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Summer is hot. Especially if you are being active outdoors. So to avoid getting overheated, I made a simple thermoelectric cooling unit that attaches to your wrist. This is able to rapidly cool your entire body.

You can use this to cool down after a workout or between plays. The unit is small and easily portable. All you need is access to electricity such as a 12 volt battery.

Step 1: Watch the Video

Here is a video walkthrough of the project.

Step 2: How This System Works

This system uses a thermoelectric cooler (or a Peltier cooler). This is a miniature refrigerator that works by uses the Peltier effect. When a circuit is made using two different types of conductors, the junctions where those conductors meet experience a change in temperature. One junction will get hotter and the other junction will get colder. In a thermoelectric cooler, a large number of these junctions are connected together. They are arranged so that all the cold junctions are on one side and all the hot junctions are on the other side. These units can act as coolers or heaters depending on which direction the electrical current is moving. In this application we are attaching the cold side to a person's wrist in an attempt to help cool the body.

This cooler is attached to the person's wrist right next to the radial artery. At this point there is a large amount of blood flowing near the surface. By cooling this area, the body's circulatory system helps to distribute the cooling effect throughout the entire body.

Step 3: Materials

Here are the materials that you will need for this project.

Cooling Unit Materials:

Thermoelectric cooler

Heat sink

1/16" thick aluminum plate

Machine screws for the heat sink

Small 12V cooling fan

Heat resistant foam

Thermal paste

2x Large paper clips

1/8" long machine screws

Fabric scraps

Velcro

Control Circuit Materials:

555 Timer IC

8 pin IC socket (optional)

100kohm potentiomenter (variable resistor)

Potentiometer knob (optional)

220kohm resistor

47 microfarad capacitor

Printed Circuit Board

Jumper Wires

12V relay

IRF510 Power MOSFET

1A Diode

Quick disconnect power connectors

18 gauge connector wires

12V LED Lamp (or standard LED and resistor)

Insulated project enclosure

Tools:

Drill and bit set

Soldering iron and solder

Pliers

Tin snips

Wire cutters

Wire strippers

machine screw tap or spare machine screws

Step 4: Cut the Aluminum Plate to Fit the Cooler

Start by measuring the thermoelectric cooling unit. You want the aluminum plate to stick out past the cooler by about 1/2" on each side. In my case the cooling unit was 40mm x 40mm (about 1 5/8" x 1 5/8"). So I wanted the plate to be at least 2 5/8 inches on each side. I rounded this up to 2 3/4 inches so that the plate would be the same width as the heat sink.

I marked the plate with a pencil. Then I cut it out with a pair of tin snips.

Step 5: Drill and Tap Holes for the Heat Sink Screws

The heat sink is attached to the plate with two machine screws. Place the heat sink onto the aluminum plate and mark the locations of the holes. Then use a drill bit that is slightly smaller than the machine screws to drill a hole at each location.

Next you need to tap the holes (add threads for the screws). If you do not have a screw tap of the appropriate size, you can just use several additional screws as impromptu taps. Find few extra machines screws that are the same size as a the screws for the heat sink. Press one of the screws firmly into the hole and slowly turn it so that it screws itself into the hole. As it does this, it will carve the threads into the sides of the hole. This will of course destroy the screw in the process. So you will want to have several extra screws on hand. This trick only works if the plate is softer than the screw and is fairly thin. When you are done, the holes should be reasonably well threaded and you will be able to attach the machine screws from the heat sink.

Step 6: Bend the Sides of the Plate to Match Your Wrist

The aluminum plate serves as a conductor between the thermoelectric cooler and your wrist. So you want it to be in contact with your wrist over a large surface area. To accomplish this, I bent the sides of the plate up so that it follows that contour of my wrist.

The bend doesn't need to exactly match the shape of your wrist because your wrist will also change shape when it is pressed against the plate. So to just make a rough bend in the plate I used a pair of pliers. You may also want to use a vice. Hammers can also be used to shape the plate but they can be very loud.

When bending the plate, I recommend using something to prevent too much scratching. If the plate doesn't already have a protective film, you can use a small piece of cardboard to folded paper to help protect the metal.

Step 7: Make a Foam Cover for the Thermoelectric Unit

The hot side of the thermoelectric unit can cause burns if you touch it. So I used a small piece of foam to help insulate it. Make sure that you use a foam that can handle high temperatures without melting.

