Mig welder options, Old machine vs new

[yngndrw]

Hello,

I was hoping for some advice on a hobbyist home mig setup. I am limited to single phase but I have the main consumer unit close by so 32A (Or even 64A) isn't an issue. I'm looking at inverter units so that I can actually lift it myself and also for the stepless controls.

I want something reliable so I've been discounting the nameless stuff on ebay, but I also don't want to spend a fortune. I had initially been looking at the R-Tech 180 units so that was my baseline price of around £500.

The R-Tech units are of course very limited, no synergic settings and doesn't even seen to have adjustable inductance. Obviously there's no hot start or crater filling either.

Another contender was the Kemppi MinarcMig Evo 200 available for around £1000, again new with warranty. I believe this has a slightly lower minimum current and has full synergic control but again none of the really fancy options.

That leaves me with the big spanner in the works, a used unit with all of the bells and whistles. A Kemppi Pro 3200 with full pulse controls. Now this is a very old (Discontinued) unit with no warranty, but the fact that it's still working tells a story in itself. This has everything: Synergic control, hot start, crater filling, pulse and even double-pulse. This is a big three-phase unit which requires a 13.3kVA power source (With a 320A limit at 100% duty cycle!), but I've worked out that I can adapt it to run from a 32A single phase supply with a power limit of around 8kVA - Based on the rated input at its maximum power, I think that would allow me to run it at around 190A. The price for this including the parts to adapt it to single phase will end up to be around the £1000 mark, so this is in direct competition with the new MinarcMig.

Pulse is very interesting as it would allow me to use spray transfer on smaller parts in more realistic orientations. Spray interests me because of the lack of spatter - Honestly I don't really have a need, but my thought is why exclude myself from that when it's available for the same price.

So there you are, three main options: (Or any others you may suggest)
1) A cheaper option, R-Tech 180 @ ~£500
2) An expensive new option, Kemppi MinarcMig Evo 200 @ ~£1000
3) An expensive old option with all the bells and whistles, Kemppi Pro 3200 with the MXE pulse mig panel @ ~£1000

Thanks,
-Andrew.

 

[waddycall]

Might help if you say what you need it for and your level of experience.

 

[yngndrw]

Sorry I missed that, I'm just a hobbyist so nothing crazy thick - Brackets, frames, cars (both panels and chassis), maybe even a roll cage when I'm experienced enough to trust my life with it.

As for experience, beginner. I think I've gotten my head around the bulk of the theory, but I have a long way to go in terms of putting that into practice. That's part of the reason I was interested in a synergic machine, to give me a good ballpark to start from.

I know that pulsed spray is way above both my experience and requirements, but as far as I can see there's really only advantages aside from the cost of machines that support it.

 

[waddycall]

For years many have been happy with the results from a basic transformer machine. In your shoes I’d go with something simple. You need to learn to walk before you can run. A non synergic machine will probably teach you more about machine set up as you’ll have to figure it out for yourself.

 

[a111r]

There's a bargain posted today in the Classifieds, an 'as new' Clarke 151EN for £150.

An ideal starter machine that won't depreciate (unless you reverse a vehicle over it)

 

[yngndrw]

For years many have been happy with the results from a basic transformer machine. In your shoes I’d go with something simple. You need to learn to walk before you can run. A non synergic machine will probably teach you more about machine set up as you’ll have to figure it out for yourself.

Fair point, I'll certainly make sure I spend the time to learn the manual settings regardless of what I end up with. I did look at the Oxford machines but the size and weight of the transformer based machines is silly, even compared to the Kemppi 3200 that I mentioned above. It sounds like the R-Tech Mig180 is the option you'd pick out of the above then in that case? My only fear is growing out of it and then having to replace it at some point down the line, I was wondering if it's worth going with something that I can grow into if I make sure I take the time to learn the basics?

There's a bargain posted today in the Classifieds, an 'as new' Clarke 151EN for £150.

