Arcon WORKHORSE 300MS 010310-series User manual

2203 Northwood Drive, Unit #10, Salisbury Md 21801, USA
Tel: [phone] Toll Free: 888 512.7266 Fax: [phone]
[email protected] www.arconweld.com
WORKHORSE 300MS
MIG / Stick P/N 010310
240V, 400V, 480V, 575V,Dual Voltage 240/480V
OPERATING MANUAL
REVISED MARCH 2009

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Declaration of Conformity
Manufacturer's Name: ARCON Welding Equipment, LLC
Manufacturer's Address: 2203 Northwood Drive, Building 10
Salisbury, Maryland 21801 USA
Declares that the product:
Product Name: Workhorse 300MS
Model Numbers 010310-xxx
Conforms to the following standards:
Underwriters Laboratories Standard UL551
Safety: EN 60974-1 2002
Degree of Enclosure Protection IP 24 in accordance with ISO 60529
This product is in conformity with the requirements of the Low-Voltage Directive
(73/23/EEC) and Machinery directive 89/392/EEC, 91/368/EEC, 93C 133/04, 93/68/EEC.
Compliance verified by: Goran Hedberg, Design Engineer
Technical contact: Mike Bell, Product Engineering
2203 Northwood Drive, Bldg. 10
Salisbury, MD 21801
410 572-6000
Fax [phone]
[email protected]
For further details please contact the factory:
ARCON Welding LLC
2203 Northwood Drive, #10
Salisbury, Maryland 21801 USA
Tel: [phone] Toll Free: 888 512.7266 Fax: [phone]
Email: [email protected]

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Table of Contents
GENERAL INFORMATION
User Responsibility 5
Manufacturer’s Limited Product Warranty 5
Safety Standards 5
Seahorse Information Page 6
1. SAFETY
1.1 Safety Symbols 7
1.2 Safety Precautions 7
1.3 Electric Shock 8
1.4 Arc Rays and Eye Protection 8
1.5 Fumes and Oxygen Depletion 9
1.6 Welding Sparks 9
1.7 Electric and Magnetic Fields 9
1.8 Protect Yourself and Others 10
2. PRODUCT DESCRIPTION AND INFORMATION
2.1 Introduction to The Workhorse MIGweld 300MS 10
2.2 Product Specifications 11
2.3 Safety Standards 11
3. INSTALLATION
3.1 Handling and Unpacking the Welder 11
3.2 Selecting a Location 12
3.3 Selecting Suitable Supply Cables 12
3.4 Connecting the Power 12
3.5 Fuses 13
3.6 Output Connections 13
3.7 Connection to the Wire Feeder 13
3.8 Remote Pin Configuration 15
3.9 Front Panel mounted Digital Meter 15
4. OPERATION
4.1 General Description 16
4.2 Design Features 16
4.3 Controls and Settings 16
4.3.1 Circuit Breaker (Power on/Off) 16
4.3.2 Thermostatically Controlled Cooling 16
4.3.3 Range Switch 16
4.3.4 Weld Power Control 16
4.3.5 Arc Force Control 17
4.3.6 Short Arc Puddle Control 17
4.3.7 Process Control Selector 18
4.3.8 Power-On Indicator 18
4.3.9 Remote Control Connector 18
4.3.10 Input Power Cord 18
4.3.11 Output Teminals 18
4.3.12 Voltage Changeover (Dual Voltage Models) 19

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4.4 Welding Operation 20
4.4.1 Recommendations for E70S-3 Spray Transfer 20
4.4.2 Short Circuit Transfer/Short Arc 20
4.4.3 Stick Welding 20
4.5 Dual Voltage Changeover 20
5. MAINTENANCE 21
6. ELECTICAL SPECIFICATIONS AND DIAGRAMS
6.1 General Information 22
6.2 Product Specifications 23
6.3 Block Diagram of The Inverter 24
6.4 Main Control Board 25
6.5 Main Circuit Diagram 26
6.6 Front Panel 27
6.7 Rear Panel 28
6.8 Chassis Plate Drawing 1 with Part Number Reference 29
6.9 Chassis Plate Drawing 2 with Part Number Reference 30
6.10 Inductor Plate Drawing with Part Number Reference 31
7. PARTS & ACCESSORIES
7.1 Replacement Parts 32
7.2 Accessories 34
8. TROUBLESHOOTING GUIDE 36
9. MIG WELDING TIPS (Good information –author unknown) 37

