AC vs. DC Welding – What’s the Difference?

The quality and strength of the weld that you get will always be highly dependent on the electrode and polarity that you use, and so you need to ensure you get both right.

When it comes to the polarity, you will have to choose between AC and DC welders. While the two might sound self-explanatory and obvious terms for expert welders, many potential users do not understand what they are all about.

Both types still do a good enough job when welding, and if you are confused about which one to choose or when to use which, here we help you understand the key differences between AC and DC and also explain what each has to offer and their pros and cons.

AC Welding Overview

Photo: m.roadkillcustoms.com

AC welding does not refer to a type or technique of welding. Rather, AC welding is used to describe how the current will flow from the power supply to your welding machine.

Since AC stands for Alternating Current it means that when using these welders, the flow of current will not be in one direction but will constantly change back and forth. With AC welding, polarity changes about 120 times every second.

As the polarity changes from positive to negative, you will get 0 output for a split second which means the arch is extinguished. It is because of this that you will find some special electrodes built for AC welding.

The reversed polarity that you get when using AC welding delivers deeper penetration and also makes these welders great for welding magnetized materials and high-temperature welding.

Overall, the AC welders tend to be more affordable than the DC types, and they will be cheaper to operate. However, AC welding is still not as smooth as DC welding, and it will also create relatively more spatter when welding.

Pros:

• AC welders are cheaper to buy
• Works great with magnetized materials
• Great for welding aluminum
• Deeper weld penetration
• Ideal for high-temperature welding

Cons:

• Not as smooth as DC
• Creates more spatter
• Arc is more difficult to handle

DC Welding Overview

Photo: spectrumweldingsupplies.co.uk

DC or Direct Current welding will have the charge traveling in one direction at all times and hence providing a constant polarity unlike in AC where it keeps changing back and forth.

This straight current produces less heat which makes it more ideal for use on thinner substrates. Also, with DC welding, there is a quicker electrode melt off and the polarity can either be positive or negative.

There is a lower amount of spatter when using DC welding which results in higher product yield. And you will also get a much smoother weld that is more aesthetically appealing than what you get with AC welding.

Many users will appreciate that DC is more reliable than AC and hence making it easier to work with even for novice DIYers and less experienced pro welders. And because a typical DC welding machine will use both AC and DC rods, it is often more versatile and convenient.

However, like AC, DC welding also has some shortcomings such as a greater potential to suffer from arc blow and that most DC machines are both more expensive to buy and operate. Worst yet, DC welding machines are not built for portability as they tend to be large and heavier.

Pros:

• Less spatter from the weld
• Can use both AC and DC rods for stick welding
• Much better weld appearance
• Great for novice/beginner welders

Cons:

• Greater arc blow potential
• Often more expensive to operate
• Not ideal for TIG welding aluminum

Comparison Chart

AC vs. DC Welding

Choosing the right polarity when welding is vital as it helps ensure you get great results and avoid common issues like non-uniform beading, poor penetration and overheating. And to make sure you choose the right option between AC and DC, you need to understand the following differences between the two.

1. Typical Applications

How you intend to use your welding machine is always the main determinant of which type will work well for you. Hence, you must understand what each of these two is used for, and this is despite that for some uses both still do a good enough job.

AC Welding

AC allows you to weld at relatively higher temperatures than DC which makes it perfect for TIG welding aluminum which is one of its most common uses. Also, because aluminum has an oxide film on its surface when AC switches to a positive polarity, it can help remove this coating and clean the aluminum surface.

Besides the high welding temperature, AC provides a deeper weld penetration which makes it ideal for welding plate metals in shipbuilding. Unlike DC, it will be very useful for applications that involve welding magnetized metals such as in machinery repair and other industrial and construction applications.

DC Welding

DC offers you more versatility when it comes to welding and will be useful for a wider variety of applications than the AC welders.

However, DC is mostly used for stick welding applications. This means you will often find it being used for overhead and vertical welding. Also, because it does not deliver very high temperatures, it is great for welding thinner metal materials.

