Interestingly, the major influence for that better way came about during World War II when brushed DC motors in high-altitude aircraft failed when brushes rapidly deteriorate above 30,000 feet. They wear out and require regular replacement, so science found a better way of commutation. However, brushes have some inherent problems. These motors are simple to produce, are relatively inexpensive and are still in use. Figure 1: The brushes in a brushed direct current motor change the polarity of the motor’s magnets with each revolution. When the rotor gets to the proper position, the brushes, which connect the voltage to the windings that produce the magnetism, connect with the next section of the commutator to reverse the magnets’ polarity. Brushed DC motorsįigure 1 is a brushed DC motor. The trick is to change the polarity of the magnets at the proper time to keep the rotor spinning. The opposing and attracting forces between the stator and rotor poles cause the rotor to turn. Starting with the very basics, a motor requires magnets in the stator and magnets in the rotor. Both VFDs and ECMs each have their place. The trouble is, the answers are all dependent on a variety of the bounds that frame the answer, such as size, application, system components, personnel training and many other factors.
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