Friction Flashlight

Problem I am trying to solve

A flashlight is an essential tool that is part of any a natural disaster preparation kit. However, flashlights that are dependent on batteries cannot function if the battery runs out of life. I became aware of the importance of a flashlight during my Boy Scouts camping trips and also the need to use it sparingly to save battery life. This led me to the question: what use is a flashlight if it runs out of battery? And how can it be made battery independent?

Goal of my project

To construct a flashlight that converts heat generated from body friction into enough thermoelectric energy in order to power a LED in a flashlight. The other objectives of this project are to test if:

  1. The temperature difference between the palm of the hand and mediums such as air and water can be harnessed to produce enough electricity to power a LED bulb

  2. Which of the natural resource air or water would be a better cooling system for the flashlight and make it more usable in terms of light intensity, duration of light, and portability?

Research and development

Use of Peltier Tiles

Peltier tiles are made of semiconducting material on which:

  1. A temperature difference gives rise to an electric potential (Seebeck Effect)

  2. An electric potential creates a temperature difference (Peltier Effect)

Which property of Peltier tiles is used in this experiment and why?

The Seebeck effect is utilized since my project is based on having a temperature difference to produce enough electrical potential to light an LED. The Seebeck effect is a process in which a temperature difference between two dissimilar electrical conductors or semiconductors produces a voltage difference between the two substances as temperature gradient causes charge carriers in the material to diffuse from the hot side to the cold side.

How will the Peltier tiles light an LED?

Since Peltier tiles can not generate enough voltage and current to light an LED by themselves, the current must be amplified through an oscillator circuit and a transformer.

Picture 1

Picture 2

Picture 3

Picture 4

Components and Construction of the flashlight using water

  1. First an Aluminum rectangular tube is designed and welded on all sides with a larger opening at the bottom to fill with water.

  2. A threaded Aluminum nut was used to seal the bottom, so that water does not leak as show in picture 1

  3. Peltier tiles were attached on 2 side of the tube for greater contact with hand or arm-pit surface area as shown in picture 4

  4. Each of the 2 sides of Peltier tiles are connected to an amplification circuit known as LTC3108 as shown in picture 2

  5. An alternate to the amplification circuit can also be used as shown in picture 3 using n-channel MOSFET, common mode choke, resistor and protoboard. This is cheaper than the LTC3108.

  6. The amplification circuit is then connected to the LED bulbs as shown in picture 2

  7. After rubbing your hands to create heat due to friction, the flashlight can be held in the palm of the hand wrapping the Peltier tiles


Water filled flashlight at the top. Air filled flashlight at the bottom.

2 flashlight prototypes : Water filled and Air filled

The flashlight at the bottom is the one air filled chamber built by hollowing out a regular flashlight to create a heat sink for the Peltier tiles. This is an existing prototype which I decided to replicate and improve upon by creating a custom Aluminum tube and fill it with water to be used as the heat sink. The water filled flash light although a bit unwieldy generated a much more powerful light.

Conclusion

After testing my second prototype numerous times, I consider my invention an overall success because it had met all of the following testing criteria:

  1. The Flashlight produced 50 lux of intensity with just 2 LED bulbs

  2. The Flashlight was easy to carry and weighed 350 grams

  3. The Flashlight took less than 2 seconds to turn on

  4. The Flashlight stays on for as long as it is held within the palm of your hands

  5. When the Flashlight is held for 30 seconds - the light stays on for another 30 seconds

  6. The flashlight took less than $50 to construct

  7. The flashlight was sealed tightly without any room for leaks

However, my first prototype works better with air since it is small, compact and more portable. But since it is not leak proof (with water) and had only one LED bulb attached, it is good for using as a flashlight where dim lighting will serve the purpose.

Recognition

2nd Award, Physical Science and Engineering Category

Selected participant to Synopsys science fair

STEM certificate of recognition and ceremony from Mayor of Sunnyvale Larry Klien

Presentation materials and references