Abstract:
Methods and devices for controlling a welding power source based on a primary supply voltage level are provided. One method may include sensing activation of the welding power source and sensing a primary supply voltage established on a control transformer of the welding power source. The method may also include establishing a substantial current draw from a primary power supply that exceeds a predefined current threshold when the sensed primary supply voltage exceeds a predefined voltage threshold. The substantial current draw may be adapted to trip a circuit breaker of the welding power source to disallow current through the welding power source when the sensed primary supply voltage exceeds the predefined voltage threshold.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a Non-Provisional patent application of U.S. Provisional Patent Application No. 61/304,731 entitled “Method for Protecting Welding Power Source from High Primary Supply Voltage”, filed Feb. 15, 2010, which is herein incorporated by reference. 
     
    
     BACKGROUND 
       [0002]    The invention relates generally to welding power sources and, more particularly, to methods and devices that may be utilized to respond to excessive primary supply voltages present in such devices. 
         [0003]    Welding is a process that has become ubiquitous in various industries for a variety of types of applications. For example, welding processes, such as tungsten inert gas (TIG) welding and metal inert gas (MIG) welding, are utilized in industries such as shipbuilding, construction, manufacturing, and so forth. Welding power sources, which typically receive primary power from a primary power supply, are utilized to provide power for such applications. In order to couple the welding power source to the primary power supply, an operator typically connects a primary plug coupled to the welding power source to a primary power outlet that is located, for example, in a wall of a building. 
         [0004]    Unfortunately, welding power sources that have similar appearances often operate from different primary power voltage levels (e.g., 115V AC power vs. 230V AC power). Accordingly, some operators may mistakenly connect a power source configured to operate from a low primary voltage level (e.g., 115 V) to an outlet configured to provide a higher voltage level output (e.g., 230V). In such instances, certain components, such as the printed wiring board and the fan motor located within the welding power source may be damaged since such components are not designed to handle the higher voltage level. Accordingly, there exists a need for welding power sources that overcome such disadvantages. 
       BRIEF DESCRIPTION 
       [0005]    In an exemplary embodiment, a welding power source includes a fan transformer including a primary winding coupled to a fan motor and a secondary winding having a primary supply voltage. The welding power source also includes a main transformer including a main primary winding and a main secondary winding having a main voltage configured to supply a weld power output. The welding power source also includes at least two semiconductor-controlled rectifiers (SCRs) each including a gate and each being adapted to remain in a non-conductive state to restrict current to the main primary winding when a trigger pulse has not been applied to the respective gate and to enter a conductive state to allow current to the main primary winding when the trigger pulse has been applied to the respective gate. The welding power source further includes a circuit breaker adapted to be tripped to disallow current through the welding power source and a controller coupled to the secondary winding of the fan transformer and at least two SCRs and adapted to selectively apply a trigger pulse to at least one gate of at least one SCR to saturate the main transformer when the primary supply voltage exceeds a predefined threshold, wherein saturation of the main transformer trips the circuit breaker. 
         [0006]    In another embodiment, a method of controlling a welding power source includes sensing activation of the welding power source and sensing a primary supply voltage established on a control transformer. The method also includes establishing a substantial current draw from a primary power supply that exceeds a predefined current threshold when the sensed primary supply voltage exceeds a predefined voltage threshold. The substantial current draw is adapted to trip a circuit breaker of the welding power source to disallow current through the welding power source when the sensed primary supply voltage exceeds the predefined voltage threshold. 
         [0007]    In another embodiment, control circuitry for a welding power source is adapted to sense activation of the welding power source, to monitor a primary supply voltage established on a secondary winding of a fan transformer including a primary winding coupled to a fan motor, and to determine whether or not the primary supply voltage exceeds a predefined threshold. The control circuitry is further adapted to determine, when the primary supply voltage is determined to exceed the predefined threshold, whether or not a circuit breaker of the welding power source is tripped within a predefined time interval and to lock out operation of the welding power source when the primary supply voltage exceeds the predefined threshold and the circuit breaker is determined not to be tripped. 
