SMC-2 Selection Guide
The Allen-Bradley SMC Controller line offers a wide variety of products for starting and stopping AC induction motors with a power range from 1/3 HP to 6,000 HP. The controllers are designed with innovative features, a compact design, and enclosed controllers that meet global industry standards for motor control. These controllers are suitable for controlling a single motor or an integrated automation system and come in different models, such as the Starting Torque Controller (STC) and the Smart Motor Controller family (SMC-2, SMC PLUS, and SMC Dialog Plus) to meet different needs.
The SMC-2 Controller is a compact, multi-functional, and versatile solid-state controller designed for starting standard three-phase squirrel-cage induction motors. It is available in three modes of operation and comes in eight sizes with three voltage ranges. The controller can be used in two configurations: a series controller and a motor controller with an interface option. It is CE marked, CSA certified, and UL listed. The controller offers energy saving, soft start, current limit start, complete voltage start, and an optional soft stop. It also has an optional protective module for high or abnormal line transients. The interface option can be field or factory attached, eliminating the need for an additional contactor and reducing panel space requirements.
SMC-2 Smart Motor Controller
The SMC-2 Smart Motor Controller is a compact and versatile solid-state controller used to start standard three-phase squirrel cage induction motors and control resistive loads. It is available in different current ranges from 5 to 97 Amps, voltage ranges from 200 to 600V, and frequencies of 50/60 Hz. It is UL Listed, CSA Approved, and CE-labelled, making it suitable for applications up to 75 horsepower.
Modes of Operation
The SMC-2 Smart Motor Controller offers a variety of standard modes of operation within a single controller, including Soft Start, Current Limit Start, and Full Voltage Start. It also has an energy-saving feature that allows the controller to conserve energy when the motor is lightly loaded or not in use for long periods. The Soft Start mode is the most commonly used method and allows the initial torque value to be set between 0-70% of locked rotor torque. The motor voltage is increased gradually during the adjustable acceleration ramp period, which can be set from 2-30 seconds. The Current Limit Start mode limits the maximum starting current and can be adjusted from 25 to 550% of total load amperes. If the motor is not up to speed after the selected time, it will transition to full voltage. The Full Voltage Start mode is used for applications that require across-the-line starting, with a ramp time of less than one tenth of a second.
Features
The SMC-2 Smart Motor Controller has a red LED on the front for diagnostic indication. The LED will be on when the Controller is connected to three-phase power. It monitors several fault conditions, such as a shorted SCR (pre-start only), Phase Loss (line side and pre-start only), and Stalled Motor (when the stall switch is on). In the event of a shorted SCR or phase loss, the Controller will not start, and the LED will flash. The Controller will shut down and flash the LED if a stalled motor condition is detected. If the three-phase input power is lost, the LED will turn off.
Smart Motor Controller Types
The Open Type SMC-2 Controller is a standalone unit that can have an interface module, solid-state type overload relay, and protective module added to it. The Non-Combination SMC-2 Controller is housed in an IP65 or IP54 enclosure and has the option for an external reset for overloads.
Series Mode
The SMC-2 Controller is designed to operate in series with an electromechanical starter. This mode of operation has several benefits, such as simplified initial startup, as there is no need for additional wiring. The series mode also makes retrofits easy, as it can work with an existing electromechanical starter. When the SMC-2 Controller is connected in series with an electromechanical starter, the starter's contactor is used to control the power to the Motor. The SMC-2 Controller then monitors the current and voltage of the Motor and provides the necessary control for soft starting and stopping and fault protection. The series mode is a cost-effective solution for upgrading an electromechanical starter system to an intelligent motor control system.
Options
The SMC-2 Controller can be operated by an external device using an optional interface. This interface offers several features, such as direct ON/OFF control through an external device, which can eliminate the need for an additional contactor in some applications and save panel space. Additionally, it has a configurable auxiliary contact that can function as an immediate or up-to-speed contact. The interface also includes a Soft Stop feature which extends stopping time to minimize load shifting or spillage during stopping. The interface option is available as a plug-in module for the 5-16 Amp devices and as an integral part of the logic design for 24-97 Amp devices. The Soft Stop option allows the voltage ramp downtime to be set from 5-110 seconds, and the starting and stopping times can be adjusted independently. The load will stop when the voltage drops to a point where the load torque is greater than the motor torque. To connect the interface option, the control power requirement is 5VA at 120V and 15VA at 240V. The auxiliary contact rating is NEMA C300, 2.5 Amps, 20-250V AC, 1 Amp, 12-30V DC. IEC overload relays can be mounted directly to the 5-, 9-, and 16-Amp SMC-2 controllers to save more panel space.
