Miller Bobcat 250 User guide

PRINTED IN USA
May 2005 176 712D
Blue Star®145/185
•4,500 or 6,000 watt models available
•145 or 185 Amps of welding power
Why buy just a generator when you can
buy a generator that also welds? Your
best value for power is a Miller welder/AC
generator because it is…
Competitively priced compared to regular
generators.
Versatile—120 & 240 volts AC power and
welding capabilities from the same machine.
Generator Power
Application Guide
Bobcat™225
•10,000 watts of generator power
•225 Amps of welding power
Bobcat™250
•10,000 watts of generator power
•250 Amps of welding power
•Diesel and LP models also available
Trailblazer®302 and 275 DC
•10,000 watts of generator power
•300 Amps of welding power
•LP and diesel models also available
Largest fuel capacity
means longest generator run
time! See page 2.

Welder/AC Generator:
Best Value For Power Needs
While you might not need a generator or welder for daily use,
investing in a machine that performs both duties makes
economic sense.
Like a “regular” generator, a Miller welder/AC generator provides
120 and 240 volts AC generator power. The 4,500 to 10,000 watt
output capability of Miller’s mid-size generators is also suitable
for home use.
What are the biggest benefits to a Miller welder/AC generator?
At about the same cost as a “regular” generator, Miller
generators are also excellent welding power sources
capable of welding material up to 1/2 in. thick or more.
Miller’s 3-year, True Blue®Total Parts warranty is longer than
typical 1-year, generator warranties.
Low Fuel Consumption −The Bobcat will run about 14 hours
under a continuous load of 4000 watts of generator power.
Weld at 150 Amps at 40% duty cycle for 16 hours!
Accu-Rated™Miller generators means they deliver the
power that is promised. Patented self-cooling
stator allows Miller generators to perform at
100% duty cycle, even in 104°F heat! And
the Bobcat’s skewed rotor helps provide
smoother power than other brands.

•Read and follow all labels and the Owner’s Manual carefully.
•Only qualified persons are to install, operate, or service this unit according to all applicable
codes and safety practices.
•Keep children away.
•Pacemaker wearers keep away.
See Owner’s Manual for meaning of safety symbols and complete safety instructions.
For more detailed information, read Owner’s Manual, or call the Factory Applications
EngineeringDepartment at [phone].
WARNING GENERATOR POWER can be hazardous.
Table Of Contents
1. Safety 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2. How Much Generator Power Do You Need? 2. . . . . . . . . . . . . . . . . .
3. Wattage Reference Guide 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4. Frequently Asked Questions 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5. Selecting Auxiliary Equipment 5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6. Grounding Generator To Truck Or Trailer Frame 6. . . . . . . . . . . . . .
7. Grounding When Supplying Building Systems 6. . . . . . . . . . . . . . . .
8. Power Required To Start A Motor 7. . . . . . . . . . . . . . . . . . . . . . . . . . .
9. How Much Power Can The Generator Supply? 7. . . . . . . . . . . . . . .
10. Typical Connections To Supply Standby Power 8. . . . . . . . . . . . . . .
11. Wiring Optional 240 Volt, Single-Phase Plug (NEMA 14-50P) 9. . .
12. Selecting Extension Cord (Use Shortest Cord Possible) 10. . . . . . . .

Page 1
1. Safety
WARNING
ELECTRIC SHOCK can kill.
•Do not touch live electrical parts.
•Use only grounded or double insulated equipment.
•Stop engine before making internal inspection or reconnection.
•Install and ground generator according to all applicable national, state,
and local codes.
•Connect equipment grounding terminal to a proper earth ground.
•Do not connect to any electrical distribution system normally supplied
by utility power unless a proper transfer switch and grounding procedure
are employed.
•Have only qualified persons make electrical connections.
•Use all code-required methods for shock and overcurrent protection.
MOVING PARTS can cause serious injury.
•Keep away from moving parts such as fans, belts, and rotors.
•Keep all doors, panels, covers, and guards closed and securely in place.
ELECTRIC SPARKS can cause fire.
•If using generator power only and not welding, disconnect both welding
cables to prevent live electrode from causing electric shock and fire
hazards.
•Watch for fire.
•Keep a fire extinguisher nearby, and know how to use it.
The weld output terminals are electrically energized when the engine is
running and the contactor, if applicable, is energized.
LOW VOLTAGE AND FREQUENCY can damage
electrical equipment.
•Turn off or unplug all electrical equipment connected to generator power
receptacles before starting or stopping the engine.
When starting or stopping, the engine has low speed which causes low
voltage and frequency.