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GENERAL INFORMATION
USER RESPONSIBILITY
ARCON Welding warrants that The Workhorse 300MS will perform in accordance with the
product description in this manual. The Factory Warranty will be null and void should the user
attempt to operate the machine after it has malfunctioned. Parts that are broken, missing or
worn must be replaced immediately. ARCON Welding Equipment LLC or its Authorized Repair
Center will perform warranty Repairs. The Workhorse 300MS or any of its parts must not be
altered without the prior written approval of ARCON Welding Equipment LLC. Any malfunction
which results from improper use, faulty maintenance, physical damage, unapproved repair or
alteration, shall be the sole responsibility of the user or owner and any repair requested to be
performed by ARCON Welding Equipment LLC will be at the owner’s expense, and based on
ARCON’s applicable hourly labor rate and current replacement part prices.
MANUFACTURER’S LIMITED PRODUCT WARRANTY
ARCON Welding Equipment’s only warranty is that goods being sold will be free from defects in
materials and workmanship. This express warranty is in lieu of any other warranties, either
expressed or implied, and whether statutory or otherwise, including any implied warranty of
merchantability or fitness for a particular purpose.
The Manufacturer’s written warranty for The Workhorse 300MS welder has been included with
your new machine, and is limited to defect in materials or workmanship. The original purchaser
must furnish notice of defect or failure to ARCON Welding Equipment or one of Arcon’s
authorized repair centers using an approved Warranty Claim Form. Forms can be downloaded
from the company Web Site at http://www.arconweld.com. The guarantee against corrosion-
related failures can be extended to five-years by completing the Registration Form.
Any equipment that has been modified by any party other than ARCON Welding Equipment LLC,
or equipment that has been improperly installed, improperly operated, misused based upon
industry standards, improperly maintained or equipment which has been used for operation
outside of specifications will not be covered under the manufacturer’s warranty. ARCON
Welding Equipment shall in no way be liable for any consequential damages.
ARCON Welding Equipment reserves the right to make engineering and/or part changes at any
time, without notice, as improvements in quality or design are made. Owners and operators of
The Workhorse 300MS should access the company Web site listed above to keep up-to-date
with offerings, applications and technical suggestions.
SAFETY STANDARDS
The Workhorse 300MS is designed and built to comply with the following safety standards:
Underwriters Laboratories Standard UL551
Safety EN 60974-1
Degree of Enclosure Protection IP 24 in accordance with ISO 60529
•Protection against full penetration of solid foreign objects of 12.5mm diameter and larger.
•Protection against harmful effects from splashing water against the enclosure from any
direction.
Please review all safety infomation in Section 1 very carefully before operating the machine.

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This machine is protected against corrosion
ARCON’s time-proven Seahorse manufacturing process protects electrical
components prone to failure from corrosion by design and using a compound
containing cycloaliphatic-epoxides, tetramethylen-oxide and a cationic photo-
initiator (commonly called conformal coating). This protection is incorporated
as certain electrical components and printed circuit boards are produced to
ensure excellent weathering and superior protection against humidity, moisture,
dust, fungus and other contaminants.
The Seahorse process used in this machine was developed and tested on
oilrigs in the North Sea decades ago. This protection enhances reliability,
prolongs component life and adds value to all of ARCON’s rugged line of
portable welding power sources. Listed below are some of the steps ARCON
Welding has taken to increase corrosive atmosphere resistance in this
machine:
Transformer vacuum impregnated twice and dipped an additional time.
Auxiliary transformer protected and coated to resist corrosion.
Output board encapsulated in *repair-friendly material to eliminate the failures.
Control board coated to protect against salt-water arc over.
Input board coated to protect components from corrosion.
Resistors replaced with porcelain-coated ceramic resistors.
Fan motor totally encapsulated winding coil to withstand corrosive conditions.
Terminal screws coated to prevent electrical arc-overs.
This anti-corrosion process comes with ARCON’s five-year manufacturer’s guarantee against
corrosion-related electrical failure within natural operating environments. This warranty begins
the day the machine was shipped from the factory and does not apply to equipment used in
man-made environments that produce chemical residue, dust or airborne debris of man-made
substances, etc.
Because the Seahorse protection is incorporated in the manufacturing process, any circuit
modifications, repairs or component replacement with non-ARCON parts will void the Seahorse
guarantee.
Repair centers should contact the factory to obtain replacement parts for this machine.
Customers that intend to submit a warranty request for corrosion related failure should contact
the factory to obtain an RMA number before shipping their welder to the factory for evaluation.

