Figure 7-1.A 300 amp ac/dc portable welding
VOLT. A volt is the force required to make the
current flow in an electrical circuit. It can be
compared to pressure in a hydraulic system. Volts are
measured with a volt meter.
The power source used in arc welding is called a
welding machine or a welder. Three basic types of
welding machines are presently in use: motor-
generators, transformers, and rectifiers.
CHINES. These types of welding machines are
powered by electrical, gasoline, or diesel motors. The
diesel and gasoline motors are ideal for use in areas
where electricity is not available. Portable gas/diesel
welding machines are part of the equipment
allowance for Naval Mobile Construction Battalions.
These machines usually have the capability of
generating alternating or direct current. On the
newer machines, when you are welding in the direct-
current mode, the polarity can be changed by turning
a switch. Some of the older machines require
reversing the cable connections. One of the
advantages of a direct-current (dc) welding generator
is that you have the choice of welding with either
straight or reverse polarity. The welding machine, as
shown in figure 7-1, consists of a heavy-duty, ac/dc
300 amp generator powered by a diesel engine. The
generator is also capable of producing 3 kilowatts of
60 cycle ac power.
Welding machines are made in six standardized
ratings for general purposes and are listed as follows:
Figure 7-2.An ac arc-welding transformer.
1. Machines rated 150 and 200 amperes30 volts
are for light-shielded metal-arc welding and for inert-
gas arc welding. They are also for general-purpose
jobs or shopwork.
2. Machines rated 200,300, and 400 amperes40
volts are for general welding purposes by machine or
3. Machines rated 600 amperes40 volts are for
submerged-arc welding or carbon-arc cutting.
WELDING MACHINES. Practically all the
alternating current (at) arc-welding machines in use
are the static-transformer type, as shown in figure 7-
2. These types of machines are the smallest, least
expensive, and the lightest type of welders made.
Industrial applications for manual operation use
machines having 200, 300, and 400 ampere ratings.
Machines with a 150-ampere rating are used in light
industrial, garage, and job/shop welding.
The transformers are usually equipped with arc-
stabilizing capacitors. Current control is provided in
manufacturers. One such method is an adjustable
reactor that is set by turning a crank until the
appropriate setting is found. Another method is by
plugging the electrode cable into different sockets
located on the front of the machine.
One major advantage of ac transformers is the
freedom from arc blow, which often occurs when welding
with direct-current (dc) machines. Arc blow causes the arc
to wander while you are welding in corners on heavy
metal or using large coated electrodes.