Arc Welding Machine Power Source

For striking a welding arc it is essential to have the desired current in the welding circuit. Depending upon the type of current required (ac or dc) it may be obtained from the following sources.

• A welding machine or frequency changer (for ac welding machine).
• A dc generator of a welding rectifier (for dc welding).
• The no load or open circuit voltage (OCV) should be high enough to strike an arc, but not so high as to endanger the welding operator, for example, for a 2000A transformer the OCV should not be over 90 volts through for lower currents of say upto 600A OCV may be upto 100 volts.
• With direct current, the OCV must be at least 30 to 35 volts while with alternating current it should not be lower than 50 to 55 volts. An open welding arc can be sustained at 18 to 40 volts.
• The minimum voltage for arc ignition is 25 volts which must be attained within 0.05 second for the maintenance of a stable arc.
• The power of the welding source should be sufficient to provide the required welding current.
• It should be possible to tap the desired current within the available limits either in infinite steps 9stepless regulation) or in a large number of discreet steps (stepped regulation).
• The voltage of the power source should adjust itself rapidly with the change in arc length.
• The short-circuit current must be within limits of safety for power source windings.
• It should have output characteristics which match the arc characteristics.
• It should incorporate a low voltage supply for the operation of auxiliary units.
• It should have a desired duty cycle and provide the required volt-ampere characteristics.
• It should be light in weight, small in size, low in cost, convenient in service and easy to maintain.

by Ramakant Keshav Sharma

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