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1. SAFETY
Safety is eveyone’s responsibility. ARCON designs every machine with safety in mind, and a
safe work environment depends largely on you. Do not install, operate, or repair this
equipment without carefully reading this manual and observing all of the safety
precautions mentioned. If there is a question, ask your supervisor!
1.1 Safety Symbols
Every effort has been made to protect trained operators from injury or unnecessary risk. Certain
symbols are used throughout this manual to call attention to safety-related information and
instruction. The safety symbols in this manual have these meanings:
This symbol indicates Dangerous Situations. When this symbol is used in this manual,
death or serious bodily harm is possible or probable if the corresponding preventative measures
are not taken. Operators must take caution in the method and manner of handling or using the
machine when this symbol is displayed.
1.2 Safety Precautions
Do not install, operate, or repair The Workhorse welding equipment without reading this
manual and all safety precautions stated within!
This machine was designed and built with operator safety in mind, but safety begins with you!
Every effort has been made to protect the trained operator from injury. Please become familiar
with the information in this manual to minimize the risk of shock or injury.
ARC WELDING CAN BE HAZARDOUS. ALWAYS PROTECT YOURSELF
AND OTHERS FROM POSSIBLE INJURY OR DEATH. KEEP CHILDREN AWAY.
OPERATORS WHO WEAR A PACEMAKER SHOULD CONSULT WITH THEIR
PHYSICIAN BEFORE OPERATING STUD WELDING EQUIPMENT.
THIS OPERATOR’S MANUAL SHOULD ALWAYS BE KEPT WITH THE
WORKHORSE MACHINE FOR QUICK REFERENCE. ALL SAFETY WARNINGS,
SIGNS AND STICKERS MUST STAY ATTACHED TO THE MACHINE. ALL
OPERATORS MUST BE PROPERLY TRAINED AND PROTECTED BEFORE
OPERATING THIS EQUIPMENT.

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1.3 ELECTRIC SHOCK
Precautionary measures must be taken to provide maximum protection against electrical shock.
Electric shock can injure or Kill
WARNING
1. Do not touch live or energized electrical parts or store metallic objects near power.
2. Ground the work or metal to be welded to a good electrical (earth) ground.
3. Do not leave an energized machine unattended.
4. Never work in wet clothing, gloves or footwear.
5. Insulate yourself from work and ground using dry insulation. Make certain the insulation
is large enough to cover your full area of physical contact with work and ground.
6. Inspect all system components, protective equipment, cables, connectors and gas lines
prior to operating equipment. Never use cables that are longer than necessary.
7. When testing a live unit, use the one-hand method. Do not put both hands inside of the
unit. Keep one hand free.
8. Disconnect input power conductors from de-energized supply line before moving a
welding power source.
9. Always be sure the work cable makes a good electrical connection with the metal being
welded. The connection should be as close as possible to the area being welded.
10. Turn OFF welding power source before servicing unless the procedure specifically
requires an energized unit.
11. Never use the power source to provide heat for thawing frozen pipes.
1.4 ARC RAYS and EYE PROTECTION
Arc rays can injure eyes and burn skin. Arc flashes are painful.
1. Use a shield with the proper filter and cover plates to protect your eyes from sparks and
the rays of the arc when welding or while observing open arc welding.
2. Use protective clothing specifically intended for work with welding equipment. It should
be made of durable flame-resistant material to provide ample protection from the arc
rays.
3. Protect other nearby workers with suitable, non-flammable screening. Caution other
workers not to watch the arc nor expose themselves to the arc rays or to hot spatter or
metal.

