Method and apparatus for operating a hoist

Abstract

A hoist having an alternating current induction motor for rotating the drum of the hoist and an adjustable frequency power supply connected to the motor has a first control connected to the adjustable frequency power supply for directing the power supply to provide power to the motor at a first voltage level at the initiation of a raising operation. A second control is also connected to the adjustable frequency power supply for directing the power supply to provide power to the motor at the initiation of a lowering operation at a second voltage level which is lower than the first voltage level. The voltage level supplied to the hoist at the initiation of a raising operation may comprise a voltage level which is increased by a raising o first voltage boost value above the voltage level that would be applied without the first voltage boost value. At the initiation of a raising operation, the first voltage level may include a first voltage boost value. At the initiation of a lowering operation, the second voltage level is increased by a lowering or second voltage boost value above the voltage level that would be applied without the second voltage boost value during lowering operation. However, the second voltage boost value is smaller than the first voltage boost value.

Dependencies are inferred from the claim text.