Understanding Duty Cycle for Welding Machines

One of the specs we need to know about a particular welding machine is its duty cycle.  The duty cycle gives you an idea of how hard and how long you can run a welding machine before it overheats and shuts down.  Unfortunately at times we have issues with machines exceeding the duty cycle when it shouldn’t, or when we think it shouldn’t.

Although once in a great while a machine can have a faulty thermostat the main issue for a thermal overload is in fact that the duty cycle was exceeded.  Frustration sets in mainly because there is no detailed explanation about duty cycle.  We typically hear: “This welder has a 30% duty cycle at 150amps.” And although this may be correct it leaves out pertinent information such as welding voltage, ambient temperature, and proper ventilation.

Let’s take a quick look at the Millermatic 211:

Quick Specs on the Millermatic 211

Quick Specs on the Millermatic 211

Duty Cycle is the number of minutes out of a 10-minute period a welder can operate continuosly.

According the spec sheet for the Millermatic 211 as published on Miller Electric’s site this machine has a duty cycle of 30% at a rated output of 150A on 230VAC input power.  Most manufacturers do this.  They have a machine that can weld, as is the case with this one, up to 210 amps.  The name also suggests it (211), yet the rated output for duty cycle purposes is 150 amps.  If one hears that this machine has a duty cycle of 30% they may assume 30% at full output.  They would quickly find out that at 210 amps the duty cycle is much lower.

Per the definition of duty cycle stated above the Millermatic could weld continuosly, at 150 amps, for 3 minutes and must then rest for 7 minutes.  Duty cycles published are sometimes conservative and you may be able to push this a bit and get a few more minutes of welding.

So why is your welder cutting out before those 3 minutes if you are welding at 150 amps?

There are three factors that contribute to this:

Voltage – What is usually not considered is welding voltage.  The state duty cycle of 30% is at 150 amps is at 23.5 volts. However, if the we crank up the voltage to 25 volts then the duty cycle at 150 amps would be lower.  This can cause the unit to shut down after only 2 minutes.

Ambient Temperature – This is rarely shown on any spec sheet by any manufacturer.  Most duty cycles are based on an ambient temperature of 70F.  If the temperature in the shop is 100F and you are welding at 150 amps and 23.5 volts you may have a duty cycle that is much lower than the 30%. Remember, the machine is running a fan to stay cool, but the hotter the air is in the shop  the lower the cooling effect it has on the internal components.

Ventilation – If the machine is backed up against a wall this decreases the airflow generated by the fan.  Allow at least 10-12 inches of space between the unit and the wall. Without proper airflow the machine doesn’t cool as efficiently and this results in a lower duty cycle.

One last thing, for machines such as this one that can run multiple input voltages keep in mind the duty cycle is derrated the lower the input voltage. The machine above only has a 20% duty cycle running 90 amps on 110VAC.

Please note: I reserve the right to delete comments that are offensive or off-topic.

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18 thoughts on “Understanding Duty Cycle for Welding Machines

    • Tig machines are CC (constant current) and mig requires a CV (constant voltage) power source. There are machines that are multiprocess and can certainly do both. To determine the best one you need to consider the application. What is the base material, material thickness, production levels, available input power, etc. Can you provide some details?

  1. I just got a new machine. It’s rated at 220 volts 160 amps with a duty cycle of 25%. The scorce is 45 feeet away. I can’t find anyone who is willing to recomend a wire size. I don’t want to stress out my machine. Anyone willing?

    • What machine did you buy? Normally the owners manual should specify the size of the power chord. In some cases they will specify the size for given length. If you bought it used you may be able to find the owner’s manual online. Or, if you can find it because the manufacturer may no have this available you can search for a machine of a known brand (Lincoln, Esab, Miller, etc.) of similar size.
      The way to know the size is to know what the machine will draw. You can contact an electrical supply store and tell them you need an extension for 220V but you must also find out the maximum amperage draw (not welding amperage). They can then tell you exactly what size cable you’ll need.

  2. Hey,
    Thanks for this in-depth review. I need a welder machine and it should be good I have no idea about welder-machine.
    So I saw you write about this he said which one is better and mentioned something below Thank you for that.

  3. Hello,good luck with your mig welder mod, it should work good for the thinner metals like the barrow housing and the like. I am not sure of your knowege, be carefull with dc voltage,if it rises higher than expected could be real dangerous comeing off the caps,as DC voltage hangs on and dont let go,unlike ac that is safer, my mig welder has 6 caps,and a contious bleed resistor acrrost the caps at all times, so it pulls the high voltage down too safe level, directly after the caps serve there voltage stabilizing purpose.I had some 220 caps on my hho torch, and when i tested the caps for power,it sounded like a 22 pistol pop,zap, jolt, just glad i wasent the ground.The mig welder voltage should be under 30-40 open circuit voltage,much less dangerous, other than the caps.Let us know how it helps, i have a HF that may get the boost sometime.A bigger power fan will add more duty cycle too.

