hi i have just got a new generator 240v
and 850w can it run a mig welder or a grinder ? not at the same time i INFO PLEASE .....

In therory its not such a good idea to run a welder on a generator as its not a constant source.the power fluctuates therefore not having the power all the time when needed!

Grinder Should be fine!

850 watts is only 3.5 amps, don't know what a mig need but probably much more than that, should be ok for a grinder, the problem is when motors start they pull much more current than they are rated at so you need quite a bit in reserve to get them going.

From experience, youll have a mare trying to get a consistent weld. As above, the voltage fluctuates slightly, and i doubt its big enough to power a welder of any decent size. At 3.5A it might trip its thermal overload or protection if it has it. If it doesnt, youll melt the alternator.

I have a 3.5kVA genny and the MIG struggles! As you make an arc, the genny slows, which slows the wire feed so breaks the arc. Then the welder reacts and speeds up so the wire shoots out, makes the arc and the genny slows down, etc, etc..........The stick welder is OK though!

And 850VA generator wouldn't run even the smallest welder adequately. It should be ok for most 115mm grinders though.

Note that the cheap two stroke generators of this rating are pretty crap, very poor regulation and even the 850VA rating is optimistic. They are certainly very cheap however.