The volume ratio of permanent magnet and self-excited motors at the same power depends on a variety of factors, including the design of the motor, manufacturing process, materials, etc. Therefore, it is difficult to give a specific volume ratio.
Generally speaking, permanent magnet motors can generate magnetic fields without relying on external power sources due to the use of permanent magnets, so their volume may be slightly smaller than that of self-excited motors at the same power. However, this is not absolute, as the size of the motor is also related to factors such as its design, heat dissipation needs, rotor structure, etc.
If you want to obtain a specific volume ratio, it is recommended to consult the product manual of a professional motor manufacturer or consult a professional technician.
In addition to the difference in volume, permanent magnet and self-excited motors also differ in performance. Permanent magnet motors typically have higher efficiency and lower energy consumption because they do not need to consume additional energy to generate a magnetic field. This allows the permanent magnet motor to save energy costs in long-term operation. In addition, since the magnetic field strength of permanent magnet motors is high, their torque is relatively large, making them advantageous in applications that require high torque. On the contrary, the advantage of self-excitation motors lies in their speed regulation performance. Since the magnetic field of a self-excited motor can be adjusted by an external power source, its rotational speed can be adjusted as needed. This gives self-excited motors an advantage in applications that require precise control of rotational speed, such as CNC machines, textile machinery, etc. To sum up, permanent magnet and self-excited motors have their own advantages and disadvantages, and the specific choice of which type of motor depends on the needs of the actual application. When choosing an electric motor, many factors such as motor performance, volume, energy consumption and application scenarios should be fully considered. 