<P> In the past, repulsion - start wound - rotor motors provided high starting torque, but with added complexity . Their rotors were similar to those of universal motors, but their brushes were connected only to each other . Transformer action induced current into the rotor . Brush position relative to field poles meant that starting torque was developed by rotor repulsion from the field poles . A centrifugal mechanism, when close to running speed, connected all commutator bars together to create the equivalent of a squirrel - cage rotor . As well, when close to approximately 80 per cent of its run speed, these motors can run as induction motors . </P> <P> Operating at normal power line frequencies, universal motors are often found in a range less than 1000 watts . Their high speed makes them useful for appliances such as blenders, vacuum cleaners, and hair dryers where high speed and light weight are desirable . They are also commonly used in portable power tools, such as drills, sanders, circular and jig saws, where the motor's characteristics work well . Many vacuum cleaner and weed trimmer motors exceed 10,000 RPM, while many Dremel and similar miniature grinders exceed 30,000 RPM . </P> <P> Universal motors also lend themselves to electronic speed control and, as such, were an ideal choice for domestic washing machines . The motor can be used to agitate the drum (both forwards and in reverse) by switching the field winding with respect to the armature . The motor can also be run up to the high speeds required for the spin cycle . Nowadays, variable - frequency drive motors are more commonly used instead . </P> <P> Universal motors also formed the basis of the traditional railway traction motor in electric railways . In this application, the use of AC to power a motor originally designed to run on DC would lead to efficiency losses due to eddy current heating of their magnetic components, particularly the motor field pole - pieces that, for DC, would have used solid (un-laminated) iron . Although the heating effects are reduced by using laminated pole - pieces, as used for the cores of transformers and by the use of laminations of high permeability electrical steel, one solution available at the start of the 20th century was for the motors to be operated from very low frequency AC supplies, with 25 and 16 ​ ⁄ Hz operation being common . </P>

The no load speed of an electrical mixer motor is about rpm