'Augmenting' a 110 VAC welder possibility?

diode(s), "about 20 volts"

I don't think this is a good idea. Draw the circuit diagram and you will see if you connect an AC welder to the battery which has a diode in series with it, one-half the cycle will try to drive lots of current into the battery. Forget about the 20V for this since the voltage will be the open-circuit voltage of the welder when there is no arc and will range perhaps from 40 volts up. This voltage on a battery powered by a welder will boil it and likely cause an explosion or at least severe overheating. A switch, you say, well don't forget to use it everytime.

The DC welder is less hazardous as long as you get the diode the right way around but you are mixing a constant current source (the welder) with a constant voltage source (the battery). There is no current limiting mechanism on the battery other than its internal resistance so control would be poor. You would be doing current regulating by varying the length of the arc which should be set for the best weld not varying current from the battery. Off-roaders use battery welding but they typically recommend 3 batteries (36V) although 2 will work and they are using batteries only. It is important that you keep the batteries as far away from what you are welding as possible because of hydrogen gas being emitted from the batteries. Also, cover the batteries so if one does explode the sulfuric acid will be contained (this is not a joke).

IMO, a lot safer and easier to try and find an old 240V welder.

Billh

Thanks. Good advice.

I am in SE Florida. Anyone have a 220VAC welder gathering dust around here?

BoyntonStu