Simple Squeeze Led Flashlight

by Berto Aussems in Circuits > Electronics

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Simple Squeeze Led Flashlight

Nearly 200 years ago Michael Faraday has discovered electromagnetic induction. A changing magnetic field produces an electric field in a coil. Today, there is a simple way to gain electricity from a relay and a strong magnet. I call this kinetic generator the RattleGen because, by pressing the lever of the relay quickly (the only moving part!) it makes a rattling noise. This electro generator is nearly solid state and produces enough energy to power a LED. Compared to 100 years of dyna flashlight based on a rotating generator, the RattleGen squeezer is nearly indestructible because of the few mechanical parts. This Ibble is part of an ongoing investigation for smallscale, batteryless energy harvesting.

The Circuit

The electronic circuit is very elementary as you can see here. I use a resistor to reduce the LED current. Why do I call it an enhanced RattleGen? Well, doing experiments with a relay and a magnet, early 2013, I discovered on my oscilloscope screen a useful voltage. A ceramic magnet was put agains the relay coil. Pressing the contact lever made energy, as you can see in the video. A bit later I placed a strong neodymium magnet on the contact lever of the relay. As a result, the voltage was peaking 2 times higher on the screen. Then I took a small relay; the output peak voltage of the relay coil was 35 volt, without load. After the bridge rectifier the voltage peaks are smoothed by a condenser. To test the small generator I use an ultra bright LED. Take care; depending on the iron of the relay coil a stronger magnet will not give more flux, this because of the saturation. If you make the gap bigger between the contact lever and the relay coil the output will enhance. The magnet functions also as tension spring. The lever jumps back after pressing. This saves again one mechanical part. Before the LED light up you have to press the contactlever several times. The capacitor of 1000 microfarad 16 volt has to charge first.

Some Remarks

Later, I will publish the test data at my website's energy blog. More experiments are necessary to optimize the parts; the results are already promising. This kinetic energy harvester can compete with the output of existing piezo generators and is much cheaper. Soon more applications will follow, with the RattleGen as starting point. My intention is that also people in developing countries can easily build this squeeze flashlight. And don't forget the young makers. Beside de fun of making this project, it shows them also one of the basic principles and needs of our present civilisation; electricity and light.