A Historical Overview of Permanent Magnet Motors

The motor market is flushed with permanent magnet (PM) motors these days. Growth rates of PM brushless motors in excess of 100 percent1 are the norm instead of just a stroke of luck. But the attractive growth rates of PM motors today were a long time coming. Call it a circuitous route or a historical journey, the practical application of PM motors did not occur until many decades after the first electric motors were invented. The first electric motors, which were not more than laboratory gadgets, used bar magnets. Unfortunately, these magnets were of such poor quality that the first PM motors were impractical for industrial use. But this limitation set the stage for numerous inventors to experiment with magnets of different sizes, shapes, configurations and materials, which ultimately led to the powerful and compact magnets used in PM motors today.

Permanent Magnets: The First Electric Motors

All of the earliest inventors of electrical rotating machines (only later called electric motors) used permanent magnets in their designs. But these “machines” were not motors in the sense we understand them today. Michael Faraday was one the earliest experimenters in the burgeoning field of electricity and electromagnetism. He built a rotating electrical machine that is commonly dubbed as the first electric motor. Applying ideas from Hans Christian Oersted on “the generation of a magnetic field by electric current,2” as well as William Wollaston, an experimenter who got a current-carrying wire to rotate on an axis using a magnet3, Faraday built a laboratory device that converted electrical energy into mechanical (rotating) motion. This device used both fixed and rotating permanent magnets with wires attached to bowls of mercury and a battery. When a battery was connected to the wires, current flowed in the circuit and the generated electromagnetic field interacted with the permanent magnets to produce torque and cause mechanical motion.4

After Faraday’s “motor,” other inventors quickly followed with improvements that more closely resemble motors we know today. In 1882, Peter Barlow invented a spinning wheel, known as Barlow’s wheel, which caused mechanical motion when the wheel was lowered until a spoke dipped into the mercury while voltage was applied to the binding posts.5

In 1837, American inventor and blacksmith Thomas Davenport was granted the first patent for an electric motor. This motor was an improvement on previous designs he worked on with Orange Smalley and Ransom Cook and is based on a solenoid (electromagnet) he purchased from inventor Joseph Henry. “Davenport’s patented design use[d] four rotating electromagnets that are switched by a commutator and ring-shaped fixed permanent magnets. The motor rotated at about 1,000 revolutions per minute and [could] lift a 200-pound weight one foot in one minute, corresponding to a power of 4.5 W.6” Even though Davenport’s motor was an improvement, he failed to sell enough stock to finance his business and went out of business.7 While Davenport used permanent magnets in his motor, other inventors were already moving onto something better by replacing permanent magnets with electromagnets. This change led to the development of industrial quality motors that propelled the growth of the electromagnetic DC motor market for many years until high quality permanent magnets that were produced nearly one century later.

Electromagnets: A Historical Pause for Permanent Magnetic Motors

The first inventors of electric motors knew quite early on that permanent magnetic motors had severe limitations as far as their practical application was concerned. In 1882, electrician John Urquhart wrote in his treatise on electro-motors that “when the electro-motive machine is intended to exert any considerable amount of energy, it is advisable to replace the permanent magnets by electro-magnets. A considerable increase of power is yielded by motors when furnished with electro-magnets in place of PMs. Moreover, the size and weight of the motor may be greatly diminished. The cost is much less, and the machine is capable of converting a much larger power of current into mechanical effect.8

British inventor William Sturgeon is attributed as the inventor of the first electromagnet in 1825.9 A few years later in 1827, Hungarian inventor Istvan (Ányos) Jedlik invented the “first rotary machine with electromagnets and a commutator,10” which was the forerunner of the modern DC motor. But the first practical electromagnetic DC motor was invented by Moritz Hermann Jacobi in 1834. Jacobi’s motor lifted 10 to 12 pounds with a speed of one foot per second, which is about 15 watts of mechanical power.11 On an interesting (if humble) side note, Jacobi wrote in 1835 that “he was not the sole inventor of the electromagnetic motor. He indicated the priority of the inventions of Botto and Dal Negro.12

While electromagnetic DC motors were “first popularized in the 1880s when direct current was the primary source of power,13” their use would be fundamentally changed when Nikola Tesla in 1889 invented the electromagnetic AC motor. With only two parts, a stationary stator and a rotor, the AC motor was simpler than electromagnetic DC motors. “The stationary stator provided a rotating electromagnetic field while the rotor, attached to the output shaft, was given a torque by the rotating magnetic field. The magnetic field was created by two or more alternating currents out of step with each other and was called a polyphase system.14” Despite the simplicity offered by Tesla’s AC motor, it had controllability and operability problems15 that allowed DC motors to maintain a steady presence in industrial applications for many decades. But the return of PM motors was nearing as the development of high energy permanent magnets were on the horizon.

