AC Motors Buying Guide

While the first practical DC motor appeared in 1832, the invention of a British scientist, the world would have to wait just over half a century for the AC motor to appear. The eccentric genius Nikola Tesla would invent an electric motor that would work with alternating current rather than direct current.

AC motors have become an indispensable part of everyday life for both businesses and common consumers. Because these motors can power any number of end-use applications simply off of “wall power,” they are common tools in both residential and commercial applications.

Components of AC Motors

All electrical motors transform electrical energy into mechanical energy, although their components will vary according to the motor subtype. The two most important elements of an AC motor are the stator (a stationary component comprised of electromagnets situated in a cylindrical arrangement and connected with wiring) and the rotor (a spinning element that is also studded with electromagnets and connected to a shaft). These magnets are installed in such a way that, when charged, their magnetic force causes the rotor to turn, generating electrical energy.

While these two elements define an AC motor, it will also have other components, which include:

• Bearings: Supportive structures, bearings hold up the rotor, allowing it to easily turn within the engineered tolerances of the motor and to freely spin outside of the motor’s casing.
• Casing: The casing is the protective external structure that safeguards the sensitive internals of the motor against damage.
• Insulation: Grit, dust, dirt, and similar contaminants prevent proper operation in an AC motor, and many contain insulation to ensure continued functioning.

When Do I Need an AC Motor over a DC Motor?

Though DC motors are an older technology, they do offer certain distinct advantages, such as generally starting and stopping quickly, being able to reverse, having speeds that vary with voltage, and having higher initial torque. That being said, AC motors have become the dominant type of electric motor for many applications. Due to the fact that they lack brushes, they require less maintenance. They’re typically more durable than DC motors. They’re cheaper to run and operating them is generally much easier. However, one noted issue regarding AC motors is that they often cannot be found with fractional horsepower ratings.

Popular Types of AC Motors 

Before purchasing an AC motor, it helps to understand some of the common types that you’ll find on the market. They include the following: 

Induction Motors (aka Asynchronous Motors) 

As you may well know from its name, alternating current changes its magnitude constantly around a particular frequency (60 Hz in the United States). Induction motors employ a stator that employs electromagnetic induction in order to produce torque, and their rotors turn at a steady rate, one that’s not synchronized with the current. These are some of the most common AC motors, as well as being the most reliable and economical. 

Single-Phase Motors 

A type of induction motor, the single-phase motor has only a single stator, which creates currents in the rotor. These kinds of motors excel at low-power applications. 

Polyphase Motors 

These induction motors function similarly to single-phase motors, but they include two or more stator magnets, which allows them to function with higher power than single-phase motors. 

Squirrel-Cage Motors 

Another kind of induction motor, squirrel-cage motors derive their name from their cage-like stators studded with multiple magnets. While you cannot change the speed of these motors, they are relatively inexpensive, safe, easy to maintain, and energy efficient. Top manufacturers for squirrel-cage motors include General Electric, Siemens, Reliance, Toshiba, and Westinghouse. 

Synchronous Motors 

Unlike induction motors, synchronous motors move in sync with the current, which alternates. These motors will not have constant speed, but they do produce large amounts of power, making them ideal for industrial applications. However, they are also noisy, expensive, and big. The term “synchronous motors” is a catch-all phrase that includes multiple specific motor types, such as reluctance motors, hysteresis motors, and permanent-magnet motors. 

Reluctance Motors 

An advanced motor type, reluctance motors use non-permanent magnets on a rotor without any windings. It uses magnetic reluctance (which is defined as the ratio of magnetomotive force to magnetic flux) to generate rotational force. These motors typically generate great power at relatively low cost, although they can become less reliable at low speeds due to torque variability. 

Hysteresis Motors 

These synchronous motors use the principle of magnetic hysteresis (i.e., the tendency of a ferromagnet to remain magnetized even after an electric field is removed) to spin a steel rotor. Hysteresis motors are self-starting, operate quietly, do not vibrate, and can operate at varying speeds with the introduction of a gear train. 

What to Look for When Buying an AC Motor 

Once you know which kind of AC motor would work well for your end-use application, you ought to consider several common concerns that any purchasers of a new or used AC motor ought to keep in mind. These include the following: 

• Environment: Where will your motor operate, and will it need to be protected against dust, dirt, and water? 
• Spatial Restrictions: Does your end-use application for a motor include restricted spaces? If so, you will need to carefully pick a motor that will fit. 
• Life-Cycle Requirements: While owners will like a motor that functions indefinitely, no piece of machinery will last forever. What’s the preferred life span for your engine and which selections will match it? 
• Noise and Ventilation Requirements: Many businesses find themselves subject to noise ordinances, and sound concerns may rule out certain kinds of motors. The same is also true for spaces with limited ventilation. 
• Efficiency and Torque Requirements: How efficiently will the motor operate? Does it generate enough torque on startup to meet your end-use application’s needs? 
• Motor-Specific Technical Specifications: Ensure that the voltage, speed, power, torque, and frequency of the motor you’re considering will work with your application. 

Applications and Industries

Because of their general simplicity, economy, ease of use, and ease of maintenance, AC motors have become popular in both commercial and industrial products and processes. Many consumer-grade items are powered by AC motors (e.g., water heats, lawn equipment, pumps). They find use in businesses such as: 

• Light industry 
• Heavy industry 
• Construction 
• Retailing 
• Machining Shops 
• Commercial Fabrication 
• Mass Transit 
• Logistics 
• Entertainment and Hospitality 

Some specific uses of AC motors include the following: 

• Lathes 
• Precision drills 
• Consumer appliances (e.g., blenders, dryers, washing machines, blowers) 
• Pumps 
• Monorails 
• Speed controllers 
• Tube wells 
• Power plants 
• Crane drivers 
• Mills 
• Roller coasters 
• Punch presses 
• Manufacturing and fabrication 
• Conveyor belts 
• Ventilation 
• Liquid and solid material transport 

Accessories

Accessories for AC motors mostly include spare parts or specific kinds of equipment designed to adapt an AC motor to a particular space. Examples are:

• Air intake baffles
• Electronic regulators
• Fan controllers
• Blower shaft keys
• Conductive potentiometers
• Motor clamps
• Switches (mechanical and electric)
• Enclosures and cabinets
• Cables and connectors
• Coupler brakes
• Gear reducers

Whether or not you should look for specific motor accessories will depend on your end-use case and the motor or motors you plan to employ.

Tips for Finding and Buying an AC Motor

With tens of thousands of listings, Surplus Record has all the equipment you need, including AC motors. Searching our extensive offerings is easy, and you can find all of the AC motors we have on offer with just a click. After you’ve visited our Electric Motor Search page, you can sort by a range of horsepower, revolutions per minute, and voltage, as well as frame type, manufacturer, and motor condition.

Surplus Record provides more than just classified listings, too. We work with specialty dealers who can help you find the perfect AC motor for your applications. Search for area dealers near you or search dealers by name.

Looking to Buy an AC Motor? Check Out Our Listings!