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What does Duty Cycle mean in Welding

Thursday, 17th May 2018

This is a common question.  Essentially, Duty Cycle is a measure of how long a welder will operate for before it overheats and cuts out.

If you’re more of a Watcher than a Reader, you may prefer a Video Explanation

There are 3 key bits of data to Duty Cycle figures:

Amps, a Percentage Figure (%) and the Ambient Temperature the machine was tested in.

Unfortunately, whilst most manufacturers will state the first two figures, they often don’t state what the ambient temperature was when the test was carried out and this is actually a key piece of information! (more on this later).

An example of Duty Cycle data might be:

200amps @ 30% @ 40⁰C

This breaks down as follows:

200amps is what the machine was delivering during the test

30% is the percentage of the work period that the machine continuously delivered 200amps before overheating and cutting out. (in the UK a work period is defined as 10 minutes)

40⁰C (104⁰F) is the ambient temperature of the room when the test was carried out.  So the machines fan is cooling the machine with air that is at 40⁰C

What do these Duty Cycle numbers mean?

In our example, the machine delivered 200amps, for 3 minutes (30% of 10 minute work period), in a temperature of 40⁰C, before overheating and cutting out.

Clearly these figures are pretty specific and hardly anyone is ever going to match all the numbers.  For example, when is it ever 40⁰C here in the UK????  Clearly if the machine is being used in colder temps, the runtime (%) will increase.  Which is why it annoys me that a lot of manufacturers don’t state the ambient temperature the test was conducted in.

Here in Europe, 40⁰C (104⁰F) is the norm, BUT this is not mandatory and some manufacturers will carry out tests in 25⁰C (77⁰F) or even 20⁰C (68⁰F), which, in my view, is a bit naughty because a lower temp will make the % figure look a LOT better than a machine that’s tested in 40⁰C (104⁰F).  So beware!!!!!


The point of these numbers is to compare machines.  It’s a bit like comparing car fuel consumption, no one ever gets the Miles per Gallon the manufacturers claim the car will do, but you can use the numbers to compare makes/models.

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