Abstract:
A welding system includes an engine-driven welder generator that produces welding power. A welding torch receives the welding power and applies it to a stick electrode to initiate and maintain a welding arc. A parameter of the welding power, such as voltage, is monitored, such as to determine whether spikes occur during a short time after arc initiation. Based upon the monitored parameter, the engine speed is controlled. The engine speed may be increased or maintained at an elevated level if the monitored parameter indicates that particular types of electrode are being used, such as XX10 or cellulose electrodes.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a Continuation application of U.S. Non-Provisional patent application Ser. No. 13/910,033, entitled “Welder Generator Electrode Based Engine Speed Control”, filed Jun. 4, 2013, which is a Non provisional application of U.S. Provisional Patent Application No. 61/676,615, entitled “Welder Generator Electrode Based Engine Speed Control”, filed Jul. 27, 2012, both of which are hereby incorporated by reference in their entireties. 
     
    
     BACKGROUND 
       [0002]    The present invention relates generally to the field of welding systems, and more particularly to systems designed for stick welding applications. 
         [0003]    Many welding systems have been developed for providing power and other consumables for joining workpieces. In certain applications, welding processes may be based upon the use of so-called stick electrodes that typically comprise a metal rod made of a desired material formulation, and a flux coating that facilitates metal transfer, promotes proper formation of the weld bead, shields the fresh weld bead, and so forth. Depending upon the type and size of the electrode, the desired arc between the electrode and the workpiece may be difficult to start and/or maintain. Special processes have been developed to accommodate different electrodes. 
         [0004]    However, further improvement is needed. In particular, improvements are needed that permit the use of specific power regimes based upon performance of particular welding electrodes. 
       BRIEF DESCRIPTION 
       [0005]    The present invention provides a novel approach to welding power supply control designed to respond to such needs. In accordance with certain embodiments, a welding method comprises initiating a welding arc between a stick electrode and a workpiece based upon power provided by an engine-driven welder generator, and monitoring an electrical parameter of power provided to the stick electrode. Engine speed is then controlled based upon the monitored electrical parameter. The electrical parameter may be welding arc voltage, and the engine speed may be increased or maintained at an elevated level if a certain number of voltage spikes occurs within a preset time after arc initiation. 
         [0006]    In accordance with another aspect, the invention provides a welding method that comprises initiating a welding arc between a stick electrode and a workpiece based upon power provided by an engine-driven welder generator, monitoring an electrical parameter of power provided to the stick electrode, and, based upon the monitored electrical parameter, determining a type of stick electrode employed. The engine speed is then controlled based upon the determined type of stick electrode. 
         [0007]    In accordance with a further aspect, the invention provides a welding system comprising an engine-driven welder generator comprising an engine that drives a generator to produce welding power. A welding torch is configured to receive the welding power, to support a stick electrode, and to apply the welding power to the stick electrode to establish and maintain a welding arc. A sensor is configured to sense an electrical parameter of the welding power applied to the electrode. Control circuitry is configured to receive signals from the sensor, to determine a type of stick electrode employed, and to control engine speed based upon the determined type of stick electrode employed. 
     
    
     
       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  is a diagrammatical representation of an exemplary application for power conversion circuitry, in the form of a welding system; 
           [0010]      FIG. 2  is a circuit diagram for a portion of the power conversion circuitry of  FIG. 1 , particularly illustrating certain functional circuit components; 
           [0011]      FIG. 3  is a perspective view of an exemplary power conversion module in accordance with aspects of the system shown in  FIG. 1 ; 
           [0012]      FIG. 4  is an exploded view of certain of the components of the module of  FIG. 3 ; 
           [0013]      FIG. 5  is a partial perspective view of the same module with an upper enclosure element removed to reveal internal circuit components; 
           [0014]      FIG. 6  is an exploded view of an exemplary rectifier module in accordance with aspects of the present disclosure; 
           [0015]      FIG. 7  is a perspective view of the same module from a back side; 
           [0016]      FIGS. 8A and 8B  are flow charts illustrating exemplary logic for controlling the speed of an engine generator set in a welding application; 
           [0017]      FIGS. 9A and 9B  are similar flow charts illustrating logic for speed control of an engine generator; and 
           [0018]      FIGS. 10A and 10B  are similar flow charts illustrating logic for engine speed control for another exemplary application. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    Turning now to the drawings, and referring first to  FIG. 1 , an exemplary welding system  10  is illustrated that includes a power supply  12  for providing power for welding, plasma cutting and similar applications. The power supply  12  in the illustrated embodiment comprises an engine generator set  14  that itself includes an internal combustion engine  16  and a generator  18 . The engine  16  may be of any suitable type, such as gasoline engines or diesel engines, and will generally be of a size appropriate for the power output anticipated for the application. The engine will be particularly sized to drive the generator  18  to produce one or more forms of output power. In the contemplated application, the generator  18  is wound for producing multiple types of output power, such as welding power, as well as auxiliary power for lights, power tools, and so forth, and these may take the form of both AC and DC outputs. Various support components and systems of the engine and generator are not illustrated specifically in  FIG. 1 , but these will typically include batteries, battery chargers, fuel and exhaust systems, and so forth. 
