INSTRUCTIONS for
These INSTRUCTIONS are for experienced operators. If you
are not fully familiar with the principles of operation and safe
practices for arc welding equipment we urge you to read our
booklet Precautions and Safe Practices for Arc Welding,
Cutting and Gouging, Form 52-529. Do NOT permit untrained
persons to install, operate or maintain this equipment. Do NOT
attempt to install or operate this equipment until you have read
and fully understand these instructions. If you do not fully
understand these instructions contact your supplier for further
information. Be sure to read the Safety Precautions on page 2
before installing or operating this equipment.
F-12-728-C
February, 1995
MIG-28A*
WIRE FEEDER
SPECIFICATIONS
Torch Capacity (100% duty) .................................. 250 amps DC
Torch Weight, approx ..... 3 Ibs. 1.4 kg, (less wire; service lines)
Control Weight, approx ........................................ 16 lbs. (7.2 kg)
Primary Power Required.....................115 volts, 50/60 Hz, 1 ph.
Wire Feed Speed Range .................. 79-709 ipm (33-300 mm/s)
Wires Accommodated ....................... 030- through .045-in. hard
.030- through 1/16-in. soft
Dimensions, in.
Torch Control
Length ........... 15 (381 mm) Length. ..............14.7 (373 mm)
Width ........... 3-1/4 (82 mm) Width .................10.7 (272 mm)
Height ............. .8 (203 mm) Height ................ 10.2 (260 mm)
Handle Dia ....... .1-3/4 mm)
I. INTRODUCTION
The MIG-28A Wire Feeder can be used for either short
arc or spray arc welding with a constant potential (CP) or
a constant current (CC) power supply. A flip of a selector
switch readies the control for use with either type of
welding power. The control operates from a 115 volt AC
50/60 Hz power source.
The MlG-28A consists of two basic units: an SEC-7A
Control and an ST-23 Torch. This instruction booklet
covers the installation and operation of the complete
MIG-28A (torch and control). For installation of torch
accessories and torch maintenance, refer to Form 14353, ‘Instructions for ST-23A Mig Welding Torch’.**
A. DESCRIPTION
The SEC-7A Control contains a solid state governor to
F-12-728-C
maintain wire feed rate for constant potential welding,
and to regulate arc voltage for constant current welding.
Most of the control circuits in the SEC-7A are incorporated on one printed circuit board which is mounted
inside the control for easy access and removal.
The control circuitry contains a dynamic brake which
quickly stops wire feed, to eliminate freezing of wire in the
weld puddle for the vast majority of conditions. In addition, an optional Anti-Stick Kit is also available for the
SEC-7A to adjust the amount of wire burnback after wire
feed stops, to further prevent any freezing of welding wire
in the weld puddle.
The ST-23 Torch is an air cooled, spool-on-gun type
manual mig welding torch with a maximum current capacity of 250 amperes DC continuous duty. The torch
contains a complete gearmotor in the handle which pulls
the welding wire from a 4-in. diameter spool, mounted in
a molded case on the rear of the torch, and delivers it to
the torch nozzle. The case is molded from a rugged,
flame retardant, glass-reinforced polyester compound.
II. SETTING UP THE MIG-28A
A. EQUIPMENT SUPPLIED
The MIG-28A (Series A) is available in a welding outfit
under P/N 19163. Contents of the outfit are listed in Table
1.
Be sure this information reaches the operator.
You can get extra copies through your supplier.
POWER CABLE / GAS CONNECTIONS
PRINTED CIRCUIT BOARD
WELD POWER
SELECTOR SWITCH
CONSTANT
POTENTIAL
WIRE INCH RELAY
TORCH SWITCH RELAY
Fig. 1 - Interior View of SEC-7A Control
Table 1 - Contents of MIG-28A Outfit, P/N 19163
Description Qty. Part No.
