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Can someone tell me how to connect 12v computer case fans directly to a external wall mount power supply in UK? Answered

I am building a laptop cooler/stand/usb hub for my GCSE product design coursework, and I am planning on using 2 of http://www.maplin.co.uk/Module.aspx?ModuleNo=45438 fans (12v). I want to connect them both to an external power supply, but the problem is that it uses a 4 pin connection if i'm right, I think it is molex? If I am not wrong, it has 4 cables, probably 2 black,1 yellow, 1 red. Which cables should I wire to where of an external power supply, an wall mountable would be the easiest. I live in UK so if anyone can give me any insight on where I can buy an external 12v power supply for the fan, please tell me!



I thought that fan looked familiar. I bought one of those (from Maplin) a while ago to help quieten down a noisy computer. I've done a bit of testing and this is what I found . . .
The fan will run well at 9V and it is a lot quieter - important if you're planning to use 2 of them. 9V will give you plenty of air-flow.
It draws 75mA at 12V and 50mA at 9V so the 200mA power supply I suggested below would be fine (It will supply any current up to 200mA.).
The cabling I described below is correct (sorry Xellers). The yellow wire gives you 2 short pulses every revolution of the fan. To see this you would have to connect a LED and resistor between the red lead and yellow lead while the fan is on.

By the way - 'wall wart' is an American name for these things which I've picked up. If there's any confusion, it's one of these.

Case fans aren't usually molex - probably just 2 pins. I reckon you should have some redundant power supply somewhere in the house (like an old phone charger) - 9V should do you - see what's in the back of cupboards, under stairs in drawers etc. (These things don't suck much power) L

Have a hunt around your house and I'm sure you'll find a spare 9 volt 'wall wart' type power adaptor - they are pretty common. As long as the output current is over 200mA it will power the fans quite happily. Running 2 fans at a lower speed will have enough flow to cool your laptop and will run a lot quieter than the full speed. Cut the connector off the end and connect the wire with the white stripe or raised ridge to the red of the fan and the other wire to the black of the fan. The yellow one is for feeding back the speed to a motherboard and you don't need this in your application.

If you really have to buy one, don't go to Maplin - they are horrendously expensive there. Go to one of those shops which sell hardware, pottery, gardening stuff, air fresheners etc, etc - Somewhere between Poundland and Wilkinsons. They will have some sort of cheap electronic gadget with a suitable power supply.
By the way, the fans should be wired in parallel, so reds together, blacks together.
(My eldest son's starting GCSE product design next year, so will be doing a project of some sort.)

You can use any old "wall wart" for the power supply. The black wires are both negative. Yellow is 12 VDC and red is 5VDC. Take the "wall wart" cut and strip it wires and use a multimeter to determine the polarity. Then, cut and strip the wires from the computer fan. Wire a switch in between and you're good to go. The "wall wart" can be from any old electrical device as long a s it can provide 12 volts of DC current at the correct power level.If the wattage of the adaptor is greater or equal to the wattage of the fan, it will work. A power adaptor with a lower wattage than the fan will quickly overheat and die. Good Luck.