Plugging a 240 mig into a generator

ticolawnllc · Nov 26, 2014

Hi every one.
I like it weld as a hobby. Mostly I make mounts for my tractor attachments and trucks. I have a 120v flux core mig welder now and I want to up grade to the next size up. I don't have a 240 plug in the shop. So I was going to use my generator to run the welder. The generator could use the work out. What kind of specs would I need to look for on the generator?

Jesse masterson · Nov 26, 2014

Amps times volts equal watts , check input max amps on back of machine and use formula, always get a little bigger for start up!

CNC Dan · Nov 26, 2014

Jesse masterson said:
Amps times volts equal watts , check input max amps on back of machine and use formula, always get a little bigger for start up!

And if your welder has any electronic controls in it, make sure it has a low "total harmonic distortion". Less than 5% is good.

ticolawnllc · Nov 26, 2014

Thanks guy. With your help the cristmass gift I buy myself this year will actually work.

STx · Nov 26, 2014

I run a 180Amp MIG off a 3500W generator, it works but worked better when I ran it off a 5000W generator.

You will be much happier if you go ahead and bite the bullet to do what needs to be done to install a 240V plug on grid power though. It will be cheaper in the long run and will work better.

Sodo · Nov 29, 2014

Here are 3 data points to consider. I use a Miller MultiMatic 200 which is a 120/240v inverter based MIG/TIG/Stick welder.

1) On 120v MIG I weld often with two Honda 2000w generators (paired) which combine to make one 4000W generator. 4000 watts is not enough to run the MultiMatic 200 (properly) at max power (the 1/4" setting). I have to step it down one notch (to the 3/16" setting) then it welds fine. If I try to use the 1/4" thickness setting, the generator motors bog when you pull the trigger. But they do catch up and weld at the 1/4" setting. But I don't do this because then every weld has a 'cold start' which is already kind of a problem with a MIG.

2) I can run my MIG on 240v too. When I run it on my 5,000W generator (at 240v) I can weld at the 1/4" thickness setting, but not the 5/16" setting. At the 5/16 setting, the motor bogs, and does NOT recover RPMs.

3) I called Miller Tech support and they said: Our numbers say that you need a 7200watt sustained generator to weld at full power with the MultiMatic200. "Full power" is a "3/8" setting". And the tech said "we have lots of customers who report they weld fine with a 7,000w generator."

Sorry I don't know the amps, my machine does not display the amps.

Anyway, a conclusion that can be drawn from this is:
It takes 4,000 - 5,000W to MIG weld at power settings appropriate for 1/4" thick steel. This is approximately the same whether it's 120v or 240v, you need about 5,000Watts. And of course you can weld 1/4" steel at lower power settings, it just takes more 'technique" and maybe some overbuild too.

I just ordered a 8,000/10,000watt generator to weld with, but haven't tested it yet. It was $999 delivered. I'm expecting it to be sufficient to run my welder at full power. I almost always weld under 3/16" but now I can do whatever I want. But if more than 3/16" capacity is needed twice a year then at $50 (value) per weld it will take 10 years for that generator to pay itself off (in value).

ticolawnllc · Nov 29, 2014

My generator is 7,500 watts. I'm looking at a 115 amp welder I think. So I should be fine. Thanks guys.

Sodo · Nov 29, 2014

You said you should be fine, just want you to understand that you don't have twice the power you need. A 115v MIG will use the FULL capacity of of a 7500W generator.

A 7500watt generator provides 3750 watts to each 115v outlet (or pair). As I wrote before I have needed about 4,000 watts to weld 3/16" so the 3750 watts you have - is right in there. I've built lots of stuff on about 4,000w.

A 7500w generator is actually two 3750watt 115v generators turning on one shaft, (on one gas motor). If you have a 115v welder, you are using ALL of the capacity of one of the generators. This gives you the capacity weld to about 3/16". The other half of the 7500w capacity is simply un-used. If you have a 230v welder, you can use all of the capacity of both generators to weld to 3/8". Just want you to understand you do not have "7500 watts of 115v power".

However you could run two 115v welders at the same time!

Absurd example of course, but understand that if using 115v you can't really use the 7500w number, all you get is half. However if using 230v your generator can supply the full 7500watts to one welding machine.

Sorry for repeating this but it's a detail that's hard to comprehend about running welders off generators, and easy to be confused.

Mattc8832 · Dec 3, 2014

I use my Hobart champion 10000 to run my Hobart iron man 230 all the time . It works well.

MinnesotaDaveChalmers · Dec 3, 2014

Sodo said:
You said you should be fine, just want you to understand that you don't have twice the power you need. A 115v MIG will use the FULL capacity of of a 7500W generator.

A 7500watt generator provides 3750 watts to each 115v outlet (or pair). As I wrote before I have needed about 4,000 watts to weld 3/16" so the 3750 watts you have - is right in there. I've built lots of stuff on about 4,000w.

A 7500w generator is actually two 3750watt 115v generators turning on one shaft, (on one gas motor). If you have a 115v welder, you are using ALL of the capacity of one of the generators. This gives you the capacity weld to about 3/16". The other half of the 7500w capacity is simply un-used. If you have a 230v welder, you can use all of the capacity of both generators to weld to 3/8". Just want you to understand you do not have "7500 watts of 115v power".

However you could run two 115v welders at the same time! Absurd example of course, but understand that if using 115v you can't really use the 7500w number, all you get is half. However if using 230v your generator can supply the full 7500watts to one welding machine.

Sorry for repeating this but it's a detail that's hard to comprehend about running welders off generators, and easy to be confused.

To add a little to this.
Some 120/240 generators have a switch to go 120v only and provide full power, balanced across both banks of the generator.

Unfortunately, mine do not have a switch of this type.