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1.5 FUMES and OXYGEN DEPLETION
Only weld in areas or rooms where adequate ventilation of weld gases is possible, and
where there are not fire, smoke or explosion hazards.
1. When working in a confined space always have trained support personnel nearby.
Welding fumes and gases can displace air and lower the oxygen level causing injury or
death. Be sure the breathing air is safe.
3Do not weld in locations near degreasing, cleaning, or spraying operations. The heat and
rays of the arcs can react with vapors to form highly toxic and irritating gases.
4Do not weld on coated metals, such as galvanized, lead, or cadmium plated steel. The
coating must be removed from the area to be welded. Coatings and metals containing
above elements can generate toxic fumes when heated to welding temperature.
1.6 WELDING SPARKS
Heat from flames and arcs can start fires. Hot slag or sparks can also cause fires and
explosions.
1. Remove all combustible materials from the work area or cover these materials with a
protective non-flammable tarp. Combustible materials include wood, fabrics, sawdust,
liquid and gas fuels, solvents, paints and coatings, paper, etc.
2. Hot sparks or hot metal can fall through cracks or crevices in floors or wall openings and
cause a hidden smoldering fire. Make certain that such openings are protected from hot
sparks and metal.
1.7 ELECTRIC AND MAGNETIC FIELDS
Electric current flowing through any conductor causes localized Electro-Magnetic Fields
(EMF). Welding and cutting current creates EMF around welding cables and welding machines.
1. Operators having pacemakers should consult their physician before welding. EMF may
interfere with some type of pacemakers.
2. Exposure to EMF may have other health effects, which are unknown.
3. Operators should use the following procedures to minimize exposure to EMF:
a. Route the work cables together. Secure them with electrical tape when possible.
b. Never coil the work cable around any part of your body.
c. Do not place your body between the work cables. Route cables on the same side
of your body.
d. Connect the work cable to the work piece as close as possible to the area being
welded.
e. Keep welding power source and cables as far away from your body as possible.
4. Electromagnetic fields can irrevocable erase magnetic data carriers (computer memory,
credit cards, security ID cards or data storage diskettes).
5. Electromagnetic fields may magnetize and damage watches or similar digital devices.

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1.8 PROTECT YOURSELF AND OTHERS!
Some welding, cutting, and gouging processes are noisy and require ear protection. The arc, like
the sun, emits ultraviolet (UV) and other radiation and may injure skin and eyes. Hot metal can
cause burns. Training in the proper use of welding processes and equipment is essential to
prevent accidents.
1. Always wear safety glasses with side shields in any work area. In conjunction with eye
protection, welding helmets or face shields are also required.
2. Use a face shield fitted with the correct filter cover plates to protect your eyes, face, neck,
and ears from sparks and rays of the arc when operating or observing operations. Warn
bystanders not to watch the arc and not to expose themselves to the rays of the electric
arc or hot metal.
3. Wear flameproof type gloves, heavy long-sleeve shirt, cuff less trousers, and a welding
helmet or cap for hair protection, to protect against arc rays and hot sparks or hot metal.
A flameproof apron may also be desirable as protection against radiated heat and
sparks.
4. Hot sparks or metal can lodge in rolled up sleeves, trouser cuffs, or pockets. Sleeves and
collars should be kept buttoned, and open pockets eliminated from the front of clothing.
2. PRODUCT DESCRIPTION AND INFORMATION
2.1 INTRODUCTION TO THE WORKHORSE MIGweld 300MS
The MIGweld 300MS is a portable welder using an inverter-type power supply to generate the
output power.
The MIGweld 300MS is primarily designed for MIG welding (GMAW). It can also be used for
(SMAW) Stickwelding, as well as arc gouging and stud welding with a controller. Use Range I
when stickwelding, when possible. The first range produces a softer arc than that of Range 2.
The Workhorse MIGweld 300MS is available in the following models: 240V single voltage
operating in single phase or three-phase; 480V single voltage operating in three-phase; 575V
single voltage in three-phase, 240-480V dual voltage, and 400 V single voltage operating in
three-phase. The three-phase supply voltage is connected to a circuit breaker and then to a
three-pulse rectifier cicuitry and a radio noise suppression module. The AC voltage is connected
to a step-down transformer to power the welder. The AC welding voltage is first rectified to
create a DC welding current. The control logic measures the welding voltage and welding
current. It also makes the inverter create the suitable welding characteristics. The fan control
starts and stops the cooling fan. The auxiliary transformer steps down the input voltage to 48V
centertapped. This transformer powers the cooling fan and the contol logic.

