Reply to Thread

Re: Duty cycle

Okay, thanks for all the info guys.

Re: Duty cycle

Re: Duty cycle

Originally Posted by SweetMK

May I throw in the fact that when the air is humid, the moisture pushes the air molecules apart,,
so, you have less air flowing through the machine to cool it.

This came up when discussing airplane takeoffs.
When the air is high humidity, the plane engines must rev higher to get enough lift to make the plane take off.

So, now we need a humidity sensor on the welding machine.
If the humidity increases, the welding machine will have to speed up the cooling fan,,,
to maintain the same duty cycle,,,

Humidity transfers heat, that is why they make humidifiers and dehumidifiers. A human feels hot on a humid day because his sweat glands no longer supply the same cooling because the air is already saturated with water, so evaporation is slowed. However, a heat exchanger will perform better in humid air because humid air transfers heat faster. Aluminum absorbs a certain amount of water on a humid day that is one part of why the plane needs more thrust. The other more important reason is the weight of the humid air. it is lighter than dry air so you need more speed to get the same lift. When you commission a plane you want to do it on a dry day or else you may have to take a seat out of it. A substance in a thinner, lighter atmosphere will weigh more, than a substance in a heavier atmosphere that is probably why a plane weighs more on a humid day.


Sincerely,

William McCormick

Re: Duty cycle

Not to worry, if you ask this question, your grinder time will keep you under the duty cycle.

Re: Duty cycle

Like this thread.

Re: Duty cycle

Originally Posted by Munkul

Why? If it's a quality machine you can use it up to its duty cycle at that amperage and temperature. "Rated output" is a bit wide ranging since as pointed out above, most quality manufacturers produce at least two figures, often more - 60%, 100% and 30% being common... it's still "rated" at 30%...

I agree with that.

The machine can be used up to its duty cycle and yes, there is the maximum and often higher duty cycles specified for lower currents up to the current at which the machine has a 100% duty cycle. Yes, the duty is specified under certain conditions such as temperature and over a specific time period.

My welders will run far "in excess of the rated output" until they overheat

You can also rev an engine past the redline.

Some specifications include a graph of duty cycle verses current. In that case, the welder is rated for those currents but those graphs are rarely linear so that simplistic AWS calculation does not apply.

In the end, most home welders don't need to worry too much about duty cycle but that doesn't mean you can just make stuff up to suit yourself.

Jack

Re: Duty cycle

May I throw in the fact that when the air is humid, the moisture pushes the air molecules apart,,
so, you have less air flowing through the machine to cool it.

This came up when discussing airplane takeoffs.
When the air is high humidity, the plane engines must rev higher to get enough lift to make the plane take off.

So, now we need a humidity sensor on the welding machine.
If the humidity increases, the welding machine will have to speed up the cooling fan,,,
to maintain the same duty cycle,,,

Re: Duty cycle

If you are really worried you could get a small refrigerator, cut a hole for the gun lead. Call it a MIGeRator.

Re: Duty cycle

If quoting work most time a welder is lucky to welded 20% with stick.
MIG welding is around 30% to 40% of time welding. Some types of work will drop down to 10% welding time.

If you are doing carbon arc that can be 100% duty cycle.

You read books that give fantastic speed once welding hit shop floor it drops in speed and duty cycle need.

Dave

Originally Posted by upand_at_them

Does the person running the welder have to keep track of the duty cycle time? Will a typical unit auto shutoff in the middle of a weld, or will it just overheat if the person is careless?

Re: Duty cycle

For my typical welding, the fan on my 252 rarely even turns on

Re: Duty cycle

Originally Posted by upand_at_them

I have the Titanium Flux 125. It's an inverter machine. Welds well for my beginner needs. I've only done some simple stuff so far, not even coming close to the spec'd duty cycle. But I have project coming up where I'll be doing a lot of beads on 16 or 11 gauge square tubing and I was curious.

(Yes, I will get out the manual and read it now.)

One thing to consider is that although your project will need a lot of beads- the sequence you will need to weld these beads will most likely keep your machine under the duty cycle.

Fit up, weld a small section, move to a different section to keep the distortion from turning your project into a banana

Machine is resting while you are moving around the project.