An ideal starter machine that won't depreciate (unless you reverse a vehicle over it)

An interesting option to throw into the mix - Would the step-based voltage control be an issue? I know you're meant to be able to fine tune with the wire feed but I believe that it isn't a perfect replacement for stepless voltage control, would that end up being an issue that I'd have to fight with, especially with me not having the experience with exactly what the setup should be? I know plenty manage without stepless voltage control, but I'd rather now fight with it if I have the option unless it really is a non-issue?


It also raises another question which I haven't been able to find the answer for - A lot of people when comparing machines mention the minimum current but I don't really have a handle on exactly what I'd need for any thin panel work. The R-Tech Mig180 has a minimum of 25A, the Kemppi MiniarcMig 200 has a minimum of 20A/15V, the Kemppi Pro 3200 has a minimum of 12V (No idea what current that relates to, but MMA is listed as 10A so I'm going to assume around 15A?) and that Clarke 151EN has a minimum of 30A.

What kind of minimum current do I need for let's say 0.8mm steel? Are these all suitable and does the lower minimum just make it easier to manage? Is the question of minimum current just blown out of proportion by people comparing machines?

Also why are the open circuit voltage figures so strange for the Clarke 151EN, are they mis-quoting the weld voltage as the open circuit voltage or is this a key difference between transformer and inverter machines?

Welder	Minimum Current	Minimum Weld Voltage	Minimum Open Circuit Voltage
R-Tech Mig180	25A
Kemppi MiniarcMig 200	20A	15V	70V
Kemppi Pro 3200		12V	65V
Clarke 151EN	30A		21V
Oxford Migmaker 180-1	20A

 

[julianthegypsy]

I weld things together all day, mostly 5mm plate, and use the R-Tech as I had limited power at the time. It works and their service is excellent. I could happily weld thin stuff if I needed to, though you might prefer slightly lower amps.

 

[a111r]

I'm not a welding professional but my take is:
Sub 30 Amps may not equate to good penetration, car work needs some heat. 15 or 20 Amps may be all but unusable.
OCV is useful only as a technical parameter to check the machine is working properly, not in normal use. Inverter MMA OCVs will not equate to transformer MIGs.

Stepped voltage is less good than variable. But 6 steps up to 150 Amps (for example) affords OK control, via the wire speed.
This is not explained well with hobby machines; e.g. select 'power' A, B,C, at setting 1,2,...6.

Quoting from a 1984 user manual I have:
"The faster the motor speed, the higher the current drawn by the arc. Wire feed speed thus controls welding current".
I will tag @Munkul there

 

[Jack Ryan]

I was hoping for some advice on a hobbyist home mig setup. I am limited to single phase but I have the main consumer unit close by so 32A (Or even 64A) isn't an issue.

The trouble with getting stuff to grow into is that you need to buy something that does everything as you don't know initially which way you are going to grow. I'm not familiar with your regulations but I'm pretty sure you can weld at 200+ amps from a 16A outlet. An ESAB Rebel 235ic is supplied in the UK with a 16A plug. An option to go big is fine but I think not needed yet.

The R-Tech units are of course very limited, no synergic settings and doesn't even seen to have adjustable inductance. Obviously there's no hot start or crater filling either.

I don't know these, I assume it is another Chinese welder but it appears to have very good support and a good reputation. That is more important that where it was made and the truth be known, many of the name brands source equipment from China anyway.

Synergic welders can be easy to setup but synergic means different things to different manufacturers. Sometimes it just means quick parameter recall based on thickness - sometimes much more. For example some allow you to set the voltage and they automatically set the wire speed. This sounds very constrictive but it often works very well. Other units monitor the arc and adjust the parameters dynamically. You probably won't know what you prefer until you have used them.

There are lots of welders that don't have adjustable inductance. Is there a particular reason you expect to want to change it?

Are there migs that do crater filling? I guess there probably are but mostly I see that as a TIG setting. Hot start is an MMA setting - do you need that? MMA is also called "stick welding" - probably because they never used to have hot start (sorry) - do you need that?

All I am saying here is don't be too harsh on this class of welder.

Pulse is very interesting as it would allow me to use spray transfer on smaller parts in more realistic orientations. Spray interests me because of the lack of spatter - Honestly I don't really have a need, but my thought is why exclude myself from that when it's available for the same price.