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2.2 PRODUCT SPECIFICATIONS
Product Specifications for 300MS
Rated
Welding Welding
Open Input Amperes at Physical Weight
Primary Current
(Amps) Range
Amps Circuit Voltage
Rated Load Output
50/60 Hz KVA KW Efficiency
Dimensions
Input @ Duty Cycle 240 400 480 575 Net Ship
Three
Phase
400A@29%
300A@60%
250A@100%
Range 1
30-180A
Range 2
80 Max 37 25 20 18 14.9
12.05
79.60%
Height: 17.9"
45.5cm
Width: 10.5"
26.7cm
Approx.
80lbs.
36.3 kg.
Approx.
90lbs.
41.0kg.
Single 200A@100%
80A-400A 45 NA
NA NA NA NA Depth: 19.5"
Phase 28V 49.5cm
240V/480V DUAL VOLTAGE MODEL, OR 240V, 400V, 480V & 575V SINGLE VOLTAGE MODELS
2.3 SAFETY STANDARDS
The Workhorse 300MS product and manufacturing specifications comply with the following
safety standards:
Underwriters Laboratories Standard UL551
Safety EN 60974-1
Degree of Enclosure Protection IP 24 in accordance with ISO 60529
•Protection against full penetration of solid foreign objects of 12.5mm diameter and larger.
•Protection against harmful effects from splashing water against the enclosure from any
direction.
3. INSTALLATION
WARNING!
•Only qualified personnel should perform this installation.
•Turn the input power off at the disconnect switch or fuse box before working on
The Workhorse Migweld 300MS.
•Do not touch electrically hot parts.
This section provides detailed instructions for the proper installation of The Workhorse 300MS. It
is recommended that these instructions be followed carefully to allow for the best possible
operating environment.
3.1 Handling and Unpacking the welder
Since the Workhorse 300MS machine weighs approximately 90 pounds in the shipping carton,
no forklift or special handling equipment is necessary to move the machine. The shipping carton
has built-in reinforced handles to enable two people to easily transport the machine.
Immediately upon receipt of the welder, inspect the shipping box for any damage and notify the
carrier of such damage before accepting delivery. Then inspect The Workhorse 300MS for

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damage which may have occurred in transit. After removing the components from the shipping
container(s), check the container for any loose parts. Remove all packing materials. Visually
check air passages of power source for any packing materials that may obstruct airflow through
the welder. Styrofoam or shredded materials should not be used to package the machine.
If the equipment is not being installed immediately, store it in a clean, dry, well-ventilated area
until installation.
3.2 Selecting a Location
The location of the power source should be carefully selected to ensure satisfactory and
dependable service. Choose a location relatively close to a properly fused source of electrical
power.
It is important that the machine be located in an open area where air can circulate freely through
the front and rear openings. If space is at a premium, leave at least 1 foot (300 mm) of clearance
between the rear of the power source and wall or other obstruction.
3.3 Selecting Suitable Supply Cables
The standard power input cable for the Workhorse 300MS welder is a high quality #14 gauge
that is 12.5 feet long. The secondary cables for arc welding vary in length according to needs,
but are normally 1/0 diameter and 25 feet in length. Heavier 2/0 gauge cables can be used to
extend the distance between the machine and work surface. Standard ground cables are 1/0 in
diameter and 25 feet in length. Work cables, automatic wire feeders and gas related acces-
sories are not supplied with the Workhorse 300MS power source and must be furnished by the
customer.
WARNING!
•Only qualified personnel should perform this installation.
•Turn off the (input) power to the machne at the disconnect switch or fuse box
before working on The Workhorse 300MS.
•Do not touch electrically hot parts.
3.4 CONNECTING INPUT POWER
The primary cable supplied with the power source has 4 conductors. When connecting
an attachment plug or hard wiring to an electrical service box, connect the green/yellow
wire on a CE machine or the green wire on a non-CE machine to the ground. The
remaining 3 conductors can be connected to the phases in any order.
The brown conductor is not connected when input power is 240 V single phase.
Once connected to the primary power, the power source must be turned OFF before the
unit is moved.

