AC vs. DC The Ups and Downs in Operator Technology
By Rush E. Akin
There are many different “flavors” of garage door operators to choose from these days. Manufacturers often differentiate one operator model from another through options and features, including horsepower, speed, drive types and design, among others. In the United States, most residential garage door operators are primarily designed using alternating-current (AC) induction motors.
Recently, manufacturers have introduced several directcurrent (DC) motor-driven operators to residential and commercial markets. Naturally, this has led to questions about the real differences between AC operators and DC operators and their consumer benefits.
In the 1950s, residential openers were first introduced and AC-powered garage door operators were standard. This remained until the early 1990s when operator manufacturers introduced DC motor-driven operators.
Distinctions between the two operators can be attributed to characteristic differences in the actual motors. DC motors are finding their way into new products and applications that previously used AC motors exclusively. This includes such home appliances as exercise equipment, kitchen appliances and many portable electronic devices.
Compared to AC motor designs, DC motors are faster, more efficient and offer more accurate speed and position control. Even more, while AC motors produce an audible 60 Hz “hum,” DC motors are much quieter. DC motors are also usually smaller than AC motors, providing manufacturers the opportunity to design operators that are smaller with different styles and looks.
DC motors do, however, require a power conversion from AC power (distributed to the home) to DC power (supplied to the DC motor). Historically, DC conversion and control circuits were not cost-effective for manufacturers to incorporate in their designs. But as technology evolved, the continual decrease of semiconductors and logic circuitry cost has made DC power more reliable and economically feasible. Today, manufacturers can take advantage of the unique capabilities offered by DC motors and ultimately pass them along to consumers.
For consumers, DC motor-driven operators offer a smoother and safer operation, as they allow for easier and more responsive control of speed, torque and door position. In cases requiring quick stops, a DC motor eliminates the need for a mechanical brake by using dynamic or regenerative motor braking. DC motor speed can be controlled smoothly down to zero, followed immediately by acceleration in the opposite direction. Due to a high torque-to-inertia ratio, DC motors respond more quickly to changing control signals.
This control over the behavior of the operator offers benefits including soft starting and stopping of door movements, different open versus close speeds, faster obstruction response and more accurate door position control. For operators with AC motors, controlling speed and torque is more difficult because three electrical parameters (frequency, voltage-to-frequency ratio and phase relationship) must be varied to compete with DC response times.
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In today’s world of high-energy costs, the use of garage door openers can be one way to reduce monthly bills. Generally, permanent magnet (PM) DC motors draw less current (about two to four times less) and therefore require less power consumption compared to an AC motor with equal output power. With DC operators consuming less power, manufacturers have been able to offer consumers a battery-sourced operator for occasions when the power is out.
As far as operating temperature, there is no significant difference between AC and DC operators. Most operators are designed to operate in temperature ranges of -30°F to 155°F, which covers most of North America. Both offer consumers good operation with varying temperature ranges.
One strong advantage of AC motors is life expectancy. AC motors are brushless and therefore do not have any wearing parts except bearings. DC operators designed with DC brush motors can have a limited life. Operators designed with DC brushless motors eliminate brush wear and can have similar life expectancies to that of an AC motor.
DC operators can offer consumers smoother, quieter, more precise and more efficient operation, while AC operators may have a longer motor life. The optimal operator really depends on the performance desired in the garage door operation. For basic door movement between open and close limits, the AC operator may be more economical in terms of initial investment. But for improved door control, ergonomics and efficiency, the DC operator has the advantage.
Manufacturers are looking closely at DC motor technology for future designs and the benefits they provide to consumers. As technologies become more advanced and cost-effective, we should expect to see more DC operators introduced to the market featuring different designs as well as improved performance.
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There are many different “flavors” of garage door operators to choose from these days. Manufacturers often differentiate one operator model from another through options and features, including horsepower, speed, drive types and design, among others. In the United States, most residential garage door operators are primarily designed using alternating-current (AC) induction motors.
In today’s world of high-energy costs, the use of garage door openers can be one way to reduce monthly bills. Generally, permanent magnet (PM) DC motors draw less current (about two to four times less) and therefore require less power consumption compared to an AC motor with equal output power. With DC operators consuming less power, manufacturers have been able to offer consumers a battery-sourced operator for occasions when the power is out.