This project started one night while I was lying in bed trying to visualize how an AC motor worked. I knew that it was different from a DC motor as in it did not require brushes and the speed was controlled by frequency instead of voltage. After some research I came up with this project to better my understanding of AC motors.
AC Current is different from DC in that the polarity is constantly inverting in a given period. For example: Lets say you have a standard battery hooked up to a volt meter. Normally you would connect the positive lead to the positive terminal of the battery as well as the negative lead to the negative terminal. If you wish to generate an AC current you would connect the leads normally for half a second and then invert them (where the positive terminal is connected to the negative lead and the negative terminal is connected to the positive lead) for another half second. If you constantly repeat this process you will have an AC current operating at one hertz (1hz). Where a hertz is 1 / Period. The period is the time the current is positive plus the time it is negative in one cycle, so in our case 0.5s + 0.5s = 1s per period. In America AC voltage to your home is typically 110 Volts at 60hz in a smooth sine wave.
Quick Magnet Theory:
A more in depth theory about magnets can be found here. For our practical purposes all we need to know is that a magnet has two poles, north and south. Poles attract each other when placed from north to south and repel when placed north to north or south to south.
Quick Electromagnet Theory:
An electromagnet is a magnet that is created with a coil. When current passes through the coil a magnetic flux is created. Conversely when a magnetic field passes through the coil a current is created. More information can be found here.
AC Motor/Generator theory
Most of the information I used to design this motor came from this page. I placed six magnets on the rotor with alternating poles and placed 6 coils in the housing with the polarities also alternating. When an AC current is run through the coils the polarity will switch the magnets poles from north to south at the given frequency. Therefor the rotor will turn so that the poles on the magnets will always line up.
After I had a good idea of how I was going to build this motor I needed to collect parts. I already had some bolts that I can use for coils along with copper magnet wire. So off to Hobby Lobby. There I found some ultra strong magnets along with construction Styrofoam.
The base for the motor
The completed measurements
At this stage I had to determine how strong of an electromagnet I needed for the magnets I bought. Since the magnets are rated at “10” in strength, I had to create a electromagnet with enough magnetic flux to successfully repel the magnet.
Along with determining the proper coil windings, I also had to label the polarity of each magnet. I used a +5V DC power supply to test the coil. After experimenting I decided to use 350 turns with 30 gauge wire.
Once the polarity was determined for the magnets, I placed them in the rotor with hot glue.
The base fully assembled
The base with coils.
After the unit was fully assembled it was time to test it out. First I tested to see if spinning the rotor would generate an AC current. I wired all of the coils in series and hooked them up to the oscilloscope. Spinning the rotor by hand produced a rough sine wave at a about 100mv. Now it is time to try powering the motor. To generate a AC current I used a HP 200A audio oscillator at around 50hz. This device cannot supply much current so I ran it at high voltage (70v) through a step down transformer (110V to 12.6-0-12.6). After playing with lining up the coils I was able to successfully power the motor.