Introduction: Fire Power: Electricity From Heat

Lego created a robotics contest that focused on the advance of technology in students at schools and other organizations. This contest is known as FLL (First Lego League) and uses Lego's robot kit- Mindstorms. Each year, a theme is chosen to correlate with the robot and the other aspects of the contest. This year's theme is titled "Natures Fury", and it involves natural disasters. A table is set up with "missions" (also made of Legos and relating to natural disasters) that must be completed by a robot built and programmed with Mindstorms.

As well as the robot part of the contest, a project or innovative solution must also be built that solves a problem in a natural disaster. This Instructable is a collaboration of our efforts on the project and will serve as a means to present our information to judges at the FLL competition that we will be attending this month.

The grading rubric used to judge the project design states that the project should be "shared with multiple individuals or groups who may benefit." What's a better place to share than on Instructables? We would like to thank all of the viewers like you in advance for the support and the helpful feedback you will surely give.

If you would like to read about the process in which we decided to build this project, then follow along, but if you want to skip right to the building instructions jump to Step 2.

Please do not forget to vote for this Instructable in the contests if you like it. Thanks

It has finally warmed up (from -10), so I was able to get outside and test for voltage and amperage on the project. Please refer to step 4 (Use Your Stove) for more details.

FLL Website-
FLL Rubric-

Step 1: The Problem

First, we chose a community and natural disaster to study. From there, we selected a common problem in the disaster. Here is a diagram of how we narrowed down the broad topic to our project idea.

Community: Northern Wyoming > Storm: Thunderstorm > Common Problem: Power outages > a need for electricity > using available resources > fire > HEAT POWERED BATTERY CHARGER!!!

As you can see, a long process occurred between choosing a community and selecting a project. One of the many reasons that we selected power outages as a major problem was because we felt that it was a somewhat overlooked topic. In thunderstorms, many people worry about the immediate consequences (lightning, heavy rain) but forget about the prolonged problems. Power outages can last anywhere from hours to weeks. That is weeks without power. Say goodbye to phones, lights, heaters, and all electronic appliances/devices.

For our project we selected an electricity generator that uses heat to produce electricity (more on that later) because 1.) You can recharge batteries on essential things such as flashlights, radios, and phones. 2.) We killed a couple birds with one stone with this project... While you wait for your batteries to charge, you can soak up the warmth of your heat source, cook food, and have a source of lighting.

Now we realize that there are a few amazing solutions already out in the wild that could potentially solve this problem, but we still feel that our project is quite useful.

Solar power/chargers- Solar power can still be quite expensive, despite the fact that prices have dropped greatly in recent years. Also, the sun is not out all of the time. What if you would like to generate electricity after dark or when the sky is overcast?

Hand crank devices- These are great, but would be potentially harder to build and are already readily available to many people. We wanted to create a project that was innovative.

Wind generators- Hey, the wind doesn't blow all the time.

Biolite Camp Stove- We also found that a commercial version similar to our was project available. However, it only charges usb devices, and it is quite expensive at $129.95.


Step 2: Introduction/Materials

As you have probably gleaned from the previous steps, this project has something to do with using heat to generate electricity to charge batteries. This is all true, but there is much more in the science of the project than what first appears. Even for someone completely oblivious to all of the little components that make up our everyday electronics, our goal is for this project to be easy for all to build in case of a disaster.

The entire project can be built for roughly $30.

The key component of this entire project is a device called a Peltier Module. Also known as a TEC or a thermoelectric cooler, this small, 40x40mm, white ceramic square is really where the magic happens. A peltier module is normally used in small cooling applications such as wine coolers and novelty pop chillers.
A peltier module basically consists of a sandwich of a ceramic plate, a thin metal film, a semiconductor, another thin metal film, and finally an additional ceramic plate. When DC electricity is applied to the two wires protruding from the device, it pulls in heat from one side to the other; one side of the device gets cooler while the other gets hotter, creating a temperature differential. This is useful for applications such as cooling.

