Choosing a constant current (cc) DC Welder for teaching

A welding power supply, as the name indicates, is a device that supplies electric power for welding purposes. Welding, as is known, demands over 80 amperes high current and above 12,000 amps for spot welding. Low current is also used when for example, welding two razor blades at 5 amps with gas tungsten arc welding. A welding power supply can range from a car battery to an advanced machine based on silicon controlled rectifier technology.

Welding machines are of two types - constant current (CC) and constant voltage (CV). The difference is a constant current machine varies its output voltage to maintain a steady current whereas a constant voltage machine will fluctuate its output current to maintain a set voltage.

It may be noted that constant current (CC) welding machines have limited maximum short circuit current. They have a negative volt-amp curve and the voltage will change with different arc lengths while only slightly varying the amperage, thus the name constant current or variable voltage.

It is usually said that a proper understanding of a Constant Current (CC) DC welding machine distinguishes the success and failure between students who pursues a career in welding. To interpret a volt/amp curve, you must understand the relationship between arc length and voltage. A basic fact of the arc welding process is that as arc length increases, voltage goes up; as arc length decreases, voltage goes down.

Candidate testing to qualify for a stick pipe welding job using unfamiliar equipment will fail however sincere the attempt. The fact is, despite having all the skills the student had the wrong machine. An instructor saw the student's predicament, put him on a different welding machine and weld became flawless.

The nature of the CV machine is important for gas metal arc welding and flux-cored arc welding as the welder will not be in a position to control the arc length manually. If a welder attempted to use a CV machine to weld with shielded metal arc welding, the small fluctuations in the arc distance might as well cause wide fluctuations in the machine's output. With a CC machine the welder can count on a fixed number of amps reaching the material to be welded regardless of the arc distance. But, again, too much distance will cause bad welding.

A CC/CV DC inverter with an output of 350 amps at 60 percent duty cycle meets most of the welding needs. This type of unit enables training students on Stick welding and DC TIG welding in a broad variety of applications, as well as training students on the MIG and flux cored processes.

Training centers that teach Stick, TIG and MIG welding, choosing the right machine is of paramount importance as it can make or mar a student's learning career. You may be aware that industrial development is continuously creating a huge demand for skilled welding operators. The training center has the responsibility to provide trainees with the tools that will help them succeed. Inverters are generally recommended for welder training schools because:

  • Bearing in mind the type of welding technology that most industries are adopting, it is only proper to train students on the equipment they will use professionally.
  • Inverters are relatively small and compact and thus occupy very little space.
  • Inverters are a lot more energy efficient and can thus pay for themselves through power savings alone.
  • Some inverters offer the ability to connect to single- or three-phase power over broad primary voltage ranges. Further, inverters draw much less amperage, reducing breaker size or allowing more welders to be connected to a give breaker.
  • Last but not least, an inverter offers advanced arc controls that enable students to learn faster. An inverter can make a good welder out of an average student while letting excellent students express their full potential.