Faraday Flashlight:
The linear induction, Faraday flashlight, or "shake flashlight" is another type of mechanically powered flashlight. It has been sold in the US beginning with direct marketing campaigns in 2002.
This design contains a linear electrical generator which charges a batterylike supercapacitor when the flashlight is shaken lengthwise. The battery or capacitor powers a white LED lamp. The linear generator consists of a sliding rare earth magnet which moves back and forth through the center of a solenoid (a coil of copper wire) when it is shaken. A current is induced in the loops of wire by Faraday's law of induction each time the magnet slides through, which charges the capacitor through a rectifier and some other circuitry. The best designs use a supercapacitor instead of a rechargeable battery, since it will not reach end-of-life as quickly as a battery. This, along with the long-life LED lamp which does not burn out like an incandescent bulb, can give the flashlight a long lifetime, making it a useful emergency light. A disadvantage of many current models is that the supercapacitor cannot store much energy, limiting the operating time per charge. In most designs, vigorously shaking the light for about 30 seconds may provide up to 5 minutes of light, though the light may become dim after 2 or 3 minutes. Shaking the unit for 10 to 15 seconds every 2 or 3 minutes as necessary permits the device to be used continuously. It is often viewed as a toy, or an emergency backup for other flashlights. Fraudulent counterfeit versions of these flashlights have been sold, most of which incorporate coin-sized non-rechargeable lithium cells "hidden in plain sight". The expensive supercapacitor is omitted from the internal components. In some of these fake designs, the "magnet" is not a magnet or the coil is not connected, and no electricity is generated when the device is shaken. These fraudulent flashlights eventually become useless, since their internal batteries cannot be recharged or replaced, and the case is often permanently glued shut. |
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