Introduction: 5 Minute USB Wrist Cooler
My least favorite part of (but favorite excuse to avoid) exercising is sweating. That is especially true in the outdoors of the Great American South during the summer. It's currently 8pm and still 93 degrees here. That's why as a small comfort, I decided to build this wearable thermo-electric cooler to help my body cool down slightly. If I were a bit smaller, maybe toddler-sized though, this baby would reeeally cool me down. It's a 5 minute wrist cooler because without external cooling, it will last for about 5 minutes before your wrist stops feeling cool. Also, because it is so simple to build, it can be done in 5 minutes once all the materials are gathered.
Let's get started!
Step 1: Gather Materials
For this project, you'll need:
-1 USB-A cable (data wires not needed, only power).
-1 broken or old wristwatch
-1 12v 6amp Peltier module(I got 10 for $26 here)
-1 heat sink of your choice (I grabbed one from an old (2001) desktop computer)
-2 wire nuts or soldering wire and a soldering gun
The longer your USB cable, the better, as you will have to plug it into a power bank in your pocket. Your power bank will need to be able to output at least 2 amps of current.
Step 2: Build
First, separate the wrist watch bands from the clock part of the watch. It should be held in place by two small metal rods driven through a hollow inside the bands. You could use a rubber band or string instead, but the bands give this a more professional look.
Next, use insulated wire to create a frame to push the heat sink onto the Peltier module. Alternatively, use thermal paste to join the heat sink and thermo-electric cooler. Now just create a couple of parallel handles on opposite sides of the heat sink. Remember to point the wires towards you to prevent them from bending and breaking over time. I used insulated copper wire and threaded it through the hollows in the watch bands to hold the heatsink in place and allow it to wrap on my wrist.
Last, peel the power wires from the USB cable (usually black and red, sometimes white and red or white and black) and hook them up to the Peltier module's corresponding wires. DO NOT SOLDER THESE TOGETHER YET. Twist the wires together and plug in your new device. If the side on your wrist gets hot instantly, reverse the polarity. Once it cools your wrist after being plugged in, it is safe to solder the wires. I just used wire nuts because I am running out of USB cables and may need a few later on for another project.
Step 3: Understanding How It Works
Peltier modules are pretty cool both figuratively and literally. You power them and they pump heat from one side to the other, the direction depending on polarity. That is why I instructed you to switch it if the side touching your skin heated up instead of cooling down. You could have also flipped the whole module but that is a lot more work since the heat sink had already been secured. The more power you give your module, the harder and faster it will work. We are not operating this module at the full 12v 6amps it deserves because it may get too cold to be safely worn and may overheat much quicker than the advertised 5 minutes. To make your wrist cooler last longer, add a fan to the heat sink blowing the hot air outwards, or simply spray water on it. The evaporating water will create a cooling effect just like, you guessed it: sweating. Unlike sweating, however, you will not lose the water from your body or feel icky.
With this compact cooler, you'll be the envy of all outdoor athletes and protect at least one part of your body from the punishing summer heat. I'm actually working on making a full suit out of these and never have to sweat again! Anyways, I'll keep you guys posted. Stay cool.