Homemade Laptop Cooling Pad??

USB cables have four wires: data +, data -, +5V power, and ground. If you can find a fan that will run at 5V, then you canitup to the +5V and ground directly. If you want multiple fans, you can wire them to the USB 5V supply in parallel. Be careful not to draw too much current, USB is only rated for half an amp(500 milli amps).

USB specs are widely available online if you need more info.

As far as noise levels, that depends on your/your wife's preferences. Don't buy a loud fan if you know that will bother either one of you. Louder fans are usually loud because they spin faster, which means they will move more air and draw more current than slower, less noisy fans.

Any case fan can run at 5V its just under volted. The size of fan depends on the size of the intake underneath. You don't want to big of a fan because you will end up with a center dead spot that won't do much in the way of help. Max size prolly 120 mm x 25mm should keep it very slim.

http://www.newegg.com/Product/Produc...82E16811999099
thinking about this fan.

i can use the usb power block from the bad pad. but it's only a two wire hook up to the fan and all the fans i find are 3-4. which wires would i use?? black red or yellow??

You can only undervolt a fan so much before it refuses to spin. Not all fans will spin up at 5 volts.

The two wires of interest on a fan are typically the red(+V) and the black(Gnd), with yellow being used for RPM monitoring. 4-wire fans also have a wire(usually blue) for controlling the fan speed.

Get these Yate Loon. They undervolt well and aren't noisy. You really won't have to worry about using 120mm fans at 5V. They will be at the minimum speeds that they can push out so they would be pretty silent. I would suggest to allow some space at the bottom of the pad so these fans can breathe.