The Return of Permanent Magnetic Motors

Up until the twentieth century, permanent magnetic material was limited to naturally occurring magnetite, commonly called lodestone. But in the early beginnings of the century, the world saw what can be described as a renaissance in the discovery of new types of magnetic materials such as carbon, cobalt and wolfram steel. However, these first new magnetic materials were still of low quality. It wasn’t until the development of Alinco magnets that the world would have a high quality magnet that could be used for a lot of applications and opened the door for the return of PM motors.16

After extensive research in the 1930s, it was discovered that “significant additions of aluminum, nickel and cobalt in solution with iron produced a highly effective and commercially viable PM produced by conventional ingot casting. Called Alnico magnets, they were 100 times stronger than any lodestone.17” In the 1950s, ferrite (ceramic) permanent magnets appeared and were used in motors for small appliances. But, in the 1960s, another significant step occurred in the expanded use of PMs in electric motors when the compounds of rare-earth metals (samarium) and cobalt were invented. These PM materials were significant in and of themselves. Yet, they were overshadowed by the invention of neodymium-iron-boron PMs in the 1980s,18 which “yielded both a higher energy product and were more common than the rare samarium and cobalt.19” It was not until the 1970s that brushless PM DC motors began surfacing in the marketplace. The delay was due not only to the development of high energy PMs, but also the development of power devices and electronic controllers that could replace mechanical commutation with electronic commutation.20

The Future: Nanocomposite Permanent Magnets

What’s in the future for PM motors? The evidence suggests that their use will continue to grow as they are used in new applications. On the horizon though, are new innovations in the area of high energy permanent magnets. One of these innovations is nanocomposite permanent magnets. These magnets are “artificially constructed magnetic structures (referred to as metamaterials) that produce strong permanent magnets by fabricating nanostructured hard/soft phase composite materials21” with dimensions less than a than a micrometer.22 Currently, they are being used in biomedicine, magnetic storage media, magnetic particle separation, sensors, catalysts and pigments.23 In the future, the world may see nanocomposite magnetic materials finding use in future generations of PM electric motors.

  1. Jacek F. Gieras. PM Motor Technology: Design and Applications. CRC Press, Taylor and Francis Group, 2010. Page 1(Preface).
  2. Martin Doppelbauer. The invention of the electric motor 1800-1854.
  3. Joe Rosen and Lisa Quinn Gothard. Encyclopedia of Physical Science, Volume 1. Infobase Publishing, 2009. Page 220.
  4. Joe Rosen and Lisa Quinn Gothard. Encyclopedia of Physical Science, Volume 1. Infobase Publishing, 2009. Page 220.
  5. Martin Doppelbauer. The invention of the electric motor 1856-1893. Karlsruhe Institute of Technology (KIT), 2012.
  6. Martin Doppelbauer. The invention of the electric motor 1800-1854. Karlsruhe Institute of Technology (KIT), 2012.
  7. Martin Doppelbauer. The invention of the electric motor 1800-1854. Karlsruhe Institute of Technology (KIT), 2012.
  8. John W. Urquhart. Electro-motors: A Treatise on the Means and Apparatus Employed in the Transmission of Electrical Energy and Its Conversion Into Motive Power for the Use of Engineers and Others. William T. Emmott, 1882. page 103.
  9. Martin Doppelbauer. The invention of the electric motor 1800-1854. Karlsruhe Institute of Technology (KIT), 2012.
  10. Martin Doppelbauer. The invention of the electric motor 1800-1854. Karlsruhe Institute of Technology (KIT), 2012.
  11. Martin Doppelbauer. The invention of the electric motor 1800-1854. Karlsruhe Institute of Technology (KIT), 2012.
  12. Martin Doppelbauer. The invention of the electric motor 1800-1854. Karlsruhe Institute of Technology (KIT), 2012.
  13. Stanley Ryan Sifford. Multiport Analysis of Permanent Magnet DC Motors. ProQuest, 2006. page 56.
  14. Carroll Gantz. The Vacuum Cleaner: A History. McFarland, 2012. Page 40.
  15. Sakae Yamamura. Motors for High-Performance Applications: Analysis and Control. CRC Press, 1986. Page 2.
  16. Juha Pyrhonen, Tapani Jokinen, and Valeria Hrabovcova. Design of Rotating Electrical Machines. John Wiley & Sons, 2009. Page 200.
  17. Peter Kelly Sokolowski. Processing and Protection of Rare Earth Permanent Magnet Particulate for Bonded Magnet Applications. ProQuest, 2007. Page 6.
  18. Alex Goldman. Modern Ferrite Technology. Springer, 2005. Page 227.
  19. Juha Pyrhonen, Tapani Jokinen, and Valeria Hrabovcova. Design of Rotating Electrical Machines. John Wiley & Sons, 2009. Page 200.
  20. Chang-liang Xia. Permanent Magnet Brushless DC Motor Drives and Controls. John Wiley & Sons, 2012. Page 2.
  21. J. Ping Liu, Eric Fullerton, Oliver Gutfleisch, David J. Sellmyer. Nanoscale Magnetic Materials and Applications. Springer, 2009. Page 311-312.
  22. J. Carlos P. rez Bergmann. Nanostructured Materials for Engineering Applications. Springer, 2011. Page 36.
  23. J. Carlos P. rez Bergmann. Nanostructured Materials for Engineering Applications. Springer, 2011. Page 36.
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