A welding power supply, logically, is a device that supplies electric power for welding purposes. Options for welding power sources are ample. Power sources may be a car battery or an advanced machine using silicon controlled rectifier technology. You’ll find welding machines with constant current or constant voltage. Considerations include efficiency, power, ease of use, and compatibility with needs. Why so many choices? And how do you select the right one?
CC vs. CV
The welding process requires over 80 amperes high current and 12,000+ amps for spot welding. Gas tungsten arc welding uses low current. A constant current (CC) machine varies output voltage while maintaining steady current. A constant voltage (CV) welding machine will fluctuate output current while maintaining a set voltage.
CC or variable voltage welding machines have limited maximum short circuit current. Volt-amp curve is negative. Voltage will change with different arc lengths. Understanding a CC machine means the user must be able to interpret volt/amp curve (relationship between arc length and voltage). With a CC machine the welder can rely on a fixed number of amps reaching the material regardless of the arc distance.
The CV machine is important for Gas Metal Arc Welding (GMAW) and Flux Cored Arc Welding (FCAW). In this case the welder is not in a position to control the arc length manually. A CC/CV DC inverter with 350 amp output at 60% cycle will allow stick welding, DC TIG welding, and MIG/FCAW. Inverters are relatively small and compact, occupying little space. They are energy efficient and will “pay for themselves” quickly. Inverters that draw less amperage allow reduced breaker size or more welders on one breaker. Much will depend on the welding process and materials used in the shop.
MIG welding or Gas Metal Arc Welding (GMAW) needs a power source to start and maintain the arc between the wire and the base metal. The spool of wire is either housed inside the power source or fed from an external wire feeder. The solid metal wire used requires a shielding gas to protect the weld puddle. The shielding gas makes for a smooth, stable arc. The speed, simplicity, and ease of GMAW welding combined with the flexible tolerance on electrode positioning and manipulation has led this form of welding to be a very popular process. GMAW can be used on all major, commercial metals.
Flux Cored Arc Welding (FCAW) may or may not need an external shielding gas. The gas may be produced from the flux core as it burns in the arc. FCAW is used primarily on steel and stainless steel. FCAW (like GMAW) operates at 30-50 percent arc time and doesn’t require as much skill as TIG or stick welding. Both can be used on a wide range of material thicknesses and operate in all positions.
Although GMAW and FCAW are the welding process most common in fabrication and production shops, it is more costly and less portable than stick welding processes. Work is done at a welding station that reaches up to ten feet from the wire feeder.
Shielded Metal Arc Welding (SMAW), often called stick welding, is the most common arc welding form. An electrode (stick) is placed at the end of a holder. Electricity from the power source will lead to an arc being struck between the tip of the electrode and the metal welding surface. The electrode burns an exterior material, protecting the arc from the atmosphere, as the tip of the electrode melts and becomes filler material. CO2 is produced. This becomes the shielding gas.
SMAW welders are versatile. It is easy to switch metals and they are more portable. Inexpensive SMAW welders are used often by novice welders, small shops, and shops welding a variety of jobs for a large project. Electrodes are consumed quickly and must be changed when consumed.
Gas Tungsten Arc Welding utilizes non-consumable tungsten electrode and a base metal joined by an arc. The arc is typically protected by argon. GTAW welds are of high quality on the majority of metals and alloys, even at very low amperages. GTAW works well on thin metal. GTAW is slow, requires precise movements, and more involved setup.
Submerged Arc welding wire is continuously fed with granular flux. Common on heavy structural steel and high speed welding projects, SAW flux covers the whole arc. The air is very clean, with little fume production. Operating factors are high, especially with long large welds. Welders must work on a flat surface, due to granular flux. Hot flux is also known to burn shoes.
Depending on your welding needs and process, you’ll be able to determine the best power source. Your power source should accommodate the process, meet space requirements, offer the features your shop desires, and – of course – fit your budget.