Rectifier vs inverter?

  1. DennisCA

    DennisCA Member

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    I'm thinking of expanding my "machine park" (1 arc/tig DC welder in a hobby garage) and I am adverse to buying cheapo brands of Chinese manufacture. I am particularly a Kemppi man, because Kemppi is finnish and I am from Finland, so I like to support local business. But money isn't exactly in plentiful supply so I don't tihnk I'll be looking at any new machines.

    I'm probably gonna be looking at older used machines and they are more likely to be rectifiers, preferrably 3 phase but maybe single phase will do. That's kinda the reason I am making this thread... I know what a single phase rectifier isn't fun to weld with for arc-welding. I used to have an arc welder like that and it was very choppy and difficult to weld with. I am wondering if the same holds true for mig welding as well, it's quite a different process so perhaps it does not. I don't know...

    So that's the gist of my question, is there a significant difference between a rectifier mig welder and an inverter one? I know that a 3-phase rectifier is very smooth as an arc welder, because it rectifies all three phases so you don't get the 50hz choppy feel. But I have hardly any experiences with mig welders so it's all new to me.

    Just wondering if I should discard older single phase mig welders, or if the process is different enough that it doesn't matter.
     
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  2. Munkul

    Munkul Jack of some trades, Master of none

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    It's different to stick welding.
    There are plenty good single phase transformer/rectifier MIG welders, but in my experience 3 phase is smoother... depending on machine quality. The Lincoln compact 220 in our motor vehicle workshop is a good example - it's a fine machine and does right across the range no problem. There are plenty of great single phase MIGs... but you'll pay for them!
    If you have 3 phase, my advice is, just get a 3 phase machine. You'll have more choice for a better value industrial machine.
    The transformer Kempomat 4200's at work put out as nice an arc as my inverter Miller XMT. The drive roll system is fantastic, too.
    I'd reccomend a used Kempomat 3200/4200 to anyone.
     
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  3. pedrobedro

    pedrobedro Man at Matalan

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    Transformer mig (rectifier ?) is heavier. Was your old arc welder an air cooled transformer? They were notorious for sticking and poor starts till you got the hang of them. I've used single and three phase machines and can't tell the phase difference you must be more sensitive than me except three phase are usually industrial so are better quality. Inverter machines have start assistance so you don't stick (as much) and if you wander away from the puddle they will sometimes have software to compensate for your lapse in concentration. Get the best you can afford and don't over think it.
     
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  4. DennisCA

    DennisCA Member

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    My old arc welder was a kemppi as well, Super Kempak 150. I ran it in both single phase 230v and single phase 400V (using two phases). I know one guy who loves his machine but it never felt right to me. But the machine works identically to his so I guess it's personal preference. I gave it to my dad and he uses it now and then, I only paid 100€ for it.

    I would like to get a 3-phase unit definitely as I have it. In my price range I sometimes see machines like a Kemppi Kempomat 250, an early 1990s machine. Sometimes though I run across single phase kemppis like a Super Kempomat 150 and I was wondering if that was worth pursuing at all.
     
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  5. frank horton

    frank horton V twins are great but 4"s rule.........

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    my single phase 180 mig does well for me.....mostley car work n light fabrication.......it's now 20 years old n still works great ...
    had to change the wire feed assembly once and now changed to a Euro lead......swop it ...not on ur Nelly.....sorry English joke.....
    My arc welders are three phase oil cooled with 1 x 240 volt arc welder for mobile work...it doesnt stick with decent quality rods.....
    works well with a bigger fan inside than standard......
     
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  6. DennisCA

    DennisCA Member

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    I learned of another important factor when selecting a mig welder, the minimum amount of amperage it puts out. I would like to use it to weld sheet metal as well as thicker stuff, maybe that is too much to ask of most welders.

    A modern minarcMig has a range of 20-200A while an old kempomat 250 manages a range of 30-300A. I think 30A is at the limit for welding 1mm sheet metal or so?

    On the 2nd hand sites there's a Kemppi Super Kempomat 150 for 220€ but it's only 150A and single phase. Still it's a kemppi and it goes down to 18A/13V so might be useful for sheet metal welding, not sure it's any good for welding 6mm or thicker stuff.
     
  7. eddie49 Member

    On a "step-switched" transformer/rectifier machine there is a limit to the number of ranges that can be provided, even with a 12-position switch or a combination pair of Coarse and Fine switches. So if you buy a 250 or 300 Amp machine, the manufacturer will expect that you're into heavier fabrication, and will tend to start with a lowest range around 40 Amps, in order to not run out of switch steps to get up to the 300 Amp maximum.

