flat wire motor vs. round wire motor

Flat Wire Motor vs. Round Wire Motor

As we transition from the era of internal combustion engines to the age of new energy vehicles, a new debate has emerged: flat wire motor vs. round wire motor. Similar to past debates about naturally aspirated versus turbocharged engines or mechanical pumps versus high-pressure common rail technology, the competition between these two types of motors is intense. Understanding the differences between flat wire motors and round wire motors is crucial, especially for applications in electric vehicles.

What Are Flat Wire and Round Wire Motor?

Flat wire motors and round wire motors are distinguished by the shape of the copper wire used in the stator windings. In a round wire motor, the round windings use round copper wires, while in a flat wire motor, the flat wire windings use rectangular or flat copper wires. Regardless of the wire shape, these motors operate on the principle of electromagnetism, generating a controllable magnetic field when powered.

Heat Dissipation

One of the critical differences between round wire and flat wire motors lies in their heat dissipation capabilities.

Round wire motors have winding slots filled with round wires, leaving gaps between them. These gaps are poor conductors of heat, slowing down the heat transfer process. If the temperature exceeds 180°C, it can damage the insulation layer of the enamelled wire, leading to motor failure. Consequently, the instantaneous power output of round wire motors is relatively low.

In contrast, flat wire motors utilize rectangular wires, reducing the gaps between them. This design allows heat to dissipate more quickly, enabling flat wire motors to handle higher instantaneous power without overheating.

Additionally, the structure of flat wire windings forms loose pores that facilitate the flow of air or coolant, further enhancing heat dissipation. Round wire motors, with tightly bundled wires, struggle with efficient heat removal, making them more prone to overheating and damage.

flat wire motor vs. round wire winding heat dissipation

Slot Fill Factor

Maximizing the use of space within the stator slots is crucial for motor efficiency. Round wire motors suffer from lower slot fill factors due to the gaps between round wires. These gaps not only impair heat dissipation but also prevent optimal use of the available space, resulting in lower performance.

Flat wire motors, on the other hand, benefit from the rectangular cross-section of their wires, which better conforms to the shape of the stator slots. This design allows for a higher slot fill factor, increasing by approximately 29.5% compared to round wire motors. This enhanced slot fill factor translates into superior performance and efficiency.

flat wire motor vs. round wire motor slot fill factors


Efficiency is a key parameter in motor performance, and flat-wire motors significantly outperform round-wire motors in this aspect. The characteristic curves of flat wire motors show a marked improvement in operational efficiency. The high-efficiency region (represented by the 95% efficiency contour) covers a much larger area for flat wire motors, at least double that of round wire motors.

Furthermore, the highest efficiency regions of round wire motors are small and achieve only about 96% efficiency. In contrast, flat wire motors have a larger highest efficiency region, reaching up to 97.5%. Overall, flat wire motors are more energy-efficient, providing substantial savings in operational costs.

flat wire motor vs. round wire motor efficiency

Volume Control

Under the same power conditions, round wire motors need to increase in size to ensure adequate heat dissipation, requiring more wire and iron core material. Additionally, the end windings of round wire motors are bulkier due to the bundled round wires’ bending paths, increasing the motor’s overall height.

Flat wire motors, with their superior heat dissipation, do not require as much redundancy in materials. The end windings of flat wire motors are mechanically bent, resulting in a lower height and a more compact motor design. This allows flat wire motors to deliver the same power output in a smaller package, optimizing space and material usage.


The manufacturing costs of motors are primarily influenced by the cost of silicon steel sheets and copper wire. Due to their excellent heat dissipation, flat wire motors require fewer redundant materials, reducing the amount of copper and steel needed. As a result, flat wire motors can be produced at a lower cost—approximately 8.3% less than round wire motors—making them a more affordable option for users.

However, the winding process for round wire motors is relatively simple and well-suited for traditional manual or semi-automated production lines. In contrast, flat wire motors require more complex winding processes and specialized equipment for automated production, which can raise the manufacturing threshold. Nevertheless, this complexity ensures the superior quality and performance of flat wire motors.



Motor reliability is often assessed by comparing rated power and peak power. Rated power is the continuous power output the motor can sustain, while peak power refers to the maximum power the motor can achieve briefly, usually within a minute. The smaller the difference between these two values, the more advanced the motor is, as it indicates better heat management and overall performance.

Round wire motors, with their inferior heat dissipation, have a more significant difference between rated and peak power. This gap highlights their limited power output and greater susceptibility to overheating and damage. Conversely, flat wire motors, with their robust heat dissipation capabilities, maintain a smaller difference between rated and peak power, making them more reliable and advanced.


In the realm of new energy vehicles, the comparison between flat-wire and round wire motors highlights several critical differences in heat dissipation, slot fill factor, efficiency, volume control, manufacturing costs, and reliability.

Flat wire motors emerge as the superior choice in most of these key performance metrics. Their excellent heat dissipation and efficiency make them particularly suitable for demanding applications, providing better performance, lower costs, and higher reliability.

As the electric vehicle motor industry continues to evolve, understanding these differences will be essential for making informed decisions about motor selection and optimizing vehicle performance.

Lamnow is a leading electric motor lamination China manufacturer and offers stamping, winding, insulation coating, die casting, and glue bonding services. Our state winding employs round wire winding and flat wire winding, the process of flat wire winding includes Hair-pin, X-oin, I-pin, and S-winding. If your need stator and rotor lamination stacks relatives services, contact us today.

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