For about 40 years, a great debate in welding is whether to use constant-current or constant-voltage power supplies when using gas metal arc welding on aluminum. Constant-current power supplies made sense 30 years ago and are still used in some applications today, but for most applications, constant-voltage power supplies are suitable for gas metal arc welding aluminum.

I've read that constant-current (CC) power supplies are preferred for gas metal arc welding (GMAW) aluminum, but when I visit companies that sell welding equipment, they tell me I want a constant-voltage (CV) power supply. What's the real story? Can I use the more common CV power supplies or not?

This controversy has gone on for 40 years or so. At one time the statement that CC power supplies are preferred was true. However, welding power supplies have changed a lot, especially in the last 20 years.

It's helpful to know what CC and CV power supplies are and how they work.

Shielded metal arc welding (SMAW) and gas tungsten arc welding (GTAW) were developed before GMAW. Therefore, power supplies initially were developed for SMAW and, a bit later, GTAW. In both SMAW and GTAW, the operator holds a stinger, or torch, and welds manually.

During welding, it's inevitable that the welder's hand will move to change the arc length, which controls the arc voltage. This means that as the arc length changes, the arc current changes too.

In these power supplies, even large changes in voltage caused only small fluctuations in welding current. This situation applied to SMAW and GTAW. Welders still use these types of power supplies today. Strictly speaking, the term constant current is a misnomer because the current can vary a bit, but it's in common usage.

When GMAW was invented in the late 1940s, only CC power supplies were available, so they were used for GMAW as well. However, it quickly became apparent that they weren't user-friendly for GMAW.

The main reason for this is that no coupling took place between the wire feed set on the wire feeder and the welding current set on the power supply. The first important consideration in GMAW is that the filler wire is burned off at the same rate as it's being fed. If the current on a CC power supply is set too high, the wire will burn back to the tip almost immediately. If it's set too low, the wire will stub on the workpiece and the arc will be extinguished. The second concern is that a CC power supply gives no current spike on arc initiation, so it's often difficult to start large-diameter filler wires.

When welding with a CV power supply, even small changes in arc voltage can result in large changes in the welding current. In this way, the GMAW arc was made self-regulating.

If the welder pulled the torch away from the workpiece—raising the arc length and arc voltage—the power supply dropped the arc current to burn off wire at a slower rate until the preset arc voltage was re-established. If the welder pushed the torch toward the work—shortening the arc and reducing the arc voltage—the power supply quickly raised the welding current to burn off more wire until the preset arc voltage was re-established.

So the CV power supply made it eas
ier for the welder to set up the power supply and wire feeder. The welder basically had to set a reasonable arc voltage on the power supply, set a reasonable wire feed speed (WFS) on the wire feeder, and weld.


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