         [0020]    Power conditioning circuitry  20  is coupled to the generator  18  to receive power generated during operation and to convert the power to a form desired for a load or application. In the illustrated embodiment generator  18  produces three-phase power that is applied to the power conditioning circuitry  20 . In certain embodiments, however, the generator may produce single phase power. The power conditioning circuitry includes components which receive the incoming power, converted to a DC form, and further filter and convert the power to the desired output form. More will be said about the power conditioning circuitry  20  in the discussion below. 
         [0021]    The engine  16 , the generator  18  and the power conditioning circuitry  20  are all coupled to control circuitry, illustrated generally by reference numeral  22 . In practice, the control circuitry  22  may comprise one or more actual circuits, as well as firmware and software configured to monitor operation of the engine, the generator and the power conditioning circuitry, as well as certain loads in specific applications. Portions of the control circuitry may be centrally located as illustrated, or the circuitry may be divided to control the engine, generator and power conditioning circuitry separately. In most applications, however, such separated control circuits may communicate with one another in some form to coordinate control of these system components. The control circuitry  22  is coupled to an operator interface  24 . In most applications, the operator interface will include a surface-mounted control panel that allows a system operator to control aspects of the operation and output, and to monitor or read parameters of the system operation. In a welding application, for example, the operator interface may allow the operator to select various welding processes, current and voltage levels, as well as specific regimes for welding operations. These are communicated to a control circuitry, which itself comprises one or more processors and support memory. Based upon the operator selections, then, the control circuitry will implement particular control regimes stored in the memory via the processors. Such memory may also store temporary parameters during operation, such as for facilitating feedback control. 
         [0022]    Also illustrated in  FIG. 1  for the welding application is an optional wire feeder  26 . As will be appreciated by those skilled in the art, such wire feeders are typically used in gas metal arc welding (GMAW) processes, commonly referred to as metal inert gas (MIG) processes. In such processes a wire electrode is fed from the wire feeder, along with welding power and, where suitable, shielding gas, to a welding torch  28 . In other applications, however, the wire feeder may not be required, such as for processes commonly referred to as tungsten inert gas (TIG) and stick welding. In all of these processes, however, at some point and electrode  30  is used to complete a circuit through a workpiece  32  and a work clamp  34 . The electrode thus serves to establish and maintain an electric arc with the workpiece that aides in melting the workpiece and some processes the electrode, to complete the desired weld. 
         [0023]    To allow for feedback control, the system is commonly equipped with a number of sensors which provide signals to the control circuitry during operation. Certain sensors are illustrated schematically in  FIG. 1 , including engine sensors  36 , generator sensors  38 , power conditioning circuitry sensors  40 , and application sensors  42 . As will be appreciated by those skilled in the art, in practice, a wide variety of such sensors may be employed. For example, engine sensors  36  will typically include speed sensors, temperature sensors, throttle sensors, and so forth. The generator sensors  38  will commonly include voltage and current sensors, as will the power conditioning circuitry sensors  40 . The application sensors  42  will also typically include at least one of current and voltage sensing capabilities, to detect the application of power to the load. 
         [0024]      FIG. 2  illustrates electrical circuitry that may be included in the power conditioning circuitry  20  illustrated in  FIG. 1 . As shown in  FIG. 2 , this circuitry may include the generator windings  44 , illustrated here as arranged in a delta configuration, that output three-phase power to a rectifier  46 . In the illustrated embodiment the three-phase rectifier is a passive rectifier comprising a series of diodes that provide a DC waveform to a DC bus  48 . Power on the DC bus is then applied to filtering and conditioning circuitry  50  which aide in smoothing the waveform, avoiding excessive perturbations to the DC waveform, and so forth. The DC power is ultimately applied to a switch module  52 , which in practice comprises a series of switches and associated electronic components, such as diodes. In welding applications, particular control regimes may allow for producing pulsed output, AC output, DC output, and particularly adapted regimes suitable for specific processes. As will be appreciated by those skilled in the art, various switch module designs may be employed, and these may use available components, such as insulated gate bipolar transistors (IGBTs), silicon controlled rectifiers (SCRs), transformers, and so forth. Many of these will be available in packaging that includes both the switches and/or diodes in appropriate configurations. 
