SHAKER FLASHLIGHT

Shaker Flashlight

Most flashlights are battery powered. But this shaker flashlight is not like most flashlights; it does not need batteries. Instead, you – and a little elbow grease – provide the power. You shake it for a minute and voilà it is ready to light the way.

The light passing through a lens for this flashlight comes from an LED (light emitting diode). The advantage of an LED is that it is very efficient and doesn't take much electricity for an LED to make a lot of light.


The power for the LED comes from a coil of wire and a strong magnet in a tube. When you shake the flashlight, the magnet slides back and forth inside the tube. Each time the magnet slides through the coil, the magnet generates a pulse of electricity in the coil.


Now, you could simply connect the coil directly to an LED and the flashlight would work. However, there would be two problems. First, you would have to shake the flashlight as you are using it, which would make the flashlight tough to use. Second, the LED would be turning on and off with each shake.

To solve this problem, the flashlight also contains a part called a capacitor. A capacitor acts like a battery, but it has one big advantage over a battery. A capacitor charges instantly. With just a few shakes, the capacitor holds enough charge to light the LED. Then an on/off switch lets you connect the capacitor to the LED to light it up. So you shake the flashlight for a minute to charge up the capacitor. Then you flip the switch to let the energy stored in the capacitor light the LED.


There's one other necessary part - the bridge rectifier. It takes the electricity coming from the coil and flips it so it's always going in the right direction. Consider this - when the magnet slides through the coil one way, it creates a pulse of positive electricity. When the magnet slides the other way, it makes a negative pulse. The rectifier converts the negative pulse to a positive pulse, so the capacitor can store all the positive pulses.