As far as duty-cycle goes, also check the specs on the machine for the environmental conditions they measured this in.
Many machines may list something like 20% duty cycle at 100%, but the small print may show that this is with an ambient temperature of 40C/104F! Especially the 'name' brands will have this info buried somewhere in their docs.
This can then be thought of as the 'worst case' scenario so that duty-cycle is wht you'll be able to reach pretty much always.
Once the ambient is (much) lower then as a result the duty cycle also increases, so you may well hit 50% duty cycle at 100% when the ambient air is 15C/59F.
With inverters the duty cycle limit is basically heat-soak. Cooler air helps the electronics stay cool and run longer.
Of course machines with 100%/100% duty cycles also work around this problem by using 'oversized' rectifier setups that could (in theory) put out much more amps at a lower duty cycle, but they limit them to a certain level where the heat produced never exceeds the cooling capacity in the unit, so you get a 100% duty cycle at any setting.
More costly, but for full time production setups running machines in the top 20% of power most of the time it can be suitable.
If you want to you could do an experiment and open up the machine and attach a thermocouple to the fins of the main cooling blocks on the power units. Close it back up and run it at full power with that and see how hot it needs to be before the machine shuts down. May well be quite a high temperature that you'll never reach in normal use anyway.
I have a pretty basic Oerlikon CITIG 1500AC/DC (which I modded to take a pedal) and even though it's 30% duty cycle at 150A (max) I never managed to hit that with normal use.
I did measure with an external amp-meter that it does hit (and actually exceeds a little) the rated 150A on the cable to the torch. (an interesting test by itself even to see how linear the pedal response is, but not related to this..)
Bye, Arno.
