© COPYRIGHT 1999 THE ESAB GROUP, INC. LESSON I, PART B 1.9    CONSTANT CURRENT OR CONSTANT VOLTAGE Welding power sources are designed in many sizes and shapes.  They may supply either AC or DC, or both, and they may have various means of controlling their voltage and amperage output.  The reasons for this is that the power source must be capable of producing the proper arc characteristics for the welding process being used.  A power source that produces a satisfactory arc when welding with coated electrodes will be less than satisfactory for welding with solid and flux cored wires. 1.9.1 Constant Current Characteristics - Constant current power sources are used primarily with coated electrodes.  This type of power source has a relatively small change in amperage and arc power for a corresponding relatively large change in arc voltage or arc length, thus the name constant current.  The characteristics of this power source are best illustrated by observing a graph that plots the volt- ampere curve.  As can be seen in Figure 20, the curve of a constant current machine drops down- ward rather sharply and for this reason, this type of machine is often called a "drooper." In welding with coated electrodes, the output current or amperage is set by the operator while the voltage is designed into the unit.  The operator can vary the arc voltage somewhat by increasing or decreasing the arc length.  A slight increase in arc length will cause an increase in arc voltage and a slight decrease in amperage.  A slight decrease in arc length will cause a decrease in arc voltage and a slight increase in amperage. 1.9.2 Constant Voltage Characteristics - Constant voltage power sources, also known as constant potential, are used in welding with solid and flux cored electrodes, and as the name implies, the voltage output remains relatively constant.  On this type of power source, the voltage is set at the machine and amperage is determined by the speed that the wire is fed to the welding gun.  Increasing the wire feed speed increases the amperage. Decreasing the wire feed speed decreases the amperage. Arc length plays an important part in welding with solid and flux cored electrodes, just as it does in welding with a coated electrode.  However, when using a constant voltage power source and a wire feeder that delivers the wire at a constant speed, arc length caused by operator error, plate irregularities, and puddle movement are automatically 34V - 290 A 32V - 300 A 30V - 308 A VOLT / AMPERE CURVE CONSTANT CURRENT 100 200 300 AMPERES CONSTANT CURRENT VOLT / AMPERE CURVE FIGURE 20 80 70 60 50 40 30 20 10 V O L T S

Lesson 1
The Basics of Arc Welding
Lesson 2
Common Electric
Arc Welding Processes
Lesson 3
Covered Electrodes for Welding
Mild Steels
Lesson 4
Covered Electrodes for Welding Low Alloy Steels
Lesson 5
Welding Filler Metals for Stainless Steels
Lesson 6
Carbon & Low Alloy
Steel Filler Metals -
Lesson 7
Flux Cored Arc Electrodes Carbon Low Alloy Steels
Lesson 8
Hardsurfacing Electrodes
Lesson 9
Estimating & Comparing Weld Metal Costs
Lesson 10
Reliability of Welding Filler Metals


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