Page 2
ADDITIONAL
TOOL OR STARTING RUNNING STARTING
APPLIANCE WATTS WATTS WATTS
1. Refrigerator 2,200 700 1,500
2. Sump Pump 1,300 800 500
3. Table Saw 6,300 1,800 4,500
4.
5.
6.
7.
Use this easy reference to
determine the generator size
you need. To select a genera-
tor with enough power output
in watts, add the watts for the
items you want to simulta-
neously run. Tools and ap-
pliances with induction motors
may require 3 −7 times the
listed wattage when starting.
All data listed is approxi-
mate—check your tool/ap-
pliance for specific wattage
requirements. Your actual re-
quirementswill vary (see Sec-
tions 4 and 7).
This worksheet will focus on
determiningyour starting and
running watt needs.
Amount of generator power
you need depends on your
power requirements. General-
ly, a higher-wattage generator
lets you power more items at
once.
1 Select the items you wish
to power at the same time.
Using the chart in Section
3, fill in the starting watts
(Column A) and running
watts (Column B)
requirements.
2 Add all the items in the
RUNNING WATTS column
(Column B) to determine
total running watts. Enter
the total in the TOTAL
RUNNING WATTS boxes.
3 Subtract RUNNING
WATTS (Column B) from
STARTING WATTS
(Column A). Enter the
results in the
ADDITIONAL STARTING
WATTS column (Column
C). Select the ONE
INDIVIDUAL ITEM with
the highest number of
ADDITIONAL STARTING
WATTS. Take this ONE
NUMBER, add it to your
TOTAL RUNNING
WATTS, and enter the
total in the TOTAL WATTS
NEEDED box.
2. How Much Generator Power Do You Need?
EXAMPLE WORKSHEET
4,500
HIGHEST
ADDITIONAL
STARTING WATTS
3,300
TOTAL RUNNING WATTS =
3,300
TOTAL RUNNING WATTS
+
7,800
TOTAL WATTS NEEDED
=
With this example you need
a generator that produces
at least 3,300 total running
watts and 7,800 total watts.
ADDITIONAL
TOOL OR STARTING RUNNING STARTING
APPLIANCE WATTS WATTS WATTS
1.
2.
3.
4.
5.
6.
7.
EXAMPLE WORKSHEET
HIGHEST
ADDITIONAL
STARTING WATTS
(COLUMN C)
TOTAL RUNNING WATTS =
TOTAL RUNNING WATTS
+
TOTAL WATTS NEEDED
=
I need a generator that
produces at least ________
total running watts and
________ total watts.
Column A Column B Column C
Column A Column B Column C
=
−
=
−

