Lincoln Electric SVM179-B Constant Current VS Constant Voltage Wire Welding, Figure B-3

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B-7

OPERATION

B-7

 

CONSTANT CURRENT VS CONSTANT VOLTAGE WIRE WELDING

Most semiautomatic welding processes perform better using constant voltage power sources.

Welding codes usually do not address the power source selection or specifically, whether the welding process is to be operated in the constant voltage or constant current mode. Instead, codes typically spec- ify limitations on the current, voltage, heat input and preheat temperature based on the material to be weld- ed. The intention is to assure that proper weld materi- al properties will develop.

Welding is sometimes performed using constant cur- rent power sources. The operation can be more con- venient because it may allow the use of an existing stick (SMAW) power source and the power source can be placed at a distant location without any provision for adjusting the output settings.

For constant current operation, the power source is set to deliver the specified current. The power source reg- ulates this current regardless of changes in the weld- ing circuit, including cable length, electrode diameter, wire feed speed, contact tip to work distance, etc.

Changes in the wire feed speed (WFS) or contact tip to work distance (CTWD) affect the arc voltage when constant current power sources are used. Lowering the wire feed speed raises the voltage, raising the wire feed speed lowers the voltage. Lengthening the con- tact tip to work distance raises the voltage, shortening the contact tip to work distance lowers the voltage. (See Figure B.3)

If the contact tip to work distance is properly main- tained, a satisfactory operating voltage range may be achieved, and a sound weld may result. However, when a welder uses a longer contact tip to work dis- tance, an arc-sensing wire feeder compensates by increasing the wire feed speed to regulate the voltage. Even if the voltage and current remain unchanged, the increased wire feed speed may result in a deposition rate well beyond the specified range of the electrode. Under these conditions, the specified weld metal prop- erties may not be achieved.

Constant voltage power sources deliver large current surges to stabilize the arc when the electrode is short- ed or the arc length is very short. However, a constant current power source does not provide such a response to stabilize the arc. It may be difficult to achieve required weld metal properties, or to achieve the required quality of welds needed to pass nonde- structive tests, when such welds are made under con- stant current operation.

For these reasons, Lincoln Electric does NOT recom- mend constant current semiautomatic welding for applications which need to meet specified weld metal chemical or mechanical property requirements or weld quality requirements.

Constant Current

Power Source

+

-

FIGURE B-3

Current

Wire

Feeder

CTWD

WFS

Current

LN-25™ PRO

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Contents LN-25PRO Wire Feeder LN-25 PRO SafetyElectric Shock can kill ARC Rays can burn Welding Cutting For ElectricallyIii Sûreté Pour Soudage a L’Arc Précautions DE SûretéMaster Table of Contents for ALL Sections Table of Contents Installation Section Installation High Frequency Protection Safety PrecautionsLocation ELECTRIC SHOCK can KillCable Connections Wire Drive ConfigurationShielding GAS Connection Changing the GUN Receiver BushingWire Guides Procedure to Install Drive RollsPressure ARM Adjustment Loading Spools of WireGUN Connection Power Source to LN-25 PRO Cable Connection Diagrams Across the ARC SET-UPSDescription Figure A.7 Table of Contents Operation Section Operation Safety PrecautionsGeneral Description Wire Feed Speed Knob DescriptionAnalog Voltmeter Figure B.2 Wire Feed Speed, CC Operation See Figure B.2 orTable B.2 VV CC Wire Speed Setting Figure B-3 Constant Current VS Constant Voltage Wire WeldingWire Feed Speed Range Switch K2613-5 and K2613-7 only PIN GUN Trigger Connector See Figure B.1Work Sense Lead Thermal LED, Motor Overload See Figure B.1Figure B.4 Internal ControlsCV/CC Switch Step Trigger Interlock SwitchInternal Controls Description Cold Feed PushbuttonPreflow Timer Optional PREFLOW, Burnback Postflow Timer KIT K2330-2Figure B.5 Rear ControlsGAS Purge Pushbutton POWER-UP SequenceFlow Meter ScfhLN-25 PRO Table of Contents Accessories Section Factory Installed Equipment AccessoriesWire Type Drive Roll KitsAccessories Accessories K435 Spindle Adapter, for mounting Installation of the K590-6 Water Cooling KIT Table of Contents Maintenance Section Routine Maintenance MaintenancePeriodic Maintenance Calibration SpecificationWire Feed Speed CoverBoard Figure D.3. Major Component Location Control Board 1TABLE of CONTENTS-THEORY of Operation Section E-1Figure E.2 General Description Theory of OperationTRIGGER CIRCUIT Input PowerFigure E.4 Feedback & Control Circuits Feedback and Control CIR- CuitsFigure E.5 Optional Circuits & Digital Display Board Optional CircuitsLN-25 PRO Table of Contents Troubleshooting & Repair HOW to USE Troubleshooting Guide Troubleshooting & RepairPC Board Troubleshooting Procedures Fault Code Description Possible Adjustment Motor Solenoid Test Problems Symptoms Possible Areas MisadjustmentsRecommended Course of Action LN-25 PRO Case Removal Procedure Test DescriptionMaterials Needed Figure F.1 Case Removal ProcedureGAS Solenoid Test GAS Solenoid Control BOX Control BOX Cover Contactor Test Control BOX Contactor Drive Motor and Tach Feedback Test Case Control BOX Assembly Motor Overload Test Figure F.5 Control BOX Assembly Contactor Removal and Replacement Procedure Figure F.6 Control BOX Removal ProcedureFigure F.7 Buss BAR and Mounting Block Replacement ProcedureLN-25 PRO Front Panel Removal and Replacement Procedure Front Panel Troubleshooting & Repair Gas Hose Control BOX Wire Drive Panel Drive Gear Cover LN-25 PRO PC Board Removal and Replacement Procedure Figure F.11 Control PC Board Location PC BOARD Removal and Replacement ProcedureGAS Solenoid Removal and Replacement Procedure GAS Solenoid GAS Hose Control BOX Lock NUT Retest After Repair SET UPRetest a machine Operation VerificationLN-25 PRO Table of Contents Diagram Section Wiring Diagram LN-25 PRO WiriNG DiaGram lN-25 prO CODEs 11507, 11508 G5681-1 Wiring DIAGRAM- LN-25 PRO Analog WiriNG DiaGram lN-25 prO CODEs 11746, 11747 G5681-3 G5683 LN-25 PRO Wire FeederLN-25 PRO Wire Feeder ElECTriCal DiaGrams G5683-1 Pushbutton LN-25 PRO Analog G5683-2G5683 G5683-3 Circuitryconfidential Equipmenttype Xres RXD Work 624 4783-1C0 Flexiblepowerfeede R 50V OF05 Circuitryconfidential S27505-1B0 R2 CW