No other technological development in nearly 40 years has done more to revolutionize overhead crane operation and maintenance than the AC Variable Frequency Drive (VFD). Today’s Variable Frequency Controls and Flux Vector Motor Controls have become the industry standard for crane and hoist control. VFD’s have replaced the older technologies of wound rotor motor control, static step-less and eddy- current. VFD’s are also making the use of two -speed control using contactors and two speed motors less practical. Recent improvements in drive technology, such as a new generation of Insulated Gate Bipolar Transistors (IGBTs), sensor-less vector control, powerful microprocessors with flash memory, and improved algorithms, have allowed the downsizing of the power platforms and the inclusion of many high-performance features.
There are numerous benefits of using a VFD to control a hoist or crane, including:
GREATER SPEED ADJUSTMENT:
VFD controls let you choose from multiple speeds, allowing you to customize your hoist speeds to your application.
IMPROVED LOAD CONTROL:
Positioning a load using a single-speed hoist may cause shock loading or load swings. Two-speed may not give you the desired range of speeds for sensitive positioning because they typically are offered in 3 to 1 or 5 to 1 speed range. A VFD allows for smooth operation by gradually slowing down a load and offers speed ranges of 100 to 1 or more in many applications. Retrofits of existing cranes and hoists easily allow for 10 to 1 speed range. VFDs also allow for smooth acceleration to prevent load swings in the traverse motions.
CMAA Class A-F. A VFD is c matched with a braking resistor, depending on the duty cycle of the motion. A regenerative drive may also be used, which is not dependent on duty cycle.
A VFD will only consume the power that’s needed, thus saving energy compared to contactors and soft-starters.
INCREASED HOIST LIFE:
Some variable frequency drives provide thermal overload and overcurrent protection for the hoist motor, prolonging its life. VFDs also utilize a ramp-down-to-stop method of braking rather than using brake shoes to slow down. The brake is only used for parking and emergency situations, which greatly increases brake life while reducing the need for maintenance and adjustments. VFD’s eliminate the need for reversing contactors (another maintenance and repair item) for motion and speed control
Deceleration and lowering of a hoist creates regenerative energy produced by the motor. This energy can be transformed into heat using a braking resistor or conditioned and send back to the source, thus netting an energy savings. An AC regenerative drive will redistribute that energy, which would otherwise be wasted when converted to heat with a braking resistor.
Aid in maintenance and troubleshooting on the machine or remotely.
CRANE 1 Features Magnetek VFDs which are designed specifically for crane and hoist applications with various performance and safety features. A few of these features include:
SAFE TORQUE OFF:
Provides a redundant hardware safety circuit that guarantees motor and brake power are removed when an E-STOP switch or safety controller opens the drive input, eliminating the need for external disconnects.
The motor is pre-torqued to guarantee that the load can be held before opening the brake.
Continuously checks for hoist overloads and prevents the hoist from lifting when an overload condition is detected.
Monitors the opening and closing of a brake to ensure that it is safe and healthy.
Allows the operator to make slow, precise movements.
ELECTRONIC PROGRAMMABLE LIMIT SWITCHES:
Allows slow down and stop limits without physical geared limit switches.