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Answers to common questions about inverter TIG and MMA power sources, from choosing the right type to setting up and looking after one.
An MMA set uses a flux-coated electrode that is both the arc and the filler, so it needs no shielding gas bottle and copes well with outdoor work and less-than-perfect surfaces. A TIG power source strikes the arc from a non-consumable tungsten electrode, with an inert shielding gas protecting the weld and filler rod added separately if needed.TIG gives finer control of heat and a cleaner, more precise weld, which suits thin material, stainless steel and visible work. It is usually slower and needs cleaner metal and more skill. Many inverter sources can run both processes, so check the process list on the data plate and in the manual.
For TIG, the metal decides. Steel and stainless steel only need DC output. Aluminium and magnesium form a tough surface oxide, so they need AC, where the alternating current breaks up that oxide as you weld. On AC machines a balance control lets you shift the emphasis between surface cleaning and penetration.A DC-only TIG power source is a sensible choice for a steel and stainless workshop, but it cannot be expected to weld aluminium. If you may weld aluminium later, choose AC/DC from the start. Check the maker's specification for the output types and current range.
Pulsed TIG alternates between a high peak current that gives penetration and a lower background current that keeps the arc alive. The average heat going into the work is lower, which reduces distortion and the risk of burning through. It helps most on thin sheet, on stainless and other metals that hold heat, and when welding out of position.Slow pulsing gives a softer, wider bead and fast pulsing gives a stiffer, more focused arc. Pulsing is not essential for thicker steel or general repair work, and you usually need to raise the current setting to compensate for the lower average heat. Choose it if you weld thin or heat-sensitive material regularly.
An inverter power source switches the incoming supply to high-frequency AC before it reaches the welding output. That brings weight savings and better efficiency compared with older mains-frequency designs. The output is also often software-controlled, which allows high-frequency pulsing and tailored arc characteristics, and it is why most inverters can run several processes from one unit.The practical result for a buyer is a unit that is easier to move and that gives adjustable arc control. Older transformer-rectifier designs are heavier, and some are simple and robust. Compare the process list, current range and duty cycle rather than the design alone.
Duty cycle is the share of a fixed rating period that a power source can weld at a stated current without overheating. The manual states the period and the conditions the rating applies to. At lower currents the usable duty cycle is higher, and above the rated current it falls.If the unit overheats, a thermal cut-out switches the output off until it cools, but regularly forcing it to trip can damage the machine. Hot surroundings may reduce the running time, so check the manual for the conditions the rating applies to. Choose a source whose rating at your normal working current suits how continuously you weld. Manual welding often has a fairly low duty cycle in practice, because of stops for slag removal and electrode changes.
Some power sources are designed to run from a range of supply voltages, often both single and three-phase depending on the model. This makes them easier to use in different premises, but it does not mean they can simply be plugged into anything.Check the data plate and manual for the supply voltage, phase, input current and the recommended fuse or breaker rating for the voltage you will actually use. Make sure the plug, cable and supply circuit match. The equipment should be installed and connected by a competent person following the maker's instructions, and the manual's fuse table takes priority over a rule of thumb. If in doubt, ask a qualified electrician before first use.