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Last Updated on: Wednesday, October 18, 2017 05:04 AM

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Shake to Charge Flashlight -- of 4
designed by David A. Johnson, P.E.

Have you ever wondered how some of those “Forever” flashlights work?  These devices appeared several years ago and are often sold on some TV home shopping networks.  A company in Colorado:

(Applied Innovative Technologies www.appliedinnotech.com) made the original device but knock-offs from China are now popping up everywhere.  That fact that some of those devices don’t even work will be a topic for later discussions.

Circuit Circuit shake flashlight modified by David Johnson
Shake & Charge Flashlight

I bought one of the cheaper counterfeit devices and took it apart.  There were no manufacture or country of origin markings anywhere on the device.  I traced out the circuit.  It is not much more than a coil of wire, a magnet, a bridge rectifier, super capacitor and white LED.  A small magnet attached to an on/off switch is used to turn on the light by activating an internal reed relay.  This method maintains a tight weatherproof seal and is about the only thing I found cleaver about the device.  Shaking the thing forces a large magnet slug to slide back and forth inside the body of the device. Two rubber stoppers cushion the magnet at each end. In some other more expensive shake to charge flashlights, they use two more magnets as contact-less bumpers.
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