1. GMAW Power Sources Rational Power Source Output
In order to have any electric arc welding process at a high level, the operator should have a base understanding of the type of power source that is being used to drive the welding process.
Power Source Output
All power sources used to perform the GMAW and FCAW process are of the Constant Voltage or Constant Potential output type.
Simply stated, constant voltage output sources are designed to deliver a set amount of delivered voltage during the welding process in an effort to maintain the welding arc.
Although all constant voltage output welding power sources are capable of delivering large surges of welding current (amperage), the output voltage remains constant.

2. Given their design, constant voltage power sources used to perform the GMAW process are often referred to as having a “self regulating” welding arc.
In order to maintain this self regulating arc, the following five items are necessary:
The proper voltage setting for a given type and size electrode.
Current going through the electrode (a good ground).
Appropriate wire feed speed to continuously replace melted electrode wire.
A proportional burn-off rate.
Welding action proportional to the welding (arc) voltage.
Power Source Types
There are three basic types of welding power sources used to provide constant current voltage welding output.
Transformer-rectifiers
This type of welding power source uses a transformer to step down the AC line power voltage to AC welding voltage and utilizes a rectifier to change the output current from AC to DC.

3. Engine Driven Generator
Inverters
This type of welding source converts the incoming AC power line from 60 hertz to 50 kilohertz.
The AC welding power is then supplied to a transformer/rectifier unit to create welding output power.
Engine Driven Generator
This type of welding power source uses a internal combustion engine to drive a generator which creates DC welding power.