Allen-Bradley SMC-50, User Manual

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42 Rockwell Automation Publication 1560F-UM001A-EN-P - June 2019
Chapter 1 Product Overview
Functional Description
The following functional descriptions and associated control circuits are for units
using IntelliVAC contactor control modules. For units with electromechanical
(relay) control, refer to Appendix C .
Bulletin 1562F • Standard Control
When wired as shown in Figure 24 , the controller operates as follows:
Pressing the “Start” button initiates the start sequence. Relay “CR” closes and
applies control power to terminal A1 of 150-SM4 Digital I/O card that is
inserted in the SMC-50 module. The Aux #2 (“Normal”) closes, energizing “M-
IV” and “MCX”, which completes the hold-in circuit on the start button, and
closes the main contactor.
The SMC-50 module examines the line voltage, looks for fault conditions,
checks phase rotation, calculates zero crossing information, and begins gating the
SCRs to start the motor.
When the motor approaches rated speed, the SMC-50 module closes the
“Aux #1” (Ext. Bypass) auxiliary contacts, energizing “B-IV”, which closes the
bypass contactor. The motor then runs at full line voltage.
When the “Stop” button is pressed, the “CR” relay opens terminal A2 of 150-
SM4 Digital I/O card that is inserted in SMC-50 module. If terminal A2 is
programmed to be Coast-to-Stop, the Aux2 (Normal) contact opens, dropping
out the main contactor, allowing the motor to stop. The Aux1 contact is held
closed for a short time by control module. This holds the bypass contactor closed
for several seconds as set in Par 192 of SMC-50 module to protect the power
electronics from any voltage transients due to opening the motor circuits. If
terminal A2 is programmed to be Stop Option, the SMC-50 module will initiate
the option stop.
ATTENTION:
The control circuit schematics shown below assume that control
power is fed from the same source as the primary circuit. If external control
power is used, additional control interlocking may be required to avoid
unexpected motor start-up. The control interlock should ensure that a motor
start request is not inadvertently applied when the primary circuit is
disconnected.