[bryanwi]

This has surely been discussed at length, but I cannot find the right search terms. So anybody who wants to answer with links to informative threads on the question - that will be appreciated. (Or the right search terms...)

The decision - I'm mostly miller centric (great luck with them so far), and want a full featured tig machine.

My shop has circuits that could run a Dynasty 350 at full power. But a Dynasty 280 DX is (a) smaller (b) goes to lower power and (c) is cheaper. A thread by Zank (hope I spelled that right) suggests that 280 DX can be updated to have the variable amperage EN/EP feature of the 350. So it appears that anything a 350 could do a 280 DX could do, except for amperages from 281 to 350.

Which to get would obviously depend on what work one wanted to attempt. And I really don't know - what I do changes a lot over time, sometimes on very short order.

So, what rules of thumb or practical limitations would lead one to think "you should get the biggest amperage TIG your shop can run" versus "in the real world you'll never use 350 amps, but really low power is nice, and the cost difference will buy a lot of practice metal"

I'm also very interested in data of the form "if 280 isn't enough 350 won't be either...."

Hopefully that's not too vague...

[Braehill]

bryanwi,
I can give you my thoughts on the subject but I don't own either machine, I'm just speaking to the amperage debate. I have an old Dialarc 250HF that will weld at around 310 amps and over the thirty years that I've owned it there were a few ocasions where I wish I had more. Could those few times have justified spending thousands of dollars extra on a bigger machine, probably not. If I was running a shop that did exclusively Aluninum fabrication then I would buy the biggest machine I could.

I didn't have the option at the time to buy an inverter welder with all the adjustability that's available now so I didn't have to choose between features and size. I would probably be in the 280DX camp right now if the upgrades don't push the final price too far towards the cost of the 350.

That's my view, but it's your money.

Len

[zank]

You are correct about the 280DX expansion. It retails for $499, but I've heard guys getting it for as low as $440 from their local shop. I can't find an online source for it. The only other features that the 350 has over the 280DX w/ expansion are the memory slots and higher pulse rates.

I wish I could help you regarding the amps. With a highly unbalanced wave, you can put a lot of heat into a part.

[bryanwi]

Thanks guys. It's a lot more money for 350, and for all I know when I need "bigger" I'll need waaaay bigger, so I've decided to go for a 280DX for now - might add the expansion later.

Thanks again, and I'm still open to learning anybody else's thoughts on this.

[alex4nder]

I was on the fence with the 280DX and ended up sizing down to a 200DX. I took a hard look at what I was welding, and how much current it was taking/what duty cycle I needed, and decided that: if I ever needed to step up I could temporarily rent a bigger Dynasty, and/or sell my machine and upgrade. Having a slightly smaller unit with lower voltage flexibility for cheaper, was worth it to me. Also it didn't help that my LWS basically told me I should plan on selling any inverter I buy before the warranty was up; although, that might just have been for his benefit.

I'm sure you'll be happy with the 280DX. Just my two cents.

[MinnesotaDave]

My thoughts on power are to look at the duty cycle where you weld the most - if it's high enough for your use (and your patience level), then you've bought enough power.

[soutthpaw]

You can also run an Argon/Helium mix to make the machine bigger. Or even straight Helium with DC

[bryanwi]

Sanity check (correct rule of thumb to start?):

1. Co2 -> NOT for Tig.

2. 100% Argon - what you use for Tig unless there's a reason to do otherwise

3. 25%He or 50%He or 100%He (rest Argon) -> make for hotter welds and thus increase penetration, or solve other problems.

And so soutthpaw's comment refers to "if we don't have quite enough amps, we can switch to say 25%He and that may make it up" - right?

[Or am I confused?]

[Braehill]

bryanwi,
It's correct that you can use Helium to increase the heat input into the material and in a sense increase your welding capacity. I'm no expert on inverter welders but it's my understanding that different settings can also increase the size Aluminum that can be welded at a lower amperage, other will be able to speak to those particulars. Peheat is also an option for this.

I've never found a need while Tig welding on DC for much more than around 160 amps. to weld even very heavy pipe and plate, just use more passes.

Len

[soutthpaw]

bryanwi,
It's correct that you can use Helium to increase the heat input into the material and in a sense increase your welding capacity. I'm no expert on inverter welders but it's my understanding that different settings can also increase the size Aluminum that can be welded at a lower amperage, other will be able to speak to those particulars. Peheat is also an option for this.

