Hello.

I literally just made an acount here to ask about this.
I took a 12v fan from an old computer and I'm trying to wire it to a usb cable.
My friend knows more about this computer than me because he is the one who made it, but I can tell that there are 2 usb ports on the side which are for the mouse and keyboard, while there are 2 other usb ports on the inside, but only one of them is being used by 2 little 5v fans. (1 usb splits into 2 fans)

After experimenting, I found out that the usb ports inside make the fans spin faster, so I'm wondering if it will be able to power the 12v fan. That isn't the only thing that concerns me though. I'm having some trouble wiring the fan to the usb cable. I'll make a diagram showing what I have so far because it'll probably take a bit to explain.

The red and black wires from the usb side react when touching, so they work. I don't know how to wire these up, since I've been trying the red-red, black-black method. The little fans work on all 4 usb ports, but the big one doesn't work on any.
Any suggestions?

 

Why are you trying to run a 12V fan on a 5V USB supply?

 

Why are you even trying to hook fans to usb ports when you have that big box with a thick loom of wires coming outta it called the PSU which have 12V coming out of it.

Unless you cut it off, pc case cans always come with a molex plug to plug into the psu.

So why on earth are you involving USB at all ???

 

There doesn't seem to be a molex plug anywhere. I was trying to get it to work with USB because the other fans were working while plugged in the USB ports.

 

I wouldn't recommend running 12V fans off of the USB ports. You'll probably just damage the ports - not all computers have safety cut-off.

You can buy fans that run on 5V or 6V and use very low current, and they can run off the USB ports, but you don't get something for nothing - smaller power consumption usually means less air movement.

A 12V splitter to run your fan will be far less expensive than repairs to a computer with fried USB ports.

 

Alright, thanks for the info.
I have bought some 5V fans from ebay for a really good price, so I'm not sure I have to worry about this any more.

But this is still a pretty interesting project. I can attach the 5V and 12V usb fans to my phone charger, but the 12V fan won't budge. Is it because of the voltage the charger is giving?

 

Is it because of the voltage the charger is giving?

Almost certainly.