         [0025]    Finally, an output inductor  54  is typically used for welding applications. As will be appreciated by those skilled in the welding arts, the size and energy storage capacity of the output inductor is selected to suit the output power (voltage and current) of the anticipated application. Although not illustrated, it should also be noted that certain other circuitry may be provided in this arrangement, and power may be drawn and conditioned in other forms. 
         [0026]    While only certain features of the exemplary systems have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. For example, in addition to the output terminals illustrated in  FIG. 2 , power may be drawn from the DC bus for use in other conversion processes. This may allow for DC welding, for example, as well as for the supply of synthetic AC power for various auxiliary applications. The synthetic auxiliary power may be adapted, for example, for single phase power tools, lighting, and so forth. Where provided, such power may be output via separate terminals, or even conventional receptacles similar to those used for power grid distribution. 
         [0027]    Various physical arrangements may be envisaged for packaging some or all of the circuitry discussed above. A presently contemplated arrangement is illustrated in  FIG. 3 .  FIG. 3  shows an integrated power module  56  that incorporates essentially the rectifier circuitry of  FIG. 2 , the filtering and conditioning circuitry, as well as the switch modules. As discussed below, the integrated power module  56  also includes at least a drive board for the switches. Various bus structures are also included in the package as discussed below. The integrated power module  56  is illustrated as including an upper housing  58  and a lower housing  60 . These may be made of non-conductive or insulative materials, such as injection molded plastic. The illustrated housings facilitate covering the components, supporting them mechanically, and also separating them as needed for electrical insulation purposes. Shown in  FIG. 3  are input terminals  62  which lead into rectifier modules  64  discussed below. Each of these input terminals will be coupled to an output phase of the generator in a three-phase application. 
         [0028]      FIG. 4  shows an exploded view of the exemplary module illustrated in  FIG. 3 . As mentioned above, the module  56  includes and upper housing  58  and a lower housing  60  with the various circuit components disposed in these housing sections and mechanically supported by the housing. In the illustration of  FIG. 4 , a pair of rectifier clamp bars  66  are shown that coupled to output of diodes within the rectifier modules as described more fully below. These clamp bars are conductive, and apply power to an upper bus plate  68 . Bus plate  68  forms one side of the DC bus discussed above with reference to  FIG. 2 . A lower bus plate  72  is also illustrated and will make contact with diodes of the rectifier modules  64  to form the lower branch of the DC bus. An insulator plate is positioned between lower bus plate  72  and upper bus plate  68  for maintaining voltage potential between the plates. An output bus bar  70  is provided for channeling output power from the power module. Capacitors  74  are shown exploded from the lower housing  60 . In the illustrated embodiment the lower housing  60  comprises apertures and structures designed to receive these capacitors, to mechanically support them, and to allow them to be coupled to the bus bar plates. The switch modules are comprised in a subassembly, in this case a buck converter module  76 . The buck converter module is also secured to the lower housing, and supports a driver board for applying drive signals to the switches of the buck converter module. The buck converter module is in contact with the upper and lower bus plates when the integrated power module is assembled, as well as with the output bar  70 . Finally, an output resistor  78  is provided that will extend between terminals external to the housing in the currently contemplated embodiment. 
         [0029]      FIG. 5  is an illustration of the same module, from a different perspective and with the upper housing removed to show the interconnection of various components. Here the module  56  can be seen as comprising the lower housing with the rectifier modules  64  at an input end of the structure. The rectifier clamp bar  66  is in contact with upper diodes forming the rectifier. The upper bus plate  68  is also visible and is in contact with this same side of the rectifier modules and with the output terminal. The capacitors, one of which is visible in  FIG. 5 , are electrically and mechanically secured to both the upper bus plate  68  and to the lower bus plate  72 , corners of which are visible in corner cut-outs of the upper bus plates. A driver circuit board  80  is shown in  FIG. 5 . As will be appreciated by those skilled in the art, the driver circuit board is populated with electronic circuitry that allows for application of drive signals to the power electronic switches of the buck converter module. These drive signals will typically be generated based upon control signals from the one or more processors within the control circuitry discussed above. As also shown in  FIG. 5 , conforming housing sections  82  may be defined for receiving and securely holding various components, such as the capacitors  74  in this case. Moreover, one or more of the circuits may be designed with fins to assist in air or forced cooling. Such fins  84  illustrated for the buck converter module shown in  FIG. 4 . 
