Which TIG welder to buy... I've read the archives but still have Q's.

I learned TIG welding on an old Linde unit (the model slips my mind, it was a very large ac/dc unit - I thank my research director for
teaching me this skill. I am now in the market for a TIG machine - I am a hobbyist gunsmith. I have read the pros and cons of the machines out there, and need something that will weld thin sheetmetal and cast aluminium (also thin) but also has the flexibility to weld much thicker material if the job demands (some tripod mounts and misc projects that come up). I decided on the Miller Dynasty 200dx, but upon further reading saw reports that these machines may only be good for the warranty period due to being solid state inverters... I want a machine that will last like my boss' Linde (he bought his after grad school) but also need that low amp stability - where do I go from here (will the synchrowave units function ok for my needs running 5-10 amps at the low end?) ? Any advice is appreciated. Regards Gavin Tucson, AZ
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

If you want durability go for a Syncrowave 250DX. I love mine.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Thu, 29 Apr 2004 06:03:31 GMT, Ernie Leimkuhler

Assuming neither machine (Dynasty 200 DX or Syncrowave 250 DX) gets abused, is there really a durability or longevity difference between the two machines? It seems that the Dynasty hasn't been on the market long enough to exhibit its repair record.
Andy S.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

The problem is type of technology. Inverters work great, but all the components are compressed into a much smaller space. The few boards in inverters are sealed in blocks of plastic or silicone rubber. Each board costs about $500 to replace.
Transformer machines are larger and have more space inside. Repairs have the potential to be much cheaper since you can replace a $30 relay, rather than a $500 main board.
Also transformers don't get moved around as much, and having more air space tend to run cooler.
Inverters have a 10-15 year lifespan at best, before repairs become prohibitive. We have transformer machines at school that are 40 years old, and still work fine. Parts can be hard to find, but they don't cost much.
I love inverters, and have had my Maxstar 200DX for 3 years. Just this month it went out of warranty. I treat it very well, but it still makes me think about selling it for a newer one.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

10-15 years of getting used daily?
What kills inverters most efficiently?
Jostling from being moved? Grinding dust / iron filings in the airstream? Running into the duty cycle too often?
I'm hoping that not abused, I can get more than 10-15 years out of a TA185. Used a few times a month as opposed to daily like your Maxstar.
Hopefully age itself isn't too much of a killer.
When you buy an old car or m/c, you figure on replacing the rubber bits.
Speaking of old cars...        What model body/engine is your Toyota(s)?
Cheers--Jeff Dantzler
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

The internal parts are not made from adamantium. Materiels age, insulators dry out and plastics deteriorate. The most common cause of death for old tranformers is whenthe varnish on the transformer wires breaks down and the whole coils shorts out.
The same thing can happen to a inverter, just on a smaller scale.

In order to make sure I wasn't just making stuff up, I just had a chat with one of my welding machine repair buddies.
He said that an inverter that was left in a shop, running from one voltage all the time, that had the dust blown out regularly, and was never bumped or knocked around, should live indefinitely.
The most common parts that fail are the IGBT power diodes, which should be available for the next 10-15 years as replacement parts. He sees longevity as being limited by the availablility of replacement parts. As he said:
Transformers have pretty much reached their ultimate state. All they change now are the interfaces, and figuring out how to make some of the parts cheaper. Inverters are still evolving, and have yet to reach the state of electrical perfection that the transformers have reached.
The most coommon causes of death for inverters are: 1. Physical abuse, which breaks parts free inside cauising internal shorts. 2. Dirt and dust which prevents parts from cooling properly. 3. Running from many different voltages all he time.
So you can see that what kills inverters is being used as portable machines at multiple jobsites, being tossed in and out of trucks, and not being cleaned.
A inverter that lived in a shop and never moved, should live a long time.
He did recommend having it professionally cleaned every 5 years.

I own 3 toyota trucks. Truck 1 is my old '85 1-ton, longbed, 22REC Fuel Injected. 289,000 miles
Truck 2 is my new '86 1/2-ton, long bed, Xtra-cab, 22RE, Carb. 140,000 miles
Truck 3 is an '85 1/2-ton, shortbed that I bought for parts for $100 234,000 miles
So far I have yanked the engine from Truck 3 and installed it in Truck 1 to get it moving. I plan on rebuilding the engine from Truck 1 and re-installing it. I will then clean up the engine from truck 3 and put it back in truck 3. Truck 3 will get rebuilt and sold to my neighbor. I swapped the rear springs in truck 2 for those from an '86 4WD, so now it is closer to a 3/4-ton.
Truck 1 will be converted to a flatbed, so I have a 1-ton flatbed for hauling large things. Truck 2 has the overhead rack for long things.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I once had a Millermatic 200 (which I know is NOT an inverter machine, but anyway .................) that I owned for 13 years. I used it for commercial production of ornamental metal. The ONLY thing I did to that machine in 13 years is change guns. I was really surprised that the contactor points lasted that long, and an unknown time after I sold the machine.
Point is, IMHO, that anything that stays in a shop lasts longer. And anything that is only used by the owner and not employees or students, lasts indefinitely.
Just musing ...........
Steve
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:> The most coommon causes of death for inverters are:

