Duty cycle in welding and how to calculate duty cycle of welding machine?


What is Duty cycle for a Welding Machine?

In simple words, Duty Cycle for a Welding Machine refers to how long a welding machine will weld at a given current before it overload or overheat. Duty cycles are measured per 10 minutes and not for 1 hour or longer duration.  A machine if used with a 300 ampere current for welding @ 60% duty cycle will give an output of 300 amps for 6 minutes before overheating.  A cooling or rest period maintained for 4 minutes must then be observed. So, the machine can be used for 6 minutes every 10 minutes at 300 amperes.

Refer to the below picture for a practical understanding. Here, based on the data from the nameplate or rating plate of the welding power source. The machine minimum output is 30A & 15.5V and the maximum is 140A & 21V. So, the machine can give a maximum of 140 amperes current but if you wish to use this current the machine duty cycle is only 20%. This means, with 140A current, the machine can be run only for 2 minutes in every 10-minute cycle. The welding machine requires 8 minutes to cool down.

Similarly, the machine can be used for continuous operation with 60 amperes and 17V only.

As per the European Directive, number EN 60974-1, the time period for one complete cycle is 10 minutes.

Duty Cycle is spoken by most welding sales personnel and welding engineers while only a handful is aware of its actual meaning. So, understanding what it means, Its importance, and how it can affect a decision for welding machine purchase.

While buying a new welding machine, understanding the importance of the duty cycle can save future maintenance costs, help to increase production, and avoid wrong purchase decisions.

Duty Cycle is printed on the welding power sources nameplate (mostly front side or back side of the machine) and generally, you will see 20, 60%, and 100% duty cycles welding parameters.

Watch this video to learn how to read the Rating Plate or Nameplate of a welding power source.

How to calculate duty cycle of a welding machine?

Using this duty cycle formula you can find the duty cycle of a welding machine for an unspecified welding current & an unspecified duty cycle on the welding nameplate. Refer to the below formula for the duty cycle of a welding machine:

Duty cycle (%)= D/[( A/mA)*2]

Where: A = Rated Current at the required Duty Cycle

mA = Maximum Current at the required Duty Cycle

D = Rated Duty Cycle [%]

Example calculation:

A power source having a duty cycle of 60% at a rated current of 200Ampere. What will be the duty cycle at 250 amperes:

Solution:

Using the formula Duty cycle (%)= ( A/mA)2 x D, we will have:

Duty cycle of: 60/[(200/250)2]

= 37.5%

So, this formula is very helpful to find the value of the duty cycle for any unknown welding current which is not specified on the rating plate of the welding machine.

Meaning of 60% duty cycle

The duty cycle of 60% on the machine is most commonly highlighted by the machine manufacturer to show the maximum efficiency of the welding machine. Assume, a machine if used with a 300 ampere current for welding @ 60% duty cycle will give an output of 300 amps for 6 minutes before overheating.  A cooling or rest period maintained for 4 minutes must then be observed. So, the machine can be used for 6 minutes every 10 minutes at 300 amperes.

Why must a welding machine duty cycle never be exceeded?

Running a machine more than the stated duty cycle can ruin the welding machine easily. Duty cycles are limit for a machine. Using the welding machine above the stated rating will overload and overheat the welding machine. This will easily can burn the delicate electronic circuit of the machine. These electronic cards are quite costly and hence you will be billed for negligence.

Welder Duty cycle calculator

You can use the duty cycle calculator given below to find the duty cycle of a welding machine easily:

Importance of Welding Duty Cycle

The duty cycle has a direct relationship with the ambient temperature of the welding power source. With the current advanced welding power source with sophisticated electronic circuits which need control on temperature for normal working, a higher ambient temperature can make big difference. The duty cycle measured at 25 degrees and 40 degrees temperatures can be totally different as higher ambient temperature can interfere with the welding machine cooling system. One must keep this in mind especially while making decisions in hot weather countries like in middle east, African countries, and some places in the USA.

Knowledge of the Duty cycle can impact the right selection of the welding machine.

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