    Therefore you may want to consider a big-iron cheap 3-phase 300A Kemppi for 2mm to 10mm, plus a tiny shiny new 140A inverter for 0.7 to 4mm.
    Whether that one can also be cheap depends on how much you are going to use it, and how long you would like it to last.
     
  8. Munkul

    Munkul Jack of some trades, Master of none

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    Or... buy a big inverter :) a Miller XMT 304 has a 5-400 amp full range and 10-35v stepless adjustment in CV mode. Using it for thin metal is a pleasure, even with 1.0mm wire you can weld 1.6mm sheet easily. With 0.8 or even 0.6 you'd have the control for really thin sheets and precision work.
     
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  9. DennisCA

    DennisCA Member

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    I'm not sure I understand eddie49, is the implication the plate on the machine isn't listing the actual usable or actual welding amperages?

    Plate of a Kempomat 250:
    [​IMG]

    edit: I understand there is a limited number of steps to choose from, but it seems to me the first step ought to coincide with the plate, otherwise the plate would've said different.
     
  10. eddie49 Member

    I was just talking generally, that it is normal for big MIGs in the 200/300/400A range to start high, and a 40 Amp "minimum" would not be unexpected.

    I am sure that you can trust what Kemppi say on the dataplate of that Kempomat 250, it does start at 30A, which is going to be OK on fresh 1mm sheet.
     
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  11. eddie49 Member

  12. DennisCA

    DennisCA Member

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    I'm mainly looking for an older 2nd hand machine. I've never seen a Miller around here, it's mainly ESAB and Kemppi and the stray Wallius (another finnish brand). Then a dearth of chinese hobby junk sold by remorseful buyers.

    Found a manual for the smaller 150 model and it says stepless adjustements of welding power and feed rates. Downside, says only 20% intermittance at 125A, doesn't even list 150A despite being called a 150. I think it'd be great for body work, but to be honest I forsee doing it once on my car, then it'd be general fabricating for when I don't feel like tigging or stick welding which involves both sheet stock and materials between 3 - 10 mm. Only takes 0.6 and 0.8 wire.

    The lookout continues. Eventually something shows up if you are not in a hurry.
     
  13. Munkul

    Munkul Jack of some trades, Master of none

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    it's true :D sometimes you'll get lucky, sometimes not.

    The later XMTs were all (IIRC) autolink which means you can use them on single phase or 3 phase, but 11kva apparent power on single phase looks like they're pretty gutsy for the power (225 amps at 60% duty). Definitely better on 3 phase. I'm running mine on a C20 breaker and had it up to 350 amps no problems.
     
  14. AndersK Member

    Messages:
    967
    Location:
    Sweden
    I've never tried any 1 phase transformer machines but you need something yellow in your life :rolleyes:

    Their 3ph arc welders where so easy to learn on when I was at school.

    (Can't fault the orange ones neither I must admit)
     
  15. DennisCA

    DennisCA Member

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    I was offered an ESAB Power Compact 200 but I declined it because it didn't go lower than 50A/15V, otherwise it looked like a good candidate.
     
  16. eddie49 Member

    The ESAB Power Compact 200 is a step-switched MIG with no less than 12 power ranges, and yet it starts at 50 Amps minimum ... strange !
     
  17. DennisCA

    DennisCA Member

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    It's bigger brother the compact 250 goes down to 30A, whch I found strange.

    I also looked at my dads mig welder, a finnish made Wallius LKM-220, he has used it for all kinds of things including body work and it also goes down to 30A. In the manual it says it's good down to .5mm sheet metal. So a wallius might be a good choice, they are not very well known outside Finland. Often found in industry though, think my dad bought his from his work place. Used to be a welder during and before he turned farmer.
     
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  18. Memmeddu

    Memmeddu Member

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    IMHO the answer depends on machine's habitat
    Outside jobs will require smaller units , light weight , compact and portable machines so in this case inverter welder would be my choice
    In a shop stationary environment a big bulky transformer based welder would be my choice
     
  19. stanbester Member

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    Location:
    United Kingdom West Yorkshire Halifax
    If you like kemppi and you're after secondhand three phase mig with good range of settings, try to find kemppi RA230.
    They were made to last and nice to use if in good condition. They have 32 steps power settings and start very low on amps.
     
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  20. DennisCA

    DennisCA Member

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    I looked those up and they seem to have a range of 40A to 300A, seems a bit high on the low end but better than 50A. The kempomat 180/250 does better down to 30A.
     
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