Real amps from 110v or 220v

[wallythacker]

Ok, first, I'm no electrician or engineer.

I'm contemplating purchasing a mig/flux welder for around the house. I don't have 220v in my shop. I do have a 110v 20a circuit.

Here's my question.

If some 110v mig/flux units are rated at 140+ amps output, which I find hard to believe unless they have close to 100% transformer efficiency, (how do they get such high amperage from a 110v line?) then why do the 220v models only pack an extra 40 amps?

After all, running on a 220v circuit nearly doubles the available power so shouldn't it double the available output amps?

I'm also confused when I read the fine print on the 110v units. They're labelled as 140 amp units but then hidden somewhere in the manual or webpage is a statement that goes like

Maximum output: 88amps/18v/20% duty cycle.

So where's the 140 amp rating come from? Is that like the current flow in a dead short condition for a millisecond or so? Is it the DC power equivalent into the mains of the transformer (before transformer losses), assuming an arc voltage of 17v ?

Finally, if you really can get 140 amps of current from a 110v unit why doesn't anyone make a 110v buzz-box that puts out 140 amps?

Hopefully someone has the answers for me.

[Clay Walters]

Wally,

Not sure I can answer this to your satisfaction but:

The duty cycle is the key. MIG is a constant voltage process. SMAW is constant amp. You'll also note that a 220v machine at the same amp level usually will do so at a higher voltage and probably greater duty cycle. My understanding is this permits a better, more stable arc in the inert gas environment of MIG, and minimizes the inherently cold start. Various machines seem to have an optimum operating point with certain wires and certain gases on certain materiels. The larger & more capable machines also seem to offer the most flexibility. Best to get the machine designed for the intended application and not push a lesser one.

I know that's a broad perspective but its my take,

Clay

[Pin Head]

So where's the 140 amp rating come from? Is that like the current flow in a dead short condition for a millisecond or so? Is it the DC power equivalent into the mains of the transformer (before transformer losses), assuming an arc voltage of 17v ?

Finally, if you really can get 140 amps of current from a 110v unit why doesn't anyone make a 110v buzz-box that puts out 140 amps?

Hopefully someone has the answers for me.

You can get 140 A from a 110V 20A circuit (assuming 100% efficiency), but only at a voltage of 15.7 V.

You don't see 110V 140A buzz boxes because stick electrodes will not run at voltages that low.

[Sberry]

It takes half the input amps at 240 to = the same wattage, increases the incoming wire efficiency and these circuits are usually over wired, minimal voltage drop and the circuit itself isn't maxed out, add a long wire and the problem gets worse. You can only get so many watts out of a common outlet. Thats usually the problem with small stick machines, the circuit will only deliver what it can and everyone knows weldors want more heat and a bigger rod. If the garage is attached its simple to run another circuit, if you are using the same one and running a couple lights from the same wire it adds insult to injury.

[wallythacker]

Thanks for the replies gents,

I think I have a handle on things now. It's the fine print, ie: 88amps/18v/20%duty that matters.
That's the real current at the real working voltage the unit produces.

When I bought my first MIG 15 years ago (an 88a Century) there were no models on the market that advertised any more than 85-90 amps of real working current. IIRC, even the 110v Lincolns of that era were advertised as about 90a max.

I didn't see how things could change that much in 15 years unless there was a substantial breakthrough with transformer efficiency.

As an aside, when did the industry start advertising 140+ amp output from the 110v units?

[Sberry]

Just like everything else, they all want to make it seem like more and better, add 5A to the label and it makes it a new model.... ha

[wallythacker]

Just like everything else, they all want to make it seem like more and better, add 5A to the label and it makes it a new model.... ha

You said it. Explains all the different models from 100->140 over the years.
God forbid I live long enough to see a "200 amp" 110v MIG.

[Blacksmith]

Its kind of like horsepower in your truck. You may have 325 horsepower, but most engines cannot run continuously at that, but since there are few places where you can safely or legally run that fast for long, its not an issue and no one publishes "continuous" ratings for trucks. Work boats, not to confuse the issue, are another matter and it's not unusual to see contiuous hp ratings at about 2/3s the pleasure or light duty ratings, just like the difference between 135-140 amps maximum and 88-90 amps at rated duty cycle.