There are various types of power source, but what is the difference?

Single-phase AC type is generally used in stationary welding machines because of its simplest structure and low cost, and it is capable of welding most of the objects to be welded.
MFDC type is often used when weight reduction is required, such as for a servo spot gun. Converting commercial frequency (50/60Hz) to a frequency more than 20 times makes it possible to downsize the transformer core, which enables the welding transformer itself to be smaller and lighter. However, as the secondary current becomes difficult to flow when the frequency increases, a rectifier is placed on the secondary side of the transformer to convert the alternating current to a direct current.The MDFC type may be selected because it can alleviate expulsions for thin-plate welding and because the weld time can be set more finely in millisecond increments, in comparison to the cycle increments of the AC type.
In the case of the capacitor type, it is possible to reduce the power-supply capacity because the capacitor banks are charged first then discharged all at once upon welding.Therefore, it is adopted when power source situation is unstable or when a large current is required, such as a large projection welding machine.Compared to other power source, it can weld at a high current in a short period of time with less thermal impact on the surroundings, resulting in less post-weld deformation or residual stress.Today, the capacitor type is also increasingly used for projection welding of nuts and bolts to hot stamping materials.
In addition, there are other power sources such as AC inverter type, single-phase rectifier type, three-phase rectifier type, and three-phase low-frequency type. Selection is made by considering requirements and various parameters for the object to be welded.