Page 3
3. Wattage Reference Guide
HOUSEHOLD
Appliances Starting Watts Running Watts
Dishwasher (cool dry) 1,400 700
Electric Range (6-inch element) 0 1,500
Microwave Oven (625 watts) 800 625
Refrigerator or Freezer 2,200 700
Automatic Washer 2,300 1,150
Clothes Dryer (gas / electric) 1,800 / 1,800 700 / 5,750
Garage Door Opener (1/4 hp) 1,100 550
Furnace Fan, Gas or Fuel Oil (1/4 hp) 1,000 600
Well Pump (1/3 hp) 1,400 750
Sump Pump (1/3 hp) 1,300 800
Central Air Conditioner (20,000 BTU) 3,300 2,500
CONTRACTOR TOOLS
Tool Starting Watts Running Watts
Hand Drill (1/2 in) 600 600
Circular Saw (8-1/4 in) 1,400 1,400
Table Saw (10 in) 6,300 1,800
Band Saw (14 in) 2,500 1,100
Air Compressor (1-1/2 hp) 8,200 2,200
Electric Chain Saw (2 hp, 14 in) 1,100 1,100
Spectrum®625 Plasma Cutter (30 amp, 230 volts, 1/2 in cut) 3,500 3,500
Millermatic®210 MIG Welder (30−210 amps, 230 volt) 6,500 6,500
Flood Lights (vapor) 1,250 1,000
Submersible Pump (400 gph) 600 200
Centrifugal Pump (900 gph) 900 500
High Pressure Washer (1 hp) 6,100 1,600
Wet & Dry Vac (1.7 hp) 900 900
FARM EQUIPMENT
Machine Starting Watts Running Watts
Barn Cleaner (5 HP) 11,600 3,000
Silo Unloader 12,200 4,300
Portable Conveyer (1/2 hp) 3,400 1,000
Milker, Vacuum Pump (2 hp) 10,500 2,800
Farm Duty Motors—Conveyers, Feed Augers,
Air Compressors, Etc. (1-1/2 hp) 8,200 2,200
Washer, 2 gal/min (550 PSI) 4,500 1,400
INDUSTRIAL MOTORS
Motor Starting Watts Running Watts
Split Phase (1/2 hp) 3,175 875
Capacitor Start, Induction Run (1-1/2 hp) 8,200 2,200
Capacitor Start, Capacitor Run (1-1/2 hp) 8,100 2,000
Fan (1/2 hp) 3,500 1,100

Page 4
4. Frequently Asked Questions
VOLTS 115
4.5
60
AMPS
Hz
S-0623
How many watts does it take to power basic items in an average size house?
In a typical home, essential items use about 4000 −6000 watts of power. Select a gen-
erator that can provide the necessary power while maintaining rated voltage. Low volt-
age may damage appliances and other equipment (see power curve example below).
Resistive Load
(requires constant amount of power) Non-Resistive Load
(Motors require as much as 3 −7 times more
power when starting than when running)
Rating Data
What is the difference between running watts and starting watts?
Running watts are the continuous watts needed to keep items running. Starting watts are
extra watts needed for two to three seconds to start motor-driven
products like a refrigerator or circular saw.
Why is only one additional starting watt item used to calculate your total watt re-
quirement?
Unlike running watts, starting watts are only needed during the first few seconds
of operation. In most cases, only one item will start or cycle at the same time, therefore
this is the most accurate estimate.
What if I can’t determine the running or the starting watt requirement for a tool or
appliance?
If the running watts are not on the tool or appliance, you may estimate using the following
equation: WATTS = VOLTS x AMPS.
Only motor-driven items will have an additional starting requirement. The additional start-
ing watts required in most cases may be estimated at 3 −7 times the rated running watts.
300
264
250
216
150
50
0
100
200
150
132
125
108
75
25
0
50
100
AC POWER VOLTS
0 20 40 60 80 100 120 140 160 180 200 220
0102030405060708090100110
AC POWER AMPS AT 120 VOLTS
AC POWER AMPS AT 240 VOLTS
10,000 watts 10%
GENERATOR POWER CURVE −BOBCAT
Tools and motors are designed to operate within 10% of 120/240 VAC. The Bobcat’s
power generator provides strong power while keeping the voltage within 10%of 120/240
VAC. This increases tool/motor performance and life.