Attachment 1731219

Re: Duty cycle

Attachment 1731215

At the OP : I wouldn't worry to much about duty cycle when doing tubing, you'll find you spend more time setting up, grinding, brushing, squaring up, and moving things around. If your truly curious, find a 12"x12"x 1/8" plate and start padding some beads on as fast as you can, occasionally cooling it with water, until the light comes on. Then you'll have an idea where that limit feels like. I don't think it well trip out that easily, and you may find that your 115v circuit is you limiting factor.

Good Luck

Re: Duty cycle

Originally Posted by Jack Ryan

Currents in excess of the rated output can be achieved but only fleetingly

Maybe on your welders.

My welders will run far "in excess of the rated output" until they overheat (when the current "droops" and the welder gets "colder" presumably due to an excess of cold particles building up) or catch fire...but this takes quite a while.

Where do you get this stuff?

Re: Duty cycle

Originally Posted by Jack Ryan

Currents in excess of the rated output can be achieved but only fleetingly - the mean current should remain at or below the rated output and within the duty cycle and temperature stated.

Why? If it's a quality machine you can use it up to its duty cycle at that amperage and temperature. "Rated output" is a bit wide ranging since as pointed out above, most quality manufacturers produce at least two figures, often more - 60%, 100% and 30% being common... it's still "rated" at 30%...

Re: Duty cycle

Nonsense, Bart. You're obviously basing this on the assumption that the user will empty out all the "cold particles" from their machine at regular intervals to replace the "positrons" getting sucked up by the tungsten.

Re: Duty cycle

Originally Posted by Jack Ryan

You can do those calculations but you are only assuming that is is permissible to extrapolate higher than the rated output of the machine. I have not read what the AWS has to say on the subject but it is not its job to second guess a manufacturers specifications. Those calculations can be used to determine the duty cycle for welding currents less than the rated output but not more.

Currents in excess of the rated output can be achieved but only fleetingly - the mean current should remain at or below the rated output and within the duty cycle and temperature stated.

Jack

No need to extrapolate when the manual has a chart showing the duty cycle up to max amperage. As I said previously, my Millermatic 350P shows 400A max with a 30% duty cycle, which is what some companies use as their normal "rated amperage". I wouldn't call that "fleetingly" at all.

Re: Duty cycle

Originally Posted by Jack Ryan

Duty cycle is generally given at the rated output of the welder. This ESAB welder has a maximum output current of 240A (probably limited) but the rated output is 235A. The duty cycle is given as:

40% duty cycle 235 A
60% duty cycle 200 A
100% duty cycle 160 A



Smaller welders usually don't specify an absolute maximum output current, just the rated current.

The machines are generally named for the rated output current, not the absolute maximum and there are no performance figures for operation above the rated output current.

Jack

I don't know why you think that's a general rule because it's not. Many machines have a duty cycle chart that show all the way up to maximum amperage, so the "rated output" isn't just one number. Often manufacturers will list a "rated output" on spec sheets using a set duty cycle percentage, but that varies so it's far from an industry standard. Some use 30% because it makes the machine appear to be more powerful, some use 40% to be more conservative, some use something else like my Everlast which uses 35%. Heck, my Hobart is rated at 100% duty cycle.

Even Harbor Freight's little Titanium 125 welder has an owner's manual that lists it being 30 to 125A output. They list a rated output of 30% at 90A, but clearly list 125A as a max, and still call it a 125A welder. I'm sure some inexpensive machines don't have max output listed, but it's certainly common for them to have the full range given in their manual and some are named after their maximum output rather than rated output.

No performance figures for anything above rated output? That might be true for some machines, but it's certainly not a general rule. As mentioned above, the duty cycle charts supplied with many machines cover more than just the "rated output" number given in spec sheets. My Millermatic 350P has several rated outputs listed: 300A output at 60% duty cycle, 350A output at 40% duty cycle. The chart goes up to the max of 400A output at 30% duty cycle as well.

Regardless of all of that, my comment above was correct..."rated output" is rarely at a machine's maximum output.

Re: Duty cycle

Originally Posted by Kelvin

My Millers all spec the DC at about 3/4 or 4/5 of the max output but also give DC at maximum current (often on a graph).

For example, my Sync 250 has a DC of 40% at 250A, about 28% at 300A and max current of 310A.

When the duty cycle at the max current isn't specked, you can figure it out. This is from AWS:

You can do those calculations but you are only assuming that is is permissible to extrapolate higher than the rated output of the machine. I have not read what the AWS has to say on the subject but it is not its job to second guess a manufacturers specifications. Those calculations can be used to determine the duty cycle for welding currents less than the rated output but not more.

