Fridge Fan Wiring

[JFowler]

As recommended on this forum, i've fitted a small (60mm) computer fan to extract warm air from the fridge compressor space. The fan works but doesn't run very fast, so doesn't move much air.
The fan has 3 wires- live / neutral / and a 3rd which i suspect is a control wire. I suspect the 3rd wire is used to control fan speed, but i've nowhere to connect it, so it's redundant on my set-up
Does anyone know for sure what the 3rd wire is for and has anyone faced and solved the problem?

Thanks,
John

[aluijten]

Normally the third wire is only a pulse wire so it's possible to determine the RPM of the fan. So it's not actually used to control the fan but to determine how fast it's spinning (and to make sure it actually does spin). Speed is regulated simply by changing the applied voltage.
There are lots of different fans you can buy, the nominal RPM and the diameter is the best indicator for airflow: Bigger diam = More air , More RPM = More air. Bigger fans tend to be less noisy as well.

[nimbusgb]

Try connecting it to 0v through a 1k resistor. If no difference then 12v through the same resistor.

[pappaecho]

Normally the smaller PC fans run at a higher speed than the bigger fans which often have the third wire.

The best source for fans is the power supplies of old computers, which I can gt for a couple of bob down our local tip. I have a 60 cm fan built into the air ventilator in the heads, and its shift a considerable volume of air, replacing the original "solar" fan which was seized and hence useless

[nigelmercier]

Try connecting it to 0v through a 1k resistor. If no difference then 12v through the same resistor.

Then throw the resistor away because it didn't make any difference!

The 3rd wire is a tachometer output, it's only the 4-wire fans that have a PWM control input.

And a larger fan would be better if you have room.

[JFowler]

Thanks for the replies.
I have an 80mm fan which i can fit- all i need is to find an 80mm hole saw!

Thanks again,
John

[nimbusgb]

Then throw the resistor away because it didn't make any difference!

The 3rd wire is a tachometer output, it's only the 4-wire fans that have a PWM control input.

And a larger fan would be better if you have room.

Like I said TRY! I have a case fan that doesn't have a tacho output and has two 'power' feeds.

[skipper_stu]

As recommended on this forum, i've fitted a small (60mm) computer fan to extract warm air from the fridge compressor space. The fan works but doesn't run very fast, so doesn't move much air.
The fan has 3 wires- live / neutral / and a 3rd which i suspect is a control wire. I suspect the 3rd wire is used to control fan speed, but i've nowhere to connect it, so it's redundant on my set-up
Does anyone know for sure what the 3rd wire is for and has anyone faced and solved the problem?

Thanks,
John

The third wire tells the bios in the motherboard of the computer what revs it is turning at.
Stu