MOTOR AND CRANE CONTROL RESISTORS FOR SEVERE DUTY APPLICATIONS	Controlling motors with resistors is a universal method of speed control. The resistors are used to limit the in-rush current and adjust the torque and speed characteristics of an ac and dc motor. This section provides a fundamental understanding on how resistors are used for motor speed control, and the information required to design a resistor assembly. To order a resistor assembly, simply obtain the motor information required for your particular requirements and contact the engineering department at the Filnor Inc. factory to design a resistor assembly for your application. AC WOUND ROTOR INDUCTION MOTOR CONTROL For resistor applications used on Wound Rotor Motors, the resistors are connected in a wye connection on the rotor ( secondary ) of the motor. By changing the resistant on the rotor ( through contactor ), you can limit the starting torque and speed of the motor for your specific application. Data Requirements: • Motion ( Hoist or Travel ) • Secondary Voltage and Current • NEMA Class • Horsepower • Type of Control Scheme • Number of Speeds Typical reversing control schematic using 5 speed / 4 step acceleration resistor on an AC wound rotor motor AC SQUIRREL CAGE MOTOR CONTROL For resistor applications used on squirrel cage motors, the resistors are connected in line with the motor leads to reduce the voltage applied to the motor. The resistors will drop the starting voltage to the motor, therefore limiting the inrush current ( torque ) to the motor. The resistors are referred to as “Ballast Resistors “ and provide a soft-start condition from the motor. Data Requirements: • Application • Primary Voltage and Current • Horsepower • Number of Speeds Typical reversing control schematic using 2 Speed / 1 Step ballast resistor on an AC squirrel cage motor DC SERIES WOUND MOTOR CONTROL For resistor applications used on DC series wound motors, the resistors are connected in line with the motor armature and field to reduce the voltage and current applied to the motor. The resistors will drop the starting voltage and current to the motor, therefore limiting the inrush current ( torque ) to the motor. Data Requirements: • Motion ( Hoist or Travel ) • Control Manufacturer • Number of Speeds • Voltage and Current • Horsepower • Type of Control Scheme • NEMA Class ( Reverse, Reverse Plugging, Dynamic Lowering, Etc. ) Typical reversing plugging control schematic using 3 Speed / 2 Step acceleration resistor on an DC series wound motor STAR (WYE)-DELTA STARTING MOTOR For resistor applications used on Star (Wye) -Delta type motors, ( CLOSED TRANSITION ) the resistors are connected to the motor winding before the delta contactor is closed. The resistors are used to avoid the possibility of high inrush current when the winding is momentarily open – circuited when switching from Star (Wye) to Delta Winding configuration on the motor, therefore providing a smoother acceleration of the motor. Data Requirements: • Line Voltage • Horsepower • Current Typical reversing control schematic using resistor on a Star (Wye)-Delta motor starter (closed transition)
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