How can I create a USB powered cooling unit for my HTPC?

[Ranash]

Hello everyone,

i have my HTPC inside cupboard, thus when stressed it overheats.
on top of the cupboard i have some slits, and i wanted to build a cooling unit to circulate the air inside.
i thought of using there fans: http://www.thermaltake.com/product_info.aspx?PARENT_CID=C_00000498&id=C_00000500&name=Performance+DC+Fan-4PCS+Value+Pack&ov=n&ovid="
i tried to connect it 8 of them with 1(A), 12(v) transformer, and it worked beautifully, problem is i have to shut them down manually.

i tried plugging only 1 in with a usb to molex cable, and it just didnt get enough airflow, my guess because usb is limited to 5(v).
is there any way to amplify the voltage? or if u have other creative ideas, id like to hear them :)

Thank you all very much in advance,
Ran A.

 

[vk6kro]

If you can get a low powered 5 volt relay, you could use this to switch the 12 Volt supply to the fans. This would turn off the supply when the computer was turned off.

You would need to put a diode across the 5 volt line where it meets the relay coil to avoid negative voltages being fed down the USB power supply + line.

This diode would have its cathode toward the positive 5V line and its anode towards the grounded side of the 5 V supply. Preferably it should be a Schottky diode.

 

[Shalashaska]

You could just get a mini desk fan and have the air blowing across the slits, which would draw air up and out. Less elegant, but as easy as using a handheld battery powered fan, or a wall outlet.