In many ways, when you purchase a welding power source you have to make sure that you look at all of your options, because there are a few of them. You have to make sure that the piece of equipment you purchase has enough juice, is efficient, and fits all of your needs. To speak more clearly, the variables that come into play when you choose a power source are:
- The current you’ll need
- Level of convenience you need
- The power available to use
- How much you’re willing to spend
- The process/es used: You’ll figure out the process/es to use when you know the base materials you’re going to use.
3 General Power Source Types for Welding
AC Transformer
Transformers are electrical devices that use induction to pass AC signal between circuits (they typically change the voltage and electric current while doing so).
AC/DC transformer rectifier
AC/DC transformer rectifiers are electrical devices that converts AC (alternating current), to DC (direct current) through a process called rectification.
DC generator and inverter
An inverter is a method using a direct current (DC) to produce an alternating current (AC). They draw power from sources such as solar panels and use electronic circuits to turn / “invert” the DC into an AC.
Below are a couple welding processes and the typical power source used
MIG Welding Power Sources
For most MIG welding direct current, constant potential power sources are used. MIG welding uses power sources offer the arc (when welding) a constant voltage. The voltage then determines the arc length.
When there is a sudden change in arc length or wire-feed speed the power source you use will increase/decrease the current. This change will either cause the current to increase or decrease depending on the change in arc length (this also effects the wire burn off rate). The burn off rate will actually adjust automatically to restore the original length of the arc.
With that, if you want to make a change in the arc length you can make a permanent change in the output of your power source.
Other Considerations
There are a few variables that must be taken into consideration so you can control things such a spatter, heat, etc.
These variables are:
- Slope: The slope of the power source refers to the way an increasing current cause output voltge to decrease. The slope of the power source isn’t the slope of the arc system.
In MIG welding the slope is used to limit the short circuit current which helps reduce spatter when short circuits between the workplace and wire electrode are cleared. Greater slopes have lower short circuit currents and less spatter (with limitations).
- Inductance: When inductance is introduced to a weld it helps to reduce spatter in the weld.
- Voltage: The Arc voltage is the voltage between the workplace and the end of your wire. You cannot read arc voltage on your voltmeter because of voltage drops you encounter in your welding system.
Arc length or welding voltage plays a large role in choosing which type of metal transfer chosen. For example, short arc welding needs much lower voltages compared to spray arc welding which requires higher voltages.
TIG Welding Power Sources
TIG welder power sources can actually be either AC or DC – however, in both types the output is called drooping/constant current. This means that the welding current and arc voltage relationship has a constant current for any power source setting.
Length of the arc has a direct relationship with consistency of the welder’s ability to hold the torch above the workpiece. Not only that, but there is also a relationship between arc length and arc voltage – higher voltage means you have a shorter arc and vise versa. TIG power sources are designed to have a lower range of current as well as a reduced variation on changing voltage.
DC Power Source
DC power sources produce a concentrated arc with the majority of it’s heat being placed in the workpiece, making it a great power source for welding. Arcs with their cathode roots on the electrode result in little cleaning of the workplace surface.
AC power source
Materials such as aluminum have an oxide film on their surface, which means that an AC power source must be used. When you switch between negative or positive polarity, the periods when the electrode is positive both cleans the surface and removes the oxide.
Shielded Metal Arc Welding Power Sources
Manual Metal Arc welding or Shielded Metal Arc welding needs a power source that is capable of giving a constant current even if the arc experiences voltage changes due to small changes in the length of the arc.
Submerged Arc Welding Power Sources
SAW can be operated with either an AC or DC power source. AC is supplied by a transformer and DC is supplied by a transformer-rectifier. The current for a single wire will range from, at a low point, 200A (1.6mm diameter wire) to around 1000A (6 mm diameter wire). Generally speaking, welding is usually done on a thick plate where single wires are normally used over a limited range of 600 to 900A, with twin wire systems operating between 800 and 1200A.
