Self made USB fan

wannabedamned · 27 Jun 2011 at 18:13

I just chopped a USB cable, and chopped the end off a 12cm Case fan. Wired red to red and black to black. Hey presto, USB fan.

Now this has made me curious... How many 12CM case fans could you run off 1 USB port? Without a hub. Although the idea of a hub is interesting

Evoss · 27 Jun 2011 at 18:22

I did this with an old exhaust fan xD

PhillyDee · 27 Jun 2011 at 19:15

As many until the 500mA on a single port is reached. So probably not many tbh! Though some now provide 1A on a single port (The plug and charge ones)

Rroff · 27 Jun 2011 at 19:19

At 12v most 120mm fans draw about 300-400mA.

IIRC driving a 12v fan off 5v will cause a rise in the amperage drawn tho.

Tealc · 27 Jun 2011 at 21:41

Rroff said:
At 12v most 120mm fans draw about 300-400mA.

IIRC driving a 12v fan off 5v will cause a rise in the amperage drawn tho.

Typically a fan will draw less current as it has less voltage. If a fan starts with 0.3A at 12v it may only be drawing 0.2A at 5v or maybe even less. Or at least that is how I understand it.

I wouldn't be adding too many more fans to a USB port.

Ripshod · 28 Jun 2011 at 12:15

Tealc said:
If a fan starts with 0.3A at 12v it may only be drawing 0.2A at 5v or maybe even less.

I'm not gonna get too technical here, the site aint big enough. It depends on the design of the motor but in a nutshell it's Down to back EMF. A motor is a motor til it starts running. When running it is not just a motor but a generator too. Everyone knows that in a motor the current running through the windings in a magnetic field causes movement, so the motor spins. But a spinning motor is also a generator, in that the movement of the wire through the magnetic field induces a current in the opposite direction. It's this effect that reduces the current drawn as the motor spins up to full speed (If you stall a running motor expect it to draw maybe 5 times the full speed current).
There are no fixed formulae that can be applied to all motors, but it's safe to say all motors are different. Two 12V motors drawing 100mA at full speed - one may draw less at 5 volts the other more because of the reduced speed and voltage.

d_brennen · 28 Jun 2011 at 12:19

Better idea to get a Molex to SATA adaptor for a quid or so and chop the SATA plug off. You could then have a choice of 12v or 7v on a switch.