I took a block of foam and I traced the outline of the thermoelectric unit on one side. Then I cut the outline and trimmed it so that it was about 1/4 inch thick and had about 1/2 inch of foam on each side of the thermoelectric unit.

Step 8: Attach the Plate, the Cooler, the Foam and the Heat Sink

Before assembling anything, apply a thin layer of thermal paste/compound to both sides of the thermoelectric unit. This paste fills in any air gaps and improves the conductivity between two plates. Press the thermoelectric unit firmly against the heat sink. Then place the foam around the thermoelectric unit. Then press on the aluminum plate. Insert the mounting screws through the heat sink and screw them into the aluminum plate. Trim any excess foam that sticks out around the sides.

Step 9: Attach the Cooling Fan

The cooling unit works more efficiently if it has a fan blowing over the heat sink. I found a small 12V PC fan that was about the same size as the heat sink. To attach the fan to the heat sink, I used a pair of bend paper clips.

First I straighten the paper clips. Then I bend a small loop in the center that would fit around the heat sink screw. Then I bend the two sides up where they lined up with the mounting holes on the fan. Then I bent a hook that would fit into each hole. This was enough to keep the fan securely in place. But you can use any method that you find convenient.

Step 10: Add Connectors to the Thermoelectric Unit and the Fan

To make it easier to connect the cooling unit to the power source, I added insulated quick disconnects. First I soldered the wires of the fan to the wires of the thermoelectric unit. Then I crimped on the connectors.

Step 11: Cut Fabric for the Wrist Strap

To attach the cooler to a person's wrist, I decided to use a simple strap of fabric. I cut several inches of material from the shoulder strap of an old bag.

Step 12: Drill and Tap Holes for the Wrist Strap Screws

I decided that the easiest way to attach the strap to the plate was with a couple of machine screws. So I marked the outline of where the strap would be. Then I drilled holes near each end on both sides of the plate. Then I used some spare machine screws to tap the threads into each hole just as I did for the heat sink mounting screws.

Then I pressed the screws through the fabric straps and screwed them into each hole.

Step 13: Attach Velcro to the Straps

To close the straps around the wrist, I added velcro. This can be sewn, glued, or melted in place depending on the kind of velcro that you are using.

Step 14: The Control Circuit

If you would like to make your cooling unit adjustable, you can add a simple control circuit. I chose to use a simple 555 timer circuit to turn the cooler on and off at a set frequency. The arrangement of the components is slightly different from a typical 555 timer circuit. R2 is a 100kohm potentiometer (variable resistor). R1 is a 220kohm fixed resistor. C is a 47 microfarad electrolytic capacitor.

This timer circuit controls the cooler with a relay driver. The timer sends a signal to a IRF510 power MOSFET which switches the relay on and off. The relay connects and disconnects power to the cooling unit.

Step 15: Solder the Control Circuit Onto a Circuit Board

After testing the circuit on a breadboard, I soldered the components onto a printed circuit board.

Step 16: Trim the Board So That It Can Fit Inside the Housing

I used a dremel with a cutting wheel to trim the sides of the circuit board so that it could fit inside the housing.

Step 17: Cut Holes in the Housing

Next I cut holes in the side of the housing to accommodate the wires and the potentiometer.

Step 18: Add an Indicator Light (optional)

To indicate when the cooling unit is on I decided to add an indicator light. I used a simple 12V LED indicator. I drill another hole for the LED and connected it to the output of the relay so that the light will turn on any time that the cooling unit is on.

Step 19: Cut the Knob of the Potentiometer

The knob of the potentiometer sticks out quick a ways past the side of the housing. So I use a hack saw to cut it shorter. Then I attached a large knob cover with an indicator arrow.

Step 20: Power the Cooling Unit

Now all you need to do is hook up power to your cooling unit. This thermoelectric cooler requires 12V and 2.5 Amps to operate at full capacity. The simplest power source is a large 12 volt battery such as a car battery. You can also use a large power supply such as the one that I built in my project on how to convert a computer power supply into a bench power supply.

Whatever you use, you should carefully monitor all the parts to make sure that they don't over heat.

Step 21: Enjoy Your Personal Cooling System

This cooling unit is able to quickly cool down your body temperature. This can be really useful when dealing with outdoor sports in the middle of summer. Or you can just use it to make yourself more comfortable without having to air condition the whole building. Why not build one for yourself and stay cool this summer.

