Input power

Does your machine need to be self-powered, or will AC power be available at the location where it’s primarily used?

• For locations where an electrical hookup is not practical, consider a gas- or diesel-powered engine-driven welder/generator to supply welding and generator power.
• For locations where AC power is available, you need to know its type—and whether it’s a match for the machine you’re considering:
  
  Single-phase power is found in most homes and garages. Check to see if the machine you’re considering requires single-phase power, and whether its voltage requirements (120 or 240 volts) are met by the electrical service at the intended location.
  
  Three-phase power is common in industrial settings. Check to see if the machine you’re considering requires three-phase power and whether its voltage requirements are met by the electrical service at the intended location.

Output Power

After determining the process(es) you want, you then need to determine output power requirements. There are two factors that determine output power. The first is material thickness, and the second is the electrode diameter and type. As a general rule of thumb, you need 1 amp of power for every .001" of mild steel. For example, to weld 1/8" (.125") mild steel, you would need approximately 125 amps. Stainless steel needs about 10% less power, while aluminum requires about 25% more. Remember that for thin material you need a machine with good "low end" performance. For thicker material, you'll need a machine with a high duty cycle (see next section).

Mild steel thickness	1/8"	3/8"	1/2"	5/8"	7/8"	1"	1-1/4"
Rated Output of Unit (Total power=Amps x Volts DC	12A at 110V	27A at 90V	40A at 140V	50A at 110V	55A at 110V	55A at 110V	100A at 120V

Amperage for a Rated Plasma Cut on Mild Steel

To provide a standard for measuring cut quality and cutting speed, Miller uses the terms "Rated cut." A Rated cut is the smoothest cut possible at a minimum cutting speed of 10 inches per minute using a hand-held torch.

About duty cycles

Duty cycle is an indication of how long a power source can continuously weld (at a specific amperage and voltage) in a 10-minute period of time before it needs to cool down. For example, a machine with a 60 percent duty cycle at 300 amps and 32 volts of welding output can be used (at 300 amps and 32 volts) for 6 minutes out of a 10-minute period. When comparing two similarsized power supplies it is important to pay close attention to both the amperage and voltage values that determine the rated load.

When considering duty cycle for a Stick machine, note that most Stick electrodes are consumed in less than two minutes. Further about 80% of all Stick welding is done with a 1/8-inch diameter electrode, which takes about one minute to consume.

To see if a machine meets your needs, consider the following power classifications.

• Light Industrial products typically have a 20% duty cycle and a rated output of 230 amps or lower.
• Industrial products typically have a 40-60% duty cycle and a rated output of 300 amps or lower.
• Heavy Industrial products typically have a 60-100% duty cycle and a rated output of at least 300 amps.

Generator power

Out in the field, you may need an engine-driven welder/generator to supply 120- or 240-volt AC power to run tools and lights, or supply 12-volt DC power to charge automotive batteries and jump-start vehicles. Miller welder/generators are packed with power; larger units even offer option packages that add 10 to 20 kW of generator power.

Portability

Can you bring the work to the machine, or does the machine need to go to the work? Check the product detail pages for types of portability:

• Shoulder strap, handles, running gear, carts, etc.
• Many engine-driven welding generators fit in the back of a pickup truck, enabling them to be driven to wherever the welding is needed. Heavy-duty trailers are also available for engine drives.