Common Issues with Motor Outer Rotors

In the structure of an external rotor motor, magnets are typically bonded to the inner wall of the rotor housing, where they are subjected to centrifugal forces caused by high-speed rotation over extended periods, compounded by factors such as temperature rise and vibration. Consequently, several common issues and their causes often arise with external rotor magnets during actual operation.

First, magnet detachment is one of the most common and high-risk issues in external rotor motors. The root causes are primarily related to unreliable bonding, such as adhesive with insufficient temperature resistance or shear strength, or manufacturing defects like uneven adhesive application or incomplete curing. If oil residue or oxidation layers on the magnet surface are not thoroughly cleaned, adhesive adhesion is significantly reduced. Combined with long-term thermal cycling, the adhesive layer ages and cracks, ultimately leading to magnet detachment.

Second, magnet displacement is another common issue. Although the magnet has not completely detached, a shift in its position or angle directly disrupts the symmetry of the magnetic field distribution, causing torque fluctuations and increased noise. This problem is primarily caused by bonding failure, such as improper adhesive selection or an adhesive layer that is too thin.

Demagnetization or a decline in magnetic performance is equally common. During operation, an external rotor motor generates a certain degree of temperature rise. If this exceeds the temperature rating of the magnetic material itself, irreversible demagnetization will occur, leading to a decrease in motor torque and reduced efficiency. Additionally, under abnormal operating conditions, such as high-current surges or control failures, a strong reverse magnetic field may be generated, which can also cause demagnetization of the magnets.

In addition to the issues mentioned above, dynamic imbalance is another problem that cannot be overlooked in external rotor motors. Since the magnets themselves contribute to the rotor’s mass distribution, any weight discrepancies, deviations in bonding positions, or localized missing sections will directly disrupt the rotor’s dynamic balance. This leads to increased motor vibration and noise, and may even affect bearing life. The issues listed above are the most common ones.