Currents in excess of the rated output can be achieved but only fleetingly - the mean current should remain at or below the rated output and within the duty cycle and temperature stated.

Jack

Re: Duty cycle

Originally Posted by Jack Ryan

The machines are generally named for the rated output current, not the absolute maximum and there are no performance figures for operation above the rated output current.

My Millers all spec the DC at about 3/4 or 4/5 of the max output but also give DC at maximum current (often on a graph).

For example, my Sync 250 has a DC of 40% at 250A, about 28% at 300A and max current of 310A.

When the duty cycle at the max current isn't specked, you can figure it out. This is from AWS:

Attachment 1731211

For my Sync 250:

(250/310) x (250/310) x 40 = .26 = 26% at 310A...meaning that for every 10-minute period, you can weld at 310A for 2.6 minutes with 7.4 minutes of cool-down time in-between.

My 251D is rated at 100% DC at 250A, and goes down to (according to the graph in the owner's manual) 40% at 400A. Or supposedly. Got overhead?

Re: Duty cycle

Here's a rough rule of thumb: if your MIG set is 115v only, then it's likely you'll run into duty cycle issues on bigger stuff

All manufacturers rate their machines differently. It USED to be that Lincoln and Miller set their model numbers in line with the output at 60% duty - that being for professional production use.
Nowadays they seem to mostly have joined all the other manufacturers in numbering their models at the maximum output... mostly anyway.

Remember temp comes into it too... 40 degC ambient temps, I'll never see in my workshop... maybe 30. So my two Lorch machines which are rated at 40%DC max current at 40degC, I've never ever managed to come close to heating them up... in fact I rarely even hear the fans speed up to max, even with the TIG set at max current for long periods.

Re: Duty cycle

I weld every day for a living. For most light work I never give it a second thought. Occasionally, when I have the machine cranked welding heavy steel or aluminum I have to start paying attention. I have used a timer on occasion. Usually at those Amos and length of weld the heat of the welding gives your body a duty cycle that is less than the machine.

Re: Duty cycle

Originally Posted by G-ManBart

I'm not sure where you're getting that, but more often than not the duty cycle is listed at quite a bit less than full amps. For example, your Millermatic 175 has a max of 175A, but it's duty cycle rating is 30% at only 130A. The Miller 250 family of MIGs were all actually 300A machines, but they called them 250, 251, 252 etc because the duty cycle was at 250A. Lincoln and Hobart machines tend to follow that same general pattern.

Duty cycle is generally given at the rated output of the welder. This ESAB welder has a maximum output current of 240A (probably limited) but the rated output is 235A. The duty cycle is given as:

40% duty cycle 235 A
60% duty cycle 200 A
100% duty cycle 160 A



Smaller welders usually don't specify an absolute maximum output current, just the rated current.

The machines are generally named for the rated output current, not the absolute maximum and there are no performance figures for operation above the rated output current.

Jack

Re: Duty cycle

Originally Posted by mla2ofus

To the OP: duty cycle is usually rated at full amps. The further you are down from that the longer the duty cycle.

I'm not sure where you're getting that, but more often than not the duty cycle is listed at quite a bit less than full amps. For example, your Millermatic 175 has a max of 175A, but it's duty cycle rating is 30% at only 130A. The Miller 250 family of MIGs were all actually 300A machines, but they called them 250, 251, 252 etc because the duty cycle was at 250A. Lincoln and Hobart machines tend to follow that same general pattern.

Re: Duty cycle

The only time I had keep track of duty cycle is very long welds that lasted over 10 minutes.
Most welding is 2 minutes out of 10 minutes.
So if welder 60% duty cycle you ok with all your welding.

Dave

I also included a excel worksheet for calculations duty cycle.

Originally Posted by upand_at_them

Does the person running the welder have to keep track of the duty cycle time? Will a typical unit auto shutoff in the middle of a weld, or will it just overheat if the person is careless?

Re: Duty cycle

Originally Posted by upand_at_them

Does the person running the welder have to keep track of the duty cycle time? Will a typical unit auto shutoff in the middle of a weld, or will it just overheat if the person is careless?

Depends on what you see in your head as "typical". My HTP welders are very conservative, but will shut off before internal components reach a critical (damaging) temperature. My previous Millermatic 211 inverter did not shut off, and stupid me didn't see the over-temp light. Kept running until it blew the main board.