Minimum Current on a MIG set.

[Drains]

Rightho folks. There's a subject that had been confusing me for some years now. Mig welders have a fixed voltage (which the operator sets); the current is then infinitely variable, according to wire thickness, wire stickout, wire feed speed, shielding gas type etc etc.

The world and his dog always seems to be speccing migs on the basis of their MINIMUM current use (at least, if a bit of car bodywork is in the offing). See the pics below for an example of what a typical data plate might say:-

Now, it is my contention that the current on the data plate actually represents the MAXIMUM draw, for the voltage set, (eg 35A at 15.7 volts) not the minimum, (then again, it could be the average) and that people who buy welders on the basis of that lower amp setting are mistaken! In fact, it's the minimum voltage they should be going by. The welder will only draw current according to the way it is being used, not the way it's been designed/built. (that will still matter, but nothing like as much)

I'm more than happy to be shown to be wrong, but I really think there is an important question to be answered.

Opinions?

Edit - just to be a little clearer - the common assumption would be that the minimum amperage of the welder shown in the plate would be 35A. I say that is an incorrect assumption, and that the current could be less than that in use. So if you're looking for a welder to weld thin material, going by the current accompanying the minimum voltage on the data plate to choose a set would be a mistake.

 

[malcolm]

Does anyone know how the manufacturers work out voltage and current for their spec plates? I'd imagine it's like duty cycle where respected manufacturers follow a time honoured standard and the cheapo ones make up their own rules.

You are right of course, but in my limited research for the calculator I couldn't find any way to accurately work out any real voltage settings and found the manufacturer's amp figures closest to my experience. A massive botch, and possibly easilly abused by manufacturers.

Good question.

 

[scarecrow]

I thought that mig welders were measured in volts and arkwelders in amps as the Welder has just one or two transformer taps each one with the different voltage and the shunt changes the amps with a mig welder there is usually loads of transformer taps because each tap is the different voltage not sure how that affects the amps going by the plate and also increase with voltage

I presume that the dat plate gives a minimum and maximum voltages and amps the rest depends on the user

I read your question again and now I get what you at ( some of them have different voltage settings for the same amps )Ill have a look and see what I can come up with

 

[GeorgeB]

Now, it is my contention that the current on the data plate actually represents the MAXIMUM draw, for the voltage set, (eg 35A at 15.7 volts) not the minimum, (then again, it could be the average) and that people who buy welders on the basis of that lower amp setting are mistaken! In fact, it's the minimum voltage they should be going by...Opinions?

I would hope there's some international or European standard (IEC 6094 perhaps?) which sets the paramaters and basis for measurement. By way of comparison, I recently posted a photo of the data plate from the Aldi MIG welder. This shows a minimum of 30A/15.5V so the Aldi spec is 5A and 0.2V lower than on the above data plate. I doubt if 0.2V is very significant and I trust the 5A is more meaningful. You may be correct that it's the maximum current on the minimum setting, but the Aldi should still go lower, I reckon. Likewise, there are two or three Clarke's which claim to go down to 25A or 27A. I'd take the 25A for use on thin sheet, given a free choice, so I still subscribe to current being relevant. I see it as being entirely feasible for the manufacturers to design and build a transformer to provide whatever minimum and maximum current and voltage they require.

I know the data plates can sometimes be a bit misleading, though. For example on transformer-based arc welders, they often state the OCV as 48v. This is already below the recommended minimum OCV of 50V stated on many/most rod packs. But you only get 48V if the welder is set on maximum, e.g. 130A for my Cosmo. If I move the shunt to get mimium current (40A in my case) then the actual OCV is only 43V which is then seriously short of the 50V rod minimum. They don't tell you that. I measured it.

 

[snowcat]

I was explaining this movable feast of currents to a pal of mine the other day, I really don't know how they work these data plates....

with multitude of wires, sizes, operator skill levals... there must be a "mean" way they measure the amps to quote a set specs to........

over to one of the forums resident equipment suppliers......

 

[Hitch]

Anyone got one of them clamp on ammeter jobbies... a few experiments is in order i fancy.

 

[snowcat]

This throws no answer to Simon's original question, but adds some pointers on messurement........

 

[R Kraft]

If you run the volt/amp specs of various machines, through a graphing program, they all are calculating the same way.
Must be factoring in the arc channel resistance
I suppose.
The voltage on the plate is the volts while welding at 35a with a normal arc gap.
To weld at 25a and a normal gap you would need about 14.7 volts.
An arc at 14+ volts is almost impossible to sustain.
A efficient (low impedance) transformer and a precision wire feed would be a necessity.