         [0030]    It has been found that the particular arrangements of the packaging shown in the figures is well suited to compact and efficient design, manufacturing, assembly and operation. In the illustrated embodiment, the circuit components may be formed in advance and sub-assemblies made, particularly of the converter module and the rectifier modules, as well as the drive circuit board. These are then simply assembled in the package as described. The resulting package is space and energy efficient, and allows for cooling of the power electronic devices during operation. The package may be used in wide range of applications and is particularly well-suited to the presently contemplated welding and plasma cutting applications, based upon inputs from a welder generator which is, together with the integrated power module, positioned in a mobile enclosure. 
         [0031]      FIGS. 6 and 7  illustrate a presently contemplated design for the rectifier modules that is useful in allowing them to be easily integrated into the power module. As shown in  FIG. 6 , for example, each rectifier module comprises a housing  86  which is made of an injection molded conductive material, such as aluminum or an aluminum alloy. The housing includes multiple integral features that are formed in the molding process. Ideally, little or no further machining is required following molding. The housing includes an integral terminal extension  88  to which an input conductor is coupled during assembly of the integrated power module into the welder generator. The body  90  of the housing  86  is unitary such that the entire body is placed at the potential applied to the terminal extension  88 . Thus, when used in applications as a portion of a rectifier of AC input power, the rectifier module body will typically receive an AC waveform that is applied to the entire body during operation. The body comprises fin extensions  92  on rear side thereof to aid in cooling of the body and the entire module. Recesses  94  are formed in opposite face of the body and receive diode modules  96 . In the illustrated embodiment for such diode modules are received, although it should be noted that the four diode modules function in the circuitry as only two diodes. That is, the upper two diode modules illustrated in the figures function as the upper diode in the rectifier circuitry of  FIG. 2  (for one of the phases) while the lower pair of diodes function as the lower diode (for the same phase). Each diode module comprises a conductive body  98  within which the diode itself is formed. This conductive body forms the input side of each individual diode module, which is placed at the input potential when the diode modules are received within the recesses  94  of the body  90 . Output conductors  100  of each module extend from a center of the prospective diode module. Electrical connection is made with these output conductors (which are sandwiched between the rectifier clamp bars discussed above).  FIG. 7  illustrates the same diode module from a rear side. Here the fins  92  can be seen extending from the body  90 , as well as the input terminal extension  88 . The bodies  98  of the individual diode modules  96  are illustrated before they are pressed into the recesses  94  of the body. 
         [0032]    It has been found that the foregoing design allows for a highly efficient manufacturing process, simple assembly, and robust performance. In particular, with each rectifier module body being placed at the input potential, multiple phases of the rectifier can be separated from one another by the non-conductive material of the housing (see, e.g.,  FIG. 5 ). It should also be noted that the flanged arrangements of the module body and the tongue-in-groove mounting allow for environmental isolation of the modules and diodes, which may be particularly important in mobile applications in which the circuitry may be subjected to weather and environmental factors, even when placed in a unit enclosure. In practice, one or multiple phases can be rectified in this manner. Moreover, it should be noted that while pairs of diodes are utilized to perform the function of individual diodes illustrated diagrammatically in  FIG. 2 , in practice, one, two or more such diodes may perform this function. Thus, the body of the rectifier module may be re-configured and the recesses reduced or multiplied, and their position changed to accommodate the particular packaging envisaged. 
         [0033]    The circuitry and systems described above may be controlled in various manners, depending upon the particular application or load. In the case of a welder driven by an engine generator set, it is presently contemplated that control may be made to the speed of the engine in order to optimize output of the generator and power conditioning circuitry. This optimization will typically allow for reduced speeds when appropriate for providing power to the welding load, with increased speeds where additional voltage and/or power are required. This allows for reduced fuel usage, noise and exhausts where lower power and/or voltage requirements are demanded, while nevertheless accommodating higher requirements within the capabilities of the system.  FIGS. 8 ,  9  and  10  illustrate exemplary logic for carrying out this type of control. 