     
    
     
       DRAWINGS 
         [0008]    These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein: 
           [0009]      FIG. 1  illustrates a perspective view of an exemplary welding power source in accordance with aspects of the present invention; 
           [0010]      FIG. 2  illustrates exemplary circuitry that may be located in the welding power source of  FIG. 1  in accordance with embodiments of the present invention; 
           [0011]      FIG. 3  is a flow chart illustrating exemplary control logic that may be implemented by a controller to control the welding power source of  FIG. 1  in accordance with aspects of the present invention; and 
           [0012]      FIG. 4  is a flow chart illustrating exemplary logic that may be implemented by a controller to control the welding power source of  FIG. 1  when a circuit breaker error occurs in accordance with aspects of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    As described in detail below, embodiments of a welding power source adapted to shut down operation and/or to communicate an error message to an operator in the presence of a high primary supply voltage are provided. For example, in instances in which a welding power supply designed to operate with a lower supply voltage (e.g., 115V) is connected to an outlet configured to provide a higher supply voltage (e.g., 230V), embodiments of the power sources disclosed herein are capable of responding to the high voltage situation to reduce or prevent the possibility of damage to electrical components. In one embodiment, the primary voltage is sensed in a fan transformer that is coupled to a fan motor. A controller may compare the sensed voltage to a predefined threshold to determine whether or not the sensed voltage exceeds the threshold. If the primary voltage exceeds the predefined threshold, the controller may trigger one semiconductor-controlled rectifier (SCR) of a pair of alternating SCRs, thereby saturating a main transformer of the welding power source. Such saturation triggers the tripping of the main circuit breaker in the power supply, thus prohibiting further operation of the welding power source to substantially reduce or prevent the occurrence of damage to the electrical components disposed therein in the presence of a high primary supply voltage. 
         [0014]    Turning now to the drawings,  FIG. 1  is a perspective view of an exemplary welding power source  10  configured for use in a gas metal arc welding (GMAW) process or a flux cored welding (FCAW) process. The welding power source  10  includes a housing  12  including a top panel  14 , a side panel  16 , and a front panel  18 . The top panel  14  includes a handle  20  that facilitates transport of the welding power source  10  from one location to another by an operator if desired. The side panel  16  includes a breakaway view illustrating a controller  22  configured to control operation of the welding power source  10 . The front panel  18  includes a control panel  24  adapted to allow an operator to set one or more parameters of the welding process, for example, via knobs  26 . 
         [0015]    A main electrical connector  28  couples to the welding power source  10  via the front panel  18 . A cable  30  extends from the main connector  28  to a welding torch  32  configured to be utilized in a welding operation to establish a welding arc. A second cable  34  is attached inside the welding power source through an aperture in the front panel  18  and terminates in a ground clamp  36  that is adapted to clamp to the workpiece during a welding operation to close the circuit between the welding power source, the welding torch, and the workpiece. During such an operation, the welding power source is configured to receive primary power from a primary power supply (e.g., a wall outlet, a main power grid, etc.), to condition such incoming power, and to output a weld power output appropriate for use in the welding operation. Accordingly, the power source  10  is configured to receive and condition a primary power input having a predetermined voltage level. As described in detail below, embodiments of the welding power sources disclosed herein are adapted to reduce or eliminate the likelihood of damage to or destruction of internal electrical components due to the presence of a primary supply voltage above which such electrical components are rated to handle. 
         [0016]      FIG. 2  illustrates exemplary internal circuitry  38  that may be located within the welding power source  10  of  FIG. 1  in some embodiments. The circuitry  38  includes a control board  40  connected to a variety of electrical inputs and outputs. Specifically, the control board includes controller  22  and is coupled to lead circuitry  42 , fan circuitry  44 , and weld power generation circuitry  46 . The lead circuitry  42  includes a first lead  48 , a second lead  50 , and a ground lead  52  coupled to ground  54 . The lead circuitry  42  further includes a main circuit breaker  56  and main power switch  58 . The fan circuitry  44  includes a fan transformer  60  with a primary winding  62  and a secondary winding  64 . A fan motor is disposed on the primary winding  62  of the fan transformer  60 . The weld power generation circuitry  46  includes one or more SCRs  68 , a main transformer  70  with a primary winding  72  and a secondary winding  74 , a rectification circuit  76 , a capacitor  78 , an inductor  80 , and output terminals  82  and  84 . The rectification circuitry  76  includes a first diode  86 , a capacitor  88 , a second diode  90 , and a second capacitor  92 . The PC control board  40  is further configured for a variety of other circuitry (e.g., spool gun circuitry, trigger circuitry, thermal overload circuitry, etc.) via connections  94 . 
         [0017]    During operation, the components of the circuitry  38  are configured to operate to reduce or prevent the likelihood of damage to electrical components, such as the control board  40  and the fan motor  66 , in instances of high primary supply voltages that occur after the power source is powered ON. In one embodiment, the power source is powered ON when an operator flips a switch on the control panel of the power source, and the switch  58  changes position to allow current. Once the power source is activated, the level of the primary supply voltage may be determined by the controller  22  by equating the voltage level present on the secondary winding  64  of the fan transformer  60  to the primary supply voltage level. 