Other welding applications where DC will come in handy include stainless steel TIG welding, carbon single brazing and when dealing with heavy weld deposits.

2. Best for

Given their typical applications above, it should now be clear whom each of these welders will work well for. But with that said, both can still work well for different kinds of users as it mostly depends on the tasks at hand.

AC Welding

Because AC is not always easy to work with it is often best suited for professionals, and this is more so those that are into shipbuilding as it delivers deeper weld penetration.

Also, because these welders can work with magnetized metals, they will be ideal for professionals that deal with machinery repair. But, any seasoned DIYers that deal with thicker metals and have more experience using welders can still work with AC welders effectively.

DC Welding

If you are just starting or do not have enough welding skills and experience, you will be better off sticking with DC welding as it will give you an easier time.

DC welding is the best for hobbyists, beginners and regular DIYers that will only need to weld occasionally and prefer something less complicated that is easier to start and use.

Also, there is relatively less risk involved when using DC welding which makes it even better for the less experienced users.

3. Versatility

Tools can be quite expensive, and this is more so when you have to buy several of them, and so it is always great to get something that you can use for various tasks as this saves you the cost of buying different tools.

Overall the DC welders are more versatile than the AC welders, which should explain their ever-growing popularity. With DC welders, you can do almost everything you would do with your AC welders, but the reverse is not true.

While AC excels when it comes to making specific types of welds and for use on a certain type of metal, DC is a more all-round welder.

Better yet, DC will work well for overhead and vertical welds something that the AC welders might struggle to achieve. And you get to choose whether to use DC positive or DC negative which further enhances the versatility.

But, if you are looking for a truly versatile welding machine, the best idea will be to go for one of those modern types that are built to support both AC and DC.

4. Arc Blow

Arc blow is one of the most common issues that welders will have to deal with when welding, and it can delay projects and make you ruin the weld. Hence, you need to keep it in mind when trying to decide whether to buy AC or DC welder.

Using AC is often one of the best ways to fix the arc blow problem when welding. The key causes of arc blow in welding will include magnetism of the metal or arc current. Hence, with the alternating current on AC, you will get a studier arc even when welding magnetized metals.

Modern DC welders try to provide a more stable arc, but they are still not as effective as the DC welders.

But, it is also worth noting that arc blow can be caused by external things like wind. Hence, changing your work environment where possible can also help you deal with the issue.

5. Size and Weight

Given that in many instances you will need to use your tools in different locations, you will also need to consider the size and weight as you choose between AC and DC welding.

When it comes to portability, the AC welders carry the day as they are often much smaller and lighter than the DC machines which makes them easier to carry from one job site to the other.

While DC welders can still be portable enough given that many models will also include some wheels for mobility, a typical one will be larger and heavier than a similar AC welder. Hence, if portability is crucial for you, it will be better to go for AC welders.

6. Cost

There are now almost countless models of AC and DC welders out there, and they will come in different sizes and with different features. What this means is that you can get something for almost any budget.

With that said, the AC based welders tend to be more affordable than the DC-based machines given that they are much smaller and feature a simpler design. Also, the AC machines are more widely available given that they have been in use for long which further pushes their prices down.

Both AC and DC welding machines are available in budget models that will cost a little over $100, but to get top-quality models of either, you will need to spend at least $300 for AC and over $400 for DC.

Because the power supply in most places is AC-based, the AC machines will also be more affordable to operate when compared to the DC machines which might require a conversion kit to work with the AC power.

Conclusion

Welding is often part of the job for most people, and it is no longer a preserve for professional welders as you might need to weld for your DIY and home improvement projects. Hence, you need to know what will work best for you between AC and DC welding.

The two are ideal for different kinds of projects, and if you are not sure which one you will need, the wiser idea will be to buy machines that support both AC and DC welding. These machines might be more expensive but will not limit you to using one welding polarity, and so you can use them for more jobs.

But, if you have to choose between the two, DC will be more appropriate if you are looking for a good all-round and versatile welding machine. AC is perfect if you deal with aluminum and magnetized materials a lot or most of your projects require deeper weld penetration.