SEC-7A Control 1 2075159
ST-23A Torch/30-ft. service lines 1 19164
Control Cable, 6-ft., 6-cond., 19 pin 1 36618
Gas Hose, 12-1/2-ft. 1 40V77
Contact Tip (.030" Hard & Soft) 3 996994
Contact Tip (.035" Hard & Soft) 3 996995
Contact Tip (3/64" Soft & .045" Hard) 3 996999
Contact Tip (1/16" Soft) 3 996997
Feed Roll (.030" & .035" Hard & Soft) 1 636343
Torch Liner (.030 & .035 Wire) 1 19166
No. 8 Nozzle Std. Duty 3 999471
No. 10 Nozzle Std. Duty 2 999472
B. REQUIRED COMPANION EQUIPMENT AND
ACCESSORIES
1. R-5007 Argon Regulator-Flowmeter, P/N 998124.
2. 2/0 Welding Cable (customer supplied) in suitable
lengths to connect the power supply to the control and
workpiece. Terminal lug with fiber cover, P/N 81F64,
is available for connecting the cable to the power
supply.
3. Gas Hose Coupling, P/N 11N17 permits you to extend
gas hose by ordering additional hose (40V77).
4. One of the following types of power supplies:
a. A D.C. Rectifier-Type Constant Potential Power
Supply (such as VI-206, VI-300, VI-450, etc.) as
shown in Figure 2.
b. A D.C. Generator or D.C. Rectifier-Type Constant
Current Power Supply which does not have a built-
CONSTANT
CURRENT
SWITCH ON P/C BOARD
P.C. Board location of
SLOW INCH DOWN TRIMPOT
(See Section IV-D-2.)
TRANSFORMER
in contactor. For this type unit, a 300 Amp. Secondary Contactor Assembly (P/N 677333) will be required to interrupt the welding current between the
SEC-7A Control and the power source as shown in
Figure 3. (Refer to Form 12-825 for complete
installation instructions.)
c. A D.C. Rectifier-Type Constant Current Power
Supply that contains a built-in contactor with a
115-volt coil. This type unit can be operated directly from the SEC-7 control as shown in Figure 4.
d. A Heliarc 306/Heliarc 350 AC/DC Power Supply may
also be used; however, in this case an Adaptor Kit
(P/N 995313) will be required. (Refer to Form 12324 for complete installation instructions.)
5. Standard Welders Helmet with proper shade of
glass. A No. 12 glass should be used for currents
of 75 to 200 amperes.
C. OPTIONAL ACCESSORIES
1. Torch Control Cable Extension Assy., (30-ft.) P/N
636968. Used to extend the length of the torch cables
(see Fig. 5)
2. Torch Power and Gas Extension Adaptor, P/N 993457.
This adaptor is used in conjunction with extension
636968 above. Both parts enable you to extend the
torch service lines up to 60-ft. (See Fig. 5.)
3. Control Adaptor Cable (3-ft., 6-cond.) P/N 996736.
Required to connect the control to any power supply
which does not contain a remote contactor receptacle.
4. Control Extension Cable (25-ft.) P/N 996738. Used to
extend the control to power supply cable (see Fig. 2).
3
5. Anti-Stick Kit, P/N 2075076. Kit permits precise adjustment of amount of burnback after wire feed stops,
to eliminate freezing of wire in weld puddle. For
installation refer to Section III-B
III. INSTALLATION
A. HOSE AND ELECTRICAL CONNECTIONS
B. ANTI-STICK KIT
All components of the Anti-Stick Kit are mounted on a PC
board connected to the anti-stick potentiometer. To
install the kit simply insert potentiometer through knockout on back panel. Then with hardware provided tighten
potentiometer, and install knob. For electrical connections refer to Figure 10.
CAUTION: Be sure the Main Line Switch (MLS) on the
IV. ADJUSTMENTS AND OPERATION
control cabinet and the power supply are OFF
before making any connections.
Depending on the type of power supply used, make the
necessary cable and hose connections in accordance
with one of the following interconnection diagrams.