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3.5 Fuses
It is recommended that input fuse sizes be in accordance with the table below:
Input Voltage Welder input
Maximum Amperage Recommended Fuse Capacity
240 V 3-Phase 37 35
240 V Single-phase 45 50
400 V 25 25
480 V 20 25
575 V 18 25
Table 3.0
3.6 OUTPUT CONNECTIONS
Female Dinse type (manufactured by DIX) are the standard output connectors. Optional
connector types (Tweco or Cam-Lok) may be special ordered.
There are several manufacturers of automatic wire feeders, spool guns, electrode holders,
ground clamps and gas regulators. These accessories are designed for specific uses and output
currents. Customers should use care in determining the accessories that they will require.
Always consult the manuals or instructions provided with these accessories to ensure safe use
and that the connections are properly made.
3.7 CONNECTION TO THE WIRE FEEDER
The MIGweld power source uses the same type of Amphenol 14-pin
connector that Miller and several other manufacturers are using today. The
pin locations are marked with letters to allow users to interface the wire
feeder to the power source. The illustration to the right designates the pins.
The male connector required for the remote plug must have
the same pin configuration as shown in the illustration above.
There are several different plugs that use varied pin
configurations and are constructed from various materials that
will not fit properly. Take care to use the correct plug when
connecting the wirefeeder.

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FIGURES FOR SECTION 3.7
The schematic
diagram to the right
illustrates how the
typical wire feeder
should be connected
to the remote plug for
either 24 Volts* or
115 Volts, depending
on the power
requirement for the
wire feeder.

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3.8 Pin configuration for the MIGweld 300MS power source:
A24VAC* 5A Supply
B 24VAC* Remote Contactor
C +15V DC to Remote Current Control
D Remote Current Common (PCB Ground)
E Remote Current Level
F Current Feedback, 1V DC per 100A output
G 24VAC / 115VAC Common
H Voltage Feedback, 1V DC per 10V output
I 115VAC 5A Supply
J 115VAC Remote Contactor
K Ground (Earth)
L Contactor Remote Enable
M
N Contactor Remote On (Take to 0)
* Note: A 42V AC Supply may optionally replace the 24V AC Supply. This is an option
from the manufacturer and can also be converted by a qualified repair technician.
3.9 Front Panel mounted Digital Meter
The Digital Meter provides real-time Voltage and Current (switchable) output readings.
The front panel meter can be switched into two modes by pressing the black mode button:
1. Output Voltage of the welder in real-time.
2. Output Current of the welder.
During welding, the meter shows the current that is being delivered.
When welding stops, the meter will show the last Current that was delivered for a
period of 3 seconds, and then revert back to real time.

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4. OPERATION
WARNING!
PLEASE READ CHAPTER 1REGARDING SAFETY
4.1 General Description
The Workhorse power source combines time-proven technology with modern technology to
provide high-quality performance. The digitally controlled SCR type inverter is very reliable in
welding applications and able to deliver up to 400 Amps of power (@29% Duty Cycle).
4.2 Design Features
The Workhorse power source is designed to be portable and easily transported to provide many
benefits. No special lifting devices are required to move or maintain the machine. The machine
provides Constant Power output with Inverter-smooth arc, incorporating digitally-controlled
start/stop with no mechanical contactor. Other features include regulated output, step-less weld
power and time adjustment, short-circuit protection, automatic line voltage protection and 5-
zones of thermal protection. The sound the machine generates is somewhat different from the
sound of other inverter and non-inverter machines due to the Workhorses unique SCR type
inverter frequency. Operators should rest assured that the sound is normal and not a defect.
4.3 Controls and Settings –Front and Rear Panels. See Figure 4
4.3.1 Circuit Breaker (Power On/Off)
The Circuit Breaker is located on the control panel at the rear of the machine. Move
the switch lever up to the ON position to start the machine. This also activates the
Thermostat-controlled Cooling Fan for approximately 6 minutes indicating that
correct power connections have been made.
4.3.2 Electronically Controlled Cooling Fan
The cooling fan starts automatically when welder warms up and the welding current
exceeds 100 A. If the current drops below 100 Amps, the fan will stop after
approximately 6 minutes. If the fan is operating when the work is discontinued, the
fan will continue to run and stop after approximately six minutes.
4.3.3 Weld Current Range Selector
Two different settings (30 -180 A and 80 -400 A) are available. Each setting
defines a specific range of output current for the welder.
DO NOT adjust the range switch while under load!
4.3.4 Weld Power Control
This continuous control is used to adjust the welding current from minimum to
maximum value, depending on the setting of the Weld Current Range Selector.

