The electric motor is a technology that’s nearly three centuries old, one that got its start with a Scottish Benedictine monk and one of America’s founding fathers. Age and maturity have caused motors to develop to the place where they’re both highly advanced and ubiquitous in their applications. You will find electric motors in everything from children’s toys to top manufacturing plants. And one very common motor is the traction motor.
In this guide, we’ll explain what traction motors are, their component parts, the most popular types of traction motors, and how to select the best one for your end-use application.
Components of Traction Motors
One thing to understand about traction motors is that they aren’t fundamentally different from other kinds of motors. Their distinctives come from their intended end use rather than their employed technology.
As such, the oldest and most established kind of traction motor is direct current (DC) motor. It functions by having direct electrical current generate a magnetic field through the use of a stator. In most DC motors, this is a stationary element that contains magnets that interact with a rotor. The rotor contains insulated wiring and its own array of electromagnets, which are arranged in such a way that the opposing magnetic forces cause the rotor to spin. While these are the most important elements of any DC motor, other noteworthy components include the commutator (essentially a copper-containing rotary switch), bearings (which support the rotor), and a containing case. Sometimes DC motors will contain brushes that keep the magnets magnetized.
Alternating current (AC) motors work similarly to DC motors, but use different power (as evidenced in their name). They contain many of the same components, including a stator, a rotor, bearings, a casing, and insulation. However, AC motors can vary significantly regarding the ways in which the magnets and windings are arranged.
Because traction motors are typically used to power and propel vehicles, their designs will vary from motors intended for other applications. As such, you will notice that components of traction motors are implemented specifically to dissipate heat, generate torque, and withstand rough operating conditions where jarring, vibrations, and exposure to contaminants such as dirt, dust, and moisture are common.
Popular Types of Traction Motors
Though traction motors all have propulsion as their purpose, their specific configurations can vary significantly based on the type of movement required. Some common kinds of traction motors include the following:
- DC Motor: This may be the oldest type of traction motor, but its ongoing advantages mean that it remains popular. If a load suddenly increases, it can easily compensate. However, because these kinds of motors contain brushes to maintain magnetism and those brushes will invariably wear down, they can require constant servicing.
- Brushless DC Motor: One of the simplest types of traction motor, brushless DC motors eliminate the use of brushes by including permanent electromagnets. While they may have a higher upfront cost than DC motors, they are generally cheaper to operate.
- Linear Induction AC Motor: Whereas the internals of most rotary motors have a circular shape, linear induction motors uncoil that spindle and lay it flat. The rotor becomes a reaction plate, and the motor delivers force that moves in a line. These motors are particularly effective at moving loads at quick speeds.
- Three-Phase AC Induction Motors: Most AC motors cannot generate the high starting torque provided by DC motors, but three-phase AC induction motors compensate for this by including an inverter circuit. These motors can be larger than other similar types.
How to Properly Size a Traction Motor
Sizing any motor is a complex task that requires lots of knowledge about your end-use scenario, the environment in which the motor will operate, the measurements of the load that will need to be moved, and more. Dr. Alaa Khamis of General Motors offers an online guide on motor sizing calculations that highlights how, at the basic level, you will need to know the speed, load torque, and load inertia required for your particular task as you try to size a motor.
However, traction motors have several additional factors to consider. They require consistently high torque in almost any application, including high torque at low speeds and upon initial motor start up. Sizing a traction motor will require you to consider factors such as efficiency and power to weight ratio. Why? Most traction motors get used in vehicles, and any shortfall in operational capacity must be balanced by an increase in battery size. Such compensations can start a vicious cycle of chasing power even as weight continues to increase — which will necessitate a need for even more power. Additionally, though the need for maintenance doesn’t necessarily factor in to selecting a correct traction motor size, it is a practical consideration that you should take into account.
For more technical discussions of how to size traction motors, read Gobbi, Mastinu, Ramakrishnan, and Stipetic’s paper on sizing traction motors with scalable electric machine models in IEEE Transactions on Transportation Electrification, as well as S.P. Khade’s work on sizing electric train motors in Electrical Monitor.
What to Look for When Buying a Traction Motor
Like all motors, you will need to consider factors such as speed, voltage, RPMs, and other such common considerations. However, because traction motors are typically used on vehicles, you should take a look at a particular motor’s size (will it fit in the space dedicated for it?), power requirements (will it necessitate an increase in battery size, which could increase the vehicle’s overall weight?), and operational context (will the motor require special housing, insulation, heat dissipation, or regular maintenance due to common usage?).
Applications and Industries
As we have mentioned in this article, traction motors are typically used to power vehicles of some sort. However, that’s not the only place where these motors appear. Common applications include:
- Electric carts
- Power escalators
- Electric and diesel locomotives
- Elevated trains
- Subway cars
- Washing Machines
- Mining equipment
- Agricultural equipment
Traction motors do not normally require specialized accessories, and most of what you’ll find on offer includes spare parts and adapters, such as the following:
- Motors brushes
- Shim spacers
- Bearing caps and housings
Tips for Finding and Buying a Traction Motor
It’s not hard to find the kind of traction motor you want on Surplus Record. Click on the search bar on our website’s header and type in “traction motors” to see what we have available.
Surplus Record provides more than just classified listings, too. We work with a variety of specialty dealers who can help you find the perfect Traction motor for your applications. Search for area dealers near you or search dealers by name.