A permanent magnet motor is a motor that uses permanent magnets as the excitation source. In the permanent magnet motor, the permanent magnets are usually AlNiCo magnets, ferrite magnets, samarium cobalt magnets and neodymium iron boron magnets.
NdFeB magnets include sintered NdFeB magnets and bonded NdFeB magnets. Sintered NdFeB magnets are usually designed as arc-shaped tile magnets or rectangular magnetic strips, and are installed in an alternating sequence of S/N poles. This structure allows NdFeB magnets to provide a stable and strong magnetic field. Ring motor magnets are generally bonded neodymium magnets, and ring motor magnets usually require multi-pole magnetization. Although the magnetic force of NdFeB magnets is very strong, eddy current loss is a problem that must be considered when choosing NdFeB magnets. The working temperature of NdFeB magnets is usually between 80°C and 230°C depending on the magnetic grade. (For the operating temperature of NdFeB magnets, please refer to the article on the effect of temperature on NdFeB magnets.) Once the high temperature caused by eddy current loss exceeds the working temperature of NdFeB magnets, it will cause irreversible demagnetization.
2. Samarium Cobalt Magnet
Sintered samarium cobalt magnets play an irreplaceable role in some specific motor applications. It has very good temperature stability. Unlike NdFeB magnets, changes in temperature have little effect on the magnetic properties of samarium cobalt magnets. The magnetic properties of samarium cobalt magnets are close to those of neodymium iron boron magnets, but due to their high price, samarium cobalt magnets are usually used in high temperature motors such as aviation motors.
3. AlNiCo magnets
Alnico magnets are less magnetic than rare earth magnets and are therefore rarely used in motors. Under some special conditions, the motor needs to work above 350°C. At this time, the samarium cobalt magnet with a temperature resistance of 350°C is powerless. We can only choose alnico magnets. The maximum working temperature of alnico magnets is usually 550 Celsius.
4. Permanent magnet ferrite magnet
Ferrite magnets have a large market share in permanent magnet motors. In addition to low cost, corrosion resistance, and a wide operating temperature range, ferrite magnets are immune to eddy current losses due to their high resistivity. Due to the relatively low magnetic energy of permanent magnet ferrite magnets, permanent magnet motors made of ferrite are usually bulky.