It is claimed by the advocates of this system that good results cannot be obtained unless current of ample volume and pressure be used. Current from power wires is generally inadequate. It is best to have a special dynamo of not less than 75 to 100 kw. For reasons given below, the current should be direct. Where the current supplied is alternating, a direct-coupled motor-generator is used to transform to direct current. The motor-generator coupling must be flexible to prevent the armature from burning out. This generator will be much the most expensive part of the apparatus - costing more than all the other mechanism.

Shunt Field with Rheostat

Fig. 13. - Diagram of Bernardos arc welder.

Direct current is much better and cheaper than alternating. As is well known, the greatest heat is found near the positive pole of the arc. For this reason the metal object to be welded is made the positive pole of a direct current. If it were the negative pole, more heat would be lost and the carbon from the pencil would enter the weld and harden the metal. While if an alternating current were used, some of the carbon would enter the hot metal, while the weld would not receive more than half the heat of the arc.