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Modding a cheap MIG welder?

I recently bought a cheap mig gasless mig welder and I was doing some online reading about it. So I found out a mig welder should be DC, with gasless having the clamp at + and the torch at - . However when I looked at the schematic (in the images) and inside the welder to confirm it, and it was AC. So it turned out really cheap welders are ac. So my I want to try mod it to be DC. My question was, what diodes should I use? What Capacitors and capacitance do I need? And how do I design a Choke? I was looking at getting this diode: http://www.ebay.com.au/itm/MBRP400100CT-400A-100V-SBD-Schottky-Barrier-Rectifier-Diode-Module-/160930207205?pt=AU_B_I_Electrical_Test_Equipment&hash=item25783015e5&_uhb=1 

And then putting two of them together to make a full wave bridge. Would a Schotty diode Work? Or do I need a stud diode? And about what capacitance do I need? Would lots of 2200uF 50v capacitors in parallel work? Could I put in a variable ballast? and where would it go, on the 240v side or the output? Lastly, could I also add a modded microwave oven transformer for low voltage high current in parallel to boost the power? I guess I would have to wind it to have a similar voltage. Thanks

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You can experiment with it, but the cost of even a semi decent inverter is so low now, I wouldn't spend much time with it. You COULD try a single diode, a nice fat stud diode, but you'd be much better with a bridge made of studs. Don't bother trying to smooth the resulting DC.

Gasless MIGs aren't very good, the whole process of gasless isn't popular professionally, because the quality isn't really there. You aren't going to see a vast difference in weld quality switching to DC on gasless

makincoolstuff (author)  steveastrouk3 years ago

ok thanks for responding, ill just have to get a proper welder from somewhere, but aside from that, is it possible to use a schottky diode?

I haven't seen 500A schottkys. Schottkys' are typically less than 20A
makincoolstuff (author)  steveastrouk3 years ago

I found some 400amp ones, (ebay link in the question). So, theoreticaly, would they work fine for this sort of application, or do you need normal diodes?

Use normal diodes. Schottkys DIE horribly from reverse voltage spikes that a standard Silcon diode would laugh at. Look at the spec. Vrrm = -100V - you could EASILY get a -500V transient as you brake your DC at the end of a weld, just from the inductance of the welding cable, and the energy stored in that.

makincoolstuff (author)  steveastrouk3 years ago

Ok, thanks for your help