Questions about converting an AC welder to DC capability

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I was pondering this question in depth for the last two months, as I had an AC225 too.  I loved it.  I ended up buying an AC/DC Hobart stick welder and selling the Lincoln so that I could do better out of position welds on the bottom of my car, but I sure loved that old tombstone.You can get heavy enough diodes from Newark or Allied Electronics, and possibly from DigiKey.  I've bought diodes like that for my roll-around battery charger/jump starter box that I bought for a song at a garage sale with bad diodes.  It worked great!As for the DC welder, I'm curious about this conversion.  What voltage is commonly seen (max) from a Lincoln AC225?  The capacitor will need to be large, at least 1/4 Farad I'd bet, and of sufficiently high voltage to withstand the max open circuit voltage of the rectified DC.  AC capacitors are commonly used in power transmission (power company or large industrial facility) for correcting a lagging power factor, and in capacitor start motors.  An AC capacitor would work fine but the cost would be quite excessive compared to a DC capacitor, unless you find a used one.I'm also curious about whether or not there is more to the circuits in DC welders than just a filter cap and a rectifier.  Are there special inductors?  If so, might these LC networks be tuned for max performance somehow?  Any thought or experience on this?Hobart Stickmate LX AC/DC, Millermatic 252 & 30A spoolgun, Thermal Arc 185 TIG, Miller BWESmith Oxy-AcBridgeport 2J , South Bend 42" 9AHusky 7.5 HP 22.3 CFM 80 gal compressor
Reply:I can't get into all the electronics fundamentals of making a DC welder out of an AC only buzzbox, but I can tell you what I've figured out so far.  Bare bones, you can go with a full wave bridge rectifier and get pulsating dc, put a capacitor on it and smooth it out.  I don't know how much of a capacitor you need.  Best I can tell, the Hobart 210 ironman only uses a 120,000 microfarad capacitor, probably a 75 or 80 vdc cap.  I've seen some homebrew welders on the internet that used about 80,000 microfarads.  My goal is 100,000.  I think the Lincoln AC/DC buzzbox uses some sort of choke that drops the top DC amperage down to 125 or 140 (don't remember off the top of my head).I can pretty much figure out how to get a decent DC CC source built.  Can't find all the parts (large capacitors for one).  I'm trying to figure out how to convert the DC signal back to AC squarewave with SCR's.  That's a head scratcher for me right now.patrick
Reply:Originally Posted by Patrick_76 I'm trying to figure out how to convert the DC signal back to AC squarewave with SCR's.  That's a head scratcher for me right now.
Reply:just go buy the welder you need