I've never found a need while Tig welding on DC for much more than around 160 amps. to weld even very heavy pipe and plate, just use more passes.

Len

Yes, inverters with high frequency, advanced waves such as square wave, independently adjustable AC amplitude, balance etc can all contribute to more penetration from the same amount of amps. I have a friend who uses helium mix daily in his shop. Even a 5-10% helium with AC current can make a difference. So just buying a small helium tank and a flowmeter and Y adapter for when you need a little umph would be a good setup option or just get the tank as 75/25 Ar/He.

[Otto Nobedder]

I must make one remark here...

I doubt the 280 is limited to 280.

280A is likely the certified 40% duty-cycle point.

Our Miller SW250DX's at work have 40% at 250A, but will weld 310A at 10% (and even that is an underestimation).

I welded at 300A, on a 250DX, with a 250A torch, for 6 hours, with the only relief for the machine being the time to pick a fresh rod or me to take a leak and get more coffee... I actually blew a 30A fuse in the 3-phase before the machine shut down (and it never did). I completely smoked a torch lead and never hurt the machine.

Read the specs in detail. Understand what the machine's ratings mean. Some companies label their machines "250" because that's all they can produce. Others, because that's all they can produce for extended periods.

Steve S

[MinnesotaDave]

Steve, I think I've noticed a trend in inverters, they seem to use the max current as the name - unlike the older machines that used the rated amps.

For example, my Airco 300 is 300 amps at 60% - but maxes out at 470 amps.

But my little maxstar 150s tops out at 150 amps.
My invertec v250-s maxes at 250 amps (but claims a hot start striking ability of 300 amps)

The only data I saw on the 280dx says 280 is it's top amps.

I could be wrong, but it seems like that's what I've been seeing.

[Otto Nobedder]

Dave,

That sucks, and is a horrible, if predictable, trend.

It sells unsuspecting old-school folk like us if we don't read the details.

We're accustomed to getting more than promised out of every quality tool we buy. If we have to adjust to getting "just as promised", I'm going to be seriously dissappointed in the marketing department of every manufacturer.

The salesman's creed: "Under-promise, over-deliver!"

Steve S

[MinnesotaDave]

Steve, I suspect it will swing even farther into "just barely as promised...on a good day...if the sun is shining...and you hold your tongue just right..."

[TamJeff]

Even with machines that will weld higher than their rating, it's an utter pain in the ass to use the 'tricks' on a job of any size. Then you need the torch and cables to carry it as well. These days, competition and the market doesn't typically allow for too many extras in the bid. The cost of the extra consumables alonr can add up to the price difference in a more robust machine as far as aluminum is concerned. I blew two waterlines just this past week just welding 250 amps from a 250 amp syncrowave, and with a dynasty 300dx. In a shop environment, where I will often be called on to weld 3/8-1/2" stock, I suffer through it.

Also, there is the distortion factor with aluminum. Get on it and get off and it's much less distortion of the part, or perhaps even concerns with heat fatigue from dawdling on a weld for too long. Guess what else you will likely not have for that occasional beef job. . . and that is, the proper fixturing for such things. A truly capable machine can make all the difference in that regard.

So really it depends on how serious you are and if you are going to do this professionally and if you can afford to turn work away. Otherwise, you will end up better off just specializing within your machine's capability and sending the heavier duty stuff down the road. It will be cheaper yet just to pay someone with the right equipment to do it.

If I have the money to buy the cheaper machine today, I will have enough to buy the more expensive one a month or three from now. If my livelihood is not immediately dependent on it, it's just a matter of waiting and some patience. I would go by my personal expectations of; "I can weld some things, I can weld most things, or I can weld just about anything", or let who I want to be in my field decide the rest.

['Stang]

You can also run an Argon/Helium mix to make the machine bigger. Or even straight Helium with DC

You can do that, but you have to be careful. The helium mix puts more heat into the weld-but, it also puts more heat into your torch. If you are running a gas cooled torch at max amps, you can smoke your torch in a hurry. I have three torches for my Dynasty. I have a Weldcraft 17, CK Flexlock 150, and a Weldcraft 26. When I run higher amps, I switch to the 26. It feels like a club in my hand, but it will handle 200 amps.

If you are not running a cooler, you have to pay attention to the duty cycle of your torch as well as your welder. Helium downgrades your duty cycle on the torch. It doesn't affect the welder-just the torch.