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Automatic Gates - Which voltage?

An Overview of AC v DC Motor Drive Technology for Gate Openers

In recent years, manufacturers have increased their range of direct current (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 benefits.

There are many different types of gate operators to choose from these days and manufacturers often differentiate one operator model from another through options and features, including horsepower, speed, drive types and design, among others. In the past most gate operators were primarily designed using alternating current (AC) induction motors but this is rapidly changing.
When residential and commercial openers were first introduced AC powered gate operators were standard due mainly to their low manufacturing cost. There were one or two manufacturers like TAU who focused on low voltage DC operators but they were few and far between - not to mention expensive. This remained until the early 1990s when mainstream gate operator manufacturers introduced DC motor driven operators in a larger and more economical way.

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 home appliances such as exercise equipment, kitchen appliances and many motor driven 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, therefore providing manufacturers the opportunity to design operators that are smaller with different styles and looks. DC motors can be used in high duty cycle applications as they do not have capacitors like AC motors do, therefore the DC motor runs cooler in high cycle applications and does not retain motor heat such as in AC motors  
DC motors do, however, require a power conversion from AC power to DC power (supplied to the DC motor). Historically in the past, 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 costs 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 & gate 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 and gate movements, different open versus close speeds, faster obstruction response and more accurate door and gate 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.
In today’s world of high-energy costs, the use of garage door and gate openers can be one way to reduce energy 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 backup operator for occasions when there is a power outage to supply. Also with DC motors there is the option of solar power supply which is useful with automatic gates where providing 240 volt supply to the gate location is uneconomical or impractical.
As far as environmental operating temperature, there is no significant difference between AC and DC operators. Most operators are designed to operate in temperature ranges of -10°C to 70°C. Both offer consumers good operation with varying temperature ranges.
One strong advantage of AC motors is life expectancy. AC motors are brush less and therefore do not have any wearing parts except bearings. Early DC operators designed with DC “brush” motors can have a limited life span, however newer technology operators designed with DC “brush less” 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 or gate operation. For basic door or gate movement between open and close limits, the AC operator may be more economical in terms of initial investment. But for improved door and gate control, ergonomics and efficiency, the DC operator has the distinct 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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