Page 5
1 Generator Power
Receptacles −Neutral
Bonded To Frame
2 3-Prong Plug From Case
Grounded Equipment
3 2-Prong Plug From Double
Insulated Equipment
Do not use 2-prong plug
unless equipment is
double insulated.
5. Selecting Generator Equipment
OR
2
Be sure equipment
has this symbol
and/or wording.
3
1
Ref. ST-159 730 / ST-800 577
6. Grounding Generator To Truck Or Trailer Frame
Electrically bond generator
frame to vehicle frame by
metal-to-metalcontact.
GND/PE
1
2 3
Always ground gener-
ator frame to vehicle
frame to prevent elec-
tric shock and static
electricity hazards.
1 Metal Vehicle Frame
2 Equipment Grounding
Terminal
3 Grounding Cable
Use #10 AWG or larger insu-
lated copper wire.
If unit does not have
GFCI receptacles, use
GFCI-protected exten-
sion cord.
S-0854

Page 6
1 Equipment Grounding
Terminal
2 Grounding Cable
Use #10 AWG or larger insu-
lated copper wire.
3 Ground Device
Ground generator to
system earth ground if
supplying power to a
premises (home, shop,
farm) wiring system.
7. Grounding When Supplying Building Systems
GND/PE
1 2
Use ground device as stated
in electrical codes.
23
ST-800 576-B

Page 7
8. Power Required To Start A Motor
1 Motor Start Code
2 Running Amperage
3 Motor HP
4 Motor Voltage
To find starting amperage:
Step 1: Find code and use
table to find kVA/HP. If code
is not listed, multiply running
amperageby six to find start-
ing amperage.
Step 2: Find Motor HP and
Volts.
Step 3: Determine starting
amperage (see example).
Welding generator amper-
age output must be at least
twice the motor’s running
amperage.
Single-PhaseInduction Motor Starting Requirements
Motor Start
Code GH J K LMNP
KVA/HP 6.3 7.1 8.0 9.0 10.0 11.2 12.5 14.0
VOLTS AMPS
HP
230 2.5
1/4
Hz
PHASE
CODE 60
1
M
AC MOTOR
12
EXAMPLE: Calculate the starting amperage required for a 230 V, 1/4 HP
motor with a motor start code of M.
Starting the motor requires 12.2 amperes.
11.2 x 1/4 x 1000
230 = 12.2 A
kVA/HP x HP x 1000
VOLTS = STARTING AMPERAGE
Volts = 230 HP = 1/4 Using Table, Code M results in kVA/HP = 11.2
3
4
S-0624
9. How Much Power Can The Generator Supply?
1 Limit Load To 90% Of
Generator Output
Always start non-resistive
(motor) loads in order from
largest to smallest, and add
resistive loads last.
2 5 Second Rule
If motor does not start within
5 seconds, turn off power to
prevent motor damage. Mo-
tor requires more power than
generator can supply.
2
803 636 / S-0625
1

Page 8
10. Typical Connections To Supply Standby Power
Have only qualified per-
sons perform these
connections according
to all applicable codes
and safety practices.
Properly install and
ground this equipment
according to its Own-
er’s Manual and nation-
al, state, and local
codes.
Customer-supplied equip-
ment is required if genera-
tor will supply standby
power during emergen-
cies or power outages.
1 Utility Electrical Service
2 Transfer Switch
(Double-Throw)
Switch transfers the electrical
load from electric utility ser-
vice to the generator. Transfer
load back to electric utility
when service is restored.
Install correct switch (custom-
er-supplied). Switch rating
must be same as or greater
than the branch overcurrent
protection.
3 Fused Disconnect Switch
Install correct switch (custom-
er-supplied) if required by
electrical code.
4 Welding Generator Output
Generator output voltage and
wiring must be consistent with
regular (utility) system voltage
and wiring.
Connect generator with tem-
porary or permanent wiring
suitable for the installation.
Turn off or unplug all equip-
ment connected to generator
before starting or stopping en-
gine. When starting or stop-
ping, the engine has low speed
which causes low voltage and
frequency.
5 Essential Loads
Generator output may not
meet the electrical require-
ments of the premises. If gen-
erator does not produce
enough output to meet all re-
quirements, connect only es-
sential loads (pumps, freez-
ers, heaters,etc. −See Sec-
tion 2).
Transfer Switch
Essential
Loads
Fused
Disconnect
Switch
(If Required)
Utility
Electrical
Service
1234
5
Properly install and ground this equipment according to
its Owner’s Manual and national, state, and local codes.
Welding
Generator
Output

