The electric motor as we know it was first designed by Nikola Tesla and then vastly improved for commercial use by George Westinghouse with many improvements along the way.  Today’s motors follow two dominating designs called permanent magnet and induction that are descriptions of the rotating assembly inside the case that delivers the twisting force of energy.

The case for both designs is “about” the same.  There are electromagnets, wound wiring around a metal core shaped to fit the case, long as needed for the tube and tall just to clear the rotor.   They’re caller stator windings and together make up the stator, which one assumes is because they are the stationary magnetic force.  Lots of engineering of the fine details, material choices and other elements affect the cost and performance.  A good stator that’s not contaminated or over heated or rubbed by a loose rotor can last indefinitely.

The rotor is the rotating assembly, obviously, and can come in two types.  The first is the induction form.  That comes from the electricity also flowing into the rotor for direct current designs (there is also a similar AC design) or inducted by the stator’s electromagnetic field into the rotor’s electromagnets in an alternating design arranged around the central shaft.  The flow design requires that the current enter and exit, so two contacts are needed on the shaft meeting two brushes connected to the electrical source.  These are parts that generate particles, heat, and wear out.  With that is current flowing induction motors can be quite powerful, less costly to make, and don’t need exotic materials.  Even poorly developed economies can build these kinds of motors.

An electromagnetic field induction motor is somewhat more complex in understanding, yet can also be quite inexpensive to manufacture.  There are wide variations depending on expected use, available current such as single phase or three phase, and choices in how the motor would be started.

Induction Permanent Magnet Motor Comparison. Click image for the largest view.

The second type of motor is the permanent magnet design.  These rotors hold permanent magnets arrayed around the shaft.  Seemingly simple, the magnets need positioned to be timed with the stator magnets, and to make good power, rare earths are needed which quickly drives up costs.  Failing a reasonable supply of permanent magnet material that holds its magnetism,  “permanent magnets” can be not very permanent.

Currently, most of the rare earth minerals to make reliable long life magnets are coming from China, which give some reason for pause, as a single element embargo would have worldwide market stopping effects.

For more information click here for the Wikipedia page on induction motors. At the end of Wikipedia’s page there are links to the other designs in detail plus a link to an Italian educational site with an interactive motion shown. The site also has a very good translation to English. This is the link to the Wikipedia Electric Motor page.

To decide what would be the best, the keys are in the current source and starting.  Here the current supply, alternating or direct current split the choices – battery fed motors are usually DC, line or grid fed motors are usually AC.  Stationary locations that are being installed or updated almost inevitably will be a form of AC.  Mobile units can be either, with DC needing no inverter to change the DC battery current to AC.

The motor starting matter is where the complications arrive.  As the Wikipedia site explains there are choices for the AC three phase motor, which should be the optimal solution in mobile uses.  For stationary use the phase supply is the first metric, then the load requirements.  What’s interesting is how the manufacturers are choosing for the electric vehicles on the market now and coming over the next few years.

EVs are capable of operating over a much wider speed range than typical fixed-speed industrial motors, necessitating new materials, sophisticated electronic controls and some clever design variations.  The Chevrolet Volt will use a permanent magnet design. Permanent-magnet motors generate less rotor heat than inductive types, which aids efficiency. But as the motor’s size grows, magnetic losses increase proportionately, reducing efficiency.

Induction motors do not suffer proportionate losses as size increases, and the design makes them capable of generating high power by operating at high speeds.  The motor in the Tesla Roadster spins up to 14,000 rpm.

Electric motor companies have been improving automotive motors.  Remy has invented a new stator-winding design that uses rectangular wire, rather than round wire, with windings that are arranged in multiple layers, said to reduce heat.  Other innovations should come soon.

The important matter though for a consumer is going to be the controllers, inverters, and electronics that manage the power and fed starts and running.  These devices may well cost more than the motor itself.  Longevity and reliability will be paramount concerns.  One can expect that the motors themselves will last as long as the heat isn’t damaging and the bearings are replaced before failure.  A bearing failure is a catastrophe.  One unseen innovation sought by this writer is a sensor that warns bearing maintenance is needed.

For low costs, more for the economy minded EV customer a permanent magnet design seems most likely, should communist controlled capitalist China stay stable.  But for efficiency, power delivery, and performance the induction rotor inevitable.  Like stationary installations mobile solutions are going to be application specific – with a large dose of interest which motor is installed and the durability of its controls.


8 Comments so far

  1. russ on February 9, 2010 12:10 PM

    ‘One unseen innovation sought by this writer is a sensor that warns bearing maintenance is needed.’

    Most likely this will be done during maintenance checkups where the mechanic will have the proper tool available to look for roughness in the bearings signature – the way it is done industrially.

    To have independent analyzers will be a bit difficult and expensive while providing little additional information. A bearing rarely fails quickly but slowly degrades.

  2. Alph on February 9, 2010 8:17 PM

    This is a great blog, informative yet not ideological.

  3. Jim Hendershot on June 20, 2010 8:10 AM

    This article although very informative for the general public does not deal with the complex issues regarding the electric motor type selection process for an electrified vehicle (of which there are many types). It is worthwhile to point out that as of the summer of 2010 every hybrid vehicle in production uses an internal magnet type PMAC synchronous motor for traction (known as an IPM). While each EV (pure electric powered by batteries only) uses an AC induction motor with a flux vector drive (known as asynchronous).

  4. Mackenzie Ward on August 12, 2010 7:21 PM

    electric motors would sometimes overheat if they are not properly ventilated,.*

  5. Tony Lease on October 6, 2010 2:16 AM

    This is so interesting, thank you for sharing. A really informative insight into the future.

  6. college scholarship on November 8, 2010 5:26 AM

    I’ve recently started a blog, the information you provide on this site has helped me tremendously. Thank you for all of your time & work.

  7. Digital Caliper · on November 8, 2010 7:08 AM

    electric motors can consume lots of electrical energy but they are very useful “

  8. farhan on May 5, 2011 5:21 AM

    dear sir

    this is Farhan Nazeer from Karachi Pakistan … i trying to make a magnet motor with daily basis but not success guide me for magnet motor

    thanks and regard

    waiting for Ur reply

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