Body Heat -> Electricity

This semester I attempted to build a wearable that could harnesses the power of the a humans body heat and convert it to electricity.

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To accomplish this, I did some research and came up with a system that would work.  You can read more about that process, here

The parts I used are as follows:

  • 1x TEG module (TEG2-126LDT)
  • 1x LTC3108 breakoutboard
  • 1x 100uF capacitor
  • 1x 0.1F capacitor
  • 1x 470 ohm resistor
  • 1x LED (20mA max)
  • 1x ON/OFF switch

And also fabric to make a wearable around the wrist.

The two pictures above are of the TEG module and the breakout board that accompanies it.  The board is capable of taking a very low voltage from the TEG module, and converting it to 5 volts.  There are a few options that the LTC3108 chip offers.

voltageselection

This image is of the pin out for the board.

  • Pins 1 & 8 are simply Ground pins.
  • Pin 2 (Vsrc) is the input for the TEG module
  • Pin 3 (Vstr) is a storage pin.
    • This is where you’ll place the large 0.1F capacitor
    • This allows the unit to harvest energy to be later used periodic high energy demands
  • Pin 6 (Pgd) is a signal pin, indicating that the capacitor on pin 3 is charged above 92.5%
    • It charges the capacitor to 5 volts, non-selectable
  • Pin 7 (VoutPri) Is the primary output pin, that can be set between 2.2 and 5 volts
  • Pins 9 & 10 (Vsel#) are used to set what voltage the output pin will be
    • The diagram above and to the right indicates how to assign these pins

 

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It’s always good to test out a circuit by trying it on a breadboard first.  The above picture is how I wired mine.  There’s a red LED sticking out of the left side of the breadboard, and that’s what I will be using to view any transfer of power from my body heat.  I’ll be using my wrist since that is a fairly warm part of the body.

If you place your wrist on the hot side of the TEG module, you should get the LED to glow in about 3 seconds.  It’s a pretty magical thing to see it come alive.  The key to get energy out of the TEG module is to make one side cold, and the other hot.  You can’t simply add heat.  So let’s say you put an ice cube on the cold side, and your wrist on the other, the LED will glow much brighter.  Also, if you disconnect the LED, the LTC3108 chip will begin storing power through its Vstr pin.  So when you need light, you can connect the circuit with a switch, and power a brightly lit LED for some amount of time.  That time based on how big your Vstr capacitor is and how much energy the LED takes.

So, with that working, we must make bring it to a soldered proto-board.

 

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The circuit I made is down below.  You may consider putting resistor before the LED

main-board

To make everything wearable, it’s time to breakout the sewing machine!

I used some stretchable fabric and velcrow to create a wrist strap.  Then I cut a square out of the middle and hand sewed in the TEG module in so that it would push against my wrist and absorb the heat.  On top of the TEG module, I attached a heatsink as to help cool the cold side.  If you are outside on a cold day, this will work really well.  If you are inside a room with little air movement, it may not harvest any energy.

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Future iterations can be made to be more stylish 😉

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It’s pretty cool to see it work! A 10 minute bike ride would give me a 0.15 volt increase on a 0.5F capacitor, which is a huge capacitor.  So if you used a 0.1F capacitor, you could theoretically get 1 volt per 15 minutes on a bike, so after an hour you could be fully charged.  You may be thinking, “hey, why don’t I use a battery?”  Well, that wouldn’t be the point.  Something like this in the hands of a kid could be hugely inspiring.  It’s pretty magical to see your own body heat light something up.  All it takes is a pebble to start an avalanche.

 

 

To read more, take a look at my previous posts,

  1. https://softbots2017.wordpress.com/2017/03/08/thermoelectric-generator-1/
  2. https://softbots2017.wordpress.com/2017/04/04/teg-device-2-chris/

 

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