Recirculating Bath With Global Voltage Compatibility

Abstract

A recirculating bath includes a main power input configured to receive an alternating current and a heating element that is selectively coupled to the main power input. The heating element is selectively coupled to the main power input in response to an activation signal having a duty cycle. The duty cycle of the activation signal is determined based on a voltage of the alternating current, with the duty cycle being reduced in response to an increase in the voltage of the alternating current. The heating element is thereby de-rated at higher alternating current voltages. A power unit coupled to the main power input provides direct current having a voltage independent of the alternating current voltage to portions of the recirculating bath, such as direct current motors coupled to a compressor and recirculating pump. The recirculating bath is thereby configured to operate with a range of alternating current voltages.

What is claimed is: 
     
         1 . A recirculating bath, comprising:
 a main power input configured to receive an alternating current; and   a heating element that is selectively coupled to the main power input in response to an activation signal, the activation signal having a duty cycle set based on a voltage of the alternating current at the main power input.   
     
     
         2 . The recirculating bath of  claim 1 , further comprising a power unit having an input and an output, the input being coupled to the main power input, the output providing at least one direct current voltage having a value substantially independent of the voltage of the alternating current at the main power input, the direct current voltage providing power to at least a portion of the recirculating bath. 
     
     
         3 . The recirculating bath of  claim 2 , further comprising a direct current motor that is selectively coupled to the output of the power unit, the direct current motor providing torque to at least one of a compressor, a recirculating pump, and a fan in response to being coupled to the output of the power unit, wherein the at least a portion of the recirculating bath includes the direct current motor. 
     
     
         4 . The recirculating bath of  claim 3 , further comprising:
 a reservoir for receiving a working liquid; and   a cooling unit for cooling the working liquid, the cooling unit including the compressor and an evaporator coil.   
     
     
         5 . The recirculating bath of  claim 4 , wherein the evaporator coil is located in the reservoir. 
     
     
         6 . The recirculating bath of  claim 3 , further comprising:
 a reservoir for receiving a working liquid; and   the recirculating pump for circulating the working liquid.   
     
     
         7 . The recirculating bath of  claim 6 , wherein the recirculating pump is an immersion pump located in the reservoir. 
     
     
         8 . The recirculating bath of  claim 1 , further comprising a controller configured to:
 determine the voltage of the alternating current at the main power input;   set the duty cycle of the activation signal based on the determined voltage; and   selectively couple the heating element to the main power input using the activation signal.   
     
     
         9 . The recirculating bath of  claim 8 , further comprising a heater driver connected between the heating element and the main power input, wherein the controller selectively couples the heating element to the main power input by applying the activation signal to the heater driver. 
     
     
         10 . The recirculating bath of  claim 8 , further comprising:
 a reservoir configured to receive a working liquid, the controller being configured to selectively couple the heating element to the main power input to maintain the working liquid at a desired temperature.   
     
     
         11 . The recirculating bath of  claim 10 , wherein the heating element is located in the reservoir. 
     
     
         12 . The recirculating bath of  claim 1 , further comprising a controller configured to:
 determine the voltage at the main power input;   compare the voltage to a threshold;   in response to the voltage being below the threshold, set the duty cycle of the activation signal to a first value; and   in response to the voltage not being below the threshold, set the duty cycle of the activation signal to a second value different from the first value.   
     
     
         13 . A method of operating a recirculating bath, the method comprising:
 determining, with a controller, a voltage of an alternating current at a main power input of the recirculating bath;   setting, with the controller, a duty cycle of an activation signal based on the voltage; and   selectively coupling a heating element to the main power input by the controller generating the activation signal.   
     
     
         14 . The method of  claim 13 , further comprising:
 generating, with a power unit coupled to the main power input, a direct current voltage having a value substantially independent of the voltage of the alternating current at the main power input; and   using the direct current voltage to provide power to at least a portion of the recirculating bath.   
     
     
         15 . The method of  claim 14 , wherein using the direct current voltage to provide power to at least a portion of the recirculating bath comprises:
 selectively coupling a direct current motor to the direct current voltage, the direct current motor providing torque to at least one of a compressor, a recirculating pump, or a fan in response to being coupled to the direct current voltage.   
     
     
         16 . The method of  claim 14 , further comprising:
 cooling a working liquid by selectively coupling the direct current voltage to a direct current motor, the direct current motor providing torque to a compressor of a cooling unit.   
     
     
         17 . The method of  claim 14 , further comprising:
 circulating a working liquid in a reservoir by coupling the direct current voltage to a direct current motor, the direct current motor providing torque to a recirculating pump.   
     
     
         18 . The method of  claim 13 , wherein setting the duty cycle of the activation signal based on the voltage comprises:
 comparing the voltage to a threshold;   in response to the voltage being below the threshold, setting the duty cycle of the activation signal to a first value; and   in response to the voltage not being below the threshold, setting the duty cycle of the activation signal to a second threshold different from the first threshold.   
     
     
         19 . The method of  claim 18  further comprising:
 receiving a signal at the controller, the signal indicative of a temperature of a working liquid; 
 comparing the temperature of the working liquid to a desired temperature; and 
 determining an amount of time to generate the activation signal based on the comparison. 
 
     
     
         20 . A recirculating bath that provides a working liquid at a desired temperature, the recirculating bath comprising:
 a heating element thermally coupled to the working liquid;   a recirculating pump configured to circulate the working liquid;   a main power input configured to receive an alternating current;   a controller configured to selectively couple the heating element to the main power input to maintain the working liquid at the desired temperature;   a power unit having an input coupled to the main power input and an output that provides a direct current voltage; and   a direct current motor coupled to the recirculating pump, the direct current motor receiving power from the output of the power unit and providing torque to the recirculating pump.