This project, as illustrated in Figure 1, will demonstrate the basic construction and operation of an induction motor.
This project is a simplified version of a permanent capacitor split-phase induction motor. To simplify, we mean the coils only require a few hundred turns of wire instead of a few thousand; thus, making it easier to wind. However, a larger model using a few thousand turns is impressive.
There are two parts lists to choose from depending upon the availability of 120 VAC or 220 VAC. Choose the one for your location.
AC power source: 120 VAC
AC power source: 220 VAC
This set of instructions is for the 120 VAC version.
Step 1: Build two stator coils for use in the schematic diagram of Figure 2 by winding approximately 440 turns of #32 AWG (American wire gauge) enameled magnet wire over a one-inch long segment of a slightly longer section of 1.75-inch diameter toilet paper tube.
First, tape the beginning lead near the end of the tube so that the windings will cover and anchor the tape. Leave a few inches of magnet wire for the leads.
Step 2: Then, to avoid counting the turns, close-wind four layers of magnet wire over a one-inch width of the tube, as illustrated by the tube cutoff image in Figure 2 (b).
Note: Do NOT cut the final width of the cardboard tube until the winding is finished. Close wind a single layer.
Step 3: Tape or cement the first layer to prevent unwinding before proceeding to the second layer. Though it is possible to wind additional layers directly over existing layers, consider applying tape or paper between the layers, as shown in Figure 2 (b).
Step 4: Repeat this process until four layers are wound, and then glue the windings in place.
Note: If close winding four layers of magnet wire is too difficult, scramble wind 440 turns of the magnet wire over the end of the cardboard tube. However, the close-wound style coil mounts more easily to the baseboard. Keep the windings within a one-inch length.
Step 5: Cut the finished winding from the end of the cardboard tube with a razor knife allowing the form to extend a little beyond the winding.
Step 6: Strip the enamel from an inch off the ends of the pair of lead wires with sandpaper or wire strippers.
Step 7: Splice the bare ends to heavier gauge insulated hook-up wire. Solder the splice. Insulate with tape or heat-shrink tubing. Secure the splice to the coil body. Then proceed with a second identical coil.
Step 8: Refer to both the schematic diagram and the illustration for the assembly of your completed coils to the system.
Note from Figure 1 that the coils are mounted at right angles to each other. They may be cemented into an insulating baseboard like wood.
Step 9: Wire the 25 W lamp in series with one coil, as shown in Figure 2 (a). This limits the current flowing through the coil. The lamp can be substituted by an 820 Ω power resistor.
Step 10: Wire the capacitor in series with the other coil, as shown in Figure 2 (a). The capacitor also limits the current through the coil. In addition, it provides a leading phase shift of the current with respect to voltage.
Step 11 (Optional): The schematic and illustration show no power switch or fuse. Add these, if desired.
The rotor must be made of a ferromagnetic material like a steel can lid or bottle cap. Figure 3 illustrates how to make the rotor.
Step 12: Select a circular rotor either smaller than the coil forms or a little larger.
Step 13: Use geometry to locate and mark the center.
Step 14: Create a dimple in the rotor at its center.
Step 14 (a): Select an eighth-inch diameter (a few mm) nail—Figure 3(a)
Step 14 (b): File or grind the point round—Figure 3(b).
Step 14 (c): Place the rotor atop a piece of softwood—Figure 3(c)
Step 14 (d): Hammer the rounded point into the center—Figure 3(d). Practice on a piece of similar scrap metal. Take care not to pierce the rotor.
Step 14 (e): Shaping your rotor as a dished rotor or a lid, as shown in Figure 3(f) and (g), respectively, provides better than the flat rotor of Figure 3(e). The pivot point (e) may be a straight pin driven through a movable wooden pedestal or through the main board. The tip of a ball-point pen also works. If the rotor does not balance atop the pivot, remove metal from the heavy side.
Step 15: Double-check the wiring. Check that any bare wire has been insulated.
Step 16: The circuit may be powered-up without the rotor. The lamp should light. Both coils will warm within a few minutes. Excessive heating means that a lower wattage (higher resistance) lamp and a lower value capacitor should be substituted in series with the respective coils.
Step 17: Place the rotor atop the pivot and move it between both coils. It should spin. The closer it is, the faster it should spin. Both coils should be warm, indicating power. Try different sizes and styles of rotors. Try a small rotor on the opposite side of the coils compared to the illustration.
Learn more about the fundamentals behind this project in the resources below.
In Partnership with Future Electronics
by Robert Keim