Combination Controllers
Combination controllers, housed in either IP65 (Type 4) or IP54 (Type 12) enclosures, can be ordered with or without an isolation contactor. A combination controller with an isolation contactor includes a rod-operated fusible disconnect, the SMC-2 Controller, and a 3-pole thermal overload relay. For controllers with a current range of 5-97 A, the current range of the solid-state overload relay must be selected accordingly. If not specified, a eutectic alloy-type overload relay (with fewer elements) will be provided in place of the solid-state overload. Eutectic alloy overloads are standard on enclosed controllers with a current range of 24-97 A. A combination controller without an isolation contactor includes a rod-operated fusible disconnect, the SMC-2 Controller with an interface option, a control circuit transformer, and a 3-pole thermal overload relay. Again, for controllers with a current range of 5-97 A, the current range of the solid-state overload relay must be selected accordingly. If not specified, a eutectic alloy-type overload relay (with fewer elements) will be provided in place of the solid-state overload.
Applications
The SMC-2 Controller is a versatile, compact, solid-state motor controller designed to start and control standard three-phase squirrel cage induction motors and resistive loads. It offers a range of innovative features and options that can be tailored to meet the specific requirements of various industrial applications. Examples of the many possible applications of the SMC-2 Controller have been described, along with the reasons for selecting a particular control method.
A conveyor was used to transport logs where the drive chain was breaking due to uncontrolled start-up, which caused interruptions in the production schedule and a loss of productivity. The solution was to attach the SMC-2 Controller, which has a compact design, to the space vacated by the previous starter. A 10-second soft start was selected, which reduced the starting torque and the shock to the mechanical system.
Another example is a bottle-filling line with product spillage upon starting and stopping. The SMC-2 Controller was attached and set for a 10-second soft start and a 20-second soft stop. This controlled the starting torque and prevented the sudden onset that would cause the bottles to spill. The smooth finish extended the stopping time, eliminating load shift while stopping. The auxiliary contact was configured to change state when the motor was up to speed.
A towline conveyor at the end of a production line had frequent damage to the gearbox due to the across-the-line starting of the motor. To prevent this, the SMC-2 Controller with the Interface option was attached, with starting and stopping times of 15 seconds selected. This reduced torque starting prevented shock to the gearbox and kept the load from shifting on startup, while the soft stop prevented the load shifts while stopping.
A power walk at an airport required a soft start to prevent damage to the drive chain gearbox on startup. The SMC-2 Controller with the Interface option was designed into the system. A 10-second soft start with the Energy Saver enabled was selected. A 10-second soft stop was also established. This allowed the power walk to have a controlled start and stop. During periods when the walk was unloaded, the SMC-2 Controller Energy Saver reduced the voltage to the Motor, minimizing the magnetic losses of the Motor.
A tumbler used in a nail-finishing process broke the drive chain due to uncontrolled acceleration from an across-the-line start. The SMC-2 Controller was attached after the reversing contactor to control the motor's starting torque, preventing the snapping of the drive chain on startup and thus increasing the chain's life and reducing downtime.
There are several other examples of different types of applications and how the SMC-2 Controller can be used to improve the performance and productivity of the system.
Design Philosophy
The design philosophy of Allen-Bradley's SMC controllers is to provide consistent and reliable operation in industrial environments. They are manufactured to withstand line voltage conditions such as voltage transients, disturbances, harmonics, and noise in any industrial supply. The controllers are designed to operate over a wide voltage range, at 50/60 Hz, within a given controller rating and can withstand 3000V surges at a rate of 100 bursts per second for 10 seconds. Furthermore, they can withstand the showering arc test of 350-1500V for higher resistance to malfunction in a noisy environment. An optional MOV module is also available to protect SCRs from voltage transients.
