Welder duty cycle, explained as minutes of arc per ten
Duty cycle is the share of a ten minute window a welder can run before it must cool. How to turn the percentage on the badge into minutes of arc you can use.
The big number on a welder is output amps. The number that decides how your Saturday goes is duty cycle, and it is usually printed much smaller.
Duty cycle is the share of a ten minute window that a welder can run at a stated amperage before it has to stop and cool. A 20 percent duty cycle is two minutes of arc (the arc is the electrical discharge that melts the metal) and eight minutes of waiting. Multiply the percentage by ten and you have minutes of arc per ten. That is the only arithmetic involved.
| Duty cycle on the badge | Minutes of arc per ten | Minutes cooling per ten |
|---|---|---|
| 20 percent | 2 | 8 |
| 30 percent | 3 | 7 |
| 40 percent | 4 | 6 |
| 60 percent | 6 | 4 |
| 100 percent | 10 | 0 |
The percentage means nothing without the amperage
Duty cycle is always rated at one specific output. A machine sold as a “140 amp welder” is not rated to run 140 amps at its badge duty cycle.
A worked example from published specs. The Hobart Handler 140 spec sheet (stock number 500 500, copy hosted by Northern Tool, checked 2026-09-19) lists an output range of 25 to 140 amps. Its rated output is 90 amps at 19 volts DC, at 20 percent duty cycle. So the published promise is two minutes of arc per ten at 90 amps. What it gives at 140 amps is on the duty cycle chart in the manual, and it is less.
The same pattern shows on a larger machine. The Hobart Handler 210 MVP manual (OM-260 274, read on ManualsLib, checked 2026-09-19) rates it at 30 percent at 150 amps on 230 volt input, and 20 percent at 90 amps on 115 volt input. Same machine, two different products depending on the outlet. We cover that split in 110v vs 220v welders.
| Machine and input | Rated output | Duty cycle | Minutes of arc per ten |
|---|---|---|---|
| Hobart Handler 140, 115 V | 90 A | 20 percent | 2 |
| Hobart Handler 210 MVP, 115 V | 90 A | 20 percent | 2 |
| Hobart Handler 210 MVP, 230 V | 150 A | 30 percent | 3 |
When you compare two machines, compare duty cycle at the amperage you will use. A machine rated 60 percent at 100 amps and one rated 20 percent at 200 amps are not directly comparable from those two numbers, and we do not convert between them. Read each manual’s chart.
The rating assumes 104 F air
IEC 60974-1, the international standard for welding power sources, rates duty cycle over ten minutes at 40 C (104 F) ambient. Miller states that it rates its machines at that temperature. Not every import brand states the test temperature at all. When a listing gives a duty cycle with no temperature and no standard named, our spec tables mark the basis as “Not published”.
Two consequences. A closed garage in August can be hotter than the test, and the machine will cut out sooner than the badge says. And a rating made at a lower temperature flatters the machine, which is why the basis matters as much as the percentage.
What happens when you run past it
On current machines a thermostat opens and the output stops. The fan keeps running. Hobart’s manuals say to wait fifteen minutes, then reduce amperage or duty cycle before welding again. They also state that exceeding duty cycle can damage the unit or gun and void the warranty. Leave the machine switched on while it cools so the fan can do its work.
How much duty cycle do you need?
Most hobby welding is short. You tack, check the fit, weld a few inches, chip, grind and reposition. For that pattern, two or three minutes of arc per ten at your working amperage is often workable. Long continuous seams on thick plate are different, and a 20 percent machine will spend most of that job cooling.
Duty cycle is a thermal limit on the machine. It says nothing about the quality or strength of a weld. Structural work, trailers and hitches, lifting gear and anything that holds pressure belong to a certified welder.
Check the wall before the badge
Arc time is one half of “will this machine work for me”. The other half is whether your circuit can feed it. A 90 amp rated output already draws 20 amps from a 115 volt outlet on the Handler 140 (more machines in welder amp draw). Start with what size breaker a welder needs.
Frequently asked questions
What does a 20 percent duty cycle mean on a welder?
It means the machine can weld for two minutes out of every ten at the stated amperage, then needs eight minutes to cool. The percentage is always tied to a specific amperage. A figure quoted without an amperage tells you nothing.
Is duty cycle measured over ten minutes or an hour?
Ten minutes. The international standard for welding power sources, IEC 60974-1, rates duty cycle over a ten minute window at an ambient temperature of 40 C (104 F). Hobart's own manuals define it the same way: the percentage of ten minutes the unit can weld at rated load without overheating.
What happens if I exceed the duty cycle?
On most modern machines a thermostat opens, the output stops and the fan keeps running until the machine cools. Hobart's Handler manuals say to wait fifteen minutes. The same manuals warn that exceeding duty cycle can damage the unit or gun and void the warranty, so the cut-out is a backstop and not a working method.
Does a hot garage reduce duty cycle?
The rating assumes 40 C (104 F) air. In hotter air the machine reaches its thermal limit sooner, so you get less arc time than the badge states. In cooler air you may get more. Manufacturers do not publish a figure for temperatures above the rating, so we do not give one.
Can I calculate duty cycle at a different amperage?
Formulas for this circulate online, but they are estimates. Most owner's manuals print a duty cycle chart that shows the rated percentage across the output range. Read the chart for your model. If the manufacturer does not publish one, treat the duty cycle at other amperages as not published.
Is a higher duty cycle always better?
Only when it is quoted at the amperage you will use. Sixty percent at 95 amps and 20 percent at 90 amps are both published ratings for 120 volt Lincoln machines, and the first gives three times the arc time at similar output. A high percentage quoted at a low amperage, or with no amperage at all, tells you much less.