The answer is: it depends. It depends on a number of factors that are specific to the application. Read more to discover the important factors to consider when deciding which type motor and control to use. Read on to find out more about what those considerations are and how they impact the decision: AC or DC?
Advantages of AC Motor/Drive (Over DC)
- Reduced maintenance – there are no motor brushes and therefore none to replace over time
- Efficiency – federal regulations mandate a minimum level of power use efficiency for AC motors, especially those 5HP and up. DC motors use more energy than AC motors
- Flexibility – AC variable frequency drives often have 200+ configuration parameters available to program, digital and analog inputs/outputs and logic (plc) in support of the motor control. These features are attractive to the experienced user. They also require a higher level technical ability of maintenance and operations personnel
- Cost – traditional AC motors are less expensive than their equivalent horsepower rated DC counterparts (> 1HP)
- Availability – there are more AC motor manufacturers worldwide than equivalent DC
Advantages of DC Motor/Drive (Over AC)
- Starting torque and speed range – these are both much higher for DC – an inherent characteristic. AC motors require more sophisticated and expensive controls to be equivalent, possible even encoder feedback from the motor
- No bearing currents – an issue with AC motors when using an AC drive can be a phenomena called bearing currents. These are destructive and eventually will cause permanent bearing damage to an AC motor if present
- Battery / Solar applications – DC motors offer 12VDC, 24VDC (and more) options typically used in battery, solar and portable equipment applications
- Cost – below 1 horsepower DC motor and control total cost is likely less than its AC counterpart
- Ease of Use – DC motors and controls are inherently simple to install and operate
In the end, there is a market for both AC and DC, and there are clearly advantages and disadvantages to both. What do you think? What is your motor drive preference?