Figure 7-1.-A 300 amp ac/dc portable welding machine.

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.

Power Source

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.

MOTOR-GENERATOR WELDING MACHINES. - 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 amperes - 30 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 amperes - 40 volts are for general welding purposes by machine or manual application.

3. Machines rated 600 amperes - 40 volts are for submerged-arc welding or carbon-arc cutting.

ALTERNATING-CURRENT TRANSFORMER 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 several ways by the welding transformer 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.