Hardware Comparison: SMC 3 vs. SMC-50 vs. SMC Flex

Starting and stopping seem like simple concepts.  But when it comes to motor controls, not only the speed of the stop and start matter, but “how” they stop matters as well.  Starting solutions come in a wide array of options. 

Across-the-line starters are the simplest style of motor starter.  Here, full voltage is applied to the motor terminals for situations where the inrush current of the motor does not cause excessive voltage drops within the supply circuit.  This is often the case for simple pumps, compressors and conveyors.

For applications requiring greater loads and for high degrees of variation of the specific loads placed on motors, variable frequency drives (VFD) may be used.  These drives consist of an AC motor, a main drive controller and an operator/drive interface. 

Because of their range of speed and control, VFDs are used for process control across a variety of industrial and commercial applications for speed, flow, pressure, temperature and torque, as well as many others.  They are especially useful for applications with high starting torque and allow speed control during the run.  VFDs will also hold rotors at zero speed if needed.

While these two systems continue to find extensive use within industrial and commercial applications, today’s factories are “smarter” and more connected, requiring a greater degree of data monitoring and control over the motors that drive the system design.

For applications requiring a high degree of precision for monitoring smart machines and smart factories, Smart Motor Controllers (SMC)such as those in the SMC family by Allen-Bradley, offer superior data sensing to reduce programming time, minimize complexity and reduce errors.  These smart controllers are ideal for applications with low or medium starting torque and lightly or moderately loaded applications.  The limiting current of an SMC is the prime reason to use this starting method and SMCs allow power monitoring and help reduce wear and tear on the system.

Benefits of Smart Motor Controllers

Because it makes sense to monitor data from the point of the motor itself, the Allen-Bradley SMC family allows the capture of data such as:

• Thermal Capacity Utilization
• Trip and Warning History
• Current
• Voltage
• Time to Trip
• Time to Reset
• Energy and Power
• Number of Starts
• Operational Hours

Having this information available and interpreted through robust monitoring software means that SMCs can offer benefits over across-the-line and VFD controllers that include:

• Process Control – SMCs allow for efficient energy use and can be included in process optimization at the floor level.  This helps reduce wit time, improve quality and increases throughput.  Because the data that is captured can be visualized, SMCs provide real-time data as well as averages and trend data for managers to better hone parameters for process improvement.
• Motor Overloads – Once the bane of manufacturing, SMCs eliminate surprise overload on a motor with early warning and diagnostics.  This not only reduces downtime; it also allows decisions to be made prior to failure to help move the connected factory from a preventive to a predictive maintenance footing.  And studies have shown that such predictive maintenance programs can reduce maintenance costs by as much as 25%.
• Motor Underloads – SMCs also allow for monitoring of motor underloads to reduce repair time and downtime and helps technicians identify failures.
• Loss of Network – Because they allow monitoring across the system, network issues, including network signal loss does not have to impact operations.  In the event of a signal loss, local management of the process can be completed to run to the end of batch within an SMC.  This prevents product loss due to unexpected shutdown.

Comparing the SMC Flex, SMC-50 and SMC 3

The explosion of the connected factory and Industrial Internet of Things Technology (IIoT) is currently powering initiatives such as Industry 4.0.  From a mere 7 billion connected devices in 2017, it is expected that by 2021, the number will have increased to 35 billion worldwide and by 2025, that number is expected to be an astounding 75 billion devices.  As the connected factory becomes the norm, soft-start Smart Motor Controllers (SMCs) will become even more critical in manufacturing and commercial environments.

SMC Basic Comparison

SMC-3 – The SMC-3 is a compact designed controller that allows easy and secure setup.  It also has an integrated bypass for all three phases and has five start/stop modes.  It is a solid-state unit designed for three-phase motor control and has a built-in overload control.  This controller features two voltage ranges: 200…480V and 200…600V with all voltage ranges within the 50-60Hz range.  The units are also UL compliant and CE marked as well as several other compliance and approval ratings.

SMC Flex – The SMC Flex comes with removable control modules and power modules.  The fan assembly is also removable.  This modular construction simplifies installation and maintenance, and it has a built-in LCD and keyboard.  The SMC-3 has an integrated bypass with nine stop/start modes and three slow speed modes.  It also features full metering and bypass.  The SMC Flex can operate in the 1…1250A range for voltages that include 200…480V, 200…600V, or 230-690V.  The unit can also be used to control resistive loads.

SMC-50 – The highest flexibility within the SMC family is the SMC-50.  This unit offers advanced monitoring and protection as well as superior communication capabilities.  It is very energy efficient which improves downtime and increases system efficiency.  The SMC-50 allows application scalability by providing use in both normal and heavy-duty ratings.  It has expandable I/O and sensor capability and is network integration capable. 

The unit comes with either an integrated bypass or a solid-state power structure.  But it is also external bypass operational.  There are seventeen stop/start modes, three slow speed modes, and four special operating modes.  To allow maximum flexibility of integration into a connected system, the SMC-50 is scalable with two different configurations including:

1. Multilingual 20-HIM-A6 controller
2. Panel-mounted keypad with LCD display that features advanced configuration options

Control Mode Comparison

The heart of the SMC family lies in its wide range of start mode that promotes both energy efficiency and system flexibility over a wide range of control options.  With motors consuming as much as 64% of a manufacturer’s energy use, and with the increasing connectivity requirements worldwide, SMCs can help control energy cost while allowing advanced data collection for monitoring the health of the motor and the system to reduce maintenance cost.

