Old alternators may be obtained for low prices at automobile wrecking yards. Many yards have alternators already removed from the automobile, for your convenience. I do not recommend paying full price for a new alternator, as used units cost far less money and function just as well for the purposes of this experiment.
I highly recommend using a Delco-Remy brand of alternator. This is the type used on General Motors (GMC, Chevrolet, Cadillac, Buick, Oldsmobile) vehicles. One particular model has been produced by Delco-Remy since the early 1960's with little design change. It is a very common unit to locate in a wrecking yard, and very easy to work with.
If you obtain two alternators, you may use one as a generator and the other as a motor. The steps needed to prepare an alternator as a three-phase generator and as a three-phase motor are the same.
CROSS-REFERENCES
Lessons In Electric Circuits, Volume 1, chapter 14: "Magnetism and Electromagnetism"
Lessons In Electric Circuits, Volume 2, chapter 10: "Polyphase AC Circuits"
LEARNING OBJECTIVES
Effects of electromagnetism
Effects of electromagnetic induction
Construction of real electromagnetic machines
Construction and application of three-phase windings
SCHEMATIC DIAGRAM
An automotive alternator is a three-phase generator with a built-in rectifier circuit consisting of six diodes. As the sheave (most people call it a "pulley") is rotated by a belt connected to the automobile engine's crankshaft, a magnet is spun past a stationary set of three-phase windings (called the stator), usually connected in a Y configuration. The spinning magnet is actually an electromagnet, not a permanent magnet. Alternators are designed this way so that the magnetic field strength can be controlled, in order that output voltage may be controlled independently of rotor speed. This rotor magnet coil (called the field coil, or simply field) is energized by battery power, so that it takes a small amount of electrical power input to the alternator to get it to generate a lot of output power.
Electrical power is conducted to the rotating field coil through a pair of copper "slip rings" mounted concentrically on the shaft, contacted by stationary carbon "brushes." The brushes are held in firm contact with the slip rings by spring pressure.
Many modern alternators are equipped with built-in "regulator" circuits that automatically switch battery power on and off to the rotor coil to regulate output voltage. This circuit, if present in the alternator you choose for the experiment, is unnecessary and will only impede your study if left in place. Feel free to "surgically remove" it, just make sure you leave access to the brush terminals so that you can power the field coil with the alternator fully assembled.
I highly recommend using a Delco-Remy brand of alternator. This is the type used on General Motors (GMC, Chevrolet, Cadillac, Buick, Oldsmobile) vehicles. One particular model has been produced by Delco-Remy since the early 1960's with little design change. It is a very common unit to locate in a wrecking yard, and very easy to work with.
If you obtain two alternators, you may use one as a generator and the other as a motor. The steps needed to prepare an alternator as a three-phase generator and as a three-phase motor are the same.
CROSS-REFERENCES
Lessons In Electric Circuits, Volume 1, chapter 14: "Magnetism and Electromagnetism"
Lessons In Electric Circuits, Volume 2, chapter 10: "Polyphase AC Circuits"
LEARNING OBJECTIVES
Effects of electromagnetism
Effects of electromagnetic induction
Construction of real electromagnetic machines
Construction and application of three-phase windings
SCHEMATIC DIAGRAM
An automotive alternator is a three-phase generator with a built-in rectifier circuit consisting of six diodes. As the sheave (most people call it a "pulley") is rotated by a belt connected to the automobile engine's crankshaft, a magnet is spun past a stationary set of three-phase windings (called the stator), usually connected in a Y configuration. The spinning magnet is actually an electromagnet, not a permanent magnet. Alternators are designed this way so that the magnetic field strength can be controlled, in order that output voltage may be controlled independently of rotor speed. This rotor magnet coil (called the field coil, or simply field) is energized by battery power, so that it takes a small amount of electrical power input to the alternator to get it to generate a lot of output power.
Electrical power is conducted to the rotating field coil through a pair of copper "slip rings" mounted concentrically on the shaft, contacted by stationary carbon "brushes." The brushes are held in firm contact with the slip rings by spring pressure.
Many modern alternators are equipped with built-in "regulator" circuits that automatically switch battery power on and off to the rotor coil to regulate output voltage. This circuit, if present in the alternator you choose for the experiment, is unnecessary and will only impede your study if left in place. Feel free to "surgically remove" it, just make sure you leave access to the brush terminals so that you can power the field coil with the alternator fully assembled.
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