Miller Road Show - Inverters for AC vs DC

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I attended the Miller Road Show in Denver, which had lots of equipment to drool over, most of which I could not possibly afford, some of which was not even familiar to me.There was a seminar on TIG.  Most of the seminar was familiar material.  However, when I thought about it, I realized that at various times, the speaker was referencing the advantages of inverter type welders for AC aluminum/magnesium welding.    I went back and asked the speaker whether my impression was correct, that inverters are much more advantageous for AC welding than DC welding.   He agreed, and said "DC is DC".   The inverters have other advantages, in terms of size, weight, and power consumption.  But don't expect them to weld a lot better on DC than an old transformer welder.This is probably not news to most of you.  At some level I probably already knew this, but hearing it over and over seemed to sink the idea into my head.   Makes me feel better, in that I can't afford a Dynasty, but for DC, a Syncrowave will work just as well.RichardSculptures in copper and other metalshttp://www.fergusonsculpture.comSyncrowave 200 Millermatic 211Readywelder spoolgunHypertherm 600 plasma cutterThermal Arc GMS300 Victor OA torchHomemade Blacksmith propane forge
Reply:Richard,Not exactly.The frequency range of pulsing (PPS) on the inverters makes a BIG difference when doing thin gauge SS.I have both (transformer and inverter) and believe me, there is a difference.Syncro 250 DX Dynasty 200 DXMM 251 w/30A SG XMT 304 w/714 Feeder & Optima PulserHH187Dialarc 250 AC/DCHypertherm PM 1250Smith, Harris, Victor O/ASmith and Thermco Gas MixersAccess to a full fab shop with CNC Plasma, Water Jet, etc.
Reply:Originally Posted by SundownIIIRichard,Not exactly.The frequency range of pulsing (PPS) on the inverters makes a BIG difference when doing thin gauge SS.I have both (transformer and inverter) and believe me, there is a difference.
Reply:The difference between the quality of output from a 3 phase machine vs 1 phase makes sense if you think in terms of water.  Its a big simplification, but in general I believe it's correct.With 1 phase power:  Imagine the welder is instead a big tank full of water.  Welding drains water out of the tank.  The amount of water drained changes constantly all the time; sometimes its a trickle and sometimes its a flood.  Water is added to the tank by 1 man with a bucket.  The level of water in the tank can change dramaticly because there's only one guy pouring water into the tank.  And he doesn't work any faster or slower, he always moves at the same pace.  Pour, refill, pour, refill....There's a small pause between each bucketfull of water that gets poured into the tank.  It's possible that the tank could even momentarily go dry if enough water is allowed to pour out.With 3 phase power:Imagine the same situation.  But now you have 3 guys using buckets to pour water into the tank.  They also move at a the same even pace; but the water gets poured into the tank at a higher frequency; The first bucket of water is almost empty when guy #2 starts pouring his bucket into the tank, as #2 finishes #3 starts, as #3 finishes, #1 is ready to start all over again.  This keeps the water level in the tank higher and the amount of fluctuation is smaller; regardless of how much water or how fast the water is being drained out of the tank.  The tank will likely never completely run dry.Step up the input voltage and the analogy still works.  At higher and higher voltage the guys filling the tank switch from buckets to hoses.  Raise the voltage some more and the water pressure in the hoses goes up.  Raise the input amperage capacity and you're using larger buckets or larger diameter hoses to accomplish the job of filling the tank.Back in the real world of welding.  Does 3 phase power make a difference, yes.  Is is noticeable, definitely.  Does the difference make it worth paying for 3 phase power in your shop???  Depends.  A smoother arc might help when doing fine work on thin gage material.  It might(might) contribute to the amount of spatter you see when running short arc MIG; but 3 phase power isn't going to eliminate spatter or make the impossible possible...That's my opinion... Originally Posted by SR20steveWhat about a transformer sync with the pulse function? I have yet to try pulse on either even though my machine at work does have the function.But as far a smoothness, I notice a HUGE difference when welding with my 3 phase 350 LX and my 1 phase 250 dx at home, the 3 phase is much much smoother for DC- tig and DC+ stick, its really amazing IMO. And these two machines are pratically indentical minus the power input.
Reply:That's a pretty good analogy A_DAB, I'm not sure other than superior AC capability and programming work & effort, what the Miller rep was thinking when making that comment.3 phase CC power & scratch start with steel is a joy and nearly silent with a very still puddle at any amperage. By nature 3 phase CC machines supply current with less than 1% ripple. This smooth power is not so hot when sluggish materials with lots of nickel or copper are in the mix.With generators and older inverters I see the many voltage spikes per second as having the effect with sluggish materials. I think with the newer inverters switching so fast, a fast pulse program was added to have the same effect.Single phase transformers have a sawtooth profile from the caps discharging & on my Lincoln SQ275 it gets noticeable at 220 amps or so.MattLast edited by Matt_Maguire; 05-18-2011 at 08:11 AM.
