MIG minimum amp/voltage settings for bodywork

[webhead]

Hi there,

I'm looking at a bargain for a reasonable machine. It's a china thing but this one actually seems tot get good reviews : mig star 210.

One thing that's holding me back is that it only begins at 50A. According to the seller, running 17V/50A with 0.8mm wire is just fine for bodywork.
According to interweb specs I've found, it begins at 20 or 22V open voltage (?).

Any insights here? Is less truely more?

 

[keith19]

Generally speaking for small mig use the minimum amperage is most important on thin bodywork metal. The amperage defines the amount of heat going into the metal.
If the amperage is above around 30-35 output there will be problems in that too much heat is going into the sub 1.0 mm metal too quickly, causing blowthrough. With experience it is possible to weld thin metal at 35A, and easier at 30A, 25A, down to around 15A, which is exceptionally low.

In theory a welding machine with a setting that put down a series of tack or stitch welds at 50A for a few fractions of a second at a time might do the job okay, but for a human operator using the torch switch reaction times would not be fast enough.

For manual operation 50A sounds far too high for normal car or van bodywork, unless the metal is around 2 mm thick, such as chassis parts.

 

[webhead]

So it's fair to say it's just sales-talk ? I figured that might be a bit on the high side.

I found something about it over here : http://www.ecvv.com/product/1390710.html , the 210 model.

I actually found some good reviews about this chinese tank...

 

[cumbriasteve]

It's way above the desired ampage for car bodywork and even a very skilled welder would struggle to keep a run going on panel work.

 

[Engineer]

Its complete nonsense to suggest that minimum amp settings are relevant to being able to do car bodywork! I have regularly used a 450amp set with around 50-60 amps lowest setting, and it worked an awful lot better than shoddy DIY sets that went a lot lower! If that Chinese set has copper windings, I would think it would work fine for car bodywork.

 

[Drains]

Forget the minimum current settings. I don't know why manufacturers insist on using them. The set will put out what's required, and they will ALL go down to next to nothing. The minimum voltage is far more relevant.

17 volts is ok with 0.8mm wire on 0.8mm sheet. It would be better/more forgiving at maybe 16v, and depends on the gas you are using. You can get away with slightly higher voltages with co2.

This voltage/current thing should be explained in the Wiki on this site, as it's really misleading.

 

[shenion]

Jeez, copper windings. That mainly effects duty cycle. My Clarke had aluminum windings and had a smoother arc than expensive machines I have used.

Aluminum windings of the same size as copper will increase resistance. That is the higher heat loss that effects duty cycle. It also effects the voltage droop making them be less consistent. If the wire size is increased to accommodate for resistance, it is the same as copper.

Minimum amp settings are not standard. 40-amp on 0.8mm wire will be 25-amps on 0.6mm wire. Some spec the range only for one size wire.

Low amps is more on voltage and a smooth wire feeder. At the low wire speeds, any variance becomes significant.

 

[webhead]

Let me get into this.

I already read that the selector on the MIG sets the voltage. That actually makes sense. It also makes sense that the machine can max out but not on the low side. I just assume it delivers whatever required for the welding process to continue.

I also assume the current depends on the arc length and the material etc.
What about the wire? Wouldn't a thinner wire lead to a higher resistance and thus a higher current?

What about these machines that have a voltage AND current setting? Would that be the limiting current then?

 

[gavuk]

Hi webhead and welcome to the forum .....not heard of the machine you are asking about but i will post a pic of the settings from my thermal arc 180,where you can see with co2 or argon mix 17volts is not out of the ball park for car repairs...Personally I don't worry too much about amperage often using higher than recommended,but always using "the thin metal technique" which is overlapping spots , because of distortion I never weld more than 1/2" on any side of a car patch/repair in one go , it would end up a mess....I run beads on thicker material but never on car bodywork.....I'm not convinced by Engineer's views on alluminium windings either ,duty cycle and longevity may be worse but functionality is fine at least with clarke/snap-on and sealey diy sets I have used....hope this helps .............

