AC and DC Welding: Understanding the Differences

Understanding polarity is critical to being a good welder. Whether the project has the quality and strength of a good weld depends on the polarity selected. Polarity can be either AC or DC.

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AC means alternating current, which flows half the time in one direction and the other half in the other direction. It changes its polarity about 120 times a second.

DC stands for direct current, meaning the current has constant polarity since the current flows constantly in one direction.

Simply put, when you look at a welding machine and see a DC label, it means the machine has constant polarity. If it says AC, then the polarity will change and alternate directions up to 120 times per second.

Let&#;s review each of these types of welding and the differences between them.

What is AC welding?

AC welding is welding with alternating current. The welds are not as smooth as with DC welding and although DC welding is often considered superior to AC, there are definite times when AC is the welding polarity of choice. Some advantages to AC welding are:

• AC welding machines are less expensive, although many higher-end models have both AC and DC.
• AC welding is best for welding aluminum, which requires a high-intensity production of heat.
• AC welding is specifically used in the shipbuilding industry since it is better suited for high temperatures and has a higher current level, making it suitable for welding in corners and welding seams.
• The current alternates between positive and negative polarity, so it makes it possible to weld magnetized parts. This is particularly important when doing maintenance or repair work on machines that are magnetized. Also, repair work often involves rusted metal for which AC welding is a better choice than DC welding.
• The alternating current reduces the arc blow. Arc blow happens when there is a deflection of the intended arc from its original path.

The downsides to AC welding include:

• More spatter. Spatter is the drops of hot material that splash from the weld to the floor or area around where the welding is being done.
• The weld quality is not as smooth.
• It is more difficult to handle than DC welding.

What is DC Welding?

Direct current flows in only one direction. This welding method has a higher deposition rate. The deposition rate is the amount of filler metal that is melted into the weld joint. The higher deposition rate makes DC welding good for a weld that needs a build-up of deposits. It also has less spatter than AC welding, which makes the weld bead more uniform and smoother.

DC is easier to work with since the electrical arc is more stable than with AC welding.

Other advantages are:

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• A more stable arc.
• A smoother weld.
• Faster deposition rates.
• Greater penetration into the weld metal.
• Ideal for joining thinner metals.
• It is also used for stick welding and is good for welding all types of steel.
• Good for overhead and vertical applications. Vertical welds are required in different industries, primarily construction areas such as for buildings, power plant construction, oil and gas pipelines and fittings, and in shipyards where welders are required to weld huge metal structures that are in a vertical position.

Disadvantages of DC welding are:

• The machines are more expensive
• It is unable to fix problems with arc blow.

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For those who are not experienced welders or do not have any sort of certification, it may be confusing to hear about all of the different types of welding out there. This can commonly include the discussion between AC and DC arc welding. Both of these are valid types of welding, but they have their differences and proper applications. Continue reading below to learn about the primary differences between AC and DC arc welding. 

What Do AC and DC Mean?

The bottom line difference between these two welds has to do with polarity. AC means alternating current and DC means direct current. In other words, DC uses a single polarity that could be negative or positive, whereas AC uses an alternating polarity between DC positive and DC negative. There are certain benefits to both types of welding and it takes different equipment to produce each one. 

Advantages and Disadvantages of DC Welding

DC welding is the preferred form of welding for most applications. Compared to AC welding, DC tends to have a smoother welding output, less spatter, and a more stable arc. It also penetrates more into weld metal, which offers a stronger bond than AC welding in most cases. Unfortunately, DC welding is not great for welding aluminum because it cannot produce the right heat. In addition, it cannot fix arc blow back issues, which occur when the arc wanders or goes out of the joint. Furthermore, when it comes to purchasing a welder, DC equipment is more expensive because it needs an internal transformer to switch the current. 

Advantages and Disadvantages of AC Welding

Several of the disadvantages of DC welding are actually where AC welding tends to shine. It supports higher temperature welding, which makes it a great option for welding aluminum and removing the oxide film on the metal. It can also fix issues involving arc blow, and the alternating current makes it steadier when welding materials that are magnetic. Since AC welding does not require an internal transformer like DC welders, AC welders are less expensive, which can make it a better option for beginners. Conversely, AC welding falters in the areas of DC welding&#;s strengths, as well as a couple other areas. It is harder to control and less reliable than DC welding, is not as smooth, and tends to have more spatter. 

Is AC or DC Welding Better?

DC welding tends to be the preferred option for most applications. However, for certain applications or metals, AC welding can be the better choice. For home or beginner use, it really comes down to what needs to be done, but AC welders are cheaper. Price can make them a better option for arc welders who want to get used to the basics and learn to weld or complete smaller jobs before investing in a more expensive DC welder. 

The other factor to consider is the power that is drawn by the welder. AC welders are more versatile because they can be used on outlets that are limited to 110 volts. In contrast, DC welders require more power and a special outlet will need to be wired in the home or shop to provide 220 volts. This can be a significant investment, so it is recommended to gain more experience with welding before jumping right to more expensive DC welders. 

Looking to Learn How to Weld or a New Welder?

When looking for good equipment that can be used to learn to weld, we have you covered. At Welding for Less, we offer everything that you will need to get up and running as a beginner, including AC welders, safety equipment, accessories, and more. In fact, we have welders for all levels of experience, including smaller options for those new to the craft and quality DC welders for experienced users. Feel free to us at or call at (877) 219- with any questions that you may have. 

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