• Soft Start – In soft start mode, the output voltage is ramped up to a set start time.  Both the initial torque setting, and the start time are user determined.  The output voltage is steplessly increased during acceleration ramp time.  Soft start is available in the SMC-3, SMC Flex and SMC-50.

• Kickstart – Many loads require a high torque pulse to provide break away and get the motor started.  This mode provides a current pulse over a pre-selected period of time.  Kickstart is available in the SMC-3, SMC Flex and SMC-50.

• Current Limit Start – If it is necessary to limit the start current, this user adjustable mode allows both current limit start time and starting current to be adjusted.  When set, the system maintains a constant current to the motor.  Current limit start is available in the SMC-3, SMC Flex and SMC-50.
• Pump control – As pumps account for 20% of motors worldwide, pump control mode is a critical feature for the SMC family.  Pump control mode is used for reducing surges in fluid pipe systems.  This prevents the start of a centrifugal pump at full voltage and speed and eliminates hammer knock and check valve slam issues.  It also helps prevent cavitation thus increasing pump life.  The controller microprocessor generates a motor starting curve that mimics the characteristics of the pump and monitors pump performance operation during start up.  Pump control is available only on the SMC Flex and SMC-50.
• Advanced Linear Speed Acceleration – Available only on the SMC-50, Linear Speed Acceleration mode means the motor accelerates at a constant speed during a user defined ramp time.  The unit contains a proprietary motor speed feedback algorithm which senses motor speed.   Using the SMC-50 in this mode means that motors do not require external speed sensors, reducing cost further.  Current limit values can be used during the ramp time.
• Torque Control – Another mode only available in the SMC-50, torque control allows the user to set an initial and maximum torque time over a defined ramp time.  This reduces stress on mechanical components and allows a more time-controlled ramp.  The starting ramp is more linear than a soft start and current value limits can be used to limit current throughout the torque start.
• Dual Ramp Start – For applications that require load, start times or torque variations, dual ramp mode allows the user to select from two startup profiles.  This provides flexibility for operations where process variability creates widely different ranges of throughput.  Each start profile is available through any programmable auxiliary port and each can use any available starting mode.  Dual ramp is available on both eh SMC Flex and the SMC-50.
• Full Voltage Start – Some applications require across-the-line starting.  For these applications, the SMC Flex and the SMC-50 act as a solid-state contactor.  The user can program the unit to provide a full voltage start.
• Preset Slow Speed – In addition to full speed production, modern manufacturing automation includes using motors for applications that require slower speeds for positioning or aligning as well as maintenance.  The SMC Flex and SMC 50 allow preset slow speed which also enables forward and reverse motion on select at speeds selectable by the user.  The SMC-50 allows slow speeds of 1%-15% of base speed while the SMC Flex allows slow speeds of 7%-15% of base.
• Coast – Many applications can allow the motor to coast to a stop.  This feature is available on the SMC-3, SMC Flex and SMC-50.
• Soft Stop – For applications requiring an extended stop time, the entire SMC family line offer soft stop capability.  The ramp down time is different among the three units, however.  For the SMC-3, the voltage ramp down time can be set to one, two, or three times the start time.  For the SMC Flex, ramp down time can be set from 0…120 seconds and is independent of the start time.  And the SMC-50 ramp down time can be set from 0…999 seconds.  In all models, the load stops when the voltage ramp down drops to a point where load torque is greater than motor torque.
• Smart Motor Braking – Smart Motor Braking (SMB™) is used for applications where the motor must stop faster than that of a coast down.  Available on the SMC Flex and SMC-50, but not on the SMC-3, SMB also features automatic shut off integrated into the controller and requires no additional braking hardware.  The feature can be set by the user at 0…400% of the full-load current.
• Slow Speed with Braking – Many alignment and positioning requirements of equipment require the use of slow speed as well as braking for stopping.  This feature is intended for such applications but is not meant to be an emergency stop.  Slow speed with braking is available on the SMC Flex and SMC-50. 
• Accu-Stop™ – Accu-Stop™ can be used in applications where precise positioning of the stop point is required for process functions.  Here, braking torque is applied until the motor reaches ±1…±15% and then holds the motor until given a stop command.  Once the braking command is given, torque is applied to the motor until it reaches zero speed.  The braking current can be set at 0…400% of base current and is programmable by the user, as are slow speed values.  This feature is not available in the SMC-3 and is native to the SMC Flex.  It is not a parameter function in SMC-50 bit it can be used in the SMC-50 by using both the Stop Option in conjunction with the Slow Speed with Braking function.
• Resistor Loads – Available only for the SMC-50, 3-phase resistive loads can be directly controlled.  This mode is most often used in applications for resistive heating. 

Additional Comparisons

The SMC-3 unit is best suited for lighter application needs that do not require extensive data collection.  Other advanced functions are found only in the SMC Flex and SMC-50.  These include:

• DPI Communication
• Metering
• Diagnostic Faults and Alarms

Other features found only in the SMC-50 include:

DeviceLogix™

• Automatic Turning of Motor Parameters
• Individual Bit Enable of Faults and Alarms
• Resistive Load Control (Available in solid state SMC-50 and not the SMC-50 with Internal Bypass)
• Energy Saver Mode (Available in solid state SMC-50 and not the SMC-50 with Internal Bypass)

As the connected factory becomes more a reality over the next few years, more controllers will be tasked to do an ever-increasing number of functions.  The Allen-Bradley SMC family is a smart way to get ahead of the connectivity curve and build smart controls into a factory system.