There is an introduction about working principle of alternator in the alternator principle courseware, but the simple principle model has low power generation efficiency, the rotating coil is hollow, the space is air, and the magnetic resistance is extremely large, resulting in low spatial flux density. As we all know, the induced electromotive force of a moving wire depends on the magnetic flux scanned per unit time. When the wire length and the moving speed are constant, the induced electromotive force is proportional to the magnetic flux density of the scanning space. The method of increasing the magnetic field potential is very limited, a simple method is to turn the space into a material with high magnetic permeability, which is to build a rotor core with high magnetic permeability and wind the coil around the rotor core. Air gap is so narrow left between poles that the magnetic resistance of the entire magnetic circuit is greatly reduced, and the magnetic flux density through the rotor core is increased by a hundred times. The magnetic circuit of the generator model is shown in figure 1.
Figure 1 --Magnetic circuit of generator model
The following is a practical generator model, with the magnetic circuit described above, the rotor is made of high magnetic permeability material. Since the magnetic flux passing through the rotor is constantly changing, for preventing eddy current from increasing loss, high permeability silicon steel sheets are stacked, as shown in the left part of figure 2.
Figure 2--Rotor core and coil frame
Rotor coil is wound around the rotor core, for the convenience of winding and reinforced insulation, the coil frame is mounted on the rotor core, and made of an insulating material, as shown in the right side of figure 2. There are four coil frames inserted into the rotor core from both sides of the core axial direction, as shown in figure 3. The red arrow indicates the insertion direction.
Figure 3--Inserting the coil frame into the rotor core
The rotor coil is wound with an enameled wire in the coil frame neatly, as the same number of turns and the winding direction. Connect two coils into one coil, and connect two outlet ends of the coil to the two slip rings, The slip ring device (collector ring) is mounted on the rotating shaft through two insulating brass rings, seeing figure 4.
Figure 4—Rotor with finished winding coils
The rotor is mounted on the base through a bearing bracket, and a pulley is installed at one end of the rotor, for that an external power drives the rotor of the generator to rotate through the pulley. Install two brushes made of brass on the base, and the brush is elastic against the slip ring to ensure good contact, showing in figure 5.
Figure 5--Generator rotor mounted on the base
The magnetic field of the generator model is generated by permanent magnets, and the permanent magnet material with the best magnetic properties can be selected from NdFeB, as well other strong magnets as options. The permanent magnet bipolar is in close contact with the two stator poles, the magnetic pole is made of a ferromagnetic material with good magnetic properties, seeing figure 6 below.
Figure 6—Permanent poles
The stator pole is mounted on the base though a magnetic pole bracket, showing in figure 7.
Figure 7--Installing a permanent magnet stator
Mount the stator poles together with the rotor on the base, seeing figure 8, and connect the bulb to the terminal of the brush. Then the permanent magnet generator model is assembled.
Figure 8—Single phase Alternator model
Watch the animation of this generator model. For the sake of clarity, the generator rotates very slowly.
Single phase permanent magnet alternator model animation
The most common generator models used for demonstrations in science and teaching are usually permanent magnet generators of this type.