A. SHIELDING GAS FLOW
The torch trigger switch controls the flow of shielding gas
set by the flowmeter. To check the flow, first deenergize
the control by placing the Main Line Switch (MLS) in the
OFF position. Then depress the torch switch. After
Fig. 2 - Interconnection Diagram for Constant Potential
Welding
Fig. 3 - Interconnection Diagram for Constant Current
making the necessary adjustments to the flowmeter,
place the Main Line Switch in the ON position.
B. TORCH CONTROLS
Power Supplies without Built-in Contactor.
Wire feed power is provided by the permanent-magnet
Fig. 4 - Interconnection Diagram when using a Con-
stant Current Power Supply/Built-in Contactor.
type DC motor in the ST-23A torch. Wire may be inched
by pressing the button on the bottom of the torch handle
CAUTION: Do not allow metal-to-metal contact between the wire feeder (control) cabinet and a metal surface
connected in any way to a welding ground. Without insulation, a poor work lead connection may create a
difference in potential that sends part of the welding current through the safety ground wiring in the control
cable and wire feeder, resulting in burnout of that wiring and/or damage to wire feeder circuitry. If safety
ground burns out, the operator may be exposed to 115 V. shock hazard.
GAS
NOTE:
For Internal power cable & gas hose
connections, See Fig. 3
P2
SEC-7A
FRONT
TORCH POWER
CABLE (30 ft.)
ST-23A TORCH
REGULATOR/FLOWMETER
6 ft. CONTROL CABLE12-1/2 ft. GAS
HOSE-40V77
TORCH CONTROL
CABLE (30 ft.)
SEC-7A
BACK
P1
2/0 WELDING CABLE
(Customer Supplied)
GRD.
996739 (Provided)
25 ft. EXTENSIONS
CABLE - 996738
Optional
WORK
Fig. 2 - Interconnection Diagram for Constant Potential Welding
4
CONSTANT POTENTIAL
POWER SUPPLY
(Customer Supplied)
SEC-7A
FRONT
30 ft. EXTENSION
CABLE- 636968
TORCH CONTROL
CABLE (30 ft.)
REGULATOR/FLOWMETER
12-1/2 ft. GAS
HOSE-40V77
2/0 WELDING CABLE
(Customer Supplied)
POWER CABLE
ADAPTOR - 993457
TORCH POWER
CABLE (30 ft.)
ST-23A TORCH
Fig. 5 - Extending Torch Service Lines
Wire feed speed during the welding cycle is controlled by
the potentiometer on the torch.
In constant potential welding, the wire begins to feed
the instant the torch trigger is fully depressed. This is
desirable when welding with CP or CP slope control
power. During CP operation, the potentiometer on the
torch regulate the welding current by means of the wire
feed speed. Turning the potentiometer in a clockwise
direction will increase the welding current (increase wire
feed speed); turning counterclockwise will decrease
welding current (decrease wire feed speed). An initial
setting should be low to reduce the possibility of burning
through the plate.
In constant current welding, full torch switch depression immediately initiates a slow inch down sequence
until the wire touches the work and stops. After the arc is
established, normal welding speed is regulated from the
torch potentiometer. During constant current welding,
the torch potentiometer controls the arc voltage. Turning
the potentiometer clockwise will decrease the arc voltage by increasing the wire feed speed; turning it counterclockwise will increase the arc voltage by decreasing the
wire feed speed. Thus, wire feed speed is regulated the
same way in CC as in CP welding. An initial setting
should be high to avoid burnbacks.
C. CONTROL SWITCH SETTINGS (see Figs. 6- 8)
1. Place the Weld Power Selector Switch inside the
control (on the PC board) to the proper position with
respect to the type of power supply being used. Refer
to Figure 8 for correct position of the switch.
2. Place the Main Line Switch in the ON position.
3. If the optional Anti-Stick Kit has been installed, set the
potentiometer to the desired setting depending on the
amount of burnback desired. The higher the setting,
the greater the amount of time that the contactor is
held in to allow the wire to burn back out of the weld
puddle.
IMPORTANT: If the power supply you are using is
equipped for high frequency starting,
make sure that the HF. Control is in the
‘OFF ’position.
