit. Since you are not pulling the circuit from wires that come thru the original fuses you will need this fuse holder. Then run the #12 wire from the fuse holder to either directly to an on/off switch or to a relay, which ever you decide. Size the fuse as what is stated on the fan name tag or as what the manufacturer says it needs, or maybe just a tesch higher. If the fan is labeled as in Watts instead of Amps then you can figure out the amps with this formula: Amps = Watts divided by Volts. Volts being 12. Good Luck.
 

Keoke

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Note:
The fan is classified as an inductive circuit and if the fuse is rated at the fans steady state current, a fast blow fuse will blow every time the fan turns on.

When energizing electrical devices containing motors/solenoids use a slow blow fuse to protect the circuit.

Then the transient effects of the motor will be handled as well as the fault current in the event of a short in the circuit.
 
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Connect the relay's primary power to "Any Terminal that is always hot".

Connect the switched relay power to the fan directly to the battery connection on the solenoid using an appropriately sized slow blow fuse.

:encouragement:'
Keoke is right in commenting as he did upon what I said.

I have substantially rewired my car and brought 12VDC to two 6-circuit fuse boxes--one "always hot" and the other switched by the ignition key--into the engine compartment to make projects just like this easier. When I wrote the post I was thinking in my mind's eye the way my car is laid out versus stock.

In the original configuration there are not too many places to pick off a hot source that would be able to power a 20 A current, and certainly the starter solenoid would be a fine choice.
 
OP
C

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This was outstanding information - many thanks!

Any advice on a good on/off switch?

The car is positive ground BTW...
 

Keoke

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This was outstanding information - many thanks!

Any advice on a good on/off switch?

The car is positive ground BTW...

Next! upgrade convert to Neg Ground :encouragement:---:applause:

If you use the relay any single pole single throw switch that matches what is in the cockpit will work.--:cool:
 

warwick-steve

Jedi Hopeful
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Hi all
Just been reading this interesting thread. I am also just about to install a pusher fan on my BT7 using a relay. I am clear that the switched side of the relay should be attached to the solenoid but what about the other side of the relay. I thought the brown wire on the fuse holder??
cheers
Steve
 

Keoke

Great Pumpkin
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Hi all
Just been reading this interesting thread. I am also just about to install a pusher fan on my BT7 using a relay. I am clear that the switched side of the relay should be attached to the solenoid but what about the other side of the relay. I thought the brown wire on the fuse holder??
cheers
Steve

Relay contacts:------------------------- Not the coil winding connections

The unswitched side is connected to the solenoid's 12V power.
The switched side is connected to the fan via an appropriately sized fuse

does this answer your question Steve-?
 

Keoke

Great Pumpkin
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Hi all
Just been reading this interesting thread. I am also just about to install a pusher fan on my BT7 using a relay. I am clear that the switched side of the relay should be attached to the solenoid but what about the other side of the relay. I thought the brown wire on the fuse holder??
cheers
Steve

Relay contacts:------------------------- Not the coil winding connections

The unswitched side of the relay contacts is connected to the solenoid's 12V power.

The switched side of the relay contacts is connected to the fan via an appropriately sized fuse.

The ["Other side of the relay"]One side of the coil winding can be connected to any power source that is always hot via a switch the opposite side of the coil winding is grounded.

does this answer your question Steve-?
 
Last edited:
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Should you opt to use a separate switch for your pusher fan--as opposed to a thermostatically controlled one--there's the question of what kind to use and where to mount it. Some people don't mind separate switch panels but I don't think they look good, esp. on 100's.

The cleverest setup I have seen was on a 100 brought to stand for concours at a Conclave some years back--in this case for driving lights--but the same could be used for a fan or any circuit: The owner energized his dash lights through the side lights and utilized the small slider switch that normally controls them--through a relay of course--to the driving lights.

When the judges asked him how the lights were switched he challenged us to figure it out, which we couldn't, and made no deduction for correctness when he finally told us.
 

warwick-steve

Jedi Hopeful
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Hi Keoke and Michael
Yes thanks
So a suitable power source for one side of the relay coil winding could be the single brown wire on the fuse box
thanks
Steve
 

warwick-steve

Jedi Hopeful
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Gentlemen
Just to clarify something please. When you refer to a "hot power source", I presume this can be an unfused connection from the A1 terminal of the control box?? Like many new owners I am learning fast and really appreciate the help from those that have experienced with these things.
cheers
Steve
 

Keoke

Great Pumpkin
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Gentlemen
Just to clarify something please. When you refer to a "hot power source", I presume this can be an unfused connection from the A1 terminal of the control box?? Like many new owners I am learning fast and really appreciate the help from those that have experienced with these things.
cheers
Steve

a "hot power source",Refers to a 12v source that is always " ON " or HOT.

For example the brown wire in the car harness.
 
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