Invertig 221 thermal over-load torture test. Real-world results. Very surprised !

[Oscar]

So FlyFishin piqued my curiosity as to what the "real world" thermal limits are on my Invertig 221. By "real world" I don't mean worst-case scenario, but rather what the machine would experience in an average shop.

This was rather impromptu, so I don't have video footage (yet), but the data I'm presenting is factual.

Ambient temperature:



Picture showing machine at thermal overload:



test piece to absorb a lot of heat:




Machine showed 217A on the display. Not sure why not 220A, never really payed attention to it, perhaps just production tolerances.

Time until thermal over-load/shut-down (minutes:seconds):

1st & 2nd done back-to-back, 3rd-5th back-to-back, meaning as soon as the thermal overload light turned off I went back at it at full power.

1st: 4:32
2nd: 3:38
3rd: 3:20
4th: 3:02
5th: 2:51


Those time durations for arc on-time aren't all that surprising seeing as how the machine is rated at 20% duty cycle @ 220A @ 104°F, and the ambient temp was well below that.

BUT...........

I initially "felt" like the cool-down time (until the thermal switch turned off and I was able to strike an arc again) was in the neighborhood of 5 or 6 min, but I wasn't paying too much attention to that part; I was more focused on how long the arc was on. But as I did more and more of those over-loads, I started to pay more and more attention to just how long it actually took to restore itself back to full operation. After the last thermal overload duration of 2:51, I let the stopwatch on my phone keep going to then subtract the time and see just how long it takes to recover so one can get back to welding. Shockingly, the thermal light turned off at 6:30! Subtract the 2:51 that the machine actually had the arc on, and that means that it only took 3:39 to cool down!

So if you go back to the 4th thermal overload, I had the arc on for 3:02, machine cooled down for about ~3:39, and then the 5th arc duration was 2:51 before it overloaded again; that's a total of 9:32. At 9:32 it was overloaded (and would have stayed that way for the next few minutes), so say 10min flat, and out of those 10min, the arc was on (albeit not consecutively) for 5:53. So almost 6 minutes it was arc-on during a 10min span.

Before I jump to any conclusions, I speculated what would happen the next 10min. It would have been off for about 3min (because it was already overloaded), been able to weld for about 2:45 at the current rate of decrease, then another ~3:40 to recover, then on for maybe 30sec before the 10min span is up again. So the 2nd 10min would be about 32% duty cycle. Average that out with the 1st 10min span, and one would be looking at an average of about a 45% duty cycle (over a 20 minute span) at an ambient temperature of 75°F. Not too bad.

[MinnesotaDave]

Yepper, you're showing why my little 130 amp craftsman (Lincoln) from the 90's never seemed to overheat when it should have in Northern MN.

It runs a really long time at 20ºf
It's still working btw. Used it yesterday to weld a nut on a broken bolt.

Same goes for my mm210 transformer mig (also 90's). The shop temp is rarely above 70ºf.
Most of the time it welds at an ambient temp of 60ºf or less. As a result, never seems to get hot.

I welded with my brother's miller 130 one time on a super hot day (for MN) - it overheated and kicked breakers constantly at full power.
(shocker right? lol)

I've often wondered what type of math I'd use to estimate duty cycle at temps lower than 104ºf.
I suspect the modified duty cycles would graph out similar to an exponential decay.
(ambient temp decreasing on the y axis and duty cycle increasing on the x)

[Oscar]

I honestly thought it'd end up being around 30-35% as a final average, so the results were quite good IMO.

[Munkul]

Nice post, and nice reminder that you get what you pay for - advertised duty cycles are usually a little conservative if anything for a good quality machine

[MinnesotaDave]

I honestly thought it'd end up being around 30-35% as a final average, so the results were quite good IMO.

Well, it's my understanding that the over-temp is past the duty cycle.

While following the duty cycle you shouldn't hit the over-temp.

So the duty cycle at that ambient temp is likely about 30-35% like you guessed.

[Oscar]

Well, it's my understanding that the over-temp is past the duty cycle.

While following the duty cycle you shouldn't hit the over-temp.

So the duty cycle at that ambient temp is likely about 30-35% like you guessed.

I thought so too, but the kicker here is it doesn't take the remainder if the 10-minute period to fully cool down before you can get back to welding again. I suppose that us subject to interpretation, because isn't the definition of duty cycle: the maximum amount of time one can weld in a 10-min period, the rest being cool-down time? That is how I see it.

[Munkul]

I see dave's point.. so in reality the machine is about right for it's advertised duty cycle.

That's the difference between a cheap machine and a good one again. A cheap machine will over-temp around it's advertised duty cycle. A good one will run longer than it's advertised duty cycle before hitting its over-temp.

The over-temp isn't just a duty cycle timer! It's when the machine realises it's physically too hot, and any hotter will cause damage!

In real world use if you're regularly hitting overtemp, you've got the wrong machine for the job. Keep from hitting overtemp, and you're at least not stresssing the machine overly. Keep inside the advertised duty cycles and the machine will last longer.

[Oscar]

The over-temp isn't just a duty cycle timer! It's when the machine realises it's physically too hot, and any hotter will cause damage!

Perhaps....but unless you actually programmed the machine, I'll take that statement with a grain of salt. I respect that is what you believe and will not try to change your mind, but I do not believe that is always the case.

[Munkul]

Perhaps....but unless you actually programmed the machine, I'll take that statement with a grain of salt. I respect that is what you believe and will not try to change your mind, but I do not believe that is always the case.

Well it's common sense, isn't it. It's a temperature function, not a time function.

Over-temperature... the clue is in the "over" bit... If it didn't cut out, it would continue heating up as you use it, and definitely damage something.

It's like all electrics... the cooler they run, the longer they last, in general... so don't HIT the overtemp, and the machine is likely to last longer...

Like I say, it's not about clever electronics... it's simple physics and common sense.

[Oscar]

Well it's common sense, isn't it. It's a temperature function, not a time function.

Over-temperature... the clue is in the "over" bit... If it didn't cut out, it would continue heating up as you use it, and definitely damage something.

It's like all electrics... the cooler they run, the longer they last, in general... so don't HIT the overtemp, and the machine is likely to last longer...

Like I say, it's not about clever electronics... it's simple physics and common sense.

Yes I agree with this, perhaps I mis-interpreted your previous statement.