Engine-driven welders

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Something clicked in my head yesterday, maybe after reading some of the SA-200 rebuild threads here. Commutator. Exciter. I realized that those old engine-drive welders were generators, not a motor run into an alternator run into a rectifier. Is that right? It got me thinking: Is that true for all engine-drive welders, even today, or is that something of the past? I know that automobiles switched from generators to three-phase rectified alternators because they could get much better current capacity from a much smaller device. But then I got to thinking that maybe the reason those old engine-drives are in such demand is that a DC generator produces a better welding current and arc than some more "modern" technology. I got to thinking that the full-wave bridge rectifier in my old transformer welder still produced a pretty rippled waveform compared to a purpose-built engine-drive unit.Do engine-drive welders generate true DC, or do they generate AC and rectify it?I'd love to hear any comments anybody might have.
Reply:This will be better than I can put it.http://weldingweb.com/vbb/showthread.php?t=177471Dave J.Oh, and I love my SA200 Last edited by MinnesotaDave; 06-01-2013 at 08:56 PM.Dave J.Beware of false knowledge; it is more dangerous than ignorance. ~George Bernard Shaw~ Syncro 350Invertec v250-sThermal Arc 161 and 300MM210DialarcTried being normal once, didn't take....I think it was a Tuesday.
Reply:Oh sheesh. I didn't even bother searching the forum. Thanks for that.Repeat after me: I am not a unique and special snowflake.
Reply:That video is the bomb. I'm still not clear, though: are the SA series unique in that they use a DC generator, or is that standard for engine-drive welders both past and present? Do modern generator welders use rectifiers, or are generators still superior in some way? Seems to me like an alternator with enough poles fed through a rectifier array would produce a similarly ripple-free waveform to a DC generator.This is really cool. I actually had only the vaguest idea of what a DC generator was before now. I love learning new stuff like this!
Reply:Three phase rectified is smoother.In the past, TozziWelding has said:Simple comparison, weld 6010 with a Bobcat, the go to a Trailblazer. The TB has a 3 phase welding generator where as the bobuscatus has a single phase, night and day.
Reply:From the modern SAE-300 Lincoln:The machine’s pure DC generator welding output is produced from a rotating armature/field coil system manufactured by Lincoln Electric. The SAE-300 can also be used to power tools, grinders (up to 9 inches) and lights through the machine’s 115 volt AC or 230-volt AC duplex receptacles, which supply up to 3,000 watts of auxiliary power. Dave J.Dave J.Beware of false knowledge; it is more dangerous than ignorance. ~George Bernard Shaw~ Syncro 350Invertec v250-sThermal Arc 161 and 300MM210DialarcTried being normal once, didn't take....I think it was a Tuesday.
Reply:Thanks! That is very educational. I hadn't thought about the ability to run AC tools as a big argument in favor of alternator-based machines.
Reply:My local NAPA store got me a cam for my 1948 short hood with in 24-hours! Don’t pay any attention to meI’m just a hobbyist!CarlDynasty 300V350-Pro w/pulseSG Spool gun1937 IdealArc-300PowerArc 200ST3 SA-200sVantage 400
Reply:The sa200 was pure dc because its main generator created dc current and so did its exciter, which feeds the main generator with a small current then it makes the big welding current.  Since these consists of rotating armatures and fields (unlike a simple d/c battery) its important for everything to be matched up in output or some fluxation can be felt in the arc. Imo.Some of the sa250s, all of the 300d models, and now the new sae300 have an a/c exciter, instead of a d/c exciter like the old sa200 had. The exciter current is still used to excite the main d/c generator so it can make the big welding current but since its a/c it must be rectified. These exciters are single phase.Rectified d/c means half of the a/c wave is canceled out. Instead of the voltage going from 120 volts positive, through 0 volts, then to 120 volts negative at 60 times a second, it only goes from 0 volts to 120 volts positive and back to 0 volts still at 60 times a second (60 hertz). The negative part is blanked out. So a time lag happens at 0 volts while the source wave continues its negative swing and back. Once it comes back up passing 0 volts it then again begins its upward swing and is allowed into the circuit.igbt's, or switching transistors if you will, can take 60 hertz rectified current and chop it up to like 18,000 to 28,000 hertz. Some of these machines are 3 phase where some are single phase. But the main generator creates the huge welding current at welding voltage in a/c then it is rectified the chopped up.  The dig circuit is very important so the maching acts like a welder expects the arc to act.  ie, like a d/c generator machine i suppose.Single phase means there are 2 hots and 1 ground.  3 phase means there are 3 hots and 1 ground.  Since a/c  electricity alternates from negative to positive at a rate, this rate is called the hertz.  So single phase can be thought of as firing twice where 3 phase fires 3 times in the same amount of time. 1/3 smoother.Another difference is the order that the poles fire. In single phase they are 180 degrees apart, meaning when one hot is 120 volts positive the other is 120 volts negative. ie,  Opposed.  In 3 phase they are only 120 degrees apart so as one side is rising in voltage the other 2 sides are decending in voltage. ie,  rotary.  That is a big reason why 3 phase is best for electric motors because this rotart action does a push-pull deal on the armature where single phase does not (opposed) which requires more current to do the same amount of work.  More current also meaning more heat.In inverter machines like my xmt350 i hear takes the 3 phase input current anywhere between 195 volts to 500 volts, rectifies it, changes the voltage to 460 volts, chops that up with igbt's to like 48,000 hertz, rectifies it again,  drops the voltage to welding voltage (say 35 volts) then out the cable.  Processing such high voltage means the parts inside them can be so small.  I also hear that by it processing such high voltage is why the transistors can achieve the higher hertz.And btw, based soly on my experience and the fact i make my living on xray pipelines, i dont have xmt's repaired.  Really, my job is too important to me to experiment with some tech somewhere fixing my machine for me. Besides, they are only worthless if broken to people like me. Haha.If i were smart and/or rich i'd invent a little inverter box that would fit on a 300d's exciter circuit. The exciter current would then be like 48,000 hertz instead of 60.  If i had such an option available i'd buy one today i believe..... especially since at the present i'm welding with a contractors 300d right now at work on this job.  Haha.  (Just a miller xmt lover's rant) hahaHope this helps.SlowhandLast edited by slowhand; 06-02-2013 at 01:45 PM.