<p>thanks for sharing this information. You know this very interesting. I was reading on a similar prototype was created in 2013 by four students from Massachusetts Institute of Technology (MIT). surely you know, it is the famous bracelet Wristify. Interasada I am currently doing a similar project. I want to take these prototypes to poor areas of my country, where temperatures are aggressive. I am from Peru, and since I read about wristify, this project interested me since I was looking for a way to reduce the deaths of poor children in my country, by intense cold (frost) and heatstroke. While searching I found this work and caught my attention as I saw in this work an alternative to somehow help my people. It sounds crazy, but I want to.</p><p>I am electrical engineering student, so I want to. I want to make this more portable design and be able to control it with an Arduino module (I could help with some information about that. The MIT used the module INTEL Edison. I want to use arduino) ........ While searching for information I found your page and I'm glad. thanks for sharing. If you could help me with some information to better this design, I'd appreciate it (how could control the temperature at a rate of 0.4 &deg; C / s. Thanks).</p>
<p>If your goal is to help the poor in your country, you are going to want to focus on making it low cost. Arduinos and thermoelectric elements and batteries are expensive. I would highly recommend using something like an evaporative cooling system with water. This will make it much more accessible to more people. </p>
<p>This is neat!,</p><p>Can the System be adapted to cool the soles of Feet?</p><p>Because I suffer from Burning Feet, Nor can i wear any socks/Shoes due to the same. The Place where is live is very hot (40~43.C Summers, 25~35.C winters)Some cooling at feet will be most useful.</p>
<p>I had to improvise a bit since my budget was tight at the time, but I managed to make it work using an old smoke alarm for the circuitry housing and 9 volt battery contact. Fun project!</p>
<p>Can i use a 5V battery as a supply?</p><p>Will the cooling be effective??</p>
<p>A thermoelectric element should work at 5 volts. You just need to make sure that the fan can work at 5 volts. Most computer fans are designed for 12 volts,</p>
<p>Hi, </p><p>Is it possible to use a smaller battery in order to have it portable? Thinking of building the initial part without the control circuit. Therefore having it as a cooler but nothing more than maybe an on and off switch. Having it all in one gadget if its possible with a small battery.</p><p>Thanks.</p>
Yes. You can do it with a battery. The cooling unit that I used was originally designed to work with a car outlet. The only thing to consider is how long the battery will last. Take the capacity of the battery (usually labeled in mAh) and divide that by the current rating of your unit. This will let you know about how many hours the unit can be powered by the battery.
<p>Hello.</p><p>I like your project, well done, i would like to make this project in order to get heat from the plate, so i have to switch the positive and negative wires, but i have one question.</p><p>I would like to chose the temperature of the plate, there is a way in order to do this? how voltage and heat are connected?</p><p>takns.</p>
Think of the thermoelectric unit as a heat pump. You put electricity in and it pumps the heat from one plate to the other. This makes one plate cold and the other plate hot. The amount of energy that you put in determines how much heat can be moved from one plate to the other. It is based on watts not voltage. And the final temperatures depend on the temperature in the room and if either plate has a heat sink. The manufacturer will probably list some kind of temperature difference (between the two plates ) that the element can create. I hope this helps.
<p>Thanks for the answer, i guess that i will must use a LM35 in order to get a defined temperature.</p>
<p>Reverse it for winter! :D</p>
<p>Ouch my eye itched, dang that smarted.</p>
<p>I think the module used here is most common TEC12706. The thickness of the cold side heat sink is about 1.6 mm, but the area looks large and three dimensional conduction will come into picture, so temperature will vary across area on the cold aluminum. </p><p>Assuming normal thermal paste, and this 12V fan, the COP of the this system should be approx. 1.3~1.5 on wearing on wrist (34 deg. C on body ) and ambient 27 deg. C conditions.</p><p>By the way, there are no proven researches of wrist cooling affecting core body temperature yet. There are few , which slightly lowers the core body, but for that, we need to cool whole wrist and palm throughout circumference.</p>
<p>Such Products are already in Market by Indian Manufacturer (www.dhamainnovations.com), and that too without fan. </p>
<p>Did you try with anything under 1/16&quot; thick aluminum plate first? Just wondering if you chose it from testing. Also I was wondering if the fan was necessary. It looks like the prototypes for the wristify just used the heat sink. Just curious! Working on putting mine together just waiting for the timer to come in. Thanks for the instructable :)</p>
