Duty Cycle Dispute?

[jcrous]

I have read an article about a duty cycle in my search on more info before I possibly get a TIG setup.

Someone asked a question where the person compared a 140A Tonco (Oil Cooled) welder with a 20% duty cycle with an inverter with a 60% duty cycle. The person who asked the question wanted to buy just for making gates and burglar bars and for stick welding only. He was advised to rather go for the 60% duy cycle. I don't know what further happened (It was a 2011 forum thread somewhere).

I laughed it off as I was sure the person made a mistake with the 20% duty cycle advise. I thought riduculous.

I have a 160 A Tonco welder (the same make as what was advised against). I bought it on recommendation of a friend who has the same one. It replaced my 130A Easyweld, air cooled vintage welder.
This welder can take the punch. The current never fluctuate like the air cooled model. I must be honest to say that 130A was the highest setting I have used with 110A the favourite when I were making burglar bars. I have welded some times five sticks in a row with only the time brake to chanfe the stick. I worked at least half a day before the welder was very hot to the touch on the outside of the enclosure. A few hours of rest cooled it off for another long period of hard work. Some people even put the welder halfway in a container of water (I will not do that) to weld for longer.

Today I cleaned the welder to weld something. To my shock I noticed that the welder indeed is rated as 20%. Is that possible? I worked it more towards a 60-70% cycle without problems. In Cape Town in the summer months the ambient temperatures normally go above 30 degrees of C.

Or: Is it indeed 20% duty cycle but the oil enclosure prevent overheating?

Johan

 

[dannyp]

oil cooled's take longer to overheat but a long time to cool down once they have overheated.

when you really start pushing them, with big rods set flat out useieng a techinque that makes them draw more current, you'll find the limitations.

the littel cheep inverters are supriseingly good supriseing tho, they killed one of the thermal arc's at work ( numpty drove over it ) so i started useing mine it was only bought for doing od jobs but fair play to it.

it ran all day burning 4mm rods pritty much flat out. that was 15Kg of rods one after another i was inpressed with that i was expecting to let the magic smoke out

 

[pedrobedro]

Duty cycles are subjective, they usually have something in the literature telling you what duty cycle you will get at different amperages like 100% at 60 amp, 60% at 100 amps and 20% at full whack so unless you are doing long runs lasting for minutes on end burning a complete rod and fitting a new one straight away you will probably never get anywhere near your limit. 20% is 2 minutes in 10 for welding purposes.

 

[matt1978]

But another big factor is the ambient temperature that the duty cycles are tested at. The BS EN Standard is at 40 degrees. It's ok to publish the 25 deg results aswell aslong as you make it clear that they are the 25 deg and also publish the 40 deg ones too

 

[keith19]

An interesting thread. I tried to look into these Tonco arc welders some time back, and got given very little information about duty cycles, other than the stated 20%, from the people who sell them. Logically they should have a much better duty cycle than an air-cooled buzz box, being oil-cooled.

But if we suppose that the company is honest, and has tested them at full output (160A), and found that at 160A they give a 20% duty cycle at 40 degrees C, to the BS EN Standard given by Matt, and used that as their stated 20% duty cycle, then as Matt implies, at much lower ambient temperatures the duty cycle will increase in proportion.

So at 100A output in an ambient 40 degrees C the duty cycle will be around 50% anyway.
At 100A output in an ambient 30 degrees C the duty cycle could be expected to be around 60%.
At 100A output in an ambient 25 degrees C the duty cycle could be expected to be around 65%, more or less as stated by the OP in his detailed post.
At 100A output in an ambient 20 degrees C the duty cycle could be expected to be around 70%.
All of this assumes a very best case scenario, with the "20% Duty Cycle" on the case plate meaning 20% at 160A max output. Over here in the UK we are not accustomed to just one duty cycle being stated, and certainly not the lowest duty cycle alone.

So when I looked at these little oil-cooled arc welders I figured the company which made them was maybe taking a mean figure somewhere in the middle of the usable range. Say 100A output in an ambient 40 degrees C giving a 20% duty cycle. Working out from that gives a very different picture, worse than most buzz-boxes, and for the price and weight of the welder, not worth bothering with....

If the 'best case' table above is anywhere near correct, as it possibly could be, the makers of these tough little welders are doing themselves no favours by just sticking "20% Duty Cycle" on their products.

 

[jcrous]

Thanks for the responses.
I must say on average the Tonco welders for oiled bath are considered as of the best quality that is locally available, but a lot of cheaper makes are available.
If I have to choose now, I will buy Tonco again because I have tested my one under the mentioned load work and I could take the punch. What I like also is that the transformer has a lifetime guarantee.

 

[matt1978]

I've never heard of Tonco but I'd of thought if the test was at 40deg then they would of stated that, ESP when a lot of the cheaper end of the market stuff only publish results at 20 or even sometimes 15 degrees.

Your logic is correct Keith but its not that straight forward that for every 10 degrees less temp, the duty cycle performance increases by 10% but its definitely correct that the DC figures quoted at 40 deg would be lower than if the same unit was tested at 25 Deg.

The true test would involve the machine being on a load bank at a given amperage in a climatic cabinet. DC on MMA units is sometimes subjective because the nature of the process with a fixed size electrode length means that you can only weld for a short time (until the rod burns small) before you naturally have to stop anyway. But a DC of say, 60% at 120 amps would mean that the machine can output 120 amps for 6 minutes and would then require 4 minutes to cool down. Hence the reason the test should be made with a "dead short" load bank because there is no widely available electrode that is long enough that it would burn an arc for 6 mins continuously

 

[keith19]

Matt, you're right, that 'best case table' I gave is only supposition, given for purpose of illustration, based on the figures jcrous was giving from his experience.
I have heard of these Tonco arc welders spoken well of before now, which is why I originally looked into them. But anything bigger than the 140A regularly for sale on ebay is not usually obtainable here. The 140A draws around 18A at top output, so not one for the domestic socket!
They are AC welders, and are an horrendous price over here, compared to a decent s/h Pickhill or Oxford, etc. And almost as heavy to cart about!