Question about duty cycle

   / Question about duty cycle #1  


Elite Member
Apr 21, 2012
Cascade Mtns of WA state
Kubota B-series & Mini Excavator
I've seen "duty cycle" mentioned as if its a important consideration for a welder (even for newbies).

I hardly ever have to weld more than a few inches (6" ?) at a time, then I pick up a grinder or do some fitting. Cut stuff, drill holes. Or screw around. But my welder always gets time to cool down.

Yesterday I had a project where I was welding 1 x 1/8" x flatbar doublers on to increase the bending section of my brush fork tines. I decided to fit and tack everything, then go and weld continuous (as possible) until the machine shut down. I am using a Miller Multimatic 200, which has a 20% duty cycle. It's rated for 3/8" thick steel, and I had it set for 3/16" thick. When I bought it they said it will weld at full power for 2 minutes then may require 8 minutes cool down.

At this less-than-full power setting, I welded for 25 minutes straight, only letting go of the trigger for enough time to move to the next weld, and flip the device over once. It never missed a beat. Except I was pretty beat after 147 inches of weld.

I don't know how much longer I could have gone myself. My conclusion is that the duty cycle of my Miller MultiMatic is certainly "sufficient" for my usage. So here's my question, why would someone (non-pro welder) think a 20% duty cycle is insufficient?



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   / Question about duty cycle #2  
It 'sounds' too low but I have the same 20% duty on my 211 whether on 110v or 220v. I think it really just boils down to how much 'serious' true welding time you are putting in and where time is money. I am pretty dang sure the way I dink around, I will never need a higher duty cycle and capacity welder. I could probably more assuredly say that I probably don't need the capability I have now. Not complain'n.
   / Question about duty cycle #3  
I can't ever remember having a duty cycle problem with a welder. When member here roadhunter had his 120-volt Mig machine shipped to me I did an endurance test on a 15-amp breaker.

In the late 1980s when we built the Alaskan ferry terminal in Bellingham. I got stuck welding down the pre-cast concrete deck panels. I rented my Miller Trailblazer 55D to the company. I was running little over 500-amps, burning 70-pounds of wire a day. Making 6 on 12 welds. Machine never missed a beat.:cool:


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   / Question about duty cycle #4  
Well, this has come up before - but 20% duty cycle at full power, rated at 100deg Fahrenheit, will improve with a lower ambient temp.

With my brothers millermatic 130 we overheated it on a summer day several times before getting pissed and quitting - told him I'll just bring one of mine over instead.
(He ended up selling it because it pissed him off too many times by shutting down and/or popping breakers).

My first stick welder, a 225/140 AC/DC popped a diode when I ignored duty cycle wide open on DC tig.

Naturally duty cycle increases when less than wide open - now I like my machines to be 50-60% duty cycle in the ranges I normally weld in since I doubt I weld more than that in a given time period.

My little century/craftsman mig will overheat and weld like crap, or pop fuses, in the summer - but welds much longer in the winter (no thermal safety on it).

So it's just a personal choice - I believe a machine will last longer when run in their mid range instead of wide open, so I over size the machine slightly - other people don't follow this method.

Industrial machines are built different than home owner size machines and are often 100% duty cycle all the way to max amperage - so over sizing wouldn't be needed.

Trailblazer 55D shouldn't even be in this discussion with a multimatic 200 in my opinion - maxes out at 450 amps and has crazy high duty cycle :)

It's like comparing a .38 revolver to a 50 cal rifle and trying to draw similar conclusions :laughing:

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   / Question about duty cycle #5  
I think duty cycle equates to a much more robust machine with larger wiring and cooling fans. While you may not need to weld more than 20% of the time, a machine with 60% or higher would likely last much longer than a 20% duty cycle machine when doing the same work.

If you compare these to say a gasoline engine, which would last longer a 10 HP running at max power (100% duty cycle) or a 20 HP running at 50%. I think we can all agree that the 20 HP machine would last much longer. I think that is the same with electric motors or transformers.
As a bonus, the higher duty cycle machine would supply higher amps when/if needed where a lower rated machine would conk out in a few seconds of use.
   / Question about duty cycle #6  
I know that when I used the Campbell 70 amp 110 volt stick, it had a 10% duty cycle at 70 and a 20% at 50 amps. It was very easy to exceed the 10%. I burnt out the thermal protection switch, and after that you had to make your self stop when you smelt rubber burning on the wires.
   / Question about duty cycle #7  
The thing about duty cycle is largely a part of marketing. Many times a "higher" duty cycle is advertised on a machine at a point that is considerably below the maximum output. Be sure to check and see where the duty cycle is advertised. Having a 35% to 60% duty cycle may not always be at the maximum output. That is frequently done even on name brand machines, especially MIG welders. And not all machines are equipped with a duty cycle (temperature) limiting device which will interrupt current flow if it is exceeded. You are really on your own to keep it within the limits...nothing is going to jump out and grab you to say "Duty Cycle limit reached". Sometimes nothing special is going to happen the first, or second or even third time the duty cycle is reached or exceeded on a machine, especially on machines that don't have these limiters. But you will notice a slow degradation over time if nothing immediate happens.

It's best to be aware of what temperature the duty cycle is rated for too of course, but more importantly I believe is at what amperage it is rated for. Of course lower amperage means better duty cycle and it can climb rapidly the lower you go, but on the flip side, it can diminish rapidly the higher you go.

As far as what industrial is or is not, very few machines these days have 100% duty cycles at maximum amperage. Here's a blurb from Miller's site about Duty cycle. Notice their classification of "light industrial". lol
Miller - Help Me Choose - What's Duty Cycle
   / Question about duty cycle
  • Thread Starter
Good example Mark, I think "Light Industrial" covers 99.9% of everything that ever been done on TBN! I'm glad nothing kappened to my MM200 as the self-policing was non-existant. I probably wont do it again, actually it was to strenuous, and weld quality sufferred too.

Yes Dave I remember you describing that situation. I think something was wrong there. Having used a Miller 130 for 8 years I think the machine deserves a repeat test before that conclusion. Haven't found that problem described elsewhere on the internet. Its a good machine and whoever bought it possibly scored a good deal.

Pretty well established that a 120v machine at power settings to weld 3/16" is right on the edge of popping a 15A supply breaker, and higher is more likely. 20A supply is necessary for the higher settings. If you're running at max power often, and if time is money (professional use) then we all know there exists larger eqpt for that, just spend more money (and unplug the dryer)! Or hire a pro. But as Mohammed says "At TBN, we're Build-it-Yourself" :D

But its been quite a few months since I read your note Dave and in that time haven't seeing anyone else having duty-cycle problems. Haven't even seen it from the 10 percenters. Just never hear it, other than the 15A supply issue. And isn't it a feather in a welders cap to outrun his machine? So there is a lot of motivation to report such a thing and I ain't seein' it (just once). So I'm ready to say duty cycle is just a "distraction" for a hobby/maintenance discussion.

But I could be wrong,,,,, :D
   / Question about duty cycle
  • Thread Starter
Oops had my post 'in work' during breakfast while PaulHarvey reports a problem with a Century 110v stick welder.
   / Question about duty cycle #10  
I think the closest I've had a problem with duty cycle. I went down to Hoquiam for an addition on a saw mill. Most of the machinery was already installed. The superintendent wanted me to start welding everything down. All he had was a little Lincoln weldnpower, and 5/32" jet rod. I told him he needed to rent a bigger welder. His reply was "get to work"! About 2 1/2 weeks later the machine was puking oil out the exhaust pipe! He rented me a bigger welder!:laughing: