Key Differences Between Synchronous and Asynchronous Motors

When choosing a motor for industrial applications, the decision between an asynchronous motor (commonly known as an induction motor) and a synchronous motor (including permanent magnet options) is not just about power—it’s about precision, efficiency, and the unique needs of your machinery. For experienced professionals, understanding the nuances of these motors is critical to optimizing operations, improving performance, and reducing long-term costs.

Let’s delve into the mechanics, strengths, and ideal use cases for each type of industrial motor.

An asynchronous motor, commonly referred to as an induction motor, is one of the most widely used AC electric motors in industrial applications. The term "asynchronous" refers to the fact that the rotor speed always lags behind the rotating magnetic field in the stator—a phenomenon known as "slip." This slip creates the necessary current in the rotor to produce torque.

Key Characteristics:

• Slip is Required for Torque: The rotor must lag behind the stator’s magnetic field to induce current.
• Electromagnetic Simplicity: No permanent magnets or external excitation systems—just electromagnetic induction.
• Reliable Under Heavy Loads: Induction motors handle variable loads well and maintain performance without constant adjustments.

Asynchronous motors excel in applications where precise speed control isn’t necessary, but durability is. They’re commonly used in pumps, compressors, and conveyors—systems that need consistent, rugged power.

👉 Sumitomo Insight: Our induction motors are built to handle demanding conditions while minimizing maintenance downtime.

A synchronous motor differs in that its rotor turns at exactly the same speed as the stator’s magnetic field—there’s no slip. Permanent magnet synchronous motors (PMSMs) take this a step further by using powerful magnets embedded in the rotor. These magnets create a magnetic field without the need for additional energy input, making PMSMs even more efficient.

Key Characteristics:

• No Slip: The rotor in this industrial motor moves in perfect sync with the stator’s magnetic field.
• Higher Energy Efficiency: Permanent magnets eliminate the energy losses associated with slip for better performance.
• Exceptional Speed Control: This characteristic makes this AC electric motor type ideal for applications that demand precise, constant speeds regardless of load changes.

When precision and efficiency matter, synchronous motors are the way to go. They're in CNC machines, robotics, and automated production lines where speed consistency is essential.

👉 Sumitomo Insight: Our synchronous motors are engineered to deliver top-tier precision, energy savings, and reliability for industrial automation and high-performance systems.

If your operation needs robust, general-purpose power without the need for perfect speed control, an induction motor is a solid choice. The upfront cost is lower, and the design’s simplicity means there’s less that can go wrong.

Applications:

• Industrial fans and blowers
• Water treatment pumps
• Conveyor belts in manufacturing

For a detailed look at how performance, efficiency, and operating environment factor into choosing an industrial induction motor, check out our article on Factors to Consider When Buying an Industrial Induction Motor or our article regarding the top 7 signs that your induction motor needs an upgrade.

If your operation requires precise speed control and energy efficiency, permanent magnet synchronous motors are the way to go. They maintain a steady speed, no matter the load, and use less energy by eliminating the losses associated with slip. While the upfront cost is higher, the payoff comes in better performance and lower energy bills.

Common Applications:

• Robotics and automated assembly lines
• Precision grinding and machining
• High-speed material handling systems

Selecting the right motor means looking beyond the basics of speed and efficiency—it involves assessing how well the motor aligns with your operational environment, performance requirements, and long-term goals.

1. Operational Load

Is your system operating under a consistent load, or does it experience frequent shifts? For applications with variable loads, induction motors can provide dependable performance without the need for constant adjustments. If your system requires a steady load and precise speed, a permanent magnet synchronous motor may be a better fit.

2. Speed Control and Efficiency

Do you need precise speed control to keep your operations consistent, or is some fluctuation acceptable? Synchronous motors provide consistent, slip-free performance, while induction motors can handle minor speed changes without issue. If energy consumption is a concern, permanent magnet motors typically perform more efficiently under precision workloads, especially at slower speeds.

3. Motor Specifications

When choosing any industrial motor, consider the following specifications:

1. Power Rating: Ensure the motor can handle the mechanical load required for your application.
2. Torque Requirements: High-starting torque may influence whether you choose an induction or synchronous motor.
3. Service Factor: This reflects the motor's capacity to handle occasional overloads without failure, an important factor in demanding industrial environments.

4. Environmental Conditions

The physical environment of your operation plays a big role in motor selection. Consider factors such as ambient temperature, exposure to dust or moisture, and the risk of vibration or shock. Sumitomo’s motors are designed with these considerations in mind, offering rugged options that handle harsh conditions and minimize downtime.

5. Maintenance and Downtime

Some motors require more oversight than others. Induction motors tend to have a simple design with fewer components prone to wear, making them relatively low-maintenance. Synchronous motors, especially those with permanent magnets, may require less day-to-day maintenance but often need a higher level of attention during installation and tuning.

6. Budget vs. Total Cost of Ownership (TCO): 

An induction motor may have a lower upfront cost, but consider maintenance and energy consumption over the motor’s lifespan.

Choosing between an induction motor and a permanent magnet synchronous motor comes down to the specific demands of your operation. If you need a dependable, cost-effective motor for general tasks that can handle varying loads without issue, an induction motor is a solid choice. On the other hand, if your application calls for precise speed control, energy efficiency, and consistent performance, especially under fixed loads, a synchronous motor with permanent magnets is hard to beat.

Ultimately, it’s not just about the upfront cost—it’s about how well the motor aligns with your operational needs and long-term goals. A thorough assessment of your system’s requirements can help you choose the best option for efficiency and performance. Whether you need the simplicity of an induction motor or the precision of a synchronous motor, having the right motor in place makes all the difference in keeping things running reliably.

Take the time to evaluate your system’s needs, and when you're ready to make a decision, explore Sumitomo’s induction motors and synchronous motors for solutions designed to keep your operations running smoothly.