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DiscoverCircuits.com -- Hobby Corner
Last Updated on:
Tuesday, November 29, 2011 08:14 PM
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Shake to Charge Flashlight -- Page
2
designed by David A. Johnson, P.E. |
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Reed Relay to turn the
device on & off |
Super Capacitors
used to store energy |
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light from this Reed Relay is weak. It took about a minute of vigorous shaking to
get the first bit of light from it. After a few more minutes of shaking, the
capacitor was fully charged. It might be okay for finding your keys in the dark but
not much more. |
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The complete schematic for this device is shown below.
A few things should be pointed out. First, they use some very cheap 1N4001
diodes in the bridge rectifier circuit instead more efficient Schottky diodes.
They also use a small 0.5 Farad cap with a 5.5 volt rating. I noticed that that
this kind of super capacitor was originally designed for maintaining data in memory
chips and has a rather high internal equivalent series resistance. This reduces
the overall efficiency, since the device can’t be charged or discharge very quickly.
Some of the power that should go to the LED will end up being dissipated inside the
capacitor. Better super capacitors do exist. |
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Click
on Drawing Below to view PDF version of Schematic |
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