Lincoln Electric V250-S service manual Protection Circuits, Overload Protection

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E-6

THEORY OF OPERATION

E-6

 

 

PROTECTION CIRCUITS

Protective circuits are designed into the V250-S machine to sense trouble and shut down the machine before the trouble damages the internal machine com- ponents. Both overload and thermal protection cir- cuits are included.

OVERLOAD PROTECTION

THERMAL PROTECTION

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The V250-S is electrically protected from producing high output currents. Should the output current exceed 290 amps, an electronic protection circuit will reduce the current to less than 200 amps. Lincoln Electric refers to this current reduction as “Fold Back”. The machine will continue to produce this low current until the protection circuit is reset. Reset occurs when the output load is removed.

A protection circuit is included to monitor the voltage across the input filter capacitors. In the event that the capacitor voltage is too high, the protection circuit will prevent output.

On new installations, the protection circuit may pre- vent output, due to unbalanced capacitor leakages, providing the following circumstances are met:

1.Machine is connected for 380 - 460VAC input.

2.Machine did not have power applied for many months.

3.Improper connections.

4.Internal component damage.

Thermostats protect the machine from excessive operating temperatures. Excessive temperatures may be caused by a lack of cooling air or operating the machine beyond the duty cycle and output rating. If excessive operating temperature should occur, the thermostat will prevent output voltage or current and the thermal indicator light will glow.

Thermostats are self-resetting once the machine cools sufficiently. If the thermostat shutdown was caused be 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 15 minute period. If the fan is not turning or the air intake louvers were obstructed, then the power must be switched off for 15 minutes in order to reset. The fan problem or air obstruction must be corrected.

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NOTE: Unshaded areas of block logic diagrams are the subject of discussion.

INVERTEC V250-S

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Contents Invertec V250-S Safety Electric Shock can kill ARC Rays can burnFumes and Gases can be dangerous Cylinder may explode if damaged Welding Sparks can cause fire or explosionPrécautions DE Sûreté Sûreté Pour Soudage a L’ArcMaster Table of Contents for ALL Sections Installation Table of Contents Installation SectionTechnical Specifications Invertec V250-S Three Phase Single PhaseThree Phase Safety Precautions Input ConnectionsSelect Suitable Location Input Voltage Reconnect Procedure Input Fuse and Supply WirePower Input Connection for 50/60 HZ Machines Quick Disconnect Plugs Remote Control ReceptacleOutput Connections Output CablesInvertec V250-S Operation Safety Instructions Gouging SparksControls and Settings Figure B.1 Case Front ControlsAIR Carbon ARC Cutting Constant Current ProcessesManual ARC Welding Stick TIG WeldingParallel Operation Overload ProtectionThermal Protection Invertec V250-S Accessories Table of Contents Accessories SectionOptions / Accessories Remote ControlsCable Plugs Maintenance Table of Contents Maintenance SectionInput Filter Capacitor Discharge Procedure Figure D.1 Location of Input Filter Capacitor TerminalsRoutine Maintenance Filter Capacitor ConditioningFigure D.2 Location of Maintenance Components Table of Contents Theory of Operation Section Theory of OperationGeneral Description Input Line VoltagePrecharge and Protection Figure E.2 Protection and PRE-CHARGE CircuitsMain Transformer Figure E.3 Main TransformerOutput Rectification Control Figure E.4 Output Rectification and ControlProtection Circuits Overload ProtectionInsulated Gate Bipolar Transistor Igbt Operation Pulse Width Modulation Minimum OutputMaximum Output Troubleshooting & Repair HOW to USE Troubleshooting Guide Oscilloscope WarningPC Board Troubleshooting Procedures Board can be dam- aged by static electricityPossible Areas Recommended Symptoms Course of ActionPossible Areas Perform the Control Board Voltage ChecksCapacitor Balance Test Troubleshooting & Repair Perform the Output Diode Test Welding Problems Invertec V250-S Auxiliary Transformer Test Test DescriptionMaterials Needed Test Procedure Auxiliary Transformer TestAuxiliary Transformer Test Table F.1 Auxiliary Transformer Test PointsInvertec V250-S Input Rectifier Test Test Procedure Input Rectifier TestTable F.2 Input Rectifier Test Points Test Point Terminals Analog Meter X10 RangeInvertec V250-S Power Board Resistance Test Power Board Resistance Test Test DescriptionPower Board Resistance Test Table F.3 Power Board Resistance Test PointsInvertec V250-S Output Diodes Test Output Diodes Test Figure F.4 Machine Output TerminalsInvertec V250-S Diode Modules Power Board Voltage Test Power Board Voltage Test Figure F.8 Plug J6 on Power BoardTable F.4. Power Board Voltage Test Points Acceptable Test DescriptionTest Conditions Invertec V250-S Control Board Voltage Test Control Board Voltage Test Figure F.9 Plugs J1-J5 on Control BoardTable F.5. Control Board Voltage Test Points 18VACInvertec V250-S Protection Circuit Test Protection Circuit Test Figure F.10 Control Board Plug J2 Test PointsProtection Circuit Simplified Invertec V250-S Capacitor Balance Test Figure F.12 Power Board and Capacitor Test Locations Capacitor Balance TestTable F.6 Capacitor Voltages Invertec V250-S Control Board Removal and Replacement Control Board Removal and Replacement ProcedureV250S Control Power Board Removal and Replacement Power Board Removal and Replacement Figure F.14 Power Board Lead LocationsPower Board Replacement Procedure Invertec V250-S Filter Capacitor Removal and Replacement Matched PartsFilter Capacitor Removal and Replacement Figure F.15 Heatsink/Power Board RemovalPerform Power Board Replacement Procedure in this section Invertec V250-S Input Rectifier Bridge Removal and Replacement Input Rectifier Bridge Removal and Replacement Figure F.16 Input Rectifier Lead LocationsTroubleshooting & Repair Invertec V250-S Materials Needed Snubber Resistors Locking Tabs Invertec V250-S Wrench Allen type wrench Torque wrench Mounting Bolts Diode Modules Bolted Connections Troubleshooting & Repair Invertec V250-S Main Transformer Removal and Replacement Machine Codes below T3 Current Transformer Main Transformer Main Transformer Secondary Leads Figure F.22 Main Transformer Mountings Clear all leads and secure for case wrap-around assembly Invertec V250-S Main Transformer Removal and Replacement Machine Codes Above Figure F.23 Main Transformer Right Side Figure F.24 Main Transformer Left Side Figure F.25 Main Transformer Mountings Troubleshooting & Repair Invertec V250-S Retest After Repair Maximum Acceptable Output AT Minimum Output SettingsMinimum Acceptable Output AT Maximum Output Settings Input Idle Amps and Idle WattsInvertec V250-S Electrical Diagrams Invertec V250-S Wiring Diagram Codes 10102 Invertec V250SWiring Diagram Codes 10187 Return to SectionControl PC Board G2666 Layout G2666Power PC Board G2684 Layout Power P.C. BD. AsblyControl PC Board G2666 Schematic Relay CoilsPower PC Board G2684 Schematic From Control BD
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