electric fan switch?.

[Dazzerpig]

Hi all, just fitting an electric rad fan and looking to fit an on/off switch(should i need to go paddling), is it a simple task of cutting the mains cable to the fan and fitting a switch between the cable or is it a bit more involved? thanks.

[TimV]

I presume you have used a relay to power the fan?

In which case yes, just cut the power lead to the relay with a switch.

[Dazzerpig]

Thanks Times there is a relay thanks.

[Wittsend]

Here's one way you can wire-up an electric radiator fan.



There is a manual over-ride on/off switch and a warning lamp that comes on whenever the fan is working.

A further "enhancement" would be the addition of a thermostatic control switch which you place in the manual switch wire that goes to terminal 86 on the relay. A thermostatic switch enables you to set the temperature at which you have the fan come on - say 90 degrees C. The fan is off until the set temperature is reached.
Such switches can be found on  for not much money.

A further refinement would be to have the fan powered all the time, when the ignition is off. This is because when you stop the engine there is heat soak and the engine coolant temp could well increase above your target set temp. The fan will then kick in for a few minutes. You have this feature on most modern cars. The fan will run for a few moments after you park up and walk away.

[Craig T]

As mentioned, electric fans draw a huge current on startup and when running so a switch in the power line would soon melt.

The last 16" fan I wired up came with a 30amp fuse and relay kit which we used but the fuse and fuse holder melted. I re-wired it all with a larger diameter wire straight from the starter terminal (V8 engine) to a maxi-fuse at 60amp then into a 100 amp relay then onto the fan.
Overkill perhaps but it hasn't melted since.

I had a phase of fitting electric fans to my cars. In the end I went back to the mechanical fans as they are far less hassle. The 16" fan above is in a series 3 with a 4.6 V8. Electric fan is the only option unfortunately as there is no room for the engine driven version.

Craig.

[g6anz]

Just a note to add to the circuit. I have the same wiring for my fan and have noted that at high speed (50mph) the 'fan on' light starts to come on. This because the fan is driving the motor by wind speed and the motor is acting as a dynamo an producing enough volts to light the lamp.

Malcolm

[Wittsend]

Yes, that's good fun.

On another day/time you could use the glowing warning light as a speed indictor. Calibrated against one of the many government cameras

I suppose one could put a diode or something across the fan terminals 

[Alan Drover]

Not having an override switch I wonder what my electric fan was doing during my 70 mph blast along the Newbury bypass last Sunday 6th October.