Magnetic Rotor Assembly
The magnetic rotor is the non-stationary part of a motor. It may be fixed to or built into the rotating shaft that carries it as an integral component, as in a DC electric motor, or consist of a separate electromagnet assembly which rotates independently from the armature and commutator, as in an asynchronous AC electric motor. In other cases, particularly with small appliances such as fans and video players, there is no need for a power take-off mechanism since the one electrical connection serves both purposes. The permanent magnet rotor itself consists of magnets mounted on a spinning shaft so they remain upright as they rotate.
The magnetic rotor is composed with one or more magnets. The common materials used are Neodymium magnet, AlNiCo magnet, Samarium Cobalt magnet, Ferrite. The types of materials depend on the applications.
In single phase motors, two types exist: Shaded pole type and Permanent Magnet type on field current distribution. In shaded pole type, the stator with its coils is rotated at a high speed for motor rotation. As it rotates, the shading coil which is mounted in between two poles becomes electromagnetically induced by the North and South Pole of Magnet Rotor to rotate the Magnet Rotor in clockwise direction.
In Permanent Magnet type on field current distribution, Magnet Rotor consists of permanent magnets and rotor-stator made up of steel lamination. The Magnet Rotors are electrically connected across supply line (phase) and referred to as exciting current passes through that Magnet Rotor assembly only (known as single phase or mono-phase). The Magnet rotor can also be considered as an electromagnet due to magnetic field effect created by Magnet Rotor assembly. The Magnet Rotors are placed on shaft and rotated. When the Magnet Rotor is rotated, it induces electric and magnetic fields in stator winding due to electromagnetic induction depending upon relative position between Magnet Rotor magnetic field lines with that of the stator winding thus creating effect to start, run or rotate the motor at desired speed depending upon number of poles to be excited in Magnet Rotor Assembly
The rotor must be insulated from its shaft, together with any nearby conductive parts of the motor housing, otherwise a short-circuit would result when current passed through it.
Since permanent magnets are not magnetic when stationary they must be rotated, or at least held in a moving magnetic field to become magnetized. Magnet rotors produce alternating current power which is supplied directly to an electric motor instead of using mechanical gears or belts as in conventional motors. The Magnet Rotor is useful in applications requiring only low torque; hence especially suited for water pumps, fans etc. where starting needs not be very fast (the rotor does not have to speed up). Magnet rotors are used in most small household fans, including table fans and ceiling fans.
Small Magnet Rotors are also commonly found in electronic equipment such as portable cassette players, keyboards on electronic musical instruments, appliances, shavers/electric razors, some computer disk drives (as the “rotor” part of a voice coil motor), tape recorders etc.
A different type of magnet rotor is more or less common in loudspeakers for domestic PA systems. Magnet Rotor consists of permanent magnets mounted onto rotating shaft so they remain upright while turning. It can be considered as electromagnet due to its magnetic field effect created by Magnet Rotor assembly when current passes through it.