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When engineers are looking to buy a motor, the question most often asked:  Is AC or DC technology better? The answer isn’t that one is better than the other. Rather it is application and cost dependent.  Here we will discuss the options and specifically the advantages and disadvantages of each. Furthermore, it is often a matter of personal preference, and as such we encourage you to let us know your thoughts on the subject. What They Are Both AC and DC drives, simply put, control the speed and direction an electric motor. Both technologies have been around for over 100 years. AC drives, also known as adjustable speed drives or variable frequency drives (VFD’s) control motor speed by changing the frequency of the electrical supply to the motor.  With DC drives, the motor turns at a speed directly proportional to the voltage applied to the armature.