However, if a temperature differential is placed on the peltier, such as one side being placed over a heat source, and the other side cooled, electricity is generated!!! This process is known as the Seebeck Effect. (for further information on the science behind the peltier module, please check out the sources listed at the end of this step. This is the principle that we will be using to generate electricity.

Here is a list of parts that are needed to construct this project.


Step 3: Build!!!

The first step for building is to solder the circuit together. If wanted, you can prototype the circuit on a breadboard before permanately soldering. Please reference the above diagram created in Fritzing to help with the soldering process. If you need help soldering, a very thorough source can be found at:

To attach the peltier module to the heat sink, we cut an inch hole in the lid of a large can. We then centered the peltier over the hole and sandwiched it between the heat sink and the lid. We used screws and soft wire to securely fasten them together. Another option to attach the heat sink to the peltier is to use thermal compound, a sort of thermally conductive glue. Lastly, we shrunk heat shrink tubing over the peltier's wires to shield them from the heat. For the convenient carrying case we cut to fit a square out of the small plastic box and screwed the spring terminals into the box. After screwing it in, we proceeded to solder in the appropriate wires and components. In addition, we printed out labels and glued them to the spring terminals for easy connecting.

After reading about this device, you are probably curious about how the circuit works. Here is a basic rundown of the workings. First, the Peltier module produces electricity due to the temperature difference. On one side of the module extreme heat is placed, while on the other lies a heat sink. See all of those wavy bits of metal? These aren't just for beauty, they are designed to maximize the surface area for heat to be dissipated, cooling this side of the peltier. This is similar to the ridged metal surrounding the engine on a motorcycle.

Next, the electricity reaches the diode in the circuit. A diode only allows the electricity to flow one way- towards the battery. If a diode was not placed in the circuit, than the battery would drain itself by putting electricity into the peltier module and creating the cooling effect described earlier. Finally, the electricity reaches the battery and, if the voltage is higher than that of the battery, will began to charge it.


Step 4: Use Your Stove

To use the device, simply plug the red peltier wire into the voltage input (labeled VIN) spring terminal, and the black peltier wire into a ground (GND) terminal. Finally, insert the positive wire of the battery into the voltage out (VOUT) terminal, and the negative wire into the other ground terminal. It is very important to note polarity when connecting the wires. Place the peltier and heat sink over a heat source with the lid facing down. Once the peltier has heated to a high enough temperature, a suitable amount of electricity can be generated to charge the battery. To ensure that the device is working properly, first measure the voltage of the rechargeable battery at the beginning of charging time. After a little while, measure the battery again. You should find that the battery voltage increases!

Heat source ideas:
Although there is many different possibilities to heat your generator with, we have found that a rocket stove works quite well. A rocket stove is essentially some kind of a container (such as a tin can) with a hole poked into the bottom so that air can flow in. A fire in the rocket stove is very easy to light, and, after lit, becomes extremely hot. For instructions on how to build your own rocket stove check out this instructable:
For fuel, we made some fire starters using egg carton, wax, and dryer lint. They work marvelously. Check out this instructable:

I have tested the stove and recorded various readings concerning volts and amps. Here are my findings:

Heat Source: rocket stove with direct flame
Load: 1.2 volt "D" rechargable battery
Air temperature (this will effect the temperature differential): 14 degrees Fahrenheit
Volts produced: 2.2-3.2
Amperage: 350-400 mA
Watts: .77-1.28 watts

Step 5: In Closing...

Thank you to all of the viewers of this instructable. We encourage you to try this project. If you need any help or have any suggestions just post a comment below. Our main goal was to solve a problem in a thunderstorm. We feel that this has contributed to the many already available resources to prepare for a power outage. Now that the project is completed, I think that we have realized that this project could not only be useful in natural disasters, but also for camping and just getting free electricity. Thanks for viewing and good luck building.

Here are some ideas for future updates to the design.

  • a battery charge-status monitor
  • USB compatibility
  • a switch to turn the charging circuit on and off
  • a more elegant design
  • A circuit built into a stove
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