How to power a computer fan? Stick it into mains?

How should i power up this computer fan i want to put next to my 400w? it jus has 3 wires coming out of it, black red and yellow..

Get a Desktop PC out of ur neighbors garbage, and take the Power supply out of it. Plug it into the wall, and then flug your fans into the connectors on the power supply.

WOAH, dont even try that. garaunteed to blow or catch fire. you need to buy a univeral dc power adapter. you should be able to get one for just a few dollars. from just about anywhere that sells electronics.

unless you've a really high end computer fan, i doubt it's going to really do anything for the 400w light.

Usually a PC fan needs to be wired to a motherboard first, and has a small socket or 3-holed connector which connect to 3 pins (on the motherboard), not 3 loose wires.

If you're just going to run a tiny computer fan, and the power supply you use is say, 300W to power it, or even 250W, that is a lot of electricity for such a small result (small fan).

computer power suplies suply and take what is required, not what the max output is. so if you take a 1Kw power suply, power it up by shorting the two wires (black and green wire) and then plug a fan in, it's only going to use the power it requires to run the fan, not the whole 1kw.

as said, you can also just take any 12v dc charger cut the wires and connect red to red and black to black. ust totally ignore the yellow wire, that is the speed sensor for the motherboards bios

Nice post, I was trying to figure out how to rig two computer fans also. Thanks for the info everyone!

Sweet thanks i got it powered now with an ac adapter 12v.. I have a larger fan blowing on the plants also, just want to see if it would keep temps down any more with a computer fan blowing right next to the bulb.. i was aiming ta get the light closer to my plants! Will it make much difference?

I just rigged 2 cpu 12v fans to a 9v toy car charger, the fans are intertwined together and all I did was stick the 2 metal ends into the end of the car charger.
They are working great. But does anyone think I will experience any problems since I'm using a 9v charger?

most standard plug in the wall chargers are 9v and not 12v it'll be just fine, it just won't run at full speed.

to power a computer fan you need either a phone charger or a a usb cable. The two wires you need to worry about are the red and black wire. When you strip the phone charger, you will get a red wire and a black wire, connect red with red, black with black. When dealing with a USB wire, there must be red wire and black wire, if not dont use it. So usually a phone charger is about 4-10 v. The fan will spin but it wont provide much ventilation. USB ports offer about 5 v. I hope this helps. ALSO, any other wire comming out of the conmputer fan besides red or black is usually to control fan speed, I don't know what you can do with it. Maybe someone else does but i wrapped it with electrical tape and forgot about it. Make sure you use electrical tape connecting red to red and black to black, this will reduce the chance of FIRE.