         [0034]    The control logic summarized in  FIGS. 8A and 8A  is particularly directed to decisions and control logics for stick welding applications. The exemplary logic, designated globally by reference numeral  102  begins at step  104  where an initial engine speed is adopted. In particular, engines presently contemplated will have a power and voltage curve that provide for higher output power and voltage as speed increases. The nominal initial speed of 2400 RPM can be regulated by feedback control of the engine speed and throttle positions (and any other desired controlled variables), typically implemented by an engine electronic governor or control circuitry of the type described above. As indicated by reference numeral  106 , then, a process or mode will typically be selected by the operator. That is, the operator may, in a presently contemplated embodiment, enter a stick process, utilizing low hydrogen electrodes as indicated at reference numeral  108 , or a cellulose electrode process as indicated at reference numeral  110 . Moreover, synthetic auxiliary power may be generated by the system and output as indicated by reference numeral  112 . The selection of the XX18 (low hydrogen) or XX10 (cellulose) mode will typically be made by the operator interface described above. The detection of synthetic auxiliary power output may be detected by a current sensor on an auxiliary power line of the power conditioning circuitry. 
         [0035]    Based upon the mode, then, the system may detect a pre-set current for the welding output. As illustrated in  FIG. 8A , this current may fall within various ranges, such as below 158 AMPS, above 260 AMPS, or at various ranges between. The current will typically be set via the operator interface. Based upon this current setting, then, the control circuitry causes the engine to accelerate to desired engine speed, again, adapted based upon the voltage and/or power curve of the engine. In the illustrated embodiment, the new speed indicated by reference numeral  116  will be either 2800 RPM, 3200 RPM, or 3600 RPM. 
         [0036]    Thereafter, the algorithm will call for either a power calculation or a power and voltage calculation. Specifically, in a stick mode, in the illustrated embodiment, the system will sense current and voltage of the output waveform and calculate output power of the welding output based upon these measured parameters. Similarly, if synthetic power is output for auxiliary application, the auxiliary draw may be added to this welding power output to obtain the calculations indicated at reference numeral  118 . 
         [0037]    The logic summarized in  FIGS. 8A and 8B  also allow for determination of certain electrode types that may be used in stick welding, an adaptation of the engine and generator output performance based upon the electrode type. In particular, at step  118 , if the system is operating in pipe mode, the logic may determine whether a certain type of electrode, in this case an electrode recognized in the art as “XX10” is identified by monitoring voltage spikes during initial welding operations. Such electrodes may be termed “cellulose” electrodes. To operate effectively such electrodes should be powered with sufficient voltage to ride through high voltage requirements unique to these electrode formulations. The voltage will not be constant, but a transient may be repeated and is detectable by monitoring the arc voltage. If the voltage requirement is not met, the arc may be unstable, and may intermittently be extinguished. While heretofore known power sources addressed such requirements by raising the voltage potential as high as possible and sometimes beyond during a weld, or using inductors or stabilizers in series with the output, the present approach uses an adaptive technique. This adaptive technique, like the other speed increase approaches summarized, allows for running the engine as slow as possible to save on noise and fuel. The available voltage changes with engine speed and therefore the system will seek a speed just sufficient to stabilize the arc. In a presently contemplated embodiment, for example, when using XX10 electrodes, transients will be noted during the initial moments of welding. In this contemplated embodiment, if there are more than 5 (e.g., 10) such transients above a threshold (e.g., 44 volts) in the first second of welding, control moves the engine speed to the speed required as summarized in  FIG. 8A . 
         [0038]    Still more specifically, the control solution for this type of electrode allows for initiating and controlling the arc start, then monitoring for high voltage events once the arc is established. In one presently contemplated approach, if there are 10 such events, the engine speed is raised incrementally by increments of 400 RPM above the initial operating point. With cellulose electrodes, these events will be expected to happen quickly, and the engine speed change will generally be unnoticed. If the operator runs a different type of electrode but pulls the arc, the engine speed may also respond in a similar manner. This could be somewhat more noticeable, but would nevertheless provide smooth operation of the electrode. The control technique monitors the voltage of the output of the machine, which generally represents the arc voltage. In the presently contemplated embodiment, the voltage is monitored rapidly (e.g., every 100 uS). The system determines if the voltage events over the threshold represent the likely use of a cellulose electrode, and thus adapts for the electrode requirements. The higher engine speed will increase the bus voltage, and thereby the voltage output. 
