Automatic air defrost system
AssigneeJohn Bean Technologies Corporation
InventorsRyan Harrell, Alan McGinnis, John D. Woodburn
Life of this patent
Estimating the term…
Abstract
A method and apparatus for controlling the direction of a defrost device for refrigeration coils includes measuring the current drawn by or the torque produced by a permanent magnet motor, wherein the permanent magnet motor powers a defrost device recurrently back and forth along refrigeration coils and reverses the direction of the permanent magnet motor when the measured current drawn or measured torque produced are at or above a first limit. The method omits the use of switches and sensors to signal when the defrost device is reversed to reduce failures and stoppages.
Claims30
A freezer, comprising:
- cooling coils;
- a defrost device directed at the cooling coils, wherein the defrost device travels recurrently along the cooling coils;
- and
- a permanent magnet motor operatively connected to the defrost device to power the defrost device recurrently across the cooling coils, wherein the permanent magnet motor is configured to reverse direction when a speed of the motor reaches zero from a speed greater than zero.
A method for controlling the direction of a defrost device for cooling coils, comprising:
- measuring the current drawn by or the torque produced by a permanent magnet motor, wherein the permanent magnet motor powers a defrost device recurrently along cooling coils;
- and
- reversing the direction of the permanent magnet motor when the measured current drawn or measured torque produced are at or above a first limit, and wherein the permanent magnet motor is configured to reverse direction when a speed of the motor reaches zero from a speed greater than zero.
A defrost system for a freezer having a defrost device, comprising:
- a permanent magnet motor;
- an AC frequency inverter or DC drive connected to the permanent magnet motor;
- a torque meter or current meter that measures the torque produced or current drawn by the permanent magnet motor;
- and
- a controller having circuitry that compares a torque measurement or current measurement to pre-determined values representing the performance characteristics of the permanent magnet motor and reverses direction of the permanent magnet motor when the torque measurement or current measurement has reached a first limit, and
- wherein the permanent magnet motor is configured to reverse direction when a speed of the motor reaches zero from a speed greater than zero.
Dependencies are inferred from the claim text.