Emergency Light/Charger from Fire & Water

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by Joohansson

Really simple and very useful Thermoelectric Emergency Generator from very few parts available in home.
Optimized for powering with tealights/candles.

Background:
It converts heat energy (from candles) into electricity. Main usage is to power LED lights to act as an emergency product. It could also be scaled up and used in homes where electricity is not very given. It could also be used as a battery charger or power other electronic devices. I´m well aware of the commercial product tPOD1 which I think is a great idea but I´m more interesting in a DIY solution for everyone.

Concept:
I´m using a thermoelectic module, also called peltier element, TEC or TEG. You have one hot side and one cold. The temperature difference in the module will start producing electricity. The physical concept when you use it as a generator it's called the Seebeck effect. Thermoelectic modules are mainly used for the opposite effect, the Peltier effect. Then you apply a electric load and it will force a heat transfer from one side to the other. Often used in smaller refrigerators and coolers. Read more about i here:
http://en.wikipedia.org/wiki/Thermoelectric_effect

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Solution:
First I used a cheap TEC-module (8€) but it was unfortunately destroyed due to high temperatures. It was specified to handle 200ºC max temperature but somehow I got higher temp than I measured. I ran it without load, that might be the cause. I now use a 40x40mm TEG-module that produce 5.9W (4.2V/1.4A) at 180ºC difference. It has a maximum operating temp of 350ºC (180ºC cold side). It was the same module I used in my other charging project. It´s quite expensive though, about 50€. TEGs are a bit hard to come by but I think there are cheaper ones available.

To transport away all heat and cool it with air you usually need a large heat sink, or a small heat sink with a motor and fan. In this project I use water instead. That make the contruction really compact and the temperature on the "cold" side will never exceed 100ºC. Water will eventually boil but it´s easy to refill, as long as you have water.

To power LEDs you need higher voltage than the module itself produce. In my previous project I built an adjustable regulated voltage Step-up. That could be used (and is better) but I choose to use a $1 step-up from Ebay.

The best choice of heat source is 3x tealights. That produce about 0.2W electric power.


Features:
  • 90g (without LED)
  • WxH=85x78mm
  • Built in voltage step-up
  • Support for 3x tealights

Applications:
Mainy constructed to power LEDs but can be used for other things as well:
  • Battery/smartphone charger
  • External fan (cooling effect, fire booster, etc.)
  • Electronics
  • Charge super capacitor and power high intensity SOS signals
Could also be heated with lots of stuff:
  • Candles
  • Spirit burner/stove
  • Gas burner/stove
  • Wood stove
  • Camp fire
  • Barbecue
  • Hot water

Materials needed to do this:

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  • 2x cans of tuna-fish or similar (diameter=85mm). You need as flat bottom surface as possible, larger than TEC/TEG-module. Make sure it fits 3x tealights inside.
  • 2x 40x40x3mm sheets of aluminium
  • LEDs (I used a "USB notebook light" with two LEDs)
  • TEC or TEG module. I bought mine "TEP1-1264-1.5" at http://termo-gen.com/
  • Voltage step-up (1 to 5V). Search Ebay for "emergency aa battery portable dc charger". Another cheap circuit is this one: http://dx.com/p/usb-dc-1-5v-to-dc-5v-voltage-step-up-boost-module-green-143571
  • Thermal paste (better if specified for high temperature, 200+ºC
  • Optional: 3x pull springs to add stability and heat transfer
Equipment:
  • 6mm drill
  • File
  • Sand paper and/or steel wool
  • Optional: Soldering iron

Method

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Prepare Can 1:
This will be used to absorb heat from the candles. Fire needs air and that is why you need to make lots of holes in the can. Most cans are covered with some kind of varnish. That smell really bad when you heat it up. You need to remove that.
  1. Remove labels with hot water
  2. Drill 18x3=54x 6mm holes
  3. Use the file to reduce sharp edges
  4. Heat up the can, outside! I used a gas stove. It will burn and smell really bad. Then you can remove the varnish quite easy with a file or steel wool.
Prepare Can 2:
That does not need to be prepared much. It will just contain water. Remove labels with hot water.

Prepare aluminium distance plates
They will act as a distance between the cans. Depending on what can you use, you might skip those. But I think they also are good to get a more even heat transfer.
  1. Make them 40x40mm, that make them compatible with different TEG-modules. I had to also make 10x10mm chamfer on the corners to fit the flat surface of the cans.
  2. Use fine sand paper or steel wool to make them flat and nice
Assemble Mechanics:
  1. Prepare one side of plate 1 with thermal paste
  2. Place plate 1 on top of can 1 (with thermal paste facing down)
  3. Optional: Prepare plate 1 with thermal paste (depending on what TEC/TEG you use)
  4. Place the TEG module on top of plate 1
  5. Optional: Prepare TEG with thermal paste (depending on what TEC/TEG you use)
  6. Optional: Place a thermal resistor on top of plate 1 if you want to monitor temperature
  7. Place plate 2 on top of TEG
  8. Prepare plate 2 with thermal paste
  9. Place can 2 on top of plate 2
  10. The order is: Can1-Paste-Plate1-Paste-TEG-Paste-Plate2-Paste-Can2
  11. Optional: Add pull springs to hold the cans together, see pictures.
Assemble Electronics:
  1. Connect the two cables on TEG-module to your step-up booster (check polarization)
  2. Connect LEDs to output of step-up booster (check polarization)
I used a soldering iron and screw the cables to a terminal block. The terminal block was glued to can2.

RESULT

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Lit your candles and enjoy! Be careful with the temperature and make sure your TEG-module can handle it!

Output power from TEG at different water temperatures:
30ºC:  0.25W
40ºC:  0.23W
50ºC:  0.22W
60ºC:  0.21W
70ºC:  0.21W
75ºC:  0.22W

It never got over 75ºC with three candles. Water vaporizes at a rate of approx. 40ml/hour.

The efficiency of the booster/voltage step-up measured to 70% (Input=0.23W, Output=0,16W). That is enough to power some LEDs!

Updates:
  • I used the can of water and replaced the heat sink and fan in this project: Smartphone Charger
    I managed to charge my iPhone 4s with 1W power at very low gas output. I could have used only this construction to charge the phone with the gas stove but I didn´t want to mess up my thermal paste with that kind of heat.
  • Once it has started (must exceed 1V), one candle is actually enough to power the LEDs! It will vaporize less water.
  • If you don´t have fire, then just take a glass of hot water and fill the upper can with ice. That gives light for 30 min!