Spray pulse is interesting but it can be an expensive option. It is a good way to get spray transfer to work with thin panels - in or out of position. Spray pulse is also a developing technology so unless you need (want) it right now, it will be better later.

Conventional spray won't be a happening thing on entry level welders - they don't have enough grunt. Note too that spray uses a different gas so there is yet more cost.

Brackets, frames, cars (both panels and chassis), maybe even a roll cage when I'm experienced enough to trust my life with it.

A welder in the R-Tech class will do brackets, panels and some chassis but be aware that chassis welding can be a regulatory minefield. A roll cage of fancy metal (or just aluminium) might be better suited to TIG.

There are also multi process welders. These are often a MIG that can do other stuff too. Don't expect a multiprocess welder to be a fully optioned TIG welder although some are getting there - the ESAB Rebel 205ic for example.

Also why are the open circuit voltage figures so strange for the Clarke 151EN, are they mis-quoting the weld voltage as the open circuit voltage or is this a key difference between transformer and inverter machines?

I don't know that particular machine but open circuit voltage is less a welding parameter and more a shock hazard. Modern machines often have VRD (voltage reduction device) to limit the open circuit voltage to a safe level.

Sorry about all the bandwidth I've used. I could have summarised by suggesting that you take smaller machine steps so you can more accurately follow your interests.

Regards
Jack

 

[Munkul]

My tuppence:

- 32amp single phase is sensible for up to 250 amp MIG sets, that's well enough for most work - if it's a true 250 amps and has the power to drive the voltage to suit.
- Kemppi machines are great, they make very good conventional MIG sets. The resale on anything Kemppi is pretty good - as long as it works.
- You run a risk with any used inverter welder you buy - it might die tomorrow, it might die 30 years on. Hard to say. All you can do is buy something that looks like it's been treated nicely. Personally, I think it's worth the risk - especially on 3 phase industrial-grade equipment.
- I wouldn't have a machine with all bells and whistles as my first MIG machine, unless I knew exactly what I was doing and that I needed said bells.
- You won't use pulse on thin stuff, older pulse machines don't have great control on steel pulse. It's aluminium where they come into their own. So the perceived advantage of the Pro 3200 isn't something you'll end up using anyway.

- That Pro 3200 - it doesn't look like it will run on single phase at all! I would avoid, you need something that will run directly on single phase 240v

- beware "semi-synergic" sets - all this means is that it ups the wirespeed with the voltage, no finesse or actual cleverness in it, you still have to fine tune it.

- As a first machine I'd be looking at a Bohler Uranos, Gys multi-pearl, or something like that - a good quality 200 amp compact inverter that's flexible enough to do a few things, as well as having a good synergic setup.

 

[yngndrw]

Lots of replies, thank you all for the help I really appreciate it.

I don't know if this has been posted before but one of the issues I have is trying to judge the capacity of a machine which is marketed with current when none of the basic controls directly control the current and when it's dependant on a whole range of things such as wire size and stick-out. I've found this diagram which while not accurate given that many variables cannot be shown in a table, it at least approximates things: (Green is short, orange is spray)

The weird thing is that I think I understand the basic controls enough to be able to know what change to make based on the weld (Assuming consistent torch distance and travel speed which I know I'm not going to be anything close to consistent with!), but I still have a hard time explaining exactly what the controls do. From what I can see:
- Changing the wire speed in the same direction to the voltage (I.e. Keeping the same ratio between them) effectively changes the current and therefore the rate at which it heats - This in turn along with the travel speed controls the penetration and I think that in a synergic machine where you set the material thickness, this is really what it's trying to change as you change that thickness
- Changing the wire speed in the opposite direction to the voltage (I.e. Changing the ratio between them) changes the arc length which is used to get it running smooth - I'm struggling to explain exactly what the effect is though aside from that there's a sweet spot based on the sound and look
- Changing the inductance changes the shape of the weld bead, I suppose this is kind of the same as changing the current, only it doesn't seem to affect the penetration and overall heat?

If my understanding above is correct, I can't see how stepped voltage controls would be anything but annoying unless I'm missing something. Do experienced welders just correct for this by adjusting the torch height?