From what I've read on he inverter welders, and with experience in high-current choppers and inverters for subways (500-1,000 Amp), the most predominant cause is exceeding duty cycle. Thing is, anything that even "has" a duty cycle in the first place tells you that it is under rated in the first place (for the current ranges that fall under the 100% duty cycle rating). In my opinion, I'd say that you are at the mercy of the electrical design of the unit.itself. i.e. how they design the snubbing circuits, what part of the derating curve they design the rise-times of the switching elements, and the switching rates, thermal conductivity of the heat sinking, etc, etc, and the switching device itself (manufacture, part selection, etc). But yes, as always, physical abuse does play into it, I just happen to think that the above superceeds that. At Westinghouse, and for chopper/inverter design for traction motor control for subway systems, (Bart, WMATA, NYCTA etc), the inverters/choppers were designed such that the max real world current current at (even at 100% duty cycle) was almost half of what the inverter was designed to do (at 100% duty cycle). ergo, FLA w/ fully loaded car was like 650 Amps, but with switching elements rated at over 1,200 Amps (RMS), the inverter could handle over 1,000 Amps at 100% duty cycle. Course in these situations, there are strict requirements for MTBF (Mean Time Between Failure), and rated total mission time (since these are very high dollar items. This would be equivalent to never taking a Thermal Arc ProWave 185ST over about 65 Amps, even though its rated at about 110 Amps at 100% duty cycle, and 165A at what, 20% dutcy cycle or something ? So its longevity lies largely in the design. Sounds like these welding inverter designers (ThermalArc, Maxstar/Dynasty etc) have indeed found a tradeoff point of derating vs. "over" rating, MTBF, and total mission time and cost.

But I do believe that an additional factor really does lie in how it is used, and at what current.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Jeff Dantzler wrote:

These new fangled IC's and plastic Transistors, and capacitors - stuff like that dye on the shelf. Tubes hang in there - sometimes glue came apart.
Normal failure mode is usage - current through a part physically more atoms away from the part they need to be.
Just hits from the power line might do it. - sit there and the one next to it kick the power line and it rings in several box transformers.
A FA - failure analysis would have to take place...
Martin
--
Martin Eastburn, Barbara Eastburn
@ home at Lion's Lair with our computer snipped-for-privacy@pacbell.net
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

With electronic equipment it is electrolytic capacitors. They don't age gracefully, and when they fail, they often take other components with them. In high current applications like welders, electromigration is also an issue. That takes out semiconductors. Semiconductors are also very sensitive to spikes and surges.
Running with inadequate cooling, or near duty cycle limits, will accelerate aging related failures. Because the welder manufacturers seem to be in a competition to reduce the size and weight of inverters, inadequate cooling has become a serious issue. Not enough air circulation, not enough heatsink area, and not enough thermal mass are real problems for equipment that is already sensitive to heat stress.
Components which might have a nominal 20 year life at 70F, will have exponentially shortened life at elevated temperature. In other words, they might only last 2 years at 100F, or 3 months at 120F, or 1 hour at 170F. (Those are just illustrative numbers, not to be taken literally.)
OTOH, the big old transformer boxes have huge thermal inertia, plenty of room for massive heatsinks, and large fans. They're also simpler, with much less to go wrong in the first place.
The other issue with inverters is obsolescence of parts. When there is a problem, the components needed for the repair may be long out of production, and the complex and compact circuit may not allow a substitute part to be fitted. Electronic components, particularly complex semiconductors, now have a very short production lifespan. 18 months is typical before they're replaced by a new generation. It isn't unusual to not be able to get semiconductor parts for equipment that is only 3 years old, because those parts aren't made anymore.
OTOH, conventional transformer design is very mature. The same part may be in production for decades. Also, transformers can be rewound, so even if a new replacement part isn't available, you can have the old part rebuilt by any rewind shop.
However, as more features proliferate, even the transformer machines have had complex control circuitry added to them. So you could still get stuck with an unrepairable machine if a component on the control board fails.
In consumer electronics, we've already passed the point where repair is a practical option. When your TV, stereo, or computer dies, you just go out and buy another because a repair, if possible, would cost nearly as much as a new unit (which likely would have better performance and more features anyway). It is getting to that point with industrial electronic equipment too.
We're in the process of replacing a perfectly satisfactory audio console at work. The old one is less than 10 years old, but we can no longer get repair parts for it. This isn't the console manufacturer's fault, the component suppliers just don't make the parts anymore. The new console will cost $270,000. That's outrageous, but we can't live with a console we can't keep in repair, so we've got to do it.
Gary
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Ernie - will that fit my needs at the low end (welding 1mm sheet metal and thin cast aluminium)? Thanks in advance. Gavin

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Yes, and will give you more power than the Dynasty 200DX.
For cast aluminum, you want to start looking for 4047 filler rod.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.