Thermal and Overload Protection | Lincoln Electric SVM170-A specs

E-6	THEORY OF OPERATION	E-6

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THERMAL AND OVERLOAD PROTECTION

The POWER MIG 255C has built-in protective ther- mostats that respond to excessive temperatures. One is located on the output choke. The other thermostat is located on the SCR heat sink assembly. They open the wire feed and welder output circuits if the machine exceeds the maximum safe operating temperature. This can be caused by a frequent overload, or high ambient temperature.

The thermostats are self-resetting once the machine cools sufficiently. If the thermostat shutdown is caused by excessive output or duty cycle and the fan is oper- ating normally, the power switch may be left on and the reset should occur within a 15 minute period. If the fan is not turning or the air intake louvers are obstructed, then the input power must be removed and the fan problem or air obstruction be corrected.

OVERCURRENT PROTECTION

The machine will automatically reduce the output if the load on the machine exceeds 300 to 320 amperes. This protects the welding power SCR’s from excessive short circuit currents and from exceeding their temper- ature rating before the thermostats can react.

WIRE FEED OVERLOAD PROTECTION

The POWER MIG has solid state overload protection of the wire drive motor. If the motor becomes over- loaded, the protection circuitry turns off the wire feed speed and gas solenoid. Check for proper size tip liner, and drive rolls, for any obstructions or bends in the gun cable, and any other factors that would impede the wire feeding. To resume welding, simply pull the trigger. There is no circuit breaker to reset, as the protection is done with reliable solid state electronics.

POWER MIG 255C

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Lincoln Electric SVM170-A service manual Thermal and Overload Protection, Wire Feed Overload Protection

Contents

Power MIG 255C Safety California Proposition 65 Warnings Electric Shock can kill Welding Sparks can cause fire or explosion Iii Précautions DE Sûreté Sûreté Pour Soudage a L’Arc Master Table of Contents For ALL Sections Installation Table of Contents Installation Section Technical Specifications Power MIG 255C Input POWER, Grounding and Connection Diagrams Safety PrecautionsUncrating the Power MIG 255C Location Installation Figure A.2 Triple Voltage Machine Input Connections Shielding GAS GUN and Cable InstallationAuxiliary Power Receptacles Table of Contents Operation Section Operation OPERATIONB-2 Wear eye, ear and body protec- tion Welding Capability Product DescriptionRecommended Processes and Equipment Limitations Description of Controls Wire Size Conversion PartsWire Drive Roll Drive and Idle Roll Sets Procedure for ChangingWire Reel Loading Readi REELS, Spools or Coils Wire Drive Configuration Feeding Wire ElectrodeIdle Roll Pressure Setting To Start the Welder Figure B.4 Instructions to Enter Fast RUN-IN When Timer Option is not installedInstructions to Enter Slow RUN-IN Making a Weld FAN Control Avoiding Wire Feeding ProblemsWire Feed Overload Protection Input Line Voltage Protection Welding Thermal Overload Protection Overcurrent Protection Accessories Table of Contents Accessories Section K363P READI-REEL Adapter Drive Roll KitsMagnum GUN Connection KIT Dual Cylinder Mounting KIT K1702-1 K1738-1 Spool Gun Hanger Accessory Operating Instructions for Timer KITConnecting the Spool GUN to the Power MIG 255C Spool GUN Making a Weld with the Prince XL Spool GUN Making a Weld with the Magnum SG Spool GUN SG Spool Gun Wire Feed Speed Power MIG Maintenance Table of Contents Maintenance Section Contact TIP and GAS Nozzle Installation GUN Tubes and Nozzles General MaintenanceGUN Cable Cleaning Liner Removal and Replacement GUN Handle Disassembly Table D.1 MAINTENANCED-4 English Metric Description Table of Contents Theory of Operation Section Theory of Operation Input Line Voltage Main Transformer Output Rectification Feedback Control Constant Voltage Output Figure E.4 Constant Voltage Output Wire Drive Motor Feedback Wire Feed Overload Protection Thermal and Overload Protection SCR Operation Figure E.6 SCR Operation Power MIG 255C Troubleshooting and Repair Table of Contents Troubleshooting and Repair Section 2TROUBLESHOOTING and REPAIRF-2 HOW to USE Troubleshooting Guide PC Board Troubleshooting Procedures Troubleshooting Guide Output Problems Trolyte in these capacitors is Problems Possible AreasSymptoms Misadjustments Course of Action Toxic. Avoid contact with any Perform the SCR Rectifier Function Problems Wire Feeding Problems Welding Problems Welding Problems Test Description Test ProceduresMain Transformer Test Materials Needed Test Procedure ON/OFF Power Switch will be hot during these tests 115VAC 16J5 8J5 206 3J5 Rectifier Diode Bridge Test 16TROUBLESHOOTING and REPAIRF-16 Figure F.2 G3521 Rectifier Diode Bridge Location 208 206 28 VAC 209 354 206 36 VDC Power MIG 255C Static SCR Rectifier Assembly Test Static SCR Rectifier Assembly Test Active SCR Rectifier Assembly Test Power MIG 255C Active SCR Rectifier Assembly Test Active SCR Rectifier Assembly Test Figure F.7 Location Leads X2 Figure F.8 Wire Drive Motor and Tachometer Feedback Test Wire Drive Motor and Tachometer Feedback Test 4J1 Test for Supply Voltage to Tachometer 515B 206B 15 VDC 5J1 1J1 Test for Feedback Voltage to Control Board 555 206B To 3.5 VDC 6J1 1J1 Normal Open Circuit Voltage Waveform Volts Machine Loaded to 250 Amps AT 26 VDC Scope Settings Typical Output Voltage Waveform Machine Loaded Machine Loaded to 220 Amps AT 22 VDC Scope Settings Troubleshooting and Repair Typical SCR Gate Voltage Waveform Power MIG 255C Description Component Replacement ProceduresControl PC Board Removal and Replacement Removal and Replacement Procedure Figure F.11 Control Board Mounting Power MIG 255C Wire Drive Assembly Removal and Replacement Wire Drive Assembly Removal and Replacement Procedure Power MIG 255C SCR Output Rectifier Removal and Replacement SCR Output Rectifier Removal and Replacement Figure F.15 Right Heat Sink Lead Disconnection Power MIG 255C Capacitor Bank Removal and Replacement Capacitor Bank Removal and Replacement Main Transformer and Output Choke Removal and Replacement 52TROUBLESHOOTING and REPAIRF-52 Main Transformer and Output Choke TOC Power MIG 255C FAN Motor Assembly Removal and Replacement FAN Motor Assembly Removal and Replacement Open Circuit Voltage Wire Speed RangeRetest After Repair Input Volts/Hertz Power MIG 255C Electrical Diagrams Section Section G-1 Electrical Diagrams Wiring Diagram Entire Machine Code 11192 L12464 Wiring Diagram Entire Machine Code 11218 L12506 Schematic Entire Machine G4752 Schematic Control PC Board G4823-2D1 Sheet Electrical Diagrams Electrical Diagrams PC Board Assembly Control G4824-2D1 Item Used with QTY Part Number Description Schematic Display PC Board L10951 Powermig PC Board Assembly Display L10952 Lincoln Electric CO SVM Error Reporting Form