D. WELDING OPERATION
With the control Main Line Switch in the ON position and
the torch, shielding gas, and power supply properly
adjusted, welding action will begin as follows:
1. In CP Welding, partial depression of the torch switch
opens the gas flow valve in the torch (for preflow) and
full depression energizes the welding contactor and
initiates wire feed at welding speed to strike an arc.
6
Welding will continue as long as the arc is maintained
and the torch switch is fully depressed.
2. In CC Welding, partial depressing of the torch switch
opens the gas flow valve in the torch to provide
shielding gas preflow. Full torch switch depression
energizes the contactor and initiates an automatic
slow inch down wire sequence. This sequence immediately feeds electrically hot wire at a slow inch speed
and stops when the wire touches the work. After the
arc is established, normal welding speed is regulated
from the torch potentiometer. Welding will continue as
long as the arc is maintained and the torch switch is
fully depressed. The touch starting feature provided
by the “slow-inch” sequence allows the operator to
hold his torch position and eliminates the out-ofposition problems caused by scratch starting with an
extended wire.
NOTE: The slow inch control in CC welding is provided
by an adjustable trimpot that has been added in
the upper right-hand portion of all PC boards
(997245) manufactured after September, 1980.
The wire inch speed can be varied by readjusting the trim pot; however, if you still prefer the
original scratch-starting mode of operation, simply set the trim pot to its minimum setting.
To stop the welding action in CC or CP welding, slowly
(for postflow) release the trigger switch until the arc is
extinguished. Partially depressing the trigger switch allows shielding gas to continue to flow. Flow will stop when
switch is fully released.
V. OPERATING SEQUENCE
Normal
1. Partially close torch switch
—Gas valve opens (for preflow).
2a. Fully close torch switch (Constant Potential Weld-
ing)
—Gas valve remains open, torch switch relay energizes, weld contactor closes, wire feed motor runs.
2b Fully close torch switch (constant current weld-
ing)
—Gas valve remains open, torch switch relay energizes, weld contactor closes, and wire feed motor
runs at slow inch down speed until wire touches
work. After the arc is established, motor runs at
normal welding speed.
3. Partially release torch switch
—Torch switch relay opens, weld contactor opens,
wire feed motor deenergizes, brake circuit activates,
gas valve remains open (for postflow).
4. Fully release torch switch
—Gas valve closes.
With Optional Anti-Stick Kit Installed
Same as normal except when the torch switch is re-
leased the weld contactor is held in for a short period of
time to allow the wire to burnback out of the weld puddle.
The duration of this time is controlled by the anti-stick
potentiometer.
VI. TROUBLESHOOTING
If this equipment does not operate properly, stop
work immediately and investigate the cause of the
malfunction. Maintenance work must be performed
by an experienced person, and electrical work by a
trained electrician. Do not permit untrained persons
to inspect, clean, or repair this equipment. Use only
recommended replacement parts.
Listed below are a number of trouble symptoms, each
followed by the checks or action suggested to determine
the cause. Listing of checks and/or actions is in “most
probable” order, but is not necessarily 100% exhaustive.
Always follow this general rule: Do not replace a printed
circuit (PC) board until you have made all the following
checks. Make sure that the PC board is in good contact
with its receptacle when making the following checks.
Always put the main power switch in “OFF” position
before removing or installing a PC board. Take great care
not to grasp or pull on components when removing a PC
board.
A. SYMPTOM: No arc.
1. Welding cable circuit may be broken.
2. Welding work lead connection may be poor.
3 Contactor does not come in when torch switch is
closed (see B below).
4. Check main power fuses and power supply.
B. SYMPTOM: Contactor does not energize when
torch switch is closed.
1. Control cable may be faulty.
2. Contactor coil may be open.
3. Torch switch relay (TSR) may be bad; replace if
necessary (see C below).
C. SYMPTOM: Torch Switch Relay (TSR) does not
energize when torch switch is closed.
