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Dr. Mabuse
Septic Fiend
Sweden
9688 Posts |
Posted - 02/24/2013 : 14:56:25 [Permalink]
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Actually, it really is that simple. A few coils attuned to those EM-frequencies which are most energetic, like the 50Hz mains in Europe. Acting like an antenna the coil generate a small amount of AC current which could be rectified to charge a capacitor.
A few obstacles are the P-N threshold of the diode being relatively high (0,7V), but there are alternatives to that. Shottky diods have lower threshold (~0,3V), and there are some mos-fet transistor couplings which can serve as close-to-zero threshold diodes.
I've toyed with the idea of making a wall clock or an artsy wall-display perpetuum mobile powered by such a device. But I never got it done because I had other projects I felt more urgent.
There are antennas to the older generation cell-phones which as a LED which flashes when the phone is connecting for a call (or simply exchanging data with the cell tower). Those work on the same principle as the battery charger.
Charging an AA-battery within 24 hours will require close proximity to a highly radiating source though.
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Electromagnetic Harvester for Mobile Devices
