System and method for determining defrost power delivered by a defrost heater

Abstract

An adaptive defrost control system of the present invention monitors an amount of current flowing through the defrost heater to calculate the amount of power delivered thereby. The circuit utilizes a thermistor to monitor the temperature rise of the electrical trace supplying current to the defrost heater to allow the controller to calculate an amount of power delivered thereby. A second thermistor may be used to compensate for a change in ambient temperature that might otherwise be attributed to a change in current flow through the power trace. A physical modification to the power trace to enhance the temperature rise characteristic at the point of placement of the thermistor enhances the accuracy of the calculation. A secondary current flow path around the branch of thermistor placement is also provided so as to not reduce the total current carrying capacity of the power trace.

1 . A system for determining an amount of power delivered by a defrost heater, comprising: 
 an adaptive defrost control (ADC) controller;    a defrost heater; and    a sensing element from which an amount of current flowing through the defrost heater may be determined; and    wherein the ADC controller monitors the sensing element over time to determine an amount of power supplied by the defrost heater during a defrost cycle.    
     
     
         2 . The system of  claim 1 , wherein the defrost heater is a resistance-type heating element.  
     
     
         3 . The system of  claim 1 , wherein the sensing element is a current transformer.  
     
     
         4 . The system of  claim 1 , wherein the sensing element is a first thermistor.  
     
     
         5 . The system of  claim 4 , wherein current is supplied to the defrost heater via a power trace on a printed circuit board, and wherein the first thermistor is positioned in thermal communication with the power trace on the printed circuit board.  
     
     
         6 . The system of  claim 5 , wherein the power trace is divided into a first lower resistance branch and a second higher resistance branch, and wherein the first thermistor is positioned in thermal communication with the first lower resistance branch.  
     
     
         7 . The system of  claim 6 , wherein the second higher resistance branch is longer than the first lower resistance branch.  
     
     
         8 . The system of  claim 4 , further comprising a second thermistor positioned to sense an ambient temperature in proximity to the first thermistor, and wherein the ADC controller monitors the second thermistor to compensate for changes in the ambient temperature.  
     
     
         9 . The system of  claim 8 , wherein the ADC controller subtracts the temperature reading from the second thermistor from the temperature reading from the first thermistor to determine the temperature rise resulting from current flow through the power trace.  
     
     
         10 . The system of  claim 5 , wherein the ADC controller is programmed with a resistance of the power trace, and wherein the ADC controller calculated the current as a function of temperature rise of the power trace over time.  
     
     
         11 . A system for determining an amount of power delivered by a defrost heater in a refrigeration system, comprising: 
 an adaptive defrost control (ADC) controller;    a sensing element from which an amount of current flowing through the defrost heater may be determined; and    wherein the ADC controller monitors the sensing element over a defrost cycle to determine an amount of power supplied by the defrost heater during the defrost cycle, and wherein the ADC controller adjusts a subsequent refrigeration cycle based on an amount of elapsed time of the defrost cycle adjusted for the amount of power supplied by the defrost heater.    
     
     
         12 . The system of  claim 11 , wherein the sensing element is a first temperature sensing element positioned on a trace of a control board that supplies power to the defrost heater.  
     
     
         13 . The system of  claim 12 , wherein the first temperature sensing element is a thermistor.  
     
     
         14 . The system of  claim 12 , wherein the power trace is configured to provide a narrower width portion at a location where the temperature sensing element is positioned.  
     
     
         15 . The system of  claim 14 , wherein the power trace is configured to provide a secondary path around the narrower width portion.  
     
     
         16 . The system of  claim 15 , wherein the narrower width portion has a lower resistance than the secondary path.  
     
     
         17 . The system of  claim 11 , further comprising a second temperature sensing element positioned to sense ambient temperature in proximity to the first temperature sensing element.  
     
     
         18 . The system of  claim 17 , wherein the ADC controller subtracts an output from the second temperature sensing element from an output from the first temperature sensing element to remove affects of changes in ambient temperature.  
     
     
         19 . The system of  claim 17 , wherein the second temperature sensing element is a thermistor.  
     
     
         20 . A system for adapting a refrigeration cycle time for changes in voltage from a supply to a defrost heater, comprising: 
 an adaptive defrost control (ADC) controller;    a thermistor positioned in proximity to a power trace supplying power to the defrost heater; and    wherein the ADC controller monitors the thermistor to determine a temperature rise of the power trace, and wherein the ADC controller calculates a current flowing though the power trace based on the temperature rise over time, the ADC controller calculating an instantaneous amount of power supplied by the defrost heater based on the current and a known resistance of the defrost heater, and wherein the ADC controller adjusts a subsequent refrigeration cycle based on a time of the defrost cycle and the power supplied by the defrost heater.