Welding Current – (AC) vs. (DC)

Welding Current – (AC) vs. (DC)

Welding Current – (AC) vs. (DC)

If you have been looking at purchasing a welder, you may have seen that most welders are (DC) capable. Some are AC/DC capable. What do these terms mean and why is it important to pay attention to them when purchasing a welder?

Lets take a moment . . .

to examine electricity and how it flows. Think of electrical current like water running through a garden hose. Say for now your faucet was the Negative terminal and the end of the hose was the positive terminal. When you turn the water on and it flows from the house this would be known as Direct Current (or DC.) The “water” would be flowing from negative to positive. To relate, direct current in welding is when electricity flows directly from one pole to the other without oscillation.

Take a look at this image below. The bold, straight lines located horizontally next to the 150 amp indicator point on both the DC+ and DC- poles, shows the “Direct” pattern of the DC current over an undisclosed amount of time. We will compare this with AC in just a moment.

Welding with DC current certainly has its advantages including more stable arcs, easier arc starting, fewer arc outages, less spatter and easier vertical welding. However with some types of base material, it may be necessary to use A/C or “Alternating current.”

current is alternating 60 times (cycles) per second, between positive/negative (in the US, 50 in EU.) Without getting too technical, the advantage Alternating Current can offer, is that you can often balance or choose whether more of the “heat” is being put into your electrode, or into the work piece. A/C current can also help mitigate arc blow if you are experiencing difficulty adequately penetrating two pieces of a joint evenly. This is common to see in a shipyard setting where there are many corner joints that require even penetration and fill.

Going back to the balance control for just a moment. On a welder such as the Arccaptain TIG200 for example, the balance control allows you to achieve 70% DCEN (Direct Current Electrode Negative) and 30% DCEP (Direct Current Electrode Positive.) This is especially important for welding aluminum. The DCEP cycle cleans the oxidation off the aluminum while the DCEN cycle, creates heat in the plate to achieve fusion and penetration. This balance can be adjusted if more cleaning action is needed for a more highly oxidized aluminum.

AC current also has the effect of penetrating less than DC. For thinner material or welding on joints that may burn through easily, AC current can often be preferred to help balance the penetration effect and achieve a more shallow weld. It is important to understand that not all electrodes are capable of running AC current. In fact, most rods are meant to run DC only! That means it is very important when choosing an electrode to select a classification that excels with AC current.

6013 rod classification is outstanding for sheet metal. The AC current helps to keep penetration shallow and 6013 has an outstanding bead appearance and arc characteristics. Great for body work if you don’t have a MIG welder.

7018 is a common structural steel rod and while primarily run on DCEP, excels on AC current. The 7018 low hydrogen gives an extremely smooth bead appearance but be sure your workpiece is clean! 7018 does not dig through rust and paint as well as something like 6011.

So what does all this mean?

Evaluate what type of welding you will be doing. Choose a welder that has the capabilities you need. If you purchase something like the MIG multiprocess welder, you can use MIG for thinner sheet metal, a spool gun for aluminum, DC tig for everything else, and DC stick where high penetration, high deposition welds are required.

If thinner auto body welds aren’t what you will be doing, look into something like the Arccaptain MIG130. You will be able to achieve extremely high quality TIG welds on all base materials including aluminum and the stick function will give you the high pen. high dep. welds for heavier base material.

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