SECTION 3
OPERATION
11
Important Digimig/Digimatic
Operational Note
All ESAB microprocessor-type wire feeder/controls
are designed to provide good arc starts with power
supplies that utilize a FLAT-SLOPE volt-ampere curve
characteristic. Since this power supply also allows
you to select a MEDIUM or STEEP slope characteris-
tic, you may have to readjust the microprocessor’s
factory-set "starting" characteristics to provide the
best arc-starts possible using the "steeper" volt-
ampere curves. The procedures required to recalibrate
the microprocessor "hot-start" characteristics are
provided in all of the appropriate Digimig/Digimatic
instruction booklets.
3.4 POWER SOURCE WELDING
CONTROLS
A. On-Off Line Switch (LS).
Placed in the ON
position, this switch (located on the rear panel)
provides primary input power to start the cooling
fan motor and energize the secondary control
circuitry. Power light (PL1) on the front panel
should illuminate.
B. Digital Voltmeter/Ammeter (DPM) and Selec-
tor (SW2).
This instrument provides direct digital
reading of open-circuit or welding, or welding
current depending on the position of the VOLT/
AMP selector switch.
C. Troubleshooting Lights.
1. Temperature (PL2).
This will light if compo-
nents in the power source overheat. The contactor
will then deenergize. Allow the power source to
cool with the line switch in the ON position (the
fan will help cool the power source) before con-
tinuing welding operations when light goes off.
2. Fault (PL3).
This light functions as a visual
detector for two specific fault conditions:
overcurrent or over/undervoltage indication. In
either case, if a fault is detected in the inverter
bridge, the contactor will deenergize and the
power source will stop welding. If an overcurrent
condition caused the problem, the fault light will
energize and remain "steady-on." Do not attempt
to restart welding (refer to Section 5). If an over
or undervoltage condition occurs, the fault light
will flash. Since this can often be caused by a
transient, retry the torch switch to resume weld-
ing. If tripping continues, stop and refer to section
5.
3.1 INTRODUCTION
This section is intended to familiarize personnel with the
operational procedures applicable to the SVI 450i cvcc
power source. Information contained in this section should
be read carefully before operation of the power source.
Never, under any circumstances, operate the power
source with the cover or side panels removed. In
addition to the safety hazard, improper cooling may
cause damage to internal components. Also make
sure you are adequately protected before welding.
Welding helmet, gloves, safety glasses, and ear pro-
tection should always be worn.
3.2 DUTY CYCLE
Duty cycle is defined as the ratio of load time to total time.
Standard current ratings are based on a 10-minute cycle.
The SVI 450i cvcc power source has a 60% duty cycle
rating which allows 450 amperes @ 38 V dc (see Figure
3-1). The 60% duty cycle rating means that the 450-
ampere rated load can be applied for a total of 6 minutes
and shut off for a total of 4 minutes in a 10-minute period.
If the welding current is decreased, the duty cycle can be
increased. Conversely, if the welding current is increased,
the duty cycle must be decreased.
3.3 VOLT-AMPERE (SLOPE)
CHARACTERISTICS
The curves shown in figure 3-2 represent the volt-ampere
static characteristics for the power supply in the MIG (cv)
and TIG (cc) modes. The slant of these curves is referred
to as the ‘slope’ and is generally defined as the ‘voltage
drop per 100 amperes of current rise.’ These curves show
the output voltage available at any given output current
between the minimum and maximum settings of the
voltage/current control. Typical curves are shown for
other settings between the minimum and maximum curves.
Because the volt-ampere slope is fixed, it is possible to
select optimum welding conditions by approximating the
open-circuit voltage required for a particular load current.
If you require greater slope (shown as dotted curves at
maximum setting) for your MIG welding applications, you
may change the slope switch position located on the front
panel. The static volt-ampere slope is not affected by the
inductor rheostat setting. For welding aluminum or stain-
less steel, the steeper slope settings are recommended.
