Here is a technical description of the ‘duty cycle’ that I have copied exactly
from a leading MIG welder user booklet:
Duty Cycle >Definition>
The duty cycle expresses a value of time during which
the welding machine can operate at a user defined current level within safe guidelines as legislated: e.g. X = 40% at I2 =
100 A. Current I2 = 100A for 4 units out of 10, i.e. 40%.
End of correct technical description,
& now you fully understand what duty cycle means!
Read that again, and then read my technical
Mark the welder’s technical description of ‘Duty Cycle’.
Almost all welding machinery for all welding process has a ‘usability rating’ called
the ‘duty cycle’.
The ‘usability quality’ of a welding machine is reflected by the value of the
The duty cycle really details just how long the machine can operate within a TEN minute
welding time without overheating or becoming damaged!
The whole 100% means the machine’s entire welding power output capacity.
The whole 100% is directly expressed as a time period of 10 minutes.
The value of the duty cycle ‘rating’ is normally expressed as a percentage of
anywhere from 0% to 100%.
The duty cycle value is then expressed as a percentage (part of) the 100%.
If your welding machine says ‘duty cycle =40% @ xyz amps’ this means that
out of a welding ‘on-time’ of only ten minutes, your welder can only safely weld continuously for 4 minutes
in every ten minutes , & if you exceed this 4 minutes, you will risk overheating or damaging your welder!
The ‘on-time’ that I refer to above is the actual welding time
where a welding arc is being produced.
The duty cycle is not relative to where your welder is only plugged in &
switched on, but not being used.
Read that again & get your head around the percentage of ten minutes part, then read on.
Where your welder is perhaps a DIY 100amp ‘welding output’ model, the duty cycle
also shows the usable welding current (in amps) that is available for the length of time as stated. It does not always mean
that you can weld on full power for four minutes!
There are legal guidelines that welding machine manufacturers should follow as regards the
display of the correct duty cycle rating.
But to confuse you further, the duty cycle is usually displayed as the welding
amperage available at 40% duty, or something similar, & on-line retailers often use this format.
If you are going to be needing your welding machine to earn your wages, you would not
want one that has a low duty cycle, as it will be stone dead inside a day.
You must be able to confidently select a welding machine that has very durable internal welding
transformer windings & associated parts.
My main 450amp 415v MIG welder that I have has
a duty cycle of 86% & I have only overheated it twice in as many years.
My smaller 350amp MIG has 82% duty cycle & has overheated once too often!
I have another collection of MIG welders that all have duty cycles of around the 60% level,
unfortunately they have ceased to function.
My main mobile 300amp MIG welder has a duty cycle of 100% & it has never even blinked
at any time & has over 5000hrs on the clock. Ok this is an industrial model that I had specially built at a ‘funny
money cost’, but I’m sure you get the picture here.
Always aim for the highest duty cycle rating that you can find if you need
your welding machine to operate all day every day.
You may not be into welding work or heavy fabrication that needs a major welding power source,
but just the same, you really don’t want to buy a welder that ‘cuts out’ every half an
hour, then have to wait another half an hour until it cools down before restarting your welding work, do you?
All good welding machines have overheating protection that shut down the transformer when
they get too hot, but if you do this several times your welder will quickly become an ‘expensive ornament’ in
The internal welding machine transformer that produces the high welding current
amperage with a low welding voltage, may have steel ‘transformer windings’ or copper windings.
The comparative cost of the welding machine is an immediate indication of welding transformer
quality when coupled with a high duty cycle.
When selecting an industrial welder that must earn & pay your wages for
years to come, always look for these quality features & do not skimp on the pennies when purchasing, as a repair warranty
is void if the thermal interlock overload cut-out switch has been ‘tripped’ at any point. (Don’t ask how
I know this).
Tip: copper welding transformer windings are the most durable quality
Another Tip: thermal overloads are easy to by-pass, so, when buying second
hand welders or generators, look at the actual coating of the transformer & the wires that exit the transformer. Any signs
of badly scorched or charred surfaces are a clear indication of excessive heat generation. There are photos here somewhere that
show what a good, nearly dead & very dead welding transformer looks like!
Remember that you want copper windings.
And another while I am on the subject: Do not be dissuaded by the fact that a second hand
MIG only has a dual wheel wire drive set up, as one of my best MIG’s has this, instead
look at the transformer quality & forget about needing a four wheel drive system!
& to help you out a bit more here, if you are going to be MIG welding
at 285amps all day & pushing 1mm solid wire for spray deposition, a 300amp MIG will really struggle unless
it is absolute top quality, & even then it may die on you, so always over spec & aim for a 400 or
450amp machine that will last forever & not need replacing next month!
If you are only going to run 1mm solid at say 200amps, then a 300A machine is fine for short
circuit, semi-dip & nearly full spray deposition will be available for short bursts here & there.
But as always with welding machines, the duty cycle is the key element in maintaining your
actual welding production profitability without having machine failures every week.
If you are an enthusiastic home user & only have 240v @ 16amps as an
available input supply (read my website), then you will now appreciate that to get about 120amps from your MIG, you will
need a machine with duty at around the 60% mark & it will most likely be rated at max welding current output of 200amps.
You may think that this is way too high for car bodywork & light fabrication work, but I can assure you that
this is the specification quality required for a proficient welder that enjoys his work!
Study the specs very carefully & always buy the best that you can possibly afford, just make sure that your electricity
supply can power it!
Inverter welding units are now very popular & I have a tiny portable Messer 240v 140amp
stick & tig inverter unit that I use for some site work when too far away from my main generator.
It has a 40%
duty cycle at 120 amps and it is a brilliant machine for its size.
This is the minimum spec of inverter that I find is usable for any length of welding, so if your prospective
new inverter is say only 25% duty cycle, please think carefully before purchase, as I have already killed many of the smaller
ones stone dead the same day!