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“After seeing an Instructable on Digg for making a USB powered fridge, I decided to incorporate the concept into a backpack. For those who don’t know, the USB fridge uses a Peltier Unit to cool the contents. When power is applied, a Peltier Unit makes one side extremely cool and the other side extremely hot. If the power is reversed, the cool side becomes the hot side and visa versa. The only problem with this is the fact that while cooling the users back, the hot side would be accumulating mass amounts of heat inside of the backpack. My solution to this was to use a processor heat sink along with a fan to push this heat out of the backpack. The cool side of the peltier unit is placed on a piece of sheet metal that will be exposed to the users back for cooling and/or heating. Thanks to my friend Miles for helping with the fabrication process! Go check out his site called Motor Mayhem. Here is how I made the backpack:” source...