Power Sources for Shielded Metal Arc Welding (Stick)
The first part of being successful at stick welding or shielded metal arc welding is to make sure that we have a power source that is capable of doing the work. To perform shielded metal arc welding we need to have a constant current power supply. This is a type of machine that produces welding power that has a decrease in voltage as the amperage increases. some people call this a drooping slope machine, in reference to the volt-amp curve produced by charting the machine output on a graph.
One way to identify a constant current power source is when the main knob on the face of the machine controls amperage. If you see no knob on the machine to adjust amperage but you can find one that adjusts voltage, you got yourself a constant voltage power source. A constant voltage power source is generally used for wirefeed processes like MIG and flux core arc welding and we will talk about those in another article. We can make MIG welds with the constant current power source provided we have the proper voltage sensing wire feeder, like the LN-25 from Lincoln Electric.
Understanding that we need a constant current power source for stick welding now we can consider what type of variations are available for constant current power source.
An engine driven machine is one that is powered by either a gasoline or diesel internal combustion engine. The engine rotated generator produces the welding power. These types of machine are great when we do not have local power from our utility. This is the type of machine that we want if we are going to do stick welding or shielded metal arc welding in a remote location, possibly away from workshop. The engine generally runs in an idle mode and then ramps up and increases RPM when we strike the arc and start welding.
Unlike other welding machines that plug into the wall, this type of machine requires additional maintenance to care for the engine, that's the heart of the power source. Also, this is not the type of machine we want to use if we have to weld and the power source needs to be located indoors. The exhaust from the engine will spoil the breathing and and local atmosphere rapidly.
If we have the ability to plug into the wall and get power from the local utility our options are little bit more varied.
The most basic type of welding machine powered by electricity is a type called the transformer. A transformer machine takes a high-voltage low amperage power from the utility and transforms it into high current low-voltage power we use for welding. This machine generally will have a large transformer inside and is also larger and heavier than a comparable inverter machine. These types of machines generally produce only AC power.
There is another type of machine that is very closely related to the transformer, the transformer-rectifier machine. A transformer-rectifier machine is a transformer machine that has a rectifier circuit installed in it to allow the machine to produce DC power from the AC input received from the utility. Depending upon how we have the cables configured to the output lugs on the front of the machine we can produce welding power in the DC mode either with the electrode positive or electrode negative. Which polarity we might select will depend upon the job we're doing the position were working in the electrodes we have selected to use.
Inverters seem to be the current trend in the welding industry. Inverter machines eliminate the large heavy transformer and replace it with electronic circuitry and printed circuit boards. Most inverter machines are capable of producing both AC and DC power. One characteristic of the inverter machines are that their generally smaller in size and lighter in weight than the comparable transformer counterpart. Inverter machines are also capable of changing the waveform and the frequency of the output power in ways that the transformer machines are not capable of doing. Longevity welding along with other manufacturers have pursued this technology. This looks like the future of welding power sources.
Longevity has a wide range for welding machines to fit all your welding needs. The Stickweld 140 is a great machine for doing shielded metal arc welding around your shop. Check out the Longevity website (www.longevity-inc.com) or YouTube channel (www.youtube.com/longevitywelding) for more details and information about welding.