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. |
