Why does my Miller Big 40 weld so much better then my Idealarc 250??

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I have a Lincoln Idealarc 250 that I bought at the beginning of the year used but in great condition.  I like it a lot but just the other day I got a 1986 big 40 for my truck and It is like night and day.  The arc is so tight and concentrated and easy to control.  The lincoln is all over the place and hard to dial in it seems.  Should there be this big of a difference or is there something wrong with my idealarc?-mark
Reply:Hi Mark. What rods, polarity, base metal, preparation, amperage are you using? No two identical model machines will behave identically, you have two vastly different machines there. Assuming they both are running stick, are they set for the same polarity, amperage, etc.?City of L.A. Structural; Manual & Semi-Automatic;"Surely there is a mine for silver, and a place where gold is refined. Iron is taken from the earth, and copper is smelted from ore."Job 28:1,2Lincoln, Miller, Victor & ISV BibleDanny
Reply:Well I run both machines DC reverse.  I actually notice a difference with all rods, but mainly 6011 and 6010.  99% of the time I am welding mild steel with mill stock just as it would come from the steel yard.  Maybe it's just the characteristics of the two machines.  I just can't believe how much more control there is with the big 40.  I also noticed that it is much easier with lincoln to get high spots at the beginning of the weld and flat spots at the end of the weld, any idea on how I can fix that?  I know that end of it is probably user related.  I know that the ocv of the lincoln is around 74 volts and closed is around 34, shouldn't that eliminate the initial high spot?Thanks for the help,Mark
Reply:The high and low spots sound like typical heat buildup acting on your penetration. To flatten out the start of the welds would take a bit of preheating perhaps.City of L.A. Structural; Manual & Semi-Automatic;"Surely there is a mine for silver, and a place where gold is refined. Iron is taken from the earth, and copper is smelted from ore."Job 28:1,2Lincoln, Miller, Victor & ISV BibleDanny
Reply:Hello Mark, there is a difference in how the DC output of these two machines is produced. With the idealarc you are using a transformer to reduce the voltage and increase the amperage, it is being produced with single phase power at 60 hz. This output still has a waveform and it is relatively coarse. I believe the Big 40 generates 3 phase AC which is rectified to DC output, however, since this output is 3 phase it has 3 different waveforms which overlap one another and provide the DC with a much tighter and "clean" output. I am not an electrical engineer nor an electrician so I might not be completely accurate with this description, yet I believe you will get the idea. I am sure that others can provide a much more technically correct description so I will await their responses, we'll both learn that way. Best regards, Allanaevald
Reply:aevald is correct, 3 phase rectified dc has less than 1% ripple needing little capacitance in the machine. A single phase machine will use large capacitors to smooth the output (sometimes many caps on a CV machine).You may have a failed cap in the Lincoln.Matt
Reply:Electrolytic capacitors can lose much of their capacitace ability over time, especially in extreme environments. The electrolyte paste between the insulating layers can dry a bit, greatly increasing output ripple.  How old is the IdealAc? (I wish my Bobcat225 was three phase, it welds great, but 3 phase is the bomb.)
Reply:I cant believe no one has yet suggested that its because the lincoln is a lincoln and the miller is a miller.  Have we all gone mad?
Reply:Originally Posted by sn0border88I cant believe no one has yet suggested that its because the lincoln is a lincoln and the miller is a miller.
Reply:An old rotary will out perform a non rotary transformer any day of the week. Nothing new there.aevald is on the right track.JasonLincoln Idealarc 250 stick/tigThermal Dynamics Cutmaster 52Miller Bobcat 250Torchmate CNC tableThermal Arc Hefty 2Ironworkers Local 720
Reply:aevald- what you're saying makes sense.  I actually didn't know that the big 40 was 3 phase.  I believe that may be the answer I was looking for.  My lincoln is a reconditioned Red-d-arc that I got off ebay.  I believe they buy used rental equipment and then recondition it, which make it very possible that the capacitors are shot.  What's the best way to test a capacitor of that size?-Mark
Reply:Red-d-arc IS a rental company, and yes they do "rebuild" units before sale. To what extent, I don not know."Where's Stick man????????" - 7A749"SHHHHHH!! I sent him over to snag that MIC-4 while tbone wasn't looking!" - duaneb55"I have bought a few of Tbone's things unlike Stick-Man who helps himself" - TozziWelding"Stick-man"
Reply:If you run your idealarc 250 on 460 or 575v 3 phase power, you will notice it perform better than when you run it on 230v single phase power.JasonLincoln Idealarc 250 stick/tigThermal Dynamics Cutmaster 52Miller Bobcat 250Torchmate CNC tableThermal Arc Hefty 2Ironworkers Local 720
Reply:Originally Posted by Stick-manRed-d-arc IS a rental company, and yes they do "rebuild" units before sale. To what extent, I don not know.
Reply:There's also other factors like inductance aka "Pinch" which may or may not be adjustable on the different machines.  Also some things vary depending where you are sitting in the rated work range and duty cycle.  Just because it says you can weld at the very top end of the duty cycle and rated voltage doesn't mean things like voltage droop and resistance increase won't happen to a greater degree than running a machine halfway up it's rated amperage and duty cycle. some people swear they can tell the difference between older machines that used 100% copper windings and new machines that use aluminum windings.Finally there's a notable difference between transformer and inverter machines.  I wouldn't call it better/worse  but different.Welding EngineerCertified Scrap Producer