1. Main Line Switch on control in ‘OFF’ position.
2. Fuse F1 in control may be blown.
3. Torch cable or cable connections may be faulty.
4. Torch Switch Relay coil may be open; check
resistance of coil; should be from 250 to 300 ohms.
5. Torch switch may be faulty.
D. SYMPTOM: No wire inch.
1. Main Line Switch on control in ‘OFF’ position.
2. Fuse F1 in control may be blown.
3. Torch cable or cable connections may be faulty.
4. Wire Inch Relay (WIR) coil may be open; check
resistance of coil; should be from 250 to 300 ohms.
E. SYMPTOM: Welding with CP power, wire feed
motor does not run when torch switch closed.
1. Make sure Weld Power Selector Switch (WPSS) is
in "CP" position.
7
2. Check both TSR and WIR as described in C and D.
3. If TSR and WIR check out OK; check motor brushes.
Refer to torch instructions booklet F-14-353.
4. Transistors Q4 and Q5 may be defective replace if
necessary.
5. Resistors R17 and R18 may be burnt; replace if
necessary.
6. Replace PC board.
F. SYMPTOM: Welding with CC power, wire feed
motor does not run when torch switch closed.
4. Motor armature may be shorted to feed roll. Replace
motor.
5. Replace PC board.
G. SYMPTOM: Wire sticks in puddle.
1. Motor brake defective; check contacts 3 and 7 on
Torch Switch Relay.
2. The Optional Anti-Stick Kit may be necessary.
VII. MAINTENANCE
1. Wire should immediately begin a slow inch down
A. GENERAL MAINTENANCE
sequence. If it does not, the trimpot is either in minimum setting or is defective — check setting or replace
PC board.
2. If motor still does not run after an arc is established,
refer back to the proper interconnection diagram for
correct cable connections.
3. Check (with ohmmeter, PC board removed) for possible ground in torch switch, inch switch or motor lead
connections.
Little maintenance is required to keep the wire feeder in
top operating condition. It is important, however, that
moving parts such as feed and pressure rolls, wire feed
motor, etc., be kept clean and free of dust or dirt.
Cleaning is best accomplished by regularly blowing off
these parts with dry compressed air. This should be
done once for every eight hours of operating time, more
often if necessary. Refer to the torch instructions booklet
F-14-353 for general torch maintenance.
VIII. REPLACEMENT PARTS
1. Replacement parts are keyed on the illustrations which follow. Order replacement parts by part number and
part name as shown on the illustrations. DO NOT ORDER BY PART NUMBER ALONE.
2. When ordering, be sure to state quantity of each part needed.
3. Always state the series or serial number of the machine on which the parts are to be used. The serial number
is stamped on the unit's nameplate.
4. Indicate any special shipping instructions.
5. Order replacement parts from your ESAB distributor or from ESAB Welding & Cutting Products, Customer
Service Department, Florence, SC.
COVER - 2075163
WARNING DECAL*
2091514
MLS, MAIN LINE
SWITCH - 97W64
F1, FUSE - 82W43
FUSEHOLDER - 182W15
(4) FOOT - 99W32
HANDLE - 48N65
SILKSCREEN CABINET 679593
P2, TORCH RECEPTACLE647233
(Ref.) Opening for Torch
Power/Gas Cable. Includes:
SNAP BUSHING - 647345
* Replace Decal if it Becomes
Excessively Worn or Lost.