I chose all the parts that I used because it is what I had lying around my shop.
why not put it on chest or back??
The arteries in your wrist are much closer to the surface. So it cools you down faster.
laptop cooling fan is better ...
laptop cooling fan is better ...
<p>This is awesome, but is there a way to do something similar, but with the heat side of the cooler? You know for winter and such. </p>
Switch the positive and negative wires of the power supply and disconnect the battery. A thermoelectric cooler is the same thing as a thermoelectric heater. They are just wired up in the opposite polarity.
<p>Ah ok. So with that said, would it be possible to along with your temperature adjuster to add a switch that basically does that? </p>
<p>Yes, get a double pole double throw switch (DPDT). Connect the center terminals to the cooler/heater. Then connect the power to the terminals on each side in the opposite orientation. That way it effectively switches the polarity when the switch is flipped.</p>
<p>Cool!! Reminds me of this: https://www.youtube.com/watch?v=vQ5rEbSK8tE</p>
<p>So what kind of on/off timing does that circuit give you?</p>
The on time is about 7 seconds. The off time varies based on the potentiometer.
<p>Really? Interesting. I would have figured it would have an equal on/off time based off the pot. Kind of silly, but how does it do the 7 on, variable off?<br>This makes things much easier, by the way! I mentioned the Wristify in another comment, and was looking to make one based of an arudiono, but this will be so much simpler and cheaper!! </p>
<p>The capacitor charges through R1. When the capacitor voltage is 2/3 of the supply voltage, pin 7 connects to ground and the capacitor discharges through R2. When the capacitor voltage reaches 1/3 of the supply voltage, pin 7 is disconnected and the capacitor begins to charge again. During the charging cycle the output at pin 3 is high and during the discharge cycle the output is low. The value of R1 determines the length of the &quot;on&quot; time and R2 determines the length of the &quot;off&quot; time.</p>
<p>Awesome! I never realized the 555 was that versatile! Yet another silly follow up: could you just stick in two pots in the places of the R1 and R2 to have complete control over the on/off times?</p>
<p>So crazy it's cool (pun intended), I woulda gone with headband tho...more hipster cool. Thanks for the detail, some of the best I have read.</p>
Nice man, that cooler is boss
<p>This is a really well-written Instructable. The steps are logical and methodical, and the pictures are really clear and on-target. After reading this, I am confident that I can make one of these.</p><p>My wife has carpal tunnel tenosynovitis (something like that) and needs to ice her wrists frequently for pain relief. This device would be very convenient for us. Thank you. (I have been waiting for Wristify to get their act together, but they seem to be degrading over time.)</p>
<p>haha, nice, but is that comfortable? :D</p>
This one is rather large for everyday use around the house. It is more like what you would use at outdoor sporting events. But you could easily make one half the size. Or you could build it into a chair or wrist support for your computer.
<p>awesome :D</p>
<p>Realistically, this is useless, but this operational principle can be very helpful in some projects, although, nice idea! :)</p>
<p>Actually, it's not as useless as you would think! I was shocked to learn that (if done correctly) this manner of cooling is actually rather effective. Instead of it always being on, though, you'd want to pulse the element on and off. The skin on your wrist never fully gets used to the cooler temp, and your body will reflect that. I get the feeling this was heavily influenced by the MIT project Wristify, which uses this very concept.</p>
Well, I didn't know about Wristify 'till now, at first glance it seemed to be useless, but actually it is pretty smart solution to trick you body so you can feel more comfortable. Thanks for explanation!
<p>Disregard the &quot;instead of always being on&quot; remark. I goofed and didn't read the ible before commenting.</p>
Wy did you at the resistor to the mosfet? It is useless, because a mosfet works with voltage and not with current like a normal transistor does. I would also remove the relay and at a larger mosfet to switch the fan and the peltier.
You are right. The resistor isn't really needed. I just left it in so that people can substitute a power NPN transistor and it would still work.
<p>Very nice, but you will get extra hot and tired carrying a big battery around :)</p>

About This Instructable

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Bio: My name is Jason Poel Smith I am a Community Manager here at Instructables. In my free time, I am an Inventor, Maker, Hacker, Tinker ... More »
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