Reply:A_DAB  That is a damn fine analogy.I offer three choices: Good, Fast, & Cheap. You may pick two.Hobart AC/DC StikMate LXHarbor Freight AD HoodHarbor Freight Industrial Chop SawDeVilbis 20 Gallon, 5 HP Compressor
Reply:SR20Steve,Unless you've got a "really special" 350 LX, it's a 1 Phase machine.Not sure Miller ever built a 3 Phase Syncrowave.The pulse range on the Sync 350 (and the Sync 250 w/optional pulse) is .25-10 PPS whereas the pulse range on the Dynasty 200 DX is .1-500 PPS and the Dynasty 350 is .1-5000 PPS (in DC).Big difference when hi speed pulsing is employed.Syncro 250 DX Dynasty 200 DXMM 251 w/30A SG XMT 304 w/714 Feeder & Optima PulserHH187Dialarc 250 AC/DCHypertherm PM 1250Smith, Harris, Victor O/ASmith and Thermco Gas MixersAccess to a full fab shop with CNC Plasma, Water Jet, etc.
Reply:Originally Posted by SundownIIISR20Steve,Unless you've got a "really special" 350 LX, it's a 1 Phase machine.Not sure Miller ever built a 3 Phase Syncrowave.The pulse range on the Sync 350 (and the Sync 250 w/optional pulse) is .25-10 PPS whereas the pulse range on the Dynasty 200 DX is .1-500 PPS and the Dynasty 350 is .1-5000 PPS (in DC).Big difference when hi speed pulsing is employed.
Reply:Originally Posted by rafergusonBut don't expect them to weld a lot better on DC than an old transformer welder.
Reply:Inverters do more than just make DC or AC.  The behavior of the arc at different arc gaps is very important.  With an inverter things are monitored thousands of times per second.  A little "brain" decides what voltage and amperage is suitable at the particular moment.  Many inverters allow almost infinite slope control.  This is a lot more difficult to do with a transformer - rectifier power supply.  It is odd that the presentation did not discuss "slope".   You want a different slope if you are using TIG than if you are stick welding.  Also you want to fine tune for cellulose rods and low hydrogen rods as well as on the flat, vertical or overhead.  Miller has an excellent website  article on slope and discusses why a welder kept failing his stick tests when using a GTAW power supply.  It is DC but not the right DC.
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Reply:Originally Posted by SundownIIISR20Steve,Unless you've got a "really special" 350 LX, it's a 1 Phase machine.Not sure Miller ever built a 3 Phase Syncrowave.The pulse range on the Sync 350 (and the Sync 250 w/optional pulse) is .25-10 PPS whereas the pulse range on the Dynasty 200 DX is .1-500 PPS and the Dynasty 350 is .1-5000 PPS (in DC).Big difference when hi speed pulsing is employed.
Reply:Just because it's four prong, doesn't mean all of them are hooked up.  Try reading the tag on the machine or popping the cover and counting wires.My name's not Jim....
Reply:LOLJust because it's got a "big plug" doesn't mean it's 3 Phase power.As Boostin mentioned, I'm betting not all four pins are used.  Suspect the reason they used that plug (for a quick disconnect) is because the larger plug was needed to carry the amp demand of the 350 LX (that sucker can pull 128A @ 230V)Even the Miller 330 A B/P (a power hungry beast) was a 1 Phase machine.Syncro 250 DX Dynasty 200 DXMM 251 w/30A SG XMT 304 w/714 Feeder & Optima PulserHH187Dialarc 250 AC/DCHypertherm PM 1250Smith, Harris, Victor O/ASmith and Thermco Gas MixersAccess to a full fab shop with CNC Plasma, Water Jet, etc.
Reply:Originally Posted by SundownIIISR20Steve,Unless you've got a "really special" 350 LX, it's a 1 Phase machine.Not sure Miller ever built a 3 Phase Syncrowave.
Reply:I guess thats why Im a welder and not a electrician, haha..
Reply:Bottom line is:If you're gonna TIG you need to work with the new inverter technology.For me it helps to lay down better welds.It IS a necessary evil.I run an old Miller DialArc HF at work and it sucks for TIG compared to my little Dynasty.They both have their place though.............Measure twice, cut once.Millermatic 211Millermatic 251Miller Dynasty 200DXESAB O/A Set-up