link to 6 homemade electrical generators page

DC CONVERTER AND ELECTRICAL STORAGE
FOR SHAKE-A-GEN

This simple device uses a few components to rectify the alternating current (AC) from the shake-a-gen, store it in a capacitor and convert it into a steady direct current DC. The output can be used to run a low power device. It is also wired to an LED which lights as the generator is moved and also for a little while afterwards. An LED can also be wired across the generator connections so that both the AC and smothed DC power can be observed.

storage device

Picture showing the prototype storage device. A printed circuit board (PCB) construction was used but the circuit is so simple that any construction technique could be used (even just wiring the components together directly).

HOW IT WORKS

The circuit uses diodes to switch the AC voltage produced by the generator into a DC voltage. A simple bridge rectifier is made up using 4 germanium diodes. These are better than the more common silicon diodes as far less voltage is dropped across them (about 0.1V as compared to 0.5V for silicon diodes) and so there is less power loss. Only two diodes are ON at any one time and so rougly 2 x 0.5 V would be lost on the output in a circuit containing silicon diodes. The voltage from the bridge rectifier is DC but very pulsed. The capacitor stores up this pulsed voltage and smooths it out. The smothed voltage then lights an LED and can be used to power a low voltage, low current circuit. The circuit produces about 2-3V on the simple shake-a-gen (hence the need for low voltage drop germanium diodes).

Note: all the components need to be wired correctly in the circuit for it to work but it does not matter which way the shake-a-gen is connected.

circuit diagram

The circuit diagram for the shake-a-gen storage device

PARTS LIST AND TOOLS
4 x OA91 germanium diodes
1 x 10,000 uF electrolytic capacitor (16V)
two LED's (red and yellow say)
1 x 1000 ohm resistor
1m of twin wire (bell wire) to go from generator to the circuit
soldering iron and solder

FURTHER WORK
1) remove the LED across the shake-a-gen for best results in this circuit

2) try making a larger shake-a-gen with a far bigger magnet. Can you make a gen that will produce 6-9V to run a radio ?

3) Can you fix the gen and storage device on a backpack and use it as a jogging light so that people can see you when out on a dark night ?

4) can you find a source of continious vibration or movement which will allow the gen and storage device to make electricity for a long time. If so can you use it to charge a rechargable battery ?

Acknowlegments
I would like to thank NESTA for the continued support with my Fellowship which is giving the valuable space, time and resources to follow up ideas and most importantly to dream up new ones.

link to 6 gens page

THE CREATIVE SCIENCE CENTRE
Dr Jonathan Hare, Room 3R253, Chichester Bldg. CPES, The University of Sussex
Brighton, East Sussex. BN1 9QJ. 01273 606755 x3171

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