         [0039]    As indicated at reference numeral  120  in  FIG. 8A and 8B , then, based upon the power calculation or power/voltage calculation at step  118 , the system may remain at the current speed, or may increase in speed as required. Thereafter, similar calculations are made at step  122 , and further boosts in engine speed and output are made, where appropriate, at step  124 . At step  126  further similar calculations are made, to determine whether a final boost may be made to the final engine speed. 
         [0040]    Several notes of interest should be made with reference to the logic summarized in  8 A and  8 B. First, once the arc is initiated for welding, the system may boost output to higher levels, but generally does not return to the initial speed until the arc is extinguished (i.e., after termination of a current weld). Moreover, once at a boosted speed, the system may remain at that speed or increase incrementally to higher speeds as required. Moreover, the increments in the presently contemplated design are of 400 RPM from the initial speed of 2400 RPM to a final speed of 3600 RPM. These increments could be of different magnitudes, of a different number, and could have different beginning and ending points, depending upon the engine specifications, the generator specifications, the number of steps desired, and so forth. In general, these steps will be contemplated based upon the overall engine power and voltage curves. Finally, while the power calculations as opposed to the power/voltage calculations are indicated for particular welding processes, similar calculations may be made independent of the particular selected process, particularly where certain types of electrodes with different anticipated performance may be employed. 
         [0041]      FIGS. 9A and 9B  illustrate similar control logic, here for TIG welding applications. As indicated in  FIG. 9A , this TIG control logic, designated generally be reference numeral  132  begins with an initial running condition of 2400 RPM as indicated at step  134 . The user may select a TIG or pulse TIG process as indicated at step  136 , such as via the power supply interface. Here again, synthetic auxiliary power output may be detected as indicated at step  112 . At step  138 , then, the system detects a preset current value within a desired range, as described above in the case of the stick welding logic. Based upon the selected process and the selected current, then, the engine may be caused to stay at the same speed or to increase speeds as indicated by reference numeral  140 . As indicated by reference  142 , then, a power calculation is made based upon detected current and voltage of the weld, and any auxiliary power draw may be added to this calculation ad indicated by reference numeral  154 . As shown in  FIG. 9B , then, at step  144  the system may determine to stay at the initial speed or current speed or to advance further to a higher speed. Similar power calculations are made, then, at step  146  and  150 , resulting in decisions at steps  148  and  152 . Here again, the beginning and end points for the speed range could be altered, as may the particular incremental increases based upon the power calculations. It may also be noted that, as in the case of stick welding, the logic summarized in  FIGS. 9A and 9B  generally do not allow for return to the initial engine speed until the arc is extinguished following the end of a particular weld. 
         [0042]      FIGS. 10A and 10B  illustrate similar logic for MIG welding. This logic, designated generally by reference numeral  156 , begins with an initial engine running speed at step  158 . The operator may select between different MIG welding processes, such as a solid wire process as indicated by reference numeral  160  or a flux core process as indicated by reference numeral  162 . Here again, synthetic auxiliary power may be provided as indicated at block  112 . In the embodiment illustrated, the initial engine speed for use with solid wire is 3200 RPM, and for flux cored wire, 3600 RPM, as indicated at steps  164 . For flux cored wire, this speed is held initially for 3 to 5 seconds before allowing a down-correction (as indicated at step  168 ). For solid wire, the initial speed is held approximately 1 second. 
         [0043]    Subsequently, then, once the welding arc has started, a determination may be made whether to decrease the engine speed based upon a power calculation, as indicated by reference numeral  166 , which may include addition of any auxiliary power draw as indicated at reference numeral  178 . Based upon the calculation, the speed may be decreased and maintained or further altered. It should be noted that in this algorithm, the initial speed may be maintained if the load requires higher output, as indicated by the lines extending from step  164  to step  174  (see  FIG. 10B ). If a speed reduction is possible (based on reduced power requirements) the decrease may be implemented as indicated at step  168 . Further calculations are then made at steps  170  and  174 , which may be followed by decisions to increase speed as indicated at steps  172  and  176 . Here again, once speed has increased during a particular weld, speeds are not generally decreased until that weld has terminated. Moreover, as in the logic for stick and TIG welding, the particular beginning and ending points of speed control, and the particular intervals or steps in speed may be adapted for different engines, generators and power conditioning circuitry.