Systems and methods for cathodic protection

Abstract

A water heater includes a tank defining an interior for holding water, an anode extending into the interior, and cathodic protection circuitry electrically coupled with the anode. The cathodic protection circuitry is configured to repeatedly apply current and limit application of current to the anode. Application of current to the anode occurs during a first time and limiting application of current to the anode occurs during a second time. The control circuitry is configured to measure an electrical parameter representative of a charge of the tank during the second time and adjust a level of the current applied to the anode based on a value of the electrical parameter.

What is claimed is: 
     
         1 . A water heater, comprising:
 a tank defining an interior for holding water;   an anode extending into the interior;   cathodic protection circuitry electrically coupled with the anode, the cathodic protection circuitry configured to:
 repeatedly apply current and limit application of current to the anode, wherein the application of current to the anode occurs during a first time and limiting application of current to the anode occurs during a second time; 
 measure an electrical parameter representative of a charge of the tank during the second time; and 
 adjust a level of the current applied to the anode based on a value of the electrical parameter. 
   
     
     
         2 . The water heater of  claim 1 , further comprising:
 a power source; and   a constant current circuit electrically interposing the power source and the anode, wherein the cathodic protection circuitry is configured to control the level of the current via a pulse-width modulated (PWM) signal and selectively enable the constant current circuit to control the application of the current via an enable signal separate from the PWM signal.   
     
     
         3 . The water heater of  claim 1 , wherein the electrical parameter is voltage. 
     
     
         4 . The water heater of  claim 1 , wherein the cathodic protection circuitry is configured to:
 compare the value of the electrical parameter to a target; and   increase the level of current in response to the value being less than the target and decrease the level of current in response to the value being greater than the target.   
     
     
         5 . The water heater of  claim 4 , wherein the cathodic protection circuitry is configured to:
 measure a drive voltage applied to the anode during the first time.   
     
     
         6 . The water heater of  claim 5 , wherein the cathodic protection circuitry is configured to estimate at least one of a conductivity of the water and an area of unprotected steel of a wall of the tank based on at least one of the electrical parameter and the drive voltage. 
     
     
         7 . The water heater of  claim 5 , wherein the cathodic protection circuitry is configured to selectively operate in a diagnostic mode and, in the diagnostic mode:
 apply current to the anode at a plurality of different current levels;   measure the drive voltage at each of the plurality of different current levels;   estimate a functional relationship between the current and the drive voltage; and   set the target based on the functional relationship.   
     
     
         8 . The water heater of  claim 7 , wherein the cathodic protection circuitry is configured to, in the diagnostic mode, identify a peak in the functional relationship. 
     
     
         9 . The water heater of  claim 8 , wherein the cathodic protection circuitry is configured to, in the diagnostic mode, determine a relationship between the drive voltage and the value of the electrical parameter, adjust the peak according to the relationship, and assign the target to a voltage level of the peak. 
     
     
         10 . The water heater of  claim 1 , wherein repeated application of the current is executed at a duty cycle of at least 90%. 
     
     
         11 . A method for cathodically protecting a tank of a water heater using an anode, the method comprising:
 electrically coupling the anode to cathodic protection circuitry;   repeatedly applying current and limiting application of current to the anode, wherein the application of current to the anode occurs during a first time and limiting application of current to the anode occurs during a second time;   measuring an electrical parameter representative of a charge of the tank during the second time; and   adjusting a level of the current applied to the anode based on a value of the electrical parameter.   
     
     
         12 . The method of  claim 11 , further comprising:
 controlling the level of the current via a pulse-width modulated (PWM) signal; and   selectively enabling a constant current source to control the application of the current via an enable signal separate from the PWM signal.   
     
     
         13 . The method of  claim 11 , further comprising:
 comparing the value of the electrical parameter to a target; and   increasing the level of current in response to the value being less than the target; and decreasing the level of current in response to the value being greater than the target.   
     
     
         14 . The method of  claim 13 , further comprising:
 measuring a drive voltage applied to the anode during the first time.   
     
     
         15 . The method of  claim 14 , further comprising:
 applying current to the anode at a plurality of different current levels;   measuring the drive voltage at each of the plurality of different current levels;   estimating a functional relationship between the current and the drive voltage; and   setting the target based on the functional relationship.   
     
     
         16 . The method of  claim 15 , further comprising:
 identifying a peak in the functional relationship.   
     
     
         17 . The method of  claim 16 , further comprising:
 determining a relationship between the drive voltage and the value of the electrical parameter;   adjusting the peak according to the relationship; and   assigning the target to a voltage level of the peak.   
     
     
         18 . A cathodic protection circuit for a water heater, comprising:
 a constant current circuit electrically coupled with an anode of the water heater;   a detection circuit;   an enable circuit; and   control circuitry configured to:
 selectively and repeatedly enable, during a first time, and disable, during a second time, the constant current circuit by controlling the enable circuit; 
 measure, via a signal from the detection circuit, a voltage representative of a charge of a tank of the water heater during the second time; and 
 adjust a level of the current applied to the anode based on the voltage. 
   
     
     
         19 . The cathodic protection circuit of  claim 18 , wherein the control circuitry is configured to:
 apply current at a plurality of different current levels;   measure a drive voltage at each of the plurality of different current levels;   estimate a functional relationship between the current and the drive voltage;   set a target voltage based on the functional relationship; and   compare the voltage to the target voltage during each second time to determine the adjustment.   
     
     
         20 . The cathodic protection circuit of  claim 18 , wherein repeated enabling of the constant current circuit is executed at a duty cycle of at least 95%.