AC welding and DC welding are two different forms of electric arc welding. AC means alternating current, and DC means direct current. Because they produce different effects, their applications vary.
Unless you have several years of experience and certifications, it may be challenging to understand the difference between AC and DC welding.
Depending on the model, welding machines may possess power supplies capable of either AC, DC, or both, and specific welding electrodes are only suitable for use with a particular polarity.
What Is DC Welding?
Direct current (DC) welding is the most common form of arc welding. This method uses direct current to supply the electrical energy to the electrode. Direct current possesses a constant, even flow in a single direction.
DCEP vs. DCEN Welding
There are two subforms of DC welding: Direct current electrode positive (DCEP or DC+) and Direct current electrode negative (DCEN or DC-).
With DCEP, the welding electrode is charged with a positive current, whereas the workpiece is charged with a negative current. Because electricity always flows from negative to positive, DCEP welding causes electricity to flow from the welding rod to the working metal.
DCEP is the standard polarity setting for the vast majority of MIG welding and stick welding machines. It produces a steady electric arc with minimal spatter, creating good penetration into the working metal and sufficient heat to achieve adequate fusion.
In contrast, stick or MIG welding in DCEN mode produces less penetration and more spatter, making it less suitable than DCEP for general-purpose work. However, DCEN is better for TIG welding and thin surfaces, as this method produces no slag.
Advantages of DC Welding
A big difference between AC and DC welding is the type of machine you can use. If you’re using a stick welding machine, DCEP is the best option. The stable arc and smooth output make DC welding viable for vertical and overhead welding applications.
If you’re using a TIG welding machine, DC is the best setting for stainless steel.
The ability to switch between DCEP and DCEN allows you to work on different surfaces and thicknesses, making DC welding overall more versatile than AC welding.
Disadvantages of DC Welding
Occasionally, electrodes may suffer from a phenomenon called arc blow when the welding arc deflects away from the intended welding point, reducing the weld’s quality.
Although there are multiple possible causes for arc blow, including residual magnetism, joint design, atmospheric conditions, DC welding machines are far more susceptible to suffer from arc blow. One of the best ways to eliminate arc blow is to switch to AC.
AC/DC and DC-only welding machines are also more expensive than AC-only. Power on the grid is exclusively AC; therefore, DC welders must have an internal transformer that changes the grid’s AC power into DC power, making them more complex.
In the United States, power transmission grids supply a nominal voltage of 110-120 volts. DC welders operate on 220 volts, requiring you to install a 220V outlet.
If your home shop or workshop doesn’t have a 220V circuit, you may have to call an electrician which can be costly.
What is AC Welding?
The main difference between AC and DC welding is how the welding machine uses electrical current to produce an arc.
Alternating current (AC) welding uses a rapidly alternating electric current instead of a constant flow. AC currents switch polarities, alternating between positive and negative, approximately 120 times per second.
AC is particularly suitable for transmitting electricity over large distances. Unlike DC currents, AC currents do not lose voltage if they travel long distances from the power supply.
Advantages of AC Welding
If you have to work far away from your power supply, you likely need extra-long cables. With DC welding machines, the increasing resistance causes a voltage drop, leading to poor-quality or inconsistent welds. With AC power, the voltage remains constant, eliminating the issue entirely.
AC welding also allows you to work with more confidence on surfaces with residual magnetic fields. Where DC welding machines suffer from arc blow, the AC welder typically won’t.
AC welding machines are also better for home shops or small workshops not equipped with a 220-volt circuit, as AC machines do not require it and can work on standard 110-volt power outlets.
AC and Aluminum Welding
Although professional shops rarely use AC welding, there is one specific instance where it is suitable: aluminum welding
Aluminum requires higher temperatures for effective welding, and it possesses a layer of aluminum oxide that can significantly interfere with the weld bead when using traditional methods.
With an AC welder, not only are the welding temperatures sufficiently high to permit effective welding, but the alternating current also imparts a “scrubbing” effect that can clean the oxide layer, cleaning the surface in the process.
If you’re going to weld aluminum parts, an AC welder is the only effective solution.
Disadvantages of AC Welding
AC welding always produces messier welds than DC welding, as well as a significantly higher quantity of spatter, which means more time cleaning and grinding it off of your working surface after finishing the weld.
AC constantly fluctuates between positive and negative. However, there is an extremely brief moment between each cycle during which no power goes to the electrode, making it more likely for the electrode to lose its arc and forcing you to restart it manually.
Some electrodes are coated in a special, AC-specific flux to combat the issue of arc loss. One of the most common types, 6011, uses high-cellulose potassium flux that can be used in all current modes (DC+, DC-, AC), in all positions (including vertical and overhead), and on all kinds of surfaces, even rusty or dirty ones.
Losing the arc can be a significant hassle, as it creates a break in the weld, potentially causing inconsistencies or even weakening it.
Beginners may have a tough time regaining the arc if they do not have a good starting technique. This can be very discouraging, particularly without access to a DC welding machine or a suitable power outlet for one.
Both AC and DC welding have their pros and cons, so learning both can improve your chances of having a successful welding career. Practice with both AC and DC welding techniques to become a well-rounded welder.