Understanding AC and DC for MIG Welding

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Welding is a useful trade to learn. It can be turned into a fruitful career or used for at-home repairs and hobby creations. One specific type of welding is called MIG welding. MIG welding is a very common style of welding, but it requires specific elements and tools. It is important to understand these before advancing in your welding skills. 

There are some key things you must understand about AC and DC for MIG welding. Once you have a solid grasp of these basics, you can gain a more holistic familiarity with the trade. AC and DC have very different utilities when it comes to welding. Knowing this allows you to be a more advanced welder.

The world of welding is vast and can feel overwhelming. However, learning the fundamentals can broaden your welding knowledge immensely. AC and DC are both useful for welding but in different ways. They each have their benefits and drawbacks. Read on to better understand how AC and DC fit into MIG welding.

AC versus DC in MIG Welding 

Both alternating and direct currents have their places in welding. However, it is important to note that the different current types offer very different uses. This is especially true for MIG welding, in which specific currents work best. MIG welders use direct current far more often than alternating current. 

However, alternating current can indeed be used in MIG welding. While it is much less common, it is not unheard of to use alternating current in MIG welding. MIG welding will be explained more in-depth below, as will each type of current and how they apply to the practice of MIG welding.

What is MIG Welding?

The MIG in MIG welding stands for metal inert gas welding. This style of welding is also known as gas metal arc welding or GMAW. As the term GMAW suggests, this kind of welding is a style of welding that fits under the arc welding category. 

In MIG welding, a filler metal is fed through the welding machine. This filler metal is a kind of wire that acts as both a current supplier and a heat supplier. The current from the filler metal wire maintains the welding arc. The welding machine produces an inert gas that protects the arc from reacting to outside elements in the air around it. 

Tools Needed to MIG Weld

Since MIG welding is one of the most common types of welding, most welders will have a welding machine for MIG welding on hand. These machines will all consist of the same basic parts.

  • Welder
  • Welding gun
  • Gas tank
  • Ground clamp

It is important to note that the gas tank in a welding machine is not like the gas tank in your car. It does not hold gasoline. The gas tank in a welding machine holds the shielding gas, usually argon, that protects the welding arc.

You also must have the proper safety equipment on hand. Welding can be simple and fun once you get the hang of it, but that does not mean that it is not dangerous. Proper caution and welding safety gear are always necessary.

  • Welding mask
  • Gloves
  • Leather or cotton clothing
  • Closed-toed shoes
  • Do not have skin exposed
  • Do not weld in closed spaces
  • Do not weld near flammable materials

Benefits of MIG Welding

It is no accident that MIG welding is one of the most popular means of welding. It is forgiving, so it is great for beginners. It is an extremely versatile method of welding and has many great applications. MIG welding can be used on many different types of metals and metal thicknesses.

  • Creates weld bead appearance
  • Requires less heat
  • Produces fewer fumes
  • Requires affordable materials

What is Alternating Current?

Alternating currents, or AC, have electrons that periodically switch their direction of flow. When the electrons switch directions, their polarity changes as well. This is the kind of electric current found in power outlets in residences and businesses. 

What is Alternating Current Welding?

As stated above, alternating currents are electric currents that switch direction and polarity periodically. Because these currents repeatedly switch from negative to positive polarities, there are brief instances where they emit a charge of zero. Welding materials created specifically for alternating current welding can overcome this issue. 

Benefits of Alternating Current Welding

  • Suitable for aluminum welding
  • Effective for welding magnetic materials
  • Good for thicker metals
  • More affordable
  • More portable
  • Can reach long distances

Alternating current welding machines are usually smaller than direct current welding machines. They are lighter and easier to carry from place to place. This makes them more portable. They also tend to be more affordable, due to the less expensive nature of the machines’ components.

Drawbacks of Alternating Current Welding

As stated above, alternating current welding has quite a few more drawbacks than its direct current counterpart. The following drawbacks are part of the reason many welders prefer using direct current over alternating current for their welding needs. 

  • More splatter
  • Less stable arc
  • Less control over the weld

What is Direct Current?

