©
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." 1.9.1.1
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. 1.9.2.1
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
