In recent times, manufacturers have introduced several direct current
(DC) motor-driven operators to road barrier markets. Naturally, this
has led to questions about the real differences between AC operators
and DC operators and their consumer benefits.
There are many different types of road barrier 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. Most road barrier operators are
primarily designed using alternating current (AC) induction motors.
When road barrier openers were first introduced AC powered 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 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 behaviour of the operator offers benefits including
soft starting and stopping of movements, different open versus close
speeds, faster obstruction response and more accurate 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 road barrier 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 source 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 sites where providing
240 volt supply to the 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 operation. For basic movement between open and close limits,
the AC operator may be more economical in terms of initial investment
but for improved 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.
