Motor Demonstration Using a Hand-Cranked Genecon
NAVAL ACADEMY ANNAPOLIS MD DEPT OF PHYSICS
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A Genecon is an inexpensive hand-cranked dc electric generator. You can use it to charge a one-farad supercapacitor. 1 If you stop cranking the handle, the capacitor will discharge, sending a current into the Genecon and thereby causing the handle to start turning as an electric motor. How does the current direction compare before and after you stop cranking the handle How does the direction of the turning of the handle compare before and after you stop cranking the Genecon A Genecon has a set of internal gears, coils, and commutators some of which can be seen inside the translucent case in Fig. 1 that generates an approximately steady dc voltage for a given rate of cranking of the handle. To visualize the degree of rectification, connect the Genecon across a 51-V resistor and then connect the ends of the resistor to an oscilloscope with a 1-MV input impedance.2 A photograph of the resulting trace is presented in Fig. 2 while the crank is being turned at a rate of about 1 Hz. Riding on an average dc voltage of approximately 3 V is a superimposed ripple of 1 V peak-to-peak having a 2-ms period. As one turns the handle faster, the dc voltage, ripple frequency, and ripple voltage all increase linearly,3 as the careful measurements in Table I verify. The ripple is fast enough that it gets averaged out on the timescale of seconds of the demonstrations presented here and it therefore can be ignored.
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- Electricity and Magnetism