It’s important to note here that VFDs can drive permanent magnet motors, too. The use of permanent magnets contributes to two important areas that will be covered in more detail later: higher efficiency and higher cost. The intelligence built into the controls turns the ECMs into specific-purpose devices.īeyond that definition, ECMs are most often permanent magnet motors. In the HVAC world, ECMs are generally thought of as a motor and controls integrated into a single unit. ECMs use electronics, such as Hall Effect sensors, to sense the position of the rotor for commutation of the magnets. So now, 60 or 70 years later, we have ECMs that use electronic devices like power switching transistors to replace the mechanical commutator assembly of a DC motor. Then, things really got urgent when it was discovered that brushes lasted only minutes in the hard vacuum of space. The first patent for what was then called a “commutatorless DC motor” was claimed by Harrison Brailsford in 1955. 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. Thus, the motor keeps turning.įigure 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. Are ECM controls integrated with the motor?.
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