Fig. 6 - SEC-7A Control, P/N 2975159 (Front View)
8
(Ref.) Opening for Gas
Line Connection. Includes:
SNAP BUSHING 639533
(Ref.) Opening for Power
Supply Pos (+) Output
Cable. Includes:
SNAP BUSHING 647345
POWER SUPPLY
CABLE
“+”
WELDING CABLE
GAS
Fig. 7 - SEC-7A Control (Rear View)
P1, POWER SUPPLY
RECEPTACLE - 634772
(Ref.) Knockout Plug for
Optional Anti-Stick Kit 2075076
ANTI STICK
HEATSINK - 2075164
TP4, TIE POINT 94W84
WIR, WIRE INCH
RELAY - 97W55
Q5, TRANSISTOR
2062221
(Under Heatsink)
TP3, TIE POINT 94W84
R18, RESISTOR 17120001
TSR, TORCH SWITCH
RELAY - 97W55
TB1, TERMINAL BLOCK - 91W66
TR1, TRANSFORMER - 2062227
(Ref.) 5/8-18NF - 2B
THREADS
(+), POWER/GAS CONNECTION ADAPTOR - 2075165
(Ref.) 7/8 - 14NF - 2B - LH THREADS
POWER CABLE ADAPTOR BLOCK - 674156
MOUNTING CLAMP - 993540
C1, CAPACITOR - 993539
HEATSINK - 2075164
R17, RESISTOR - 17120001
TP2, TIE POINT - 94W84
MOUNTING BRACKET - 995297
Q4, TRANSISTOR - 2062221
(Under Heatsink)
PC BOARD ASSY. - 997245
(Ref.) WELD POWER SELECTOR
SWITCH (See View “A”)
TPI, TIE POINT - 94W84
(Ref.) SLOW INCH TRIMPOT.
P3, PC BOARD RECEPTACLE
636608
CONSTANT
POTENTIAL
VIEW “A”
CONSTANT
CURRENT
SWITCH ON
P/C BOARD
Fig. 8 - SEC-7A Control (Inside View)
9
YEL
1/2 W
IW
GRY
TSR
TORCH
LOCATED ON ST-23
WIS
GRY
2
WIR
1
P2-B
YEL
2
1
BLU
TB1-3
BLU
11
VIO
TBI-8
YEL
18
RIB
GRY
R17
1/2 W
IW
BLU
TBI-7
TB1-6
GRY
19
3
7
3
BRN
WIR
VIO
RED
P2-D
TORCH
MOTOR
P2-E
ORN
7
2
3
14
BLU
YEL
9
RED
C
1
P3
17
P2-F
P2-G
P2-H
ANTI-STICK OPTION
NOTE:
1. CONNECTION FOR P/C BOARD
PI-F
" - "
WORK
" + "
ARC
TORCH
LOCATED ON ST-23
TSR
YEL
3
5
GRY
WIR
10
4
Q5
TB1-2
Q4
RED
P2-A
VIO
13
12
P3
15
22
TS
RED
1
YEL
C1
- +
1500 uF
50 VDC
TSR
4
GRN
SEE NOTE 1
GRY
BRN
PI-B
PI-D
PI-A
BRN
WHT
GRN
BLK
MLS
(4)
(3)
GND STUD
MLS
(1)
(2)
FI
1 AMP
C
TB1-1
PI-E
PI-C
TSR
TB1-4
WC
BLU
TB1-5
ORN
BLK
RED
BLK
3
2
RED
(3)
(2)
SEE NOTE 1
BLK
RED
25.2 VAC
(4)
(1)
120 VAC
10
ELECTRICAL PARTS LIST
Symbol Part No. Description
C1 993539 Capacitor, 1,500 uf, 50 WVDC
F1 82W43 Fuse, 1 Amp Standard
MLS 97W64 Switch, DPST, 15A/125V, Cutler Hammer No.
7560K5
P1 634772 Receptacle, Amphenol No. MS-3102A-18-12P
P2 647233 Receptacle, Amphenol No. MS-3102A-18-8S
P3 636608 Receptacle, PC Board
Q4, 5 2062221 Transistor, International Rectifier No. 1R3772
R-17, 18 17120001 Resistor, 1/2 Watt, 1 Ohm
TB1 91W66 Terminal Block
TP1-4 94W84 Tie Point
TR1 2062227 Transformer, 115V/25V, JWL Asso. P/N 1000-25-
20
TSR, WIR 97W55 Relay, Potter & Brumfield No. PRD11DY0
Fig. 9 - Schematic Diagram, SEC-7A Control
11
POWER SUPPLY WITH
Fig. 10 - Wiring Diagram, SEC-7A Control
F-12-728-C 2/95 Printed in U.S.A.
Loading...