Robert

 

[marknotgeorge]

I had a quick search on the BSi website for 'welding machine specification'. I found that BS2065:2001 (ISO 669:2000) is titled 'Resistance welding. Resistance welding equipment. Mechanical and electrical requirements'. There are lots of other standards relating to welding equipment manufacture, but to find the right one would cost money.

 

[scarecrow]

Maybe if people posted a few pics of the date plates of their machines with make and model might be a help to see what the difference is between different quality machines

 

[Archie]

This one's got me a little curious so I put the first three sets of data that came to hand into a spreadsheet and come up with the following. Being as every point lies on the same line it would seem that a) there is a standard way of measuring things and b) there is no difference between models. For reference the three data plates I used were: the one from the beginning of this thread, the Aldi MIG thread and my own Lincoln.



I guess what we can see from this is that when shopping around it doesn't really matter whether you go with lower amps or lower volts as they seem to be measured in a standard way and are linearly related. i.e lower amps is lower volts. I'm sure there is an argument that amps vary while voltage is constant but as far as measuring one against another it doesn't matter. The amps are down to the operator.

 

[malcolm]

Nice one Archie - they do arrange themselves in a very straight line there which suggests manufacturers are using a formula rather than measurement. Which welders did you include?

A quick browse at Machine Mart finds a Clarke 135TE with minimum of 19 volts and minimum current of 30 amps (their figures) - might screw the graph if you add it in. Down to the capacitors probably, but it half suggests a more complex calc or a measurement on their part (having used one for 10 years I don't disbelieve their figures in comparison with the others).

 

[Archie]

You're right Malcolm; the Clarke would screw with things a bit. Whether or not that's down to capacitors or not I don't know. It's getting well into the realms of electronics and that is not my strong suit! I know my welder has a bank of several massive caps yet lies on the same line as the other two which I would guess probably don't so......

 

[R Kraft]

Nice one Archie - they do arrange themselves in a very straight line there which suggests manufacturers are using a formula rather than measurement. Which welders did you include?

A quick browse at Machine Mart finds a Clarke 135TE with minimum of 19 volts and minimum current of 30 amps (their figures) - might screw the graph if you add it in. Down to the capacitors probably, but it half suggests a more complex calc or a measurement on their part (having used one for 10 years I don't disbelieve their figures in comparison with the others).

Could they be using their open circuit voltage ?
Robert

 

[malcolm]

I suspect we'll be in the dark until we figure out the methodology used by manufacturers to calculate/measure their rated volts and amps. Without that the numbers are all a bit abstract.

 

[scarecrow]

Probably in over my head here as well but still interested so let see if im getting this right amps are important when buying a mig as most of them have the same voltage per amp with only slight different but checking on eBay you sometimes see migs with a minimum of 50 are 60 amps described as suitable for car body work by people seem genuine enough could this be possible

 

[R Kraft]

Probably in over my head here as well but still interested so let see if im getting this right amps are important when buying a mig as most of them have the same voltage per amp with only slight different but checking on eBay you sometimes see migs with a minimum of 50 are 60 amps described as suitable for car body work by people seem genuine enough could this be possible

Not for any body work, I do.
Maybe for fenders on a tank.
Robert

 

[R Kraft]

You're right Malcolm; the Clarke would screw with things a bit. Whether or not that's down to capacitors or not I don't know. It's getting well into the realms of electronics and that is not my strong suit! I know my welder has a bank of several massive caps yet lies on the same line as the other two which I would guess probably don't so......

All of the welders that I graphed were on the same line, with or without capacitors.
Something that I've always meant to try, would be to add a large diode or two, between my earth clamp and the work.
Each diode drops about one volt,one diode would move the amps from 60 to 40.
Or two would move 70amps to 30amps.
Robert

 

[Drains]

The thing is though folks, the amps just won't be what it says on the plate. Put in 0.6mm wire, the amps will be lower than with 0.8 mm wire. Turn up the wire speed, the amps will go up too. Move the torch away from the job, the amps will go down.

So why are the amps on the plate relevant? Are they relevant at all?

 

[Jake SS]

Manufacturers use a "load bank" at a specific resistance for each voltage tap
so that there are no variables such as wire size, arc length, lead length, etc
All this boils down to the inductance of the circuit, efficiency, losses, on and on!
So the load bank is the most accurate way to spec the machine without variables, at a given resistance set by the manufacturers designers.

Cheers
Jake