Additionally, the controllers have a solid-state current and thermal rating to ensure reliability under the wide range of current levels and starting times needed in various applications. They also meet the same mechanical shock and vibration specifications as electromechanical starters. They can withstand a 30G shock for 11 ms in any plane and one hour of vibration of 2.5G without malfunction.
Reduced Voltage Starting
Reduced-voltage starting is a method used to limit line disturbances and reduce excessive torque to the driven equipment when starting a motor. The most common form of reduced-voltage starting is using an autotransformer, followed by the Wye-Delta method. When a reduced voltage is applied to a motor at rest, the current drawn by the motor is reduced, and the torque produced by the motor is also reduced. The magnitude of the starting torque depends on the motor design, and NEMA publishes standards for torques and currents for motor manufacturers to follow. In many applications, the high starting torque can cause excessive mechanical damage, such as belt, chain, or coupling breakage. Limiting line is a prime reason for using reduced-voltage starting, and torque control is also a critical factor in selecting a reduced-voltage starter.
Electromechanical reduced voltage starters must transition from reduced to a total voltage at some point in the starting cycle. There are two transition methods: open-circuit transition and closed-circuit transition. Open circuit transition means the Motor is disconnected from the line for a brief period, which can result in a higher current surge. Closed circuit transition, on the other hand, keeps the Motor connected to the line during the transition, resulting in a lower recent rise. The motor speed also plays a role in determining the amount of current surge that occurs at transition. It is recommended that the transfer from reduced voltage to full voltage should occur as close to full speed as possible to minimize the current surge.
In addition to electromechanical reduced voltage starting methods, electronic reduced voltage-creating methods include solid-state reduced voltage starters and variable frequency drives (VFDs). Solid-state reduced voltage starters use SCRs to control the voltage applied to the Motor, while VFDs vary the frequency of the power applied to the Motor. Both of these methods offer precise control over the voltage.
Solid-state controllers are designed to provide a soft start or a gradual reduction in voltage when starting AC motors. This method is known as reduced voltage starting and is used to limit line disturbances and reduce excessive torque on the driven equipment. Solid-state controllers offer a range of starting modes, including soft start, current limit start, dual ramp start, or complete voltage start, which can be adjusted to suit the specific application. The quiet start mode is the most used, providing a smooth start for most applications.
Solid-state controllers eliminate the need for a current transition point and allow time adjustment to reach full voltage, resulting in no significant recent surge. Additionally, solid-state controllers can provide an energy-saving function by reducing voltage to the Motor when running at a low load or idle for prolonged periods. Other features include added protection and diagnostics to aid in setup and troubleshooting.
Solid-state Starters Using SCRs
In solid-state starters, silicon controlled rectifiers (SCRs) are used to regulate the voltage output to the motor. These devices allow current to flow in one direction, and the conduction level is controlled by the pulses sent to the gate of the SCR. When two SCRs are connected back-to-back, the AC power to a load can be adjusted by changing the firing angle of the line voltage during each half-cycle. This allows for a gradual and continuous increase or decrease of voltage and current to the motor. The SMC Dialog Plus controller uses a microprocessor to manage the firing of the SCRs, and six SCRs are used in the power section to provide full-cycle control of voltage and current. This allows for a smooth and gradual start of the motor.
Advantages of SMC-2
The SMC2 Advantage offers a range of benefits for clients looking for cost-effective and efficient IT solutions. One of the key advantages is cost savings, which can be achieved by utilizing a third-party provider with a large onsite team. This can result in cost savings of at least 35% compared to maintaining an in-house team. Additionally, SMC2 has access to a large pool of IT talent and can attract better talent with an industry-leading low attrition rate.
The company also offers an easy setup process, with a proven approach that can guide clients efficiently through onboarding processes, regardless of the organization's size. This approach ensures a smooth transition into the new IT system.
Another advantage is forming partnerships with other IT vendors and startups within SMC2's network. This allows clients to take advantage of a broader range of services and technologies. Lastly, SMC2's seasoned leadership team brings a wealth of experience, providing clients with valuable insights and advice to determine the best fit for their organization. With their "walked in your shoes" experience, clients can feel confident that their IT solutions are tailored to their specific needs.
