[fredygump]

I am getting ready to buy a tig welder, and as I look at specs I see amp@voltage=dutycycle ratings. And every machine is rated at a different voltage.

For example, a miller 200dx is 100a, 14v=60%. The 280dx is 235a, 19v=60%. And the 350 with 1-phase is 225s,30v=60%, or with 3-phase power is 300a, 32v=60%


What importance do these ratings have on welder selection? Is it just the amperage that determines the heat put into the metal, or does volts*amps=watts determine the amount of heat? If voltage affects total heat, then wouldn't a welding spec have to specify both current and voltage? And if the voltage does not affect the total heat input, is there an advantage to a higher voltage machine?

I know the machine adjusts the voltage to maintain the set amperage, so is a higher voltage machine just more consistent?



It seems likely I will buy a 280dx. I have used the 200dx both at school and at work. It's a great machine, but it lacks the grunt to do much with aluminum. Plus I prefer to aim a little high than to come up short and have to buy twice.

[dynasty200sd]

The duty cycle ratings are for the amperage listed at that voltage, since the distance the tungsten is from what is being welded changes the voltage; the machine should be able to weld for 6 minutes ( for a 60% duty cycle rating) before having to cool the remaining 4 minutes (since duty cycle is based off a 10 minute period), and is then able to continue this cycle over and over (6 mins weld, 4 mins cool) without thermally overloading machine.

[fredygump]

The duty cycle ratings are for the amperage listed at that voltage, since the distance the tungsten is from what is being welded changes the voltage; the machine should be able to weld for 6 minutes ( for a 60% duty cycle rating) before having to cool the remaining 4 minutes (since duty cycle is based off a 10 minute period), and is then able to continue this cycle over and over (6 mins weld, 4 mins cool) without thermally overloading machine.

I understand that part. But what I'm trying to do is compare machines and understand why two different machines have different volt ratings at the same amp setting.

Example:

dynasty 350--180A at 27.2v = 100% (1-phase)

dynasty 200dx--200A at 18v = 20%; 150A at 16v = 60%


Based on these ratings, the 200dx set to 180A has a voltage of 17v. But the 350 set to 180A has a voltage of 27.2v!

Does this extra 10v mean that the 350 is welding hotter at a given amp setting? Is it regularly operating at that voltage?

[Coldman]

The duty cycle is based purely from the output amps. This is what you should be using for machine comparison.
The output voltage is useful to calculate energy input to the work piece while welding but has little to do with machine comparison and can be ignored for that purpose.

[fredygump]

Oh, I think I get it now....

The extra voltage must be designed to offset the resistance due to long welding leads!

A quick calculation (via online calculation website) shows that the extra voltage of the Dynasty 350 means it can run deliver 350A @ 12.5v through 300' of 1/0 copper wire! (The voltage starts at 32v, but gradually drops to 12v over the length of the wire.)

This give me a little perspective on what that machine is designed to do. Yeah, that machine would totally makes sense in a shipyard!


And the other machines I mentioned...the 200dx really can't handle any extra length, but the 280dx should be able to handle 100' of 1/0 copper (@280A) without losing too much voltage.


That's cool. Now I know something new...

[zank]

The voltage is across the arc gap, not the lead length.