AC Vs DC Stick Welding – Which One Is The Best & Why?

AC Vs DC Stick Welding – Which One Is The Best & Why?

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While AC/DC might make most reminisce about a certain era of rock music, to welders it means polarity. Stick welding is polarity-driven. Direct current (DC) is used on most stick welding applications. Alternating current (AC) is typically only used as a second option.

DC stick welding offers advantages over AC when welding steel, including smoother and more stable arcs, easier starts, fewer arc outages, less spatter and easier vertical up and overhead welding. DC positive polarity provides a high level of penetration into the steel. DC negative polarity results in less penetration, but a higher deposition rate. It is sometimes used, for example, on thin sheet metal to prevent burn-through.

"Because AC polarity is half DC positive and half DC negative, it is right in the middle," says Kevin A. Beardsley, application engineer, The Lincoln Electric Co. "You can choose AC if you don't want to go DC negative because you don't want that much penetration."

Beardsley emphasizes that AC is almost always a secondary choice. Most welders don't bother changing polarity because their other jobs run on DC positive.

When to Use AC Polarity

There are, however, a few situations where AC polarity is used. The obvious one is when the only available power supply has AC output only. This is typical with low-cost, entry-level welding machines, such as the "buzz box" welder.

"Also, there are some specific technical problems associated with using DC polarity, and the number one is arc blow," says Eric Stewart, pipe welding technologist at Lincoln. "When welding, that arc has a shape and the welder wants to direct that arc into the joint to get full penetration. When there is arc blow, that arc is blowing to one side or the other."

An effective solution to arc blow problems is switching to AC instead of DC polarity. The arc blow can be caused by magnetism in the material being welded or can be induced by the arc's current.

"You can magnetize with current flowing through, so where you put your grounds and things like that can impact arc blow. The arc is going to wander," Stewart says, also mentioning that another possible cause can be an external source, such as windy conditions.

Because AC alternates between positive and negative polarity, it enables magnetized parts to be welded.

"If you were welding in a box and pushing toward the intersection where the vertical line comes down, the two horizontals meet into a corner," Stewart says. "The magnetic forces in relation to joint geometry actually at that point create a turbulent puddle and that will result in a tremendous amount of spatter."

Applications of AC Stick Welding

One specific industry for AC stick welding is in shipbuilding, particularly when welding into a corner and arc blow becomes a problem. Another area is maintenance and repair.

"Those are the guys that will use AC stick welding more than anyone as a primary option," Beardsley says. "Maintenance and repair welding requires work on machines that are magnetized. Also, maintenance and repair work can involve a lot of rusty weld areas, where you don't want high penetration."

A switch to AC polarity requires a power supply and electrode both designed to run AC. Again, because any production type of process is probably going to be DC, "if you want an AC capability, you have to specify that," Beardsley says. AC/DC power supplies are available but on the higher end models.

The Right Electrodes

With many electrodes, the arc tends to frequently extinguish on AC polarity. At the instant of the switch, the arc actually goes out and then has to re-establish itself. Electrodes are available with specific elements in their coating that operate on AC polarity to keep the arc ignited.

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The welding rods have a high cellulose potassium-type coating. These rods can be used with AC and DC polarity for all-position welding. They work especially well for welding rusty, dirty or older metal or making repairs outside where it's windy. The rods are the AC version of the popular welding rods for DC. The rods have a high cellulose sodium-type coating, can penetrate deeply and are used for many applications in the field.

Both are fast-freeze rods, meaning the weld puddle changes from liquid to solid rapidly, and are used primarily by pipefitters and pipe welders. Sizes vary, but 1/8 in. to 5/32 in. are prominent. Other AC welding rods include [other specific models].

The rods are all-position AC or DC polarity for welding new, clean sheet metal applications because they penetrate less but don't burn through the metal.

The welding rods are used for pipe welding and structural steel welding and repair welding. This low-hydrogen, usually DC, all-position electrode can also be used with AC, which not many welders may know. The provides a good bead appearance and smooth, strong welds. It also works on higher strength steels.

The welding rods, commonly referred to as Jet Rod, run well on AC. They are a good general-purpose rod with a high deposition rate for flat and horizontal welds and are typically used to make large welds. They have a heavy iron powder content. The rods are used for general fabrication, including deep grooves and big ships where a high-deposition rate is required.

Both the rods and rods are also known as "drag rod," where the end burns off slightly inside the flux coating, allowing the welder to drag the rod along the joint. The heavy slag should just peel off leaving a smooth weld.

Arc Welding: What's the Difference Between AC and DC

To the uninitiated or those lacking certification, the numerous welding methods can be confusing. A common discussion point is the difference between AC and DC arc welding. Both are legitimate welding methods, but each has its own unique applications. Let's delve into the primary differences between AC and DC arc welding.

Understanding AC and DC

The fundamental difference between AC and DC welding is polarity. AC stands for alternating current, and DC stands for direct current. In simpler terms, DC employs a single polarity (either negative or positive), while AC switches between DC positive and DC negative. Both types have their pros and cons and require different equipment.

Pros and Cons of DC Welding

DC welding is preferred for most applications. It generally provides a smoother welding output, less spatter, and a more stable arc compared to AC welding. DC also achieves deeper penetration into the weld metal, resulting in a stronger bond. However, DC welding is not ideal for aluminum because it doesn't produce the necessary heat. It also doesn't resolve arc blow-back issues, which happen when the arc wanders out of the joint. Additionally, DC welders are more expensive due to the need for an internal transformer to switch the current.

Pros and Cons of AC Welding

Several DC welding disadvantages are strengths in AC welding. AC welding handles higher temperature tasks well, making it suitable for welding aluminum and removing oxide film on metals. It can also resolve arc blow issues, and its alternating current makes it steadier when welding magnetic materials. AC welders do not require an internal transformer, making them less expensive, which is beneficial for beginners. Conversely, AC welding is harder to control, less reliable than DC welding, is not as smooth, and tends to produce more spatter.

Is AC or DC Welding Better?

DC welding is generally the better choice for most applications. However, for specific metals or tasks, AC welding might be more appropriate. For home or beginner use, it depends on the project at hand, but AC welders are cheaper. They are suitable for those wanting to learn the basics and undertake smaller tasks before investing in a costlier DC welder.

Another consideration is the power drawn by the welder. AC welders are more versatile as they can operate on standard 110-volt outlets. In contrast, DC welders need more power and require a special 220-volt outlet, which can be a significant investment. It's advisable to gain welding experience before opting for a more expensive DC welder.

Getting Started with Welding

If you're looking to learn welding or need new equipment, we can help. At Welding for Less, we provide everything a beginner needs to start welding, including AC welders, safety gear, accessories, and more. We also cater to experienced users with smaller options and high-quality DC welders. Feel free to reach out to us with any questions you might have.

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