Last revised: October 4, 2024
Reviewed by: Scott Orlosky, consulting engineer

The invention of the electric motor had one of the most profound effects on a wide range of industries that had previously relied on brute force, water wheels, wind turbines, or large animal power.

It has been estimated that 50% of the electrical power used worldwide is used to drive motors. Locally (at a manufacturing plant for example) the percentage can be as high as 70% or more.

Electric motors have one thing in common: coils of conductive (mostly copper) coils that create electromagnetic fields designed to cause the motors to move.

Motor coils are used with motors and generators. The structures that contain the coils and make the motors work are called, stators, and armatures. There are many different types of products. Some motor coils are designed for specific types of alternating current (AC) or direct current (DC) motors. Excess heat reduces the lifetime of electric motors.  The wire coils (also called “magnet wire” are therefor given a temperature rating: B can operate up to 130° C, F works up to 155° C and is the most common and the highest is H which is rated to 180° C. Specialty motors can be sealed for severe operating environments.

Types of Motor Coils

Product categories include:

• AC motor coils (synchronous and inductive)
• DC motor coils
• linear motor coils
• stepper motor coils
• servo motor coils

Traditionally, the motor coils that produce the magnetic field on the stator are called “field coils” while the coils and the solid core of the rotor constitute the “armature." Generator coils are designed for use with electrical generators, to convert mechanical energy into electrical energy. Stator coils are designed for use with a stator, the stationary part of a generator within which a rotor turns. Armatures are devices that move under the influence of a moving magnetic field, or within which an electromotive force is induced. 

Specifications

Specifications for motor coils vary by motor coil type. Motor design is a balance between the physical constraints of containing the coils and shaping the electric fields to produce the desired output.

Stator or Field Coils

• Field coils can be flat, layered, random, or edge-style; clockwise or counter-clockwise; and carry specifications such as width, thickness, diameter, and total turn count.
• Stator coils differ in terms of core bore, core length, and coil support; support ring inner diameter (ID) and support ring outer diameter (OD); and coil length and weight.

Armature or Rotor Coils

• Armature coils carry specifications such as coil span, coil length, and coil diameter; riser width, depth, and distance; minimum and maximum diameters for rear support and front support; and lead materials and lead lengths.
• Rotor coils differ in terms of number of slots, iron diameter, iron length, number of single coils per slot, turns per coil, wire arrangement per single coil, and wire sizes. 

Applications

Motor coils are used in a variety of applications and industries. Field coils are series, compound, shunt, and edgewound coils used with DC motors, synchronous AC motors, and generators. Edgewound coils can range in size from several inches to over 10 feet. Products that weigh thousands of pounds are used in heavy-duty applications such as construction cranes and large conveyors. Specialty coils include high-energy, water-cooled coils; arc suppression, control and relay-signal coils; solenoid, transformer, reactor and choke coils (for signal dampening) as well as brake and magnet coils. Some motor coils are foam-encapsulated in their cartons or crates to prevent damage during shipping.

Motor Coils FAQs

How do users select a DC motor coil based on the required working point and power supply?

When selecting a DC motor coil, it is important to consider the available power supply voltage and current. If a catalog coil cannot achieve the desired working point, a custom-designed coil may be necessary. Key considerations include choosing a motor size based on the required mechanical power to ensure it can develop the necessary torque and dissipate heat generated through losses in the motor.

What materials are used in voice coil motors and why?

Voice coil motors may use aluminum coil wire to reduce moving mass, which is beneficial for applications requiring high dynamic performance. However, the higher electrical resistivity of aluminum can offset the benefits in systems where the load is heavy compared to the coil mass. Guidance systems in voice coil actuators often include unlubricated polymer bushes without oil or grease lubrication.

What are the best practices for maintaining motor coils to prevent overheating?

To maintain motor coils and prevent overheating, here are some best practices:

Proper Sizing and Selection:

Ensure the motor size is appropriate for the required mechanical power. The motor must be large enough to develop the necessary torque and dissipate the heat generated through losses in the motor. Not all motors run continuously, so duty-cycle should be taken into account as well.

Material Considerations:

Use materials that generate the necessary function while minimizing heat generation.

