Lincoln Electric SVM155-A service manual Figure E.5 SCR Operation

Page 28

Return to Section TOC

Return to Section TOC

Return to Master TOC

Return to Master TOC

E-6E-6

TROUBLESHOOTING & REPAIR

FIGURE E.5 SCR OPERATION

Return to Section TOC

Return to Section TOC

Return to Master TOC

Return to Master TOC

SCR OPERATION

A silicon controlled rectifier (SCR) is a three terminal device used to control rather large currents to a load. An SCR acts very much like a switch. When a gate signal is applied to the SCR it is turned ON and there is current flow from anode to cathode. In the ON state the SCR acts like a closed switch. When the SCR is turned OFF there is no current flow from anode to cathode thus the device acts like an open switch. As the name suggests, the SCR is a rectifier, so it passes current only during positive half cycles of the AC sup- ply. The positive half cycle is the portion of the sine wave in which the anode of the SCR is more positive than the cathode.

When an AC supply voltage is applied to the SCR, the device spends a certain portion of the AC cycle time in the on state and the remainder of the time in the off state. The amount of time spent in the ON state is controlled by the gate.

An SCR is fired by a short burst of current into the gate. This gate pulse must be more positive than the cathode voltage. Since there is a standard PN junc- tion between gate and cathode, the voltage between these terminals must be slightly greater than 0.6V. Once the SCR has fired, it is not necessary to contin- ue the flow of gate current. As long as current contin- ues to flow from anode to cathode the SCR will remain on. When the anode to cathode current drops below a minimum value, called holding current, the SCR will shut off. This normally occurs as the AC supply volt- age passes through zero into the negative portion of the sine wave. If the SCR is turned on early in the pos- itive half cycle, the conduction time is longer resulting in greater SCR output. If the gate firing occurs later in the cycle the conduction time is less resulting in lower SCR output.

MULTI-SOURCE

Page 27 Page 29
Image 28
Page 27 Page 29
Contents MULTI-SOURCE TM Safety California Proposition 65 WarningsElectric Shock can kill Welding Sparks can cause fire or explosion Précautions DE Sûreté Sûreté Pour Soudage a L’ArcMaster Table of Contents for ALL Sections Table of Contents Installation Section Installation Technical Specifications Multi-Source K1752-1Safety Precautions Select Proper LocationStacking TiltingFuse and Wire Sizes Input and Grounding ConnectionsOutput Connections ParallelingMULTI-SOURCE Table of Contents Operation Section Safety Instructions OperationGeneral Description Design Features and ADVAN- TagesRecommended EQUIPMENT/PROCESSES Controls and Settings Recommended EQUIPMENT/CONNECTIONSTable of Contents Accessories Factory Installed Options / Accessories Field Installed Options / AccessoriesTable of Contents Maintenance Safety Precautions Routine and Periodic MAINTE- NanceFigure D.1 Major Component Location MULTI-SOURCE Table of Contents Theory of Operation General Description Input VOLTAGE, FILTER, Contac TOR and Control Trans FormerTroubleshooting & Repair Return to Section Section TOCOperation Protection Devices and CIR Cuits SCR Operation Figure E.5 SCR OperationTable of Contents Troubleshooting & Repair Section HOW to USE Troubleshooting Guide PC Board Troubleshooting Procedures and Replacement Electric Shock can killTroubleshooting Guide Calibration Procedure Perform the Firing Board TestPerform the Main Transformer T1 TestCircuit external to the Multi Technical Specifications Main Transformer TestFunctions Problems Input Contactor TestTest Description Control Transformer T2 Voltage TestTest Procedure Figure F.1. Control Transformer Location & Leads575 VAC 43.0 VAC 460 VAC 34.50 VAC 380 VAC 28.50 VAC Secondary Thermostat Input Contactor Test Input Contactor Test 241COILRemoval and Replacement Procedure Test for Contact ContinuityMULTI-SOURCE Main Transformer T1 Voltage Test Main Transformer T1 Voltage Test Contactor TestFigure F.6. Main Secondary Lead Test Points MULTI-SOURCE Static SCR Test Static SCR Test Leads Remove Red Paint Active SCR Test Active SCR Test Active SCR Test Remove Red Paint SW1 MULTI-SOURCE Control Board Test Control Board Test See Figure F.15#341 #230 #215 #231 #263 #201 J1 MULTI-SOURCE Firing Board Test Figure F.17 Static and Active SCR TestsTable F.2. LED 7, 8 and 9 Check List Then#231 #215 #340 J8 #287 MULTI-SOURCE Meter Accuracy Check Control Board Normal Open Circuit Voltage Waveform no Load Volts Typical SCR Gate Voltage Waveform no Load MULTI-SOURCE Input Contactor Cleaning AND/OR Replacement DescriptionRemoval Procedure 240 CoilMULTI-SOURCE Control Board Replacement Procedure Control Board Firing Board Replacement Procedure Firing Board SCR Bridge / Heat Sink Assembly Replacement Procedure Bridge Assembly Mount #251 Mounting Bolt Removal of Individual SCR Heat Sink Assemblies See Figure F.26 Figure F.27Maximum Open Circuit Voltage No Load Readings FAN OFFPerform Meter Accuracy Test MULTI-SOURCE Electrical Diagrams Table of Contents Electrical Diagrams SectionWiring Diagram MULTI-SOURCESchematic Control PC Board PC Board ASSEMBLY-CONTROL Return to SectionSchematic Firing Printed Circuit Board PC Board ASSEMBLY-FIRING TP1PC Board Assembly Snubber M14312SVM Error Reporting Form

SVM155-A specifications

The Lincoln Electric SVM155-A is a state-of-the-art welding machine that excels in versatility and performance, making it ideal for both professional welders and hobbyists. This multi-process welder supports MIG, TIG, and stick welding processes, allowing users to tackle a wide range of applications with a single device. Its user-friendly design and advanced technology make it an exceptional choice for those looking to enhance their welding capabilities.

One of the main features of the SVM155-A is its robust power output, which can handle welding materials ranging from thin sheets to heavier stock. The welder offers a high duty cycle, ensuring that users can work efficiently without the need for prolonged breaks. This is especially important in industrial settings where productivity is key. Additionally, the SVM155-A is equipped with a digital display that allows for easy monitoring and precise control of the welding parameters, ensuring consistency in weld quality.

The European-designed INVERTER technology embedded in the SVM155-A significantly contributes to its lightweight and compact design. Weighing in at only 19.4 lbs, this welder is portable and ideal for fieldwork or workshops where space is limited. The inverter technology not only reduces the size and weight but also improves energy efficiency, leading to lower operational costs over time.

The SVM155-A also features advanced safety mechanisms, including over-current protection to safeguard the machine from potential damage during excessive use. It also includes a thermal overload shut-off, which prevents overheating, ensuring a longer lifespan for the welder.

Another standout characteristic of the SVM155-A is its exceptional arc stability and ease of use. The machine is designed to provide a smooth and consistent arc, reducing spatter and ensuring clean welds. Moreover, the welder is compatible with a wide range of materials, including stainless steel, aluminum, and carbon steel, further enhancing its versatility.

In conclusion, the Lincoln Electric SVM155-A is a powerful, durable, and multifunctional welding machine that incorporates advanced technologies to meet the needs of modern welding applications. Its portability, safety features, and ability to deliver high-quality welds make it an excellent investment for anyone looking to improve their welding skills or expand their capabilities in various welding projects.
Top Page Image Contents