ESAB MIGMASTER 250, Instruction Manual

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The FINE VOLTAGE ADJUSTMENT Selector is an
eight-position switch by which the operator selects the
exact amount of arc voltage (or heat) to be applied to the
weld (within the coarse range selected above). This
allows you to fine-tune the voltage required; the higher
the number selected (1-8), the hotter the weld. The Fine
Voltage Selector switch also has an "open" detent at the
six o'clock position. Placing the switch in this position
allows operation of the torch trigger to feed electrode
wire without the wire being electrically "hot". This switch
also, must
not be switched under load.
CAUTION: These tap switches carry several hundred
amperes, and must not be switched under
load, as this will cause the contacts of the
switches to arc.
4.1.3 SECONDARY WELDING CONNECTIONS
The secondary contactor, with parallel poles, is used to
make and break the circuit between the transformer
secondary and the rectifier. This contactor is turned on
and off when the torch trigger (in the 24 volt circuit) is
operated.
The secondary output welding terminals, POS.(+) and
NEG(-), are located in the right side wire feeding com-
partment and are used to set the welding polarity
(D.C.R.P. or D.C.S.P.) in which the machine will operate
(see Fig. 4.1). As shipped from the factory, the 250 is set
up to operate in D.C.R.P. (TORCH fitting is connected
to Positive, and WORK cable/clamp is connected to
Negative output). To weld using D.C.S.P., simply mount
the WORK cable to the Positive output and the TORCH
fitting cable to the Negative output terminal.
4.1.4 CONTACTOR CONTROL
Refer to the schematic diagrams. Note that the coil of
the 24 volt contactor is activated with the torch trigger
and is energized when the trigger is pulled. The gas
solenoid is in parallel with the contactor coil and is
energized at the same time.
When the trigger switch is released, the contactor drops
out and disconnects the load.
Because of the charged capacitor bank in the
secondary circuit, the output voltage will take a few
seconds before falling to zero volts.
The gas valve shuts off when the contactor opens.
The Migmaster 250 is equipped with a built-in control for
the Spool Gun which operates via the amphenol control
receptacle and a screw adaptor that provides Gas and
Power. The ST-23A Torch (see Section 2.4.3) has a
amphenol-plug control cable connection, and a gas/
power cable, see Figure 4.2.2.
To operate the unit with the ST-23A Torch connected, do
the following (refer to Fig. 4.2.2):
A. Place the STD./Spool Gun selector toggle switch
(4.1.6) in the 250 to its Spool Gun position.
B. Connect the ST-23A control cable amphenol to the
receptacle labeled CONTROL on the 250’s front
panel.
C. Remove the threaded plastic plug from the Gas/
Power adaptor (on the 250's front panel) using a
clockwise rotation. Connect the ST-23A gas/power
cable to the panel adaptor using a counter-
clockwise rotation. As shipped from the factory,
the 250's secondary output power terminals are
set-up for D.C.R.P. welding polarity (see Section
4.1.3).
4.1.5 WIRE FEED SPEED CONTROL
Wire feed speed is controlled by the wire speed potenti-
ometer knob on the front panel. The solid state control
allows for infinitely variable speeds up to 650 IPM.
This wire speed pot is used to set the speed at which the
welding wire is fed out from the torch and hence the
welding amperage. The panel-face numbers on the dial
(0-10) are used for reference and do not directly indicate
wire feed speed; the higher the number, the faster the
speed.
4.1.6 STD./SPOOL GUN SELECTOR
This two-position toggle switch is located inside the unit
on the mid-wall of the wire feeding compartment and is
labeled Standard and Spool Gun. It is used to select
standard metal inert gas welding (MIG) with the
GUNMASTER 250, or welding with the ST-23A (spool-on-
gun) torch.
4.2 PROCESS SETUP
4.2.1 STANDARD MIG SEAM WELDING W/
GUNMASTER 250
Refer to Sections 4.3.1, 4.3.2, 4.3.3, 4.3.4, and Table
4.3.3.
4.2.2 ST-23A SPOOL-ON-GUN CONTROL CONNEC-
TION/OPERATION
SECTION 4 OPERATION