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While operating in GMAW-S (short circuit) mode, the weld power control will set the
average power supplied to the weld.
Selecting an operating point requires a balanced selection of gas, wire diameter,
proper wire feed speed, and weld power. The weld puddle control should remain
at the mid-point during the initial adjustment until a suitable combination of weld
power and wire feed speed is obtained. It is after this point that an adjustment to
the weld puddle control can be made if desired.
If higher Current than in short-circuit applications is desired, the process switch can
be placed in the GMAW spray position. This process will switch the power supply
out of the Low-Current Electronic Control Mode, and into Dynamic Response
Mode. Excellent, crisp short-arcing can then be performed on a variety of plate
thickness’ and current levels.
Operators should note that the font panel calibration on the Weld Power knob is
calibrated for MIG and not for Stick welding.
4.3.5 Short Arc Puddle Control
The short arc puddle control knob only controls the puddle characteristics in the
GMAW (short) mode. In the SMAW mode, the knob controls arc force.
In GMAW, the lower settings of this control are designed for out-of-position welding
while the upper settings are designed for flat welding and cellulose.
In SMAW, the lower settings are designed for minimum arc force with the higher
settings set for maximum arc force.
NOTE:
The process selection switch must be in GMAW (short mode) for the short arc puddle control to
be operative. The puddle control can be adjusted while the unit is under load.
Use the puddle control to adjust the weld puddle characteristics you desire to suit your
application. Typically, the colder settings are for out-of-position welds while the hotter settings
are for flat welding. The weld puddle control is also responsible for regulating both the rate and
the amount of power delivered during each mode of the short circuit transfer. Adding more
puddle control (which increases the power delivered during the arcing period) will cause the arc
to become hotter. Decreasing the puddle control causes a colder arc by reversing the power
delivery schedule. Changing the puddle control will also alter the weld droplet size, which will
increase during hotter settings and decrease during colder setting. Keep in mind, the larger the
droplet size, the lower the frequency of drops.
4.3.6 Arc Force Control
This control is used to adjust the Arc Force on constant current applications. The
control is fully adjustable from 0 to 100%, with 0 being very soft and 100% being
very hard. When adjusting the Arc Force, the low settings will produce a soft arc
and the high settings will produce a more forceful or driving arc. Please note that
the higher settings will produce higher levels of spatter.

18
The higher setting will create a more stable arc for electrodes that easily become
unstable, such as cellulose (5P). If you do not know the optimal setting for the
electrode you are using, start at the highest setting and lower it until the arc just
begins to become unstable.
4.3.7 Process Control Selector
SMAW -Use for SMAW (Stick)
GMAW (Short) –Use for GMAW-S (MIG) short-arc welding.
GMAW (Spray) –Use for either GMAW spray transfer or FCAW.
4.3.8 Power-On Indicator
Indicates power on/off. The power indicator will blink if any component is
overheated. Allow the welder to cool down. This may take 3 minutes or more
depending on which component is overheated. The following components are
temperature monitored:
Main Transformer
If a 30% duty cycle is exceeded when drawing 400A output current, the Main
Transformer could overheat and shut down the welder. If overheating occurs, wait
1 minute before restarting. This condition can also occur if a 60% duty cycle is
exceeded at 300 Amps output.
Main Inductor
If welding at 250 Amps for more than 30 minutes without stopping, the Main
Inductor will overheat and shut down the welder. If this occurs, wait 7-8 minutes
before restarting.
Output Capacitor
When welding at the lower current settings in Range 2, or when arc gouging for
long periods, the Output Capacitor may overheat and shut down the welder. If this
occurs, wait 10 minutes before restarting. The temperature sensor will protect the
output capacitor.
Input Capacitor
Should one phase be lost when welding with three-phase input power, current to
the Input Capacitor could increase causing it to potentially overheat or be
destroyed. Wait 10 minutes before restarting the welder
Fan Motor
Some operation with restricted airflow will overheat the fan motor. Wait 10 minutes
before restarting the welder.
4.3.9 Remote Control Connector
Units come standard with a 14-pin panel mounted female socket metal shell
connector. The remote control function is automatically activated when a pin
compatible remote control is plugged into the connector.
4.3.10 Input Power Cord
The standard factory installed input power cable measures 12 ft. if additional length
of power cable was not ordered as an option.