Direct currents, or DC, have electrons that do not change the direction of polarity. The electrons always travel in one direction in a steady flow. Direct currents can either have positive or negative polarity, depending on how the electricity is set to flow. Direct current is used in battery-powered and rechargeable items like phones and laptops.

What is Direct Current Welding?

In direct current welding, electrons flow in one direction without changing. The polarity can be either positive or negative, but it will remain the same. Direct current welding is notorious for its stable arcs. Because the polarity and electron flow does not change, the arcs are highly reliable.

Direct current is often used in lower voltage devices. It is also used on welding projects that require vertical welds or overhead welds. This is because the arcs are easier to control than alternating current arcs. Direct current arcs are less likely to spray splatter, and they are less likely to sputter out or need reignition.

Benefits of Direct Current Welding

Due to its reliability and stable arcs, direct current offers many advantages for welders. This is why it is so widely used in all areas of welding. 

  • Stable arc
  • Stronger and smoother welding output
  • Good control over the weld
  • Less weld spatter
  • Good for thinner metals
  • DCEP (direct current electron positive) penetrates deeply
  • DCEN (direct current electron negative) deposits weld metal quickly (fast deposition rate)

The constant, steady flow of electrons creates a steady, continuous arc. This is what allows for such a steady arc and good looking weld bead. The welding strength is very strong which also contributes to the smooth looking weld. 

Drawbacks of Direct Current Welding 

There are not many drawbacks of direct current welding, but there are a few important ones that can be crucial. Depending on your welding needs, the following disadvantages of direct current welding should be kept in mind.

  • Arc blow
  • More expensive
  • Not suitable for aluminum welding

Preference for DC in MIG Welding 

It should be noted that MIG welding is most commonly done with direct current or DC. 

MIG welding is best performed with a constant voltage and constant current, which is provided by direct current welding machines.

Direct Current Electron Positive 

Direct current is preferred over alternating current in MIG welding. To be more specific, DCEP or direct current electrode positive is the most commonly used method in MIG welding. This type of current offers several benefits that cannot be found when using an alternating current.

  • Arc stability
  • Smooth beads
  • Neat metal transfer
  • Low splatter

Direct Current Electron Negative

Direct current electron negative or DCEN is not often used in MIG welding. It has many applications in other forms of welding, but in MIG welding it can cause issues that are not present when welding with DCEP. 

  • Arc instability
  • Messy metal transfer
  • Frequent arc outages
  • Less penetration

Still, direct current with a negative polarity has its place in welding, as well. It does not offer the same depth of penetration into the welding metal, but it does offer a higher rate of metal deposit. This can be useful when the metal being welded is thinner.

Applications for AC Welding

MIG welding with alternating current is done rarely and under specific circumstances. Both alternating and direct types of currents can be used for MIG welding, depending on the intent of the project.

While alternating current is not preferred in MIG welding or most other types of welding, it does still have its place. While it has drawbacks, it can outshine direct current welding under specific circumstances. This section will delve into applications of alternating current welding, as well as instances when it might be used for MIG welding. 

When is AC Welding Used?

Alternating current welding is peculiar due to its constant swapping of polarity. This makes it unreliable and unpredictable in most welding situations. However, this makes it uniquely useful for welding certain types of materials. 

  • Magnetic metals
  • Aluminum and other non-ferrous (absent of iron) metals
  • High-temperature welding
  • Deeper-penetrating welds
  • Thick metals
  • Heavy metals

AC Welding and Magnetic Metals

Because alternating current reverses its polarity frequently, it is not affected by the magnetism in magnetic materials. Magnetized metals are often found on machinery, so alternating current is great for making these repairs. This cannot be said for direct current. This is why direct current welding is so susceptible to the dreaded arc blow. 

Avoiding arc blow is one of the main advantages alternating current welding has over direct current welding. While it is not enough to put alternating current on top as the number one preferred welding method, it makes alternating current the best method for welding magnetic metals. 

AC Welding and Non-Ferrous Metals

Non-ferrous metals are metals, like aluminum, that do not contain iron. These metals are special and have different characteristics than other iron-based welded metals, like steel. The following are examples of non-ferrous metals. 

