The duty cycle is the percentage of time a welding machine can be used continuously. Most SMA welding machines cannot be used 100% of the time because they produce some internal heat at the same time that they produce the welding current. SMA welders are rarely used every minute for long periods of time. The welder must take time to change electrodes, change positions, or change parts.

The duty cycle of a welding machine increases as the amperage is reduced and decreases as the amperage are raised. Most SMA welding machines weld at a 60% rate or less. Therefore, most manufacturers list the amperage rating for a 60% duty cycle on the nameplate that is attached to the machine. Other duty cycles are given on a graph in the owner’s manual.

A 60% duty cycle means that out of every 10 minutes, the machine can be used for 6 minutes at the maximum rated current. When providing power at this level, it must be cooled off for 4 minutes out of every 10 minutes.

Note: The manufacturing cost of power supplies increases in proportion to their rated output and duty cycle. To reduce their price, it is necessary to reduce either their rating or their duty cycle.