For years, amateur experimenters did not even try to duplicate Tesla’s rotating egg experiment. The power and capacitance requirements were believed to be formidable. Surprisingly, the experiment can be powered with nothing more exotic than a modified induction motor scrounged from an old household appliance.

On May 16, 1888, Nikola Tesla astounded the scientific world when delivering a lecture on “A New System of Alternate Current Motors and Transformers” before the American Institute of Electrical Engineers. The heart of Tesla’s new system was the induction motor and the rotating magnetic field by which it functions. Heretofore, the transmission of alternating currents was limited to serving lighting systems but not for supplying power as there was no self-starting AC motor. In some cases, alternators were used as motors but they were not self-starting.

Figure 1 - The high-voltage, 400 kHz sign mounted above the entrance to the Tesla exhibit room at the Chicago Columbian Exposition of 1893.

The importance of Tesla’s discovery of the rotating magnetic field and its application to the generation, transmission, and utilization for power and light cannot be overemphasized. In simple terms, all of the wonders of our modern world would not have been possible without long distance electrification. Think about it when you next flip a switch to watch television, play a DVD, heat or cool your home, start your car, receive the benefits of modern medicine, and on and on. Those massive structures supporting high voltage transmission lines crossing the countrysides might correctly be characterized as “Tesla towers.”

When the Tesla two-phase AC system was chosen to supply power and light for the Columbian Exposition of 1893, Tesla was present to render a personal demonstration of his amazing inventions. The entrance to the Tesla exhibit was decorated with a high-voltage/high-frequency sign that spelled out “POWER.” (See Fig. 1.) One of the exhibits that amazed audiences was a demonstration of the rotating magnetic field principle. On a platform stood a large metal ring wound with hundreds of turns of wire. In the center of the ring was a large metal egg. When a switch was closed, the egg began rotating on its side and then took a vertical position while spinning at high speed. The majority of the people witnessing the demonstration viewed it as an entertaining bit of scientific magic and was unaware that the principle which caused the action would eventually bring electrification to the world.

Now fast forward to the day when a friend handed me a copy of the March 1919 issue of the Electrical Experimenter magazine. That issue featured an amazing article describing Tesla’s Columbian Expo demonstration. (See Fig. 2.)

I immediately developed an urge to reproduce the Tesla demonstration. One of the factors with which I was concerned was the huge amount of power required to create the spinning effect. It was stated that Tesla ran it on as much as 200 horsepower! Secondly, an electrical engineer friend with whom I had discussed my intentions calmly informed me that my project would demand a “huge” capacitor. Although my confidence in achieving success began to dwindle, the idea of constructing a spinning egg demo remained in my thoughts throughout the years.

Figure 3 - Disconnect the induction motor’s stator coils so that two leads extend from each. Connect lead X1, to X2 and lead Y1, to Y2 to create two sets of coils connected in series. See the schematic in Fig. 4 for the complete circuit.

As time passed, I kept attentive to the popular science magazines hoping that writers such as the brilliant Harold Strand would bring forth a simple Tesla spinning egg project. I also searched papers pertaining to science fair literature with the thought that a junior scientist would undertake such a project. It wasn’t until I came across a book written for junior-senior high school students that I found my answer. The project, I discovered, could be made to function on less than one-tenth horsepower. And as to that required “huge” capacitor, it turned out to be much smaller than I had envisioned.

Basically, the common induction motor consists of four fixed (field) coils of many turns of wire. This section is called the stator. Another coil of fewer turns is centrally mounted and free to turn. This section is referred to as the rotor. Unless you choose to wind your own field coils, you will have to obtain an induction motor to complete this project.

Induction motors are so prevalent in our society that the experimenter should have little difficulty in obtaining one. Local businesses in the home appliance trade are good sources. I have obtained several at little cost from a store that had a number of old refrigerators and washing machines that were ready to be junked. As an aside, when I was enthusiastically constructing Tesla coils, our nearby heating and cooling establishments became a good source for used ignition transformers. Some charged as little as one dollar while others allowed me to retrieve the transformers from discarded oil furnaces at no cost. I later was able to pick up some decent spending money by providing local night clubs with used ignition transformers for their weird neon light displays. Hooray for a free market economy.

Figure 4 - The complete circuit for two-phase operation with a capacitor of 125 µF and a resistor of 10 Ω. Not shown are a switch and circuit breaker (fuse). Another way to achieve two-phase action is to replace the capacitor with an inductor (choke) of about 14 mH. Do not connect the project directly to a 120 V line. Instead, use a variable transformer to power the circuit.

Figure 5 - (A) Inductors connected in series so that the current and magnetic field in both coils are in the same direction. They are said to be aiding. (B) Inductors connected in series but linked so that the magnetic fields in the coils are in opposition (bucking).

Figure 6 - The components to be mounted on the board with the connecting circuits clearly labeled. Color coding the conductors reduces any possible confusion. The author mounted the resistor inside of a perforated ceramic cylinder to prevent accidental contact with wiring (and grubby hands). The vertical cylinders are capacitors connected in parallel. The entire construction was placed inside a wood cabinet (See Fig. 11.)

Figure 7 - Testing for two-phase operation with a magnetic compass. This test is carried out at very low voltage. When circuit A-B is 90 electrical degrees out-of-phase with circuit C-D, the compass pointers will rotate at a rapid rate.

Figure 8 - A plastic Easter egg (packed with steel wool) can be made to rotate faster than a children’s toy top. The author has also made toy tops spin. (See Fig. 9.)

Figure 9 - Various elements used to demonstrate rotating field effects. Many who witnessed the demonstrations expressed their amazement when the plastic egg stood on end and rotated rapidly. The rotating Coca Cola can draw chuckles.

Figure 10 - Support stand for rotating elements.

Figure 11 - The completed project (housed in an old windup phonograph case). A variable transformer allows appropriate voltages to be applied for each demonstration.