I weld things together all day, mostly 5mm plate, and use the R-Tech as I had limited power at the time. It works and their service is excellent. I could happily weld thin stuff if I needed to, though you might prefer slightly lower amps.

That's good to know, I've heard pretty much nothing but good things about R-Tech. It's the thinner stuff that I'm more concerned with on the R-Tech with that 25A minimum being slightly higher than the others.

I'm not a welding professional but my take is:
Sub 30 Amps may not equate to good penetration, car work needs some heat. 15 or 20 Amps may be all but unusable.
OCV is useful only as a technical parameter to check the machine is working properly, not in normal use. Inverter MMA OCVs will not equate to transformer MIGs.

Stepped voltage is less good than variable. But 6 steps up to 150 Amps (for example) affords OK control, via the wire speed.
This is not explained well with hobby machines; e.g. select 'power' A, B,C, at setting 1,2,...6.

Quoting from a 1984 user manual I have:
"The faster the motor speed, the higher the current drawn by the arc. Wire feed speed thus controls welding current".
I will tag @Munkul there

This is where I get a little confused about exactly what minimum current is required - The chart I linked to would agree with you but others (Both in these forums and in welding videos) then mention issues on thinner panels. I do wonder if the issue is more around the accuracy of the machine in question, I.e. whether or not it can provide a consistent wire speed (Most cheaper machines have no feedback on the wire feed motor, so changes in load from binding as it heats up or from the liner as it is bent) will change the wire speed) or voltage (Voltage drop over the wires will change based on the current at that point in time, the power source may not be able to accurately hold that voltage or may output too high of a voltage at the start) - Or maybe it's down to technique and the welder's experience. Either way without having a machine myself it's very hard to judge.

<Snip due to the character limit>

I can't argue with your first statement about not knowing in which way you'll grow and whether or not you'll need the features in the future, it's sound advice. I suppose on the flip side there's a point about how you'll know whether or not you need something without being able to try it and I think that's the part I always struggle with.

On ratings, I'm not too worried about the upper limits on current for any of the machine listed but some of the numbers are weird. It makes you wonder how they have rated them given that the current isn't constant during welding. Have some manufacturers used the average current while others have used the peak? It's quite interesting that both of the Kemppis seem to be quite different in this regard when you look at the input power rating against their maximum output - It's almost as if they used to use the average current but then as marketing has taken over, they've all switched to quoting the peak current.

I've only been considering either fully manual machines or fully synergic machines and have been avoiding semi-synergic machines in my search as they sound really annoying, where they sort of change the settings for you but not quite. I think the fully synergic machines are essentially trying to give you a sort of "current" control, but it's hard to know without actually trying one.

Inductance is an interesting one, I believe it's the shape of the weld and again without the experience I don't know if it's something that does typically need to be changed - I have noticed that the R-Techs do seem to give a bit of a "heaped" weld bead and don't have that adjustability but I guess it's just a vanity thing. (Unless I'm completely missing the point of variable inductance??)

Crater filling and hot start - Only in the really fancy ones which is why the Kemppi 3200 is so interesting, it has all of these features you'd only see in machines costing multiple thousands of pounds. I believe hot start is there to compensate for the cold metal as you start welding and you can see where people are showing demonstration weld beads that they tend to not start off with as much penetration at the start for the first inch or so. Technically it's just boosting the power (I.e. current) slightly at the start of the weld for a pre-set period of time so I think that's why you don't see it on most machines - It only makes sense on fully synergic machines where the machine can change the current without affecting the balance between voltage and wire speed. Crater filling is just ramping down the current at the end as far as I can see, again one for the fancy machines and I think it's also limited to fully synergic machines for the same reason above. I've only ever seen good things mentioned about these sorts of features but as they are rare and expensive, you don't see much about them. Another thing that you don't really know if you need or want them without being able to try them.

I'm not worried about the cost of gas as I'll be using HobbyWeld 5 which is 93% Argon, 5% CO2 and 2% Oxygen so I think I'm covered for spray either way? Spray only seemed useful to me with pulse but it's interesting that you and @Munkul have both mention about the progression of pulse technology. I had kind of seen it as a technically basic thing where it's really just adjusting the weld current (Which as above only makes sense on a fully synergic machine) but I guess the synergic mechanism really does matter for it if it has to abruptly change settings every second or so. According to the chart above it looks like around 160A is the entry point for spray from what I can see.