         [0018]    Under normal operation, as would occur when the primary supply voltage is within an allowed tolerance, the controller controls power supplied to the transformer  70  by sending trigger pulses to the SCRs  68  such that the SCRs  68  fire in a balanced manner. For example, in one embodiment, two SCRs  68  may be provided, and the first SCR and the second SCR are controlled to fire in opposite directions, such that the transformer  70  is capable of producing power that is rectified by rectification circuitry  76  and smoothed by inductor  80  before reaching the positive and negative output terminals  82  and  84 . However, under an error condition, such as when the primary supply voltage exceeds a predefined threshold (e.g., approximately 50% above a defined voltage level), the controller  22  sends trigger pulses to every other SCR such that the activated SCRs fire in only one direction, thus quickly saturating the transformer  70 . In such instances, the saturated transformer  70  may effectively operate as a wire, thus leading to high current levels. Such high current levels trip the circuit breaker  56 , thereby reducing the occurrence of damage to the electrical components in the power source, such as the fan motor  66 . In such a way, the power sources disclosed herein are capable of self regulation to avoid deleterious effects that may occur during instances of excessive primary supply voltages. 
         [0019]      FIG. 3  is a flow chart  96  illustrating an exemplary control method that may be utilized by a welding power source to control operation to reduce the possibility of damage due to the occurrence of a high primary supply voltage. The method  96  includes the step of plugging the power supply into an outlet of any suitable primary source of power (block  98 ). Such a step is typically performed by a welding operator, and in some instances, the welding operator may plug the power source into a primary power supply that is configured to output a supply voltage that exceeds the voltage level for which the welding power source is rated. For example, the welding operator may be utilizing a device rated for 115V AC power but may plug the welding power source into an outlet that provides 230V AC power. 
         [0020]    After plugging the welding power source into the chosen outlet, the controller is configured to detect activation of the welding power supply (block  100 ), which may occur, for example, when the operator flips a switch located on a control panel. The controller then senses the voltage on the secondary winding of a first transformer (e.g., the fan transformer  60 ) to determine a received primary voltage level (block  102 ). The controller then checks if the sensed voltage level exceeds a predefined threshold (block  104 ) and, if not, allows operation of the power supply (block  106 ). In such a way, if the welding power source is connected to a primary supply voltage that is appropriate for the given welding power supply, the controller does not impede or preclude further operation. 
         [0021]    However, if the sensed voltage level does exceed the predefined threshold, the controller activates the output of the welding power supply (block  108 ) by firing every other SCR of a plurality of SCRs (block  110 ). It should be noted that in further embodiments, based on the electrical architecture of the power source, the controller may implement any of a series of control schemes, which are not limited to activating every other SCR, appropriate to create an imbalance on the main transformer. Such control schemes result in saturation of a second transformer (e.g., main transformer  70 ; block  112 ), and a main circuit breaker (e.g., circuit breaker  56 ) is tripped due to the excessive current (block  114 ). Subsequently, the power source is deactivated and shuts OFF to prevent damage to the electrical circuitry due to the presence of an excessive primary supply voltage (block  116 ). 
         [0022]      FIG. 4  illustrates a flow chart  118  including logic that may be utilized to protect the welding power source from electrical component damage during instances of high primary supply voltage when the control method of  FIG. 3  fails to cause a system shutdown. The logic  118  begins when the sensed voltage through the first transformer (e.g., the fan transformer  60 ) exceeds the predetermined threshold (block  120 ). As before, the voltage exceeding the threshold triggers the controller to activate the power supply output (block  122 ), and every other SCR of the plurality of SCRs is fired (block  124 ). The controller then allows a predefined period of time (e.g., 1 second) to elapse to allow for saturation of the transformer (block  126 ). 
         [0023]    After the desired time interval has elapsed, the controller checks if the circuit breaker has been tripped (block  128 ) and, if so, the power supply is deactivated as before (block  130 ). However, if the circuit breaker has not been tripped and the predefined time interval has elapsed, the power source is locked out and prevented from operating (block  132 ). Further, an error message is communicated to the operator (block  134 ) to alert the operator to the malfunction and to prevent further use of the welding power source. As such, when the primary supply voltage exceeds the given threshold and the primary control method does not effectively protect the internal electrical components via the main circuit breaker, embodiments of the present invention still include capabilities to reduce or prevent the likelihood of damage to electrical components. 
         [0024]    While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.