Design Optimization:

Optimize the motor's mechanical design, such as rotor and stator dimensions and pole arrangements, to improve magnetic flux paths and reduce magnetic losses. This contributes to increased power density and efficiency, which helps in maintaining cooler operation. Most motor manufacturers will have a wide selection available that can meet your requirements.

Regular Inspection and Maintenance:

Regularly inspect motor coils for signs of wear, damage, or overheating. Address any issues promptly to prevent further damage and ensure efficient operation.

Proper Ventilation and Cooling:

Ensure that the motor has adequate ventilation and cooling mechanisms in place. This can include external cooling fans or heat sinks to dissipate heat effectively.

Avoid Overloading:

Avoid operating the motor beyond its rated capacity. Overloading can lead to excessive heat generation and potential damage to the motor coils.

Use of High-Quality Components:

Use high-quality bearings and other components to ensure smooth operation and reduce friction, which can contribute to overheating.

Environmental Considerations:

Ensure the motor is operated in an environment that is within its specified temperature range. Extreme temperatures can affect the performance and longevity of motor coils.

How can I optimize the design of a motor coil for better performance?

To optimize the design of a motor coil for better performance, consider the following strategies. (Note: These are in line with best practices for overheating)

Material Selection:

Use materials that minimize electrical resistivity and heat generation. For example, using straight copper turns in the coil can maximize the effectiveness of the magnetic field, leading to minimal energy and iron losses, greater efficiency, and cooler operation.

Design Geometry:

Optimize the motor's mechanical design, such as rotor and stator dimensions and pole arrangements. This can improve magnetic flux paths and reduce magnetic losses, contributing to increased power density and efficiency.

Custom Coil Design:

If catalog coils cannot achieve the desired working point, consider a custom-designed coil that is adapted to the power supply. This can help in creating an efficient motor system tailored to specific requirements. The trade off is having a custom motor that will likely have a long lead time when it comes to replacement.

Coil Configuration:

Choose the appropriate coil configuration based on the application. For example, field coils can be flat, layered, random, or edge-style, and can be wound clockwise or counter-clockwise. These configurations can affect the performance and efficiency of the motor.

High-Quality Components:

Use high-quality components such as bearings and other parts to ensure smooth operation and reduce friction, which can contribute to better performance and reduced overheating.

Ventilation and Cooling:

Ensure that the motor has adequate ventilation and cooling mechanisms in place. This can include external cooling fans or heat sinks to dissipate heat effectively, maintaining optimal performance.

Avoid Overloading:

Avoid operating the motor beyond its rated capacity. Overloading can lead to excessive heat generation and potential damage to the motor coils, thus affecting performance.

What are the benefits of using custom-designed coils over catalog coils?

The benefits of using custom-designed coils over catalog coils can be significant, especially when specific performance characteristics are required. Here are some key advantages:

Tailored to Specific Requirements:

Custom-designed coils can be adapted to the available power supply voltage and current, creating a more efficient motor system tailored to specific application needs. This is particularly useful when catalog coils cannot achieve the desired working point.

Optimized Performance:

Custom coils allow for optimization of the motor's mechanical design, such as rotor and stator dimensions and pole arrangements. This can improve magnetic flux paths and reduce magnetic losses, contributing to increased power density and efficiency.

Enhanced Efficiency and Cooling:

Custom designs can incorporate materials and configurations that minimize energy and iron losses, leading to greater efficiency and cooler operation. For example, using straight copper turns in the coil can maximize the effectiveness of the magnetic field.

Increased Torque:

Custom-designed coils can deliver significantly more torque compared to conventional coil designs of the same size. This is due to the optimized design that minimizes losses and maximizes power output.

Adaptability:

Custom coils offer the flexibility to meet unique application requirements that standard catalog coils may not be able to address. This includes specific configurations like flat, layered, random, or edge-style coils, and winding directions (clockwise or counter-clockwise).

High-Quality Components:

Custom designs can ensure the use of high-quality components, such as bearings and other parts, to ensure smooth operation and reduce friction, which can contribute to better performance and reduced overheating.

Motor Coils Media Gallery

Resources

Electronics360—Synchronous vs. Induction Motors

GlobalSpec—Geeplus introduces bigger, more powerful voice coil motor

Image credit:

Marrrci / CC BY-SA 3.0