One for Gina and other electronics gurus ???

[Skipper Billy]

I want to install a couple of 80mm computer cooling fans in my observatory to run 24/7 to extract air and provide a sustained throughput of airflow. I have a 12v DC supply handy.

All the ones I can find are either three wire or four wire.

Rather than try to figure out by trial and error (and possibly damaging the fans) which wire does what I thought I would ask the collective wisdom if its even possible to run a three wire fan with just pos and neg 12v supply ???

Something like this... https://www.amazon.co.uk/dp/B0119SLG18/ref=emc_b_5_t 

 

[Skipper Billy]

Ooops posted in wrong section - mods can you move it please to DIY Astronomy - sorry!!

[Alex]

Yes :-)

Easiest option is to go for  3 pin and just use the + and -ve pins. The other pin a feed back of the fans actual speed, used by a speed controller.

I installed a PC fan on the back of my 200PDS with a PC fan speed controller and works a treat

[Gina]

Posted by: @AstroOlly

There should be a red and black wire in the group of 4, they are your pos and neg.... ?

Stew

Yes, that's what I do.

 

[KevS]

I have a similar system on the greenhouse, I run the extract fan slower than the input fan.

The very marginal increase in air pressure, that is probably only a few millibar has a noticeable effect on the volume of greenfly. Dependent upon how well sealed the obsy is, it may keep help the midges out. 

[Bas]

I have one in my shed powered by a cheap solar cell. And that works pretty well.

[Skipper Billy]

The fans have arrived - with black, green, white and yellow wires !! I will assume black is -ve but any ideas on which might be +ve ??

[Skipper Billy]

@7170 You're a star - many thanks. Will try it tomorrow - I am on the outside of a very nice bottle Merlot just now!