Method and apparatus for controlling a lifting magnet of a materials handling machine

A control system apparatus for selectively energizing a lifting magnet, said apparatus comprising:

• an electrical power input for connection to a voltage output of a generator;
• an electrical power output for selectively connecting the generator voltage output to a lifting magnet;
• generator excitation means for selectively electrically connecting shunt fields of the generator to an electrical power source to thereby excite said shunt fields so that a voltage is established at the voltage output of the generator and so that electrical current flows through said lifting magnet;
• and,
• means, connected to said generator excitation means, for detecting electrical current flow through said lifting magnet, said generator excitation means disconnecting the electrical power source from the shunt fields of the generator when a select electrical current flow through the magnet is detected.

A materials handling apparatus comprising:

• a prime mover;
• a separately excited generator including a rotatable armature, shunt field windings, and a voltage output for connection to a lifting magnet through a magnet circuit;
• means for rotating said armature of said generator and connected to the prime mover;
• a control system for selectively connecting said shunt field windings of said generator to an excitation power source such that voltage is established at said generator voltage output and current flows through the magnet circuit;
• and,
• a current sensor for sensing current in the magnet circuit.