Page 9
11. Wiring Optional 240 Volt, Single-Phase Plug (NEMA 14-50P)
The plug can be wired for a
240 V, 2-wire load or a
120/240V, 3-wire load. See
circuit diagram in Owner’s
Manual.
1 Plug Wired for 120/240
V, 3-Wire Load
When wired for 120 V loads,
each duplex receptacle
shares a load with one half of
240 V receptacle.
2 Plug Wired for 240 V,
2-Wire Load
3 Neutral (Silver)
Terminal
4 Load 1 (Brass)
Terminal
5 Load 2 (Brass)
Terminal
6 Ground (Green)
Terminal
Strip cord jacket back
enough to separate conduc-
tors.
Strip conductors enough to
make good contact with plug
terminals. Make plug con-
nections and reinstall outer
shell and cord grip.
Tighten assembly screws
onto shell. Do not overtigh-
ten.
Tools Needed:
1
2
3
4
56
3
4
5
6
240V
240V
120V
120V
Plug1 7/99 −120 813-D

Page 10
12. Selecting Extension Cord (Use Shortest Cord Possible)
Cord Lengths For 120 Volt Loads
 If unit does not have GFCI receptacles, use GFCI-protected extension cord.
Maximum Allowable Cord Length In Feet (Meters)
For Conductor Size (AWG)*
Current In
Amperes Load In Watts 4 6 8 10 12 14
5 600 350
(106) 225 (68) 137 (42) 100 (30)
7 840 400
(122) 250 (76) 150 (46) 100 (30) 62 (19)
10 1200 400
(122) 275 (84) 175 (53) 112 (34) 62 (19) 50 (15)
15 1800 300 (91) 175 (53) 112 (34) 75 (23) 37 (11) 30 (9)
20 2400 225 (68) 137 (42) 87 (26) 50 (15) 30 (9)
25 3000 175 (53) 112 (34) 62 (19) 37 (11)
30 3600 150 (46) 87 (26) 50 (15) 37 (11)
35 4200 125 (38) 75 (23) 50 (15)
40 4800 112 (34) 62 (19) 37 (11)
45 5400 100 (30) 62 (19)
50 6000 87 (26) 50 (15)
*Conductor size is based on maximum 2% voltage drop

Page 11
Cord Lengths For 240 Volt Loads
 If unit does not have GFCI receptacles, use GFCI-protected extension cord.
Maximum Allowable Cord Length In Feet (Meters)
For Conductor Size (AWG)*
Current In
Amperes Load In Watts 4 6 8 10 12 14
5 1200 700
(213) 450 (137) 225 (84) 200 (61)
7 1680 800
(244) 500 (152) 300 (91) 200 (61) 125 (38)
10 2400 800
(244) 550 (168) 350 (107) 225 (69) 125 (38) 100 (31)
15 3600 600
(183) 350 (107) 225 (69) 150 (46) 75 (23) 60 (18)
20 4800 450
(137) 275 (84) 175 (53) 100 (31) 60 (18)
25 6000 350
(107) 225 (69) 125 (38) 75 (23)
30 7000 300 (91) 175 (53) 100 (31) 75 (23)
35 8400 250 (76) 150 (46) 100 (31)
40 9600 225 (69) 125 (38) 75 (23)
45 10,800 200 (61) 125 (38)
50 12,000 175 (53) 100 (31)
*Conductor size is based on maximum 2% voltage drop

Miller Electric Mfg. Co.
An Illinois Tool Works Company
1635 West Spencer Street
Appleton, WI 54914 USA
InternationalHeadquarters−USA
USA Phone: [phone] Auto-Attended
USA & Canada FAX: [phone]
International FAX: [phone]
Web Site−www.MillerWelds.com