DC Welding

This varies with the type of electrodes you are using and the parent metal your welding. What issues are you having? Or is this just a general question.

Polarity matters and so does system resistance, inductance, DC ripple and its frequency as well.

What exactly are you planning to do?

Actually, it is a general question, but briefly, I've got one of those el cheapo welders to which I've installed a set of diodes and inductor etc. Not being a tradesman welder, I'm looking at techniques to improve my performance. Norm.

This sounds like it might be interesting.

You seem to have modified a welder that you purchased. What is the goal of the modification? Was the modification a kit, published plans or something else? Do the modifications seem to have worked? What metal and thickness are you welding?

What inductor and stuff did you use? I am about to do the same with my buzz box. DC electrodes positive with 7018 rods. George

The inductor I used, came out of an old 50 volt dc, Telstra power supply at the local scrap yard, consequently I don't have any idea regarding its spec's. All I ca n say is that it was fairly large with a heavy section copper winding. Norm.

Yes, it matters, as others have stated. Follow the instructions provided with the electrode you are using. You can play around with AC, DC straight polarity and DC reverse polarity and see how they behave differently with different type electrodes. Keep in mind - it always seems backwards to me - that in DC straight polarity the electrode is negative and 'ground' is positive. DC reverse polarity, obviously, is the other way around.

The reason for the dc conversion, is that I thought it would be easier to strike and maintain a stable arc. I was having trouble in maintaining an arc whilst using ac. My usage is quite varied, but 1/4 plate would be about my limit, nothing major, the occasional bracket, sometimes a bit of stainless sheet, etc. Thanks Norm.

If you're having trouble maintaining an arc (but it starts OK) on ac, it's likely deteriorated electrodes, REALLY crappy equipment, or technique. DC won't do much for these, but it is easier to maintain an arc & get nice penetration on DC & I would much rather use it for SS. Warning- you can get arc blow with DC though.

In welding, the positively charged anode will have a greater heat concentration and, as a result, changing the polarity of the electrode has an impact on weld properties. If the electrode is positively charged, it will melt more quickly, increasing weld penetration and welding speed. Alternatively, a negatively charged electrode results in more shallow welds.

http://en.wikipedia.org/wiki/Arc_welding

Your project sounds interesting.

You probably already know this but I'll add it anyway. I suspect that the abrupt start and stop of high current during welding can induce some large voltage spikes on the welder's output. If you have trouble with component damage in your modification this might be a concern to put on the upper half of your troubleshooting list.

Good Luck,
Bruce