 

[yngndrw]

My tuppence:

- 32amp single phase is sensible for up to 250 amp MIG sets, that's well enough for most work - if it's a true 250 amps and has the power to drive the voltage to suit.
- Kemppi machines are great, they make very good conventional MIG sets. The resale on anything Kemppi is pretty good - as long as it works.
- You run a risk with any used inverter welder you buy - it might die tomorrow, it might die 30 years on. Hard to say. All you can do is buy something that looks like it's been treated nicely. Personally, I think it's worth the risk - especially on 3 phase industrial-grade equipment.
- I wouldn't have a machine with all bells and whistles as my first MIG machine, unless I knew exactly what I was doing and that I needed said bells.
- You won't use pulse on thin stuff, older pulse machines don't have great control on steel pulse. It's aluminium where they come into their own. So the perceived advantage of the Pro 3200 isn't something you'll end up using anyway.

- That Pro 3200 - it doesn't look like it will run on single phase at all! I would avoid, you need something that will run directly on single phase 240v

- beware "semi-synergic" sets - all this means is that it ups the wirespeed with the voltage, no finesse or actual cleverness in it, you still have to fine tune it.

- As a first machine I'd be looking at a Bohler Uranos, Gys multi-pearl, or something like that - a good quality 200 amp compact inverter that's flexible enough to do a few things, as well as having a good synergic setup.

This is where the minimum current comes into it again, I had discounted the 250A version of the R-Tech mig machine because it has a 30A minimum current rather than the 25A of the R-Tech 180A mig but I don't know if that's an issue any more.

The pulse control comments are very interesting, I had assumed it would be great for running spray on thin steel but I can see how it's control may be limited on such an old synergic implementation. The Pro 3200 still has hot start / crater filling but the lack of usable pulse does make the newer / smaller machines (With a warranty) much more interesting.

I'm very sure I can get the Pro 3200 running from a single phase 32A supply. I'd essentially build an auto-transformer to produce around 366V single phase (Or perhaps 2 phase would be a closer description) which would be fed into two legs of the bridge rectifier and would work as normal. The machine is rated to run at 100% duty cycle down to a 360V input so the only component under stress is the bridge rectifier. This would have to be derated to about 66% but that's fine as a 32A 230V supply limits me to about 60% of the maximum rated 13.30kVA input.

I've been avoiding semi-syneric machines as they sound counter-productive.

I did look at the Bohler Uranos but it was about £500 more than the Kemppi MiniarcMig 200 and I couldn't really see much of a benefit for the extra money. The GYS Multi Pearl 200 is in the right sort of price range to directly compete with the Kemppi MiniarcMig 200 and has the same feature set as far as I can see, I'm not sure which one is better out of the two really - I guess for these two machines it comes down to how good the synergic settings are out of the box. As the synergic settings cannot be adjusted on either of these machines (That's a nice thing about the Pro 3200, you can adjust the syneric settings yourself), the synergic side is only as useful as the base settings. (I know you have to tweak them anyway, but it would be nice to have a decent base)



So after all that, I'm still unsure as there's such a range of opinions. Your comments have all been really helpful and you've all raise some really interesting things to consider. I'm actually leaning towards the Kemppi MiniarcMig 200 now but I'm just getting stuck in my mind with the concept that I'd be paying as much as the Pro 3200 (Actually slight more) and getting less in exchange for essentially just a warranty. The Pro 3200 has survived for many many years but is it ready to pack up tomorrow? Are features such as hot start and crater filling worth the risk, or even useful to me at all? Or am I better of saving the money by buying a cheaper fully manual unit and spending it on something else? I hate making decisions. Interestingly I've just had an email response from Kemppi stating that they can't share the Pro 3200 service manual with anyone but their service departments even though the machine is long since obsolete so that does make the prospect of repair more difficult, although here's the schematic I've found in case it helps anybody:

 

[slim_boy_fat]

Too much analysing, too few welds [imvho, of course ].