19
4.3.11 Output Terminals
Select output cable size based on Table 4 (following page).
Duty cycle(%) Current (A) Length (Ft) Cable Size (AWG)
30 180 1 -50 8
60 300 1 –150 1/0
60 300 150 -200 2/0
TABLE 4
4.3.12 Voltage Changeover
The Voltage Changeover opening is located on the rear panel, to the right of the
input power cable. Voltage changeover is easily facilitated by inserting a flat blade
screwdriver into the opening and rotating a quarter turn. In the Low Vorlage (240V)
setting, the blade is horizontal and for the Hight Voltage (480V), setting the blade is
vertical.
See 4.5 Dual Voltage Changeover for additional information
FIGURE 4
RANGE SWITCH
4.3.3
POWER ON
INDICATOR
4.3.8
PROCESS CONTROL
STICK
SHORT ARC MIG
SPRAY MIG
4.3.7
WELD POWER
4.3.4
ARC
FORCE/PUDDLE
CONTROL
4.3.5
CIRCUIT BREAKER
(POWER ON/OFF)
4.3.1
OUTPUT TERMINALS
4.3.11
REMOTE CONTROL
CONNECTOR
4.3.9
INPUT POWER
CORD
12 FT (3.65m) LONG
4.3.10
THERMOSTAT
CONTROLLED
VENTILATION
4.3.2
VOLTAGE
CHANGE OVER
4.3.12
I
MIGWELD
300SM

20
4.4 Welding Operation
4.4.1. Recommendations for E70S-3 Spray Transfer
Wire Range 2 Current Wire Feed Voltage
Diameter Power (A) Speed (V)
(inches) Setting (IPM)
.035 50-100 180-290 350-450 25-28
.045 60-100 200-300 250-450 25-28
*Using 98/2 AR0O2 shielding gas. The recommended power and range settings represent the
manufacturer’s best estimate and are intended only as guidelines for the Workhorse 300MS.
4.4.2 Short Circuit Transfer/Short Arc
The Migweld 300MS achieves the short circuit transfer by precisely controlling the instantaneous
power output during alternating arcing and shorting periods. An internal control circuit monitors
the output voltage to detect the shorted condition and reacts to increase the arc current during
the shorted time. This heats the filler metal in contact with the base material to the melting point;
the molten filler flows in the base, the short circuit condition ends and a period of arcing begins
again. During arcing, the increase in arc voltage is detected by the internal control which acts to
limit the arc current until a short circuit is once again detected, beginning another cycle.
4.4.3. Stick Welding
All secondary outputs must be connected to output terminals of the power source
After the primary input connections have been made, close the main wall disconnect switch or
circuit breaker. Place the primary power selector in the ON position. This will turn on the control
circuitry. The Power-On light on the front panel will be lit. Turn the Mode Selector in the ‘Stick’
position. The welding output will be energized and the electrode holder will become “electrically-
hot”. Turn the Arc Force Control Selector in its mid position. Adjust the Weld Power Control to
fit the type and diameter of electrode to be used, as recommended by the electrode
manufacturer.
4.5 Dual Voltage Changeover
Prior to changing voltage, the unit MUST BE SWITCHED OFF FOR AT LEAST 2 MINUTES.
This will give time for the capacitors to discharge. The Workhorse+ is equipped with a protection
device to prevent an overvoltage condition. If the unit is configured for 240V (horizontal slot) and
connected to a 480V supply, the circuit breaker switch will trip, disconnecting the overvoltage.
DO NOT ALLOW THIS CONDITION TO BE REPEATED MORE THAN 10 TIMES. Warranty will
be voided if the unit is exposed to excessive overvoltage trip sequence.
The Dual Voltage (240/480V) Workhorse 300MS machine uses a switch similar to the range
switch is used to change between the two voltages, 240V and 480V. The switch changes the
power capacitors, the main transformer and the auxiliary transformer when the switch shaft is
rotated 90 degrees. The opening exposing the switch shaft is located at the rear panel to the
right of the primary cable. ( See Figure 4)