  • Aluminum
  • Nickel
  • Copper
  • Alloys of the above

An alternating current is used to weld the above non-ferrous metals. When non-ferrous metals are welded, an oxide layer is formed on the outside. This layer would interact with a direct current, causing the different layers to heat unevenly and preventing a proper weld. 

Other Advantages of Welding with AC

Some welders prefer to start out using alternating current when welding because the machinery and equipment are more affordable. This is likely because they have less to offer in the grand scheme of welding. Still, when starting as a beginner, it is not uncommon to prefer more affordable materials to get the hang of the trade.


Welding Machines: AC, DC, and Multipurpose

Welding machines are designed specifically to be used with either alternating or direct current. Some machines can switch between multiple types of current, as well. There are several differences between alternating current welding machines and direct current welding machines. 

These differences are not only in the way these machines operate but in their physical aspects. Each machine has its own positive and negative aspects.

Alternating Current Welding Machines — The Positives

Alternating current welding machines do have some advantages. While they do not typically offer a better welding experience overall, there are factors to consider when choosing a welding machine. 

  • Cost
  • Size
  • Weight
  • Portability
  • Low-Maintenance
  • Can be used at long distances
  • Prevent arc blow

Alternating current welding machines are cheaper than direct current welding machines. They are also smaller, lighter, and easier to take from place to place. Some only require 110-volt outlets to operate, which are standard in most places and do not require additional breakers. 

Alternating Current Welding Machines — The Negatives

Alternating current welding machines are not built to provide the highest quality welds. These machines are often considered obsolete unless they can switch between alternating and direct current. The welder will have to use more effort to keep the weld consistent because alternating current welding machines have varied outputs.

  • Not great for welding all metals
  • Not all electrode types can be used
  • Requires AC power supply to function
  • Low power output

Direct Current Welding Machines — The Positives

Right off the bat, direct current welding machines are widely considered to be of much higher quality than alternating current welding machines. They provide the welder more control which results in better welds. There are other positive factors to consider as well.

  • Suitable for multiple metals
  • Easier to control arc
  • Higher power output
  • Multiple electrode types can be used

The thing to remember is that these machines are more complex than alternating current machines. This added complexity allows the machines to offer more power and utility, but it also can create added problems depending on what you look for in a welding machine.

Direct Current Welding Machines — The Negatives

Direct current welding machines are considered superior to alternating current welding machines overall. However, they do have drawbacks in specific areas. Most welders would not consider alternating current machines to be better than direct current machines because of these factors alone, but they are important to consider. 

  • Cost 
  • Size
  • Weight
  • Complexity
  • Arc blow
  • May require 220-volts

Direct current welding machines are much costlier than alternating current machines. This is what you might consider a “you get what you pay for” scenario. The complexity of direct current welding machines means they require costlier maintenance and higher operating expenses. An electrician may have to install a 220-volt breaker, as well.

AC/DC Multipurpose Welding Machines 

Some machines on the market are multipurpose which means they can switch between both direct current polarities, and alternating current. This could be a good choice for hobby welders who are not looking for a specific style of welding machine, or for welders who do not have a single-minded welding need in mind. 

Drawbacks of Multipurpose Welding Machines

The drawback of these multipurpose machines is that each element does not have as much dedicated to it as it would in a standalone machine. This being the case, multipurpose welding machines are not a great choice for professionals who know exactly what they are going to weld and what kind of machine they need. 

Different welding styles require different gases. In MIG welding, the most common gas used is argon or an argon mixture. However, you would need to switch argon out with helium or CO2. That could quickly get incredibly inconvenient and expensive. Consider if you need a multipurpose machine before settling for something mediocre.

Wrap Up

As you can see, both alternating and direct current have their place in the welding world. However, it is plain that direct current is the most appropriate choice when it comes to MIG welding and most other welding styles. While alternating current has potential, it is not well suited for the MIG style, other than to avoid arc blow.

Luckily, there are ways to avoid arc blow when MIG welding with direct current. You can attempt to ensure your welding metals are not magnetized. When welding non-magnetized metals, arc blow will not be a factor. You will only get the positive aspects of direct current for a pleasant MIG welding experience. 


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