 

[Tom Orrow L]

I can sort something out on a Bohler Uranos 2000 SMC, best single phase 200A multi process on the market imo. Features, technical specs and build quality are ridiculously good.

 

[Munkul]

For what you're doing, you dont need pulse-mig, hot start or crater fill, or anything fancy at all.

You want a machine which has a high quality smooth CV arc and a wide "sweet spot" for setting to get good spatter-free welds. The paper specs of bottom end amperage aren't as important as how the machine itself runs... e.g. you could buy a machine that promises a 20 amp bottom end, but has a horribly spiky delivery which makes it useless below 60 amps... if you get my drift.

I have no idea why you'd want to faff on trying to convert an old industrial machine which may or may not affect how it runs and may or may not die tomorrow, when for the same money you could have a minarcmig 200 or similar, which "just works".
I'd message Tom and see what price he can do on the Bohler if I was in your shoes it has a few more "bells and whistles" which would genuinely be useful.

 

[a111r]

Where did you find that chart (USA...)?
For the green sections, it's a bit odd. Wire sizes, mixed units, even gas type. The Amp ranges suggest 110 volts?

 

[Munkul]

Where did you find that chart (USA...)?
For the green sections, it's a bit odd. Wire sizes, mixed units, even gas type. The Amp ranges suggest 110 volts?

I agree, some of it is a bit off. We wouldn't use 98/2 gas for spray over here unless it was stainless steel... typically we'd choose at least 10% CO2 or an equivalent tri-mix type like Argoshield/sureshield, which gives you far more flexibility in short-arc as well as some spray transfer.

Lots of replies, thank you all for the help I really appreciate it.

I don't know if this has been posted before but one of the issues I have is trying to judge the capacity of a machine which is marketed with current when none of the basic controls directly control the current and when it's dependant on a whole range of things such as wire size and stick-out.

The weird thing is that I think I understand the basic controls enough to be able to know what change to make based on the weld (Assuming consistent torch distance and travel speed which I know I'm not going to be anything close to consistent with!), but I still have a hard time explaining exactly what the controls do. From what I can see:
- Changing the wire speed in the same direction to the voltage (I.e. Keeping the same ratio between them) effectively changes the current and therefore the rate at which it heats - This in turn along with the travel speed controls the penetration and I think that in a synergic machine where you set the material thickness, this is really what it's trying to change as you change that thickness
- Changing the wire speed in the opposite direction to the voltage (I.e. Changing the ratio between them) changes the arc length which is used to get it running smooth - I'm struggling to explain exactly what the effect is though aside from that there's a sweet spot based on the sound and look
- Changing the inductance changes the shape of the weld bead, I suppose this is kind of the same as changing the current, only it doesn't seem to affect the penetration and overall heat?

Sorry mate, I couldn't be bothered to reply to the whole thing

It's simple. You're not far off.
-Wire speed and stickout roughly approximate amperage. Wirespeed is the key variable.
-Voltage affects the bead shape and arc length. Too little means a peaky bead and poor burn-off. Too much means wasted heat and spatter. It's important to match with wire speed.
-Step transformers work because you set enough voltage to work with the wirespeed you want, and then finetune the ratio with wirespeed knob. Better step migs have way more voltage taps.
-Inductance affects the dynamic of the sort-circuit arc. More inductance gives a softer arc, and sometimes a more fluid puddle, as it smooths the current spikes. It's not a setting you really need to fiddle with often.

You need to work around a few things, there are certain amp and voltage ranges for certain gas mixtures where you'll have a nasty spattery spot no matter how you set it.

Some machines are just lovely to use, and you'll come to them and find a nice sweet spot easily and just crack on... some machines just seem harsh no matter what you do. It's not a setting, it's just the way the machine was designed and built. Some MIG sets are simply fantastic, and some machines are simply frustrating.

