As I’ve mentioned here before, a number of people in industry and government have expressed some concern about the supply of some of the rare earth elements. Prior to the 1980s, these were supplied by a number of countries, with the United States and South Africa being the biggest suppliers. Then China put an emphasis on the market, gaining a dominant position by virtue of its lower labor costs and (one suspects) its considerably more lax environmental standards. (Mining rare earths is a dirty business.) The rare earth elements are used, typically in small amounts, in a variety of hi-tech devices, including solar cells, wind turbines, and electric motors.
The “Babbage” science and technology blog at The Economist has an article describing how the solution to one aspect of this hi-tech problem, the construction of high-performance electric motors, may be solvable just by applying some rather old technology. Many of the motors used in new machines employ permanent magnets made with neodymium (Nd, atomic number 60):
The rare-earth the Department of Energy seems particularly paranoid about is neodymium. This is widely used for making super-strong permanent magnets. Over the past year, the price of neodymium has quadrupled, as electric motors and generators that use permanent magnets instead of electromagnetic windings in their rotors have proliferated. Cheaper, smaller and more powerful, permanent-magnet machines have been one of the main factors behind the increasing popularity of wind turbines and electric vehicles.
As the article points out, though, motors of this type, although widely used, are not a necessity; neither the Tesla Roadster, nor the Mini-E (made by BMW) uses permanent magnet technology. Some significant suppliers have also opted for other alternatives:
Meanwhile, the company that pioneered much of today’s electric-vehicle knowhow, AC Propulsion of San Dimas, California, has steered clear of permanent-magnet technology.
Toyota is apparently the latest manufacturer to seek alternatives to permanent magnet motors; it turns out that a suitable replacement may well be a technology that has been around for 123 years.
Following in AC Propulsion’s footsteps, Toyota has based its new design on industry’s electromotive mainstay, the cheap and rugged alternating-current induction motor patented by Nikola Tesla, an American inventor, back in 1888.
As the article says, the AC induction motor is an industrial mainstay. In fact, I would be surprised if your house did not contain several, powering things like washing machines, or the compressors in refrigerators and air conditioners.
There are two main reasons that permanent magnet motor technology became popular: it was (relatively) cheap, and it was simple to equip such motors with variable speed controls. The first advantage is put considerably in doubt by dependence on one, possibly unreliable, supplier; and the second is reduced in importance by the development of electronic speed controls for induction motors.
The induction motor has its own important strengths. It is simple, requires no exotic materials, and is very rugged; in particular, it can tolerate a wide range of temperatures, meaning it does not typically require a special cooling system. It can also deliver high torque over a wide range of speeds. For example, the article quotes the specifications for the motor used in the Tesla Roadster.
Weighing in at 52kg (115lb), the Tesla Roadster’s tiny three-phase induction motor is no bigger than a watermelon. Yet it packs a hefty 288 horsepower punch. More impressively, the motor’s 400 Newton-metres (295 lb-ft) of torque is available from rest to nearly 6,000 revolutions per minute.
By providing high torque at low RPMs — something a gasoline or diesel engine cannot do — much of the requirement for an expensive, complicated, and heavy gearbox is removed.
We are always hearing publicity and advertising messages talking about finding new solutions to various problems. It is worth our while to remember that, sometimes, old solutions may work just fine, even if they are right under our noses.