  4. I have some welding machines, miller Maxstar 210’s, that keep overheating and throwing codes. When I send them back to our shop for evaluation, they test out fine as if nothing is wrong. They even try and force an overheating and shut down condition, but with no success. We are doing production welding between 80 and 100 amps without consideration to duty cycles. The job site provides 440V input power. Our shop uses 220 volts to bench test and evaluate the machines. Is the duty cycle affected by the input power? Is it likely that the machines will consistently overheat with 440V input power without following a duty cycle, and will work steady with a 220V input power without following a duty cycle?

    • Duty cycle is always higher is you are running 3-phase than single phase. If you are in three-phase and you go from 220 to 480 the duty cycle doesn’t really change. However, the machine’s output will not be the same, meaning you can get more welding amperage with higher input power. A service shop is basically a lab environment. They can simulate loads (varying amperages, voltages) and in some cases weather conditions. But their power is always clean, they typically have no voltage spikes coming from other pieces of industrial equipment. Duty cycles are derrated the hotter it gets. So if the stated duty cycle is 40% at 200 amps for 70F ambient temperature it will be much lower if the temperature climbs to 100F.
      If the machine is against the wall it will overheat quite quickly (leave at least 10 inches of clearance to allow for proper air flow). Welding in a shop you can get a lot of resistance from your welding leads. If your weld and work cables are frayed you will be losing voltage. So to get the right arc voltage the welder will have to turn up his machine. In a service shop they use a load back which always has leads in perfect condition. This is necessary because they also calibrate equipment.
      Another thing. When welding, there will be significant changes to voltage (if stick or tig welding) due to the welder moving the electrode in and out. These can increase the voltage significantly. As voltage goes up duty cycle goes down. In stick and tig you set up amperage. So if the machine is 40% at 200amp it will also be at a stated output, say 17V. BUt if you pull a long arc you may increase your voltage to say 20 volts. The duty cycle at that point goes way below 40%. Hope this helps.

    • Hello Freddy, this depends on your input power and the size of machine that you get. You can go with a heavy industrial machine that has 100% duty cycle at 450 amps or go with a light industrial that is only 40% at 250. Naturally the higher the capacity (amperage) the higher the cost, assuming you stay with the same technology. The product literature for all welding machines of reputable manufacturers will state the duty cycle.

  5. Okay here goes, I know how to weld however this duty cycle has me baffled, I want to be able to weld 1/8 th inch steel with a 140 amp lincoln or if need be a larger wire feed not exclusive to a lincoln, is there a formula I can use to find what amperage I should be using? As I don’t really like to stop and wait. Any help would be very appreciative Thank you

    • Hello Tom, unfortunately if your machine is shutting down due to exceeding its duty cycle there isn’t much you can do provided you are doing things correctly. If you are welding 1/8″ thick steel, whether you are joining a T-joint or a lap-joint, you should be running a procedure at or around 300 inches a minute wire feed speed and 22 volts with an .030″ solid wire. This procedure produces about 130 amps which is about the maximum output of the machine. with Power Mig 140 (110VAC input voltage).
      The Power Mig 140C has a 20% duty cycle at 90 amps. So at 130 amps your duty cycle is at around 10% or less. So not a whole lot of welding time. So here is what you can try:
      1. Lower your wire feed speed to about 275. Assuming you are using .030″wire this will lower the amperage to 115 amps. This will buy you a bit more welding time before the duty cycle is exceeded. Don’t go much lower than this or you will risk lack of fusion.
      2. Probably your best bet is to go with an .035″ flux-cored wire. Your machine should have come with a one-pound spool of NR-211. Because this wire is tubular it requires less amperage to achieve similar penetration.
      3. Another tip, make sure you are not overwelding. On 1/8″ material your fillet welds should certainly not exceed 1/8″ legs. Welding smaller does not affect your duty cycle, but you’ll be able to weld more (inches of joint) before your machine cuts out.
      4. Lastly, as you mentioned in your comment, you can go to a bigger machine such as the Power Mig 180. If you have an electric dryer plug it into that outlet as it typically will have a 30-amp breaker. This unfortunately means spending more money on a bigger machine.

      Now, if your problem is that you are tripping the breaker instead of the machine overheating, try going to a 20-amp breaker or even 30-amp.

      Please provide more information if you can. What is your WFS and Voltage setting. This machine does not have a calibrated knob so you’ll need to feed the wire for 6 seconds, measure it and multiply that measurement by 10 to get inches per minute. Also, how long (inches or time) are you welding before the machine quits? Hope this helps.