You need to get a MIG set, some hobbyweld 5, and just get welding

 

[Munkul]

This is where I get a little confused about exactly what minimum current is required - The chart I linked to would agree with you but others (Both in these forums and in welding videos) then mention issues on thinner panels. I do wonder if the issue is more around the accuracy of the machine in question, I.e. whether or not it can provide a consistent wire speed (Most cheaper machines have no feedback on the wire feed motor, so changes in load from binding as it heats up or from the liner as it is bent) will change the wire speed) or voltage (Voltage drop over the wires will change based on the current at that point in time, the power source may not be able to accurately hold that voltage or may output too high of a voltage at the start) - Or maybe it's down to technique and the welder's experience. Either way without having a machine myself it's very hard to judge.

Most MIG sets don't have feedback on the wire feed motor, until you get up to the very best synergic pulse sets. Usually all open-loop. You as a person are responsible for making sure your equipment is running properly and it's putting out the amps it's supposed to... this is why any serious MIG set gives an actual as-welded current readout.

On ratings, I'm not too worried about the upper limits on current for any of the machine listed but some of the numbers are weird. It makes you wonder how they have rated them given that the current isn't constant during welding. Have some manufacturers used the average current while others have used the peak? It's quite interesting that both of the Kemppis seem to be quite different in this regard when you look at the input power rating against their maximum output - It's almost as if they used to use the average current but then as marketing has taken over, they've all switched to quoting the peak current.

Most MIG sets - all transformers, anyway - are rated up to a certain current, e.g. 200 amps, all that means is that it's physically capable of it, if you run a large enough wire through it at enough speed. Some are capable of more... some are barely capable of running it at all. The current should be fairly steady, plus/minus a few amps depending on how steady your hand is!

Crater filling and hot start - Only in the really fancy ones which is why the Kemppi 3200 is so interesting, it has all of these features you'd only see in machines costing multiple thousands of pounds. I believe hot start is there to compensate for the cold metal as you start welding and you can see where people are showing demonstration weld beads that they tend to not start off with as much penetration at the start for the first inch or so. Technically it's just boosting the power (I.e. current) slightly at the start of the weld for a pre-set period of time so I think that's why you don't see it on most machines - It only makes sense on fully synergic machines where the machine can change the current without affecting the balance between voltage and wire speed. Crater filling is just ramping down the current at the end as far as I can see, again one for the fancy machines and I think it's also limited to fully synergic machines for the same reason above. I've only ever seen good things mentioned about these sorts of features but as they are rare and expensive, you don't see much about them. Another thing that you don't really know if you need or want them without being able to try them.

Hot start and crater fill are really not important on steel until you're running 300a+ IMHO... and I have them on my current machine, I'd use them if I thought they were useful
They are, however, very very useful on aluminium MIG, due to the way alloy absorbs heat.

I'm not worried about the cost of gas as I'll be using HobbyWeld 5 which is 93% Argon, 5% CO2 and 2% Oxygen so I think I'm covered for spray either way? Spray only seemed useful to me with pulse but it's interesting that you and @Munkul have both mention about the progression of pulse technology. I had kind of seen it as a technically basic thing where it's really just adjusting the weld current (Which as above only makes sense on a fully synergic machine) but I guess the synergic mechanism really does matter for it if it has to abruptly change settings every second or so. According to the chart above it looks like around 160A is the entry point for spray from what I can see.

Pulse is it's own beast... MIG dynamics are complicated enough, pulse MIG dynamics are so incredibly complicated that it only works properly when the machine has total control over every aspect of the weld process, with feedback loops. The best sets from the likes of Lorch and EWM have multiple feedback loops on voltage and current, every single frequency cycle.
Honestly, I wouldn't worry about it.

I've been there and done it, I had an older Miller pulse-mig setup... worked well on aluminium only. It wasn't predictable enough for steel. Now I have a Lorch S3 speedpulse, which is night and day difference... but it's still not a "magic bullet" - it has it's own downsides.
That same Miller XMT set, on standard CV MIG, is still as good a MIG set as I've ever used. Same with the Kemppi step transformers at work. 3 controls - voltage, wirespeed and inductance. Simple.

It's still skill as much as machine, remember!

 

[arther dailey]

so to throw a spanner in the works , what about a second hand ewm pico pulse ? would that fit the bill

 

[Nick DV]

If new, transformer Oxford 180-1 from @Tom Orrow L