780 Agricultural Mechanics and Technology Systems
Copyright Goodheart-Willcox Co., Inc.
Transformer Welders
A transformer welder is the oldest type. It directs the high voltage
supplied by the power company through a primary coil wrapped around
an iron core to create a magnetic fi eld. A secondary coil is passed through
the magnetic fi eld, inducing a stepped-down or lower voltage. The actual
welding current is produced by the secondary coil. The output from a
transformer is AC power. Welding machines that incorporate a bridge
rectifi er in combination with the transformer can produce DC welding
current output. A rectifi er is an electrical device that converts AC into
DC by causing the current to fl ow through the rectifi er in one direction
only. Transformer welders are heavy machines. They are available in many
confi gurations ranging from the expensive, high-amperage, multipurpose
units used in industry to simple, low-amperage, AC machines sold to
home welders.
Inverters
A second type of welding machine uses an electronically controlled
inverter power source to produce a usable welding current. An inverter
passes single-phase or three-phase AC power through a bridge rectifi er to
create a DC current. The DC current is electronically broken into very high-
frequency AC current, which is then passed through a small, effi cient transformer
to produce low-voltage, high-current AC power useful for welding. An
additional bridge rectifi er and an inductor are used to create smooth
DC welding output. Inverter welders are lightweight and produce a smooth
welding arc. Inverter power supplies provide AC and DC welding options.
Both transformers and inverters are most often powered by common
AC electricity. Portable welders are available with their own generators
or alternators, which are powered by internal combustion engines.
These portable welders are commonly used in remote locations, such as
construction sites or pipelines. They typically provide power for welding
current as well as for other operations.
Goodheart-Willcox Publisher
Figure 29-4. SMAW power sources are available in many different designs.