 

[keith19]

With all respect to those who own very expensive mig machines, the lowest amp output on a small or hobby welder is quite important. As the low end of the output on relatively cheap migs goes up the scale, the more difficult it becomes to use the manual 'on-off' stitching technique. When you are manually stitching 0.8 to 1 mm body panels on a cheapy m/c with a low end of 50A you are really on the edge.
On an expensive machine stitching can be set to operate at much higher amperages, because the switching is done by the machine at a much faster rate than can be done manually. On an expensive machine voltage can also be set to suit the job, while on a cheap m/c it is locked to wire speed.

I worked in the lower end of the motor trade for years, and we often had to use unsuitable kit if nothing else was available at the time. I have used 'cheap' migs with a low amperage output of 50A on panel work, and they were a great deal more difficult to use than those with a minimum of 30A.

Also, if low amp output makes no difference, why are these here?
"Unique, ultra-low minimum setting of just 15 Amps! the lowest available from conventional transformer based machines, half that of most others, so outstanding on very thin materials such as car bodywork."
The above is from Weldquip's Portamig pages.

"How many amps - Minimum?
Don't forget the minimum amps. Most smaller MIG welders have a minimum of 30 amps which is OK for 1.0mm sheet, and passable on 0.8mm steel with a bit of care and technique (see welding thin metal). Some welders have 20 or 25 amp minimum which would be more usable on 0.8mm steel. Any welder with a minimum of more than 30 amps (normally only very cheap or very powerful welders) would be unusable on car bodywork. One really cheap 100 amp welder has a minimum setting of 85 amps. That'll give a range of 1.5mm to 2mm steel which is all but useless for most jobs. Many big welders designed to run all day at 300 amps will not go below 40 amp minimum."
The above is from this website's 'Buying a welder' pages.

 

[cumbriasteve]

Its complete nonsense to suggest that minimum amp settings are relevant to being able to do car bodywork! I have regularly used a 450amp set with around 50-60 amps lowest setting, and it worked an awful lot better than shoddy DIY sets that went a lot lower! If that Chinese set has copper windings, I would think it would work fine for car bodywork.

Many members can only afford 'shoddy DIY' sets and not professional sets which I agree will always run better and be easier to use.

With the cheapo DIY sets, often used by persons with little experience, then low ampage is very relevant.

 

[malcolm]

"How many amps - Minimum?
Don't forget the minimum amps.......

Need to alter that - I'd agree that a proper welder with a published minimum of 40 amps will likely be much easier to use for bodywork than a hobby welder with published minimum of 25.

Often the higher minimum is due to the bigger welder not having a roller for 0.6mm wire, but even with 0.8mm wire it will have a much more stable arc and be much faster to get to speed and allow a big range of wire speed adjustment., both of which are very important for bodywork.

The Clarkes are over-rated on here. That came from back in the day when people were asking "Is this completely rubbish Chinese MIG that will never work properly any good?" My advise for buying new at that price would still be a Clarke. But a machine that costs much more will generally be a lot nicer to use.

Careful with eBay though - some welders go on there because they don't work properly anymore. A complete beginner will not know that the welder is not working properly and end up something that doesn't work at all well.

I've got a Portamig for welding old rusty Renaults

 

[Wedg1e]

What about the wire? Wouldn't a thinner wire lead to a higher resistance and thus a higher current?

Wrong way around. If you increase the resistance of a conductor you reduce the ability of current to flow through it. Consider a tank full of water with a pipe of a given diameter exiting the bottom (via a tap, obviously ). The water will flow through the pipe at 'some rate' limted by the ability of a given volume to pass any point at any time (friction etc) - this is the 'resistance' to the flow.
Now double the diameter of the pipe (and tap, before any smart-ar53 gets in there!), the water can fall through it easier as less of it is being 'resisted'. Perhaps twice as much water would flow in a given time compared to the first pipe.
In electrical terms, if you half the resistance, you double the current flow, and vice versa: double the resistance, half the current flow. So if a smaller wire presents more of a resistance to the voltage being propelled through it, less current can flow.

 

[Drains]

To continue what Wedg1e says, less current is also required to maintain the arc with thinner wire, so the thinner the wire, the less current required. When a low voltage setting is used the wire speed is slowed down to suit, and again, lower current is required to maintain the arc.