Instructables
Picture of Wrist Cooling System

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.

 
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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

Picture of Materials
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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

LostNeutrino5 months ago

Cool!! Reminds me of this: https://www.youtube.com/watch?v=vQ5rEbSK8tE

DoctorWoo5 months ago

So what kind of on/off timing does that circuit give you?

DIY Hacks and How Tos (author)  DoctorWoo5 months ago
The on time is about 7 seconds. The off time varies based on the potentiometer.

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?
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!!

DIY Hacks and How Tos (author)  DoctorWoo5 months ago

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 "on" time and R2 determines the length of the "off" time.

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?

Horrorzilla5 months ago

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.

nintenbro645 months ago
Nice man, that cooler is boss
DanYHKim5 months ago

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.

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.)

Jan_Henrik5 months ago

haha, nice, but is that comfortable? :D

DIY Hacks and How Tos (author)  Jan_Henrik5 months ago
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.

awesome :D

ivver5 months ago

Realistically, this is useless, but this operational principle can be very helpful in some projects, although, nice idea! :)

DoctorWoo ivver5 months ago

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.

ivver DoctorWoo5 months ago
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!

Disregard the "instead of always being on" remark. I goofed and didn't read the ible before commenting.

Gabse5 months ago
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.
DIY Hacks and How Tos (author)  Gabse5 months ago
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.
carlos66ba5 months ago

Very nice, but you will get extra hot and tired carrying a big battery around :)