AC vs DC Welding: A Guide To Welding Currents

When it comes to welding, most people pay a lot of attention to the different types of welding processes and welding machines. However, while doing so, they will often ignore one of the most important aspects of any welding machine – the power supply. 

In this article, we’ll take a look at the polarity of welding machines, the differences between AC and DC, and when one type of current is better than the other (use cases).

The Basics of Welding Machine Power Supplies

The power supply of a welding machine directs the electricity to the welding gun in a specific way. Power supplies can be vastly different depending on the different types of welding machines and different models. However, if you can understand the basics of the polarity, you should be able to understand how they all work.

Power Supply

A welding power supply is a component found in welding machines that directs and in most cases, controls the flow of electricity to the welding arc. Most welding power supplies allow the welder to switch from alternating current (AC) to direct current (DC) and vice versa. A welding power supply also allows the welder to control the amperage and voltage and thus change the way they weld.

Polarity

The polarity refers to the property of any electrical circuit to create negative and positive poles when turned on. Welding machines have polarity as well and welders can change the polarity by changing settings on their welding machine. Polarity can either be electrode-positive or electrode negative, also known as straight and reverse polarity in welding. Different polarities result in welds of different qualities and strengths.

Alternating Current (AC)

As the name suggests, alternating current, commonly called AC current, alternates the flow of current, that is the electrons keep changing the direction in which they flow (back and forth). Welding machines that are rated for AC current change their polarity (direction of current) 120 times every second. 

However, to change direction, the flow of electrons must stop for an extremely small amount of time, during which the amperage drops to zero. To stop the welding arc from extinguishing, welders use special electrodes, rated for AC current that comes coated with a material, helping them stay ignited even at zero amperage.

Why are Welding Currents Important?

Welding current is an important part of a welder’s knowledge because by flipping a few switches and changing some settings in a welding machine, welders have the ability to make drastic changes to their welding process. Take, for instance, the polarity of a welding machine. 

The type of polarity the welder chooses has a huge impact on the end result. If he or she chooses the correct polarity, the welds created would be very high-quality, strong, and reliable. If he or she chooses the wrong polarity, they might end up with more spatter, lack of penetration, greater heat-affected zone (HAZ), and have less control over the welding arc.

Additionally, welders have to carefully decide on the type of current by taking into consideration the type of metal they are working on, the welding process they are using, the gases and electrode they have on hand, and a few other variables. Due to this, it’s important to have a strong understanding of welding currents and how these variables affect a welder’s choice.

Pros of AC Welding

AC welding is often the second pick for welders, especially welders, but it has its use cases. AC welding is a great welding current thanks to a number of benefits.

One of the biggest advantages of choosing AC welding over DC welding is the lack of arc wandering. Arc wandering is a phenomenon seen while welding objects that have a magnetic field. This magnetic field interferes with the welding arc and causes the arc to be erratic, resulting in messy and jagged welds.

However, AC welding does not suffer from arc wandering and arc blow which makes it the obvious choice for working on large machinery, electrical equipment, and other objects that could have their own magnetic field.

AC welding is also usually smaller than DC welding machines. The compact size is important for welders that need a portable machine that can fit in tight spaces. These smaller and lighter AC welding machines also tend to consume less energy, usually 3 and 4kWh.

On top of all this, AC welding is more affordable, not because they are bad, but rather because they are cheaper to manufacture. Additionally, the operating costs of an AC welding are also less than that of DC welding machines.

Cons of AC Welding

If you’ve been reading about welding machines already, you may have noticed a preference for DC welding machines. That’s because of the disadvantages of AC welding.

The biggest con of using an AC welding machine is a result of its key characteristic – the alternating current. The continuously changing flow of current results in a more inconsistent welding arc that’s more difficult to control and also results in welds of lower-quality.

The alternating current also leads to more spatter which reduces the overall welding efficiency and also results in poorer aesthetics.

The third drawback of using AC welding machines is a problem known as losing the arc. Since the voltage drops to zero every time the current changes direction (120 times per second), the arc sometimes extinguishes and fails to restart. 

Stopping the weld midway compromises the integrity of the weld and is also a problem for the welder who must restart the arc every time it extinguishes. To overcome this problem, welders must use specially-coated electrodes like 6011, 6013, 7018, and 7024 that keep the weld ignited.

Pros of DC Welding

Experienced welders will very often recommend DC welding machines to beginners and novice welders. Let’s take a look at some of the reasons why that is.

The biggest reason welders choose DC welding over AC welding is because it creates a more consistent welding arc that has many benefits. The weld created through a DC welding machine is almost always cleaner and better looking than the ones created with AC welding machines. 

The DC welding arc also produces less spatter and is easier to control. This difference is even more pronounced at the hands of beginner welders who need a steady arc more than experienced welders.

Cons of DC Welding

Since the electricity in our power sockets are actually AC current, it must be converted before it can power the DC welding machine. For this reason, all DC welding machines come with an additional component known as a transformer that changes the current from AC to DC.

This additional component is costly to manufacture and adds additional weight and size to the DC welding machine. For this reason, DC welding is usually more expensive, heavier, and larger than their AC counterparts.

In many use cases, the high-quality welds and user-friendliness of DC welding are overshadowed by its higher operating costs and other smaller issues.

When AC Welding Is Used?

The most popular use case for AC welding is TIG aluminum welding. AC welding is great for welding aluminum as it is much more capable of reaching the extremely high temperatures required to make aluminum welds. 

Using DC current for aluminum will actually result in terrible, messy, and low-quality welds if the layer of aluminum oxide isn’t cleaned beforehand. In fact, since aluminum oxide melts at 2000°C and aluminum at 660°C, welders are more likely to evaporate the aluminum where the weld was supposed to be. 

AC welding, on the other hand, does the cleaning and melting at the same time as it continuously switches from electron negative to electron positive.

AC welding is also used for stick welding in the shipbuilding industry as it overcomes the problem of arc blow, penetrating thick plate metal, and corner welding. AC welding is also exclusively used with appliances that have a magnetized field.

When DC Welding is Used

While AC welding is the popular method of welding aluminum, DC (electrode negative or DCEN) welding is the popular choice for welding iron, steel, and stainless steel. It is also popular among beginners who want a relatively easier to control welding machine (and numerous other benefits we’ve mentioned above). DC welding is also most commonly found in stick welding machines

Some other popular applications of DC welding include:

• DC welding is preferred for welding thinners metals
• Since DC powered welding machines are generally more efficient, have less spatter, and provide a consistent welding arc, they are often used to large deposits. For instance, DC powered MIG welding machines have a deposition rate nearly 20 times higher than that of AC powered TIG welding machines.
• DC welding is also used when the project requires vertical or overhead welding.
• Single carbon brazing is another common application of DC welding.

Wrapping Up

AC and DC are the two types of welding currents that power welding machines. Each power supply has its pros and cons as well as distinct effects on the welding arc that determine the quality of the resulting weld. 

While some welding machines offer the option to switch between AC and DC current, they are usually more expensive, heavier, and larger and many welders might prefer a welding machine that only has one of the currents instead of both. In this case, it is important to understand the intricate details of each before making a decision.

This guide includes all of the things welders need to know before they choose between AC and DC, including information regarding the basics of welding power supplies, the pros and cons of AC and DC, as well as the common applications. If you can any questions about welding currents and AC versus DC welding machines