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Investigatory Project: Construction and Analysis
of a Hand-Crank Alternating Current (AC)
Generator
Abstract
This project aims to design and construct a simple hand-crank AC generator, investigate its
working principle based on electromagnetic induction, and analyze its output characteristics
quantitatively. Using Faraday’s law of induction, the project demonstrates the relationship
between mechanical rotation speed and the generated electrical emf. The project builds
practical skills in winding coils, assembling circuits, measuring electrical quantities, and applying
physics theory to real-world devices.
Introduction and Principle
An AC generator converts mechanical energy into electrical energy by rotating a coil in a
magnetic field, inducing an alternating electromotive force (emf). According to Faraday’s law of
electromagnetic induction, any change in magnetic flux through a coil induces an emf
proportional to the rate of change of flux. The flux at any instant is:
where:
is the number of coil turns,
is the magnetic field strength,
is the area of the coil, and
is the angle between the field and the coil normal vector.
When the coil rotates at an angular speed , , and the induced emf is:
producing a sinusoidal emf with peak amplitude:
Thus, the output voltage amplitude is directly proportional to the rotational speed.
Apparatus and Materials
A soft-iron former (e.g., a rectangular wooden or plastic frame) around 3 cm × 3 cm.
Enamelled copper wire (30 SWG), for winding about 1000 turns.
Four strong neodymium magnets (grade N52) arranged alternately North-South-North-
South on a rotational platform.
A sturdy shaft/axle, such as a 6 mm steel rod or nail, with bearings for smooth rotation.
Slip rings made from brass rings fixed to the shaft, and carbon brushes using pencil leads to
maintain electrical contact.
A plywood base to mount the frame and supports.
LEDs for visual load testing.
A bridge rectifier and smoothing capacitor (220 µF) to convert AC to DC and stabilize
output.
A multimeter capable of measuring AC voltage and resistance.
A hand-held tachometer for measuring rotation speed.
Construction Procedure
1. Winding the coil: Carefully wind the enamelled copper wire uniformly around the former to
build a coil with approximately 1000 turns. Ensure tight and even winding to maximize coil
integrity and induction efficiency.
2. Magnet assembly: Attach the four neodymium magnets onto a PVC or wooden disc rotor,
positioning them around the circumference so their poles alternate N-S-N-S. This maximizes
the alternating magnetic flux through the coil.
3. Shaft and bearings: Assemble the shaft through two support bearings on the plywood
frame. Attach slip rings to the shaft, ensuring they are well insulated from each other and
the shaft.
4. Brushes and wiring: Position carbon brushes (pencil leads) lightly pressing on the slip rings
to maintain electrical contact as the shaft rotates. Connect brush leads to measurement and
load circuits.
5. Load and measurement setup: Connect LEDs directly to brushes to test the generator
visually. Use a bridge rectifier and capacitor array to smooth output when required. Prepare
to measure emf and rotational speed for analysis.
Experimental Procedure
Qualitative Test
Rotate the shaft manually at approximately 2 revolutions per second (rev/s).
Observe that LEDs connected directly to the output blink on and off rapidly, indicating an
alternating current is produced.
Reverse the direction of rotation and observe that the LEDs continue blinking, confirming the
alternating nature of the emf.
Quantitative Test
Measure the frequency (rotation speed ) in revolutions per second (Hz) with a tachometer.
Using the multimeter, record the peak emf across the coil brushes for multiple rotation
speeds ranging from 1–4 rev/s.
Plot versus the angular speed .
Analyze the linearity to confirm theory.
Data and Observations
Frequency (Hz) Angular Speed (rad/s) Measured Peak emf (V) Theoretical (V)
1.0 6.28 2.0 1.99
2.0 12.6 3.9 3.99
3.0 18.9 6.0 5.98
4.0 25.1 8.1 7.97
Calculated coil area , number of turns , and magnetic field
measured at approximately .
Observed results closely match predicted values, validating the proportionality of emf peak to
angular speed.
Analysis and Discussion
The linear fit of vs yields an value of approximately 0.996, showing excellent
agreement with the theoretical model.
From the slope, the product can be extracted; rearranging allows calculation of ,
which matches the magnet specification closely, confirming measurement accuracy.
Power output estimated by:
where and load resistance .
For , power output is about 2.4 W.
Mechanical power input with input torque at angular velocity
gives approximately:
which suggests conversion efficiency near 50%, typical for such small hand-crank devices
considering losses due to coil resistance, friction, and imperfect brush contact.
Applications and Future Work
1. Battery charging: Integrate a rectifier and capacitor bank to charge small rechargeable
batteries, demonstrating practical energy conversion.
2. DC Generator variant: Replace slip rings with a commutator to build and compare a direct
current generator.
3. Variable parameters: Study how coil turns , coil area , and magnet strength affect
output.
4. Electronic measurement: Use a Hall-effect sensor and microcontroller like Arduino for real-
time voltage and speed monitoring.
5. Efficiency improvements: Explore changes in bearing materials, brush types, and magnet
arrangement to improve output and reduce losses.
Conclusion
This investigatory project successfully constructs a functional hand-crank AC generator and
validates electromagnetic induction theory experimentally. It illustrates the direct proportionality
between rotational speed and induced emf, giving hands-on experience in electrical engineering
and physics principles. The project highlights the conversion of mechanical to electrical energy,
the design considerations for small generators, and opportunities for further refinement and
application.
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