Opinions on older TIG supply?

A significant advantage to TIG is the ability to control heat independently from rate of addition of filler metal.

Inability to control heat with a foot control would be a major compromise. I wouldn't consider a TIG without foot control. I have no problem with older transformer-based machines that do have foot control. That's what mine is. (Miller Dialarc 250HF)

Jon, Best analogy I could think of is sort of like computers.... A 286 vs. a Pentium 4 .... And the foot control is a must unless you have three hands.

Rob

Fraser Competition Engines Chicago, IL.

Thanks Don, that is what I was hoping to know.

It also brings up a desire to know what methodology is used to externally control the current output of an inductive type machine (as in with a foot switch) I wouldn't imagine it's done with servo's on the shunt, maybe a PWM at some stage?

Jon

There are a couple of ways of controlling the current. The newer machines use PWM on the output of the transformer. The older machines used a thing called a MagAmp that played games with controlling the current coupling of the AC power by saturating the core with variable DC levels. Sorry I can't give a better description, it's been a long time since I sort of understood it.

Bob

Most of thise transformer welders use SCRs and control their firing angle (timing) depending on current desired.

Some do. I think that started with the Synchrowave in the Miller line. Older ones use saturable reactors or "mag amps" as John noted. The DialArc uses a magamp.

Thanks Bob, and Iggy. I hadn't thought about the saturable reactor, but I can see that would work (would be a bit beyond a retrofit, though). Looks like I might have to play with an SCR to see if I can cobble something up....

Jon

Don, you are right.

Jon, The machine on ebay has a pedal control, the cable is on the lower left front corner.

But, if the machine you are looking at does not have a foot pedal, it's a pita. BUT, you can weld without a pedal, it takes more time to get the proper current setting.

I have a Lincoln AC buzz box, with a High Frequency unit from Power Craft (Montgomery Wards I think). Air cooled torch. With a little effort on scrap, I can get it setup and lay down a bead on Aluminum. Gets a little dicey as things warm up, and a live torch can bite you.

That's how the home shops did it in the 50's.

I don't suggest getting a TIG without a foot pedal. Been there DT. Dave

one:

Hi Dave, and thank you for the detailed response. The Airco unit in that link does indeed have a foot pedal, but (as was detailed by the owner of the other unit I was looking at) it is only for controlling the HF component (I don't know what component it varies, however).

Regarding your HF unit, is that just for arc starting, or does it actually provide an HF current for welding on aluminum?

Thanks again,

Jon

Something else to consider too is that most of the older transformer units of any size draw a lot of current on the input side even idling. There is a good chance you wouldn't be able to just plug one of them in the same place as your current buzz box without beefing up the circuit.

Make sure you check on this before getting something that calls for a lot of re-wiring. At least figure it into the cost of the unit.

In a TIG machine, HF is usually used just to start in DC mode, runs continuously in AC mode as with aluminum. It doesn't hurt to leave it running while DC welding, it just isn't necessary. Having it run continuously when AC welding helps arc stability but the HF contributes essentially no heat. The arc does the work, the HF just keeps it going.

Foot control of arc current is a great help in puddle management, particularly with aluminum. Otherwise you must start slow to get a puddle going, and then go like hell to keep up with it.

A foot-controlled box using SCR's or IGBT's would do the job. Ignoramus built such a box, don't know if he ever got it working to his satisfaction.

I would use MOSFET's, only because I have a bunch of 'em on hand.

I built an SCR controlled box, it works fine. However, it does not have foot pedal control, only pot control.

Oh. Well, nevermind then.

Jon,

I have never seen a foot control that did not control the current, but could be I guess.

My HF unit is a few milliamps, just a spark to avoid having to scratch the tungsten, (as it was done initially). Scratching contaminates the tip. It's on all the time.

I tool a Welding class a few years ago, just for the fun of it, and to brush up on Aluminum. One of the machines had a broken foot pedal, turned the machine on, but no current control. Even though there was a shortage of machines, no one wanted that one. Well, except me. On Al you need to start hot anyway, and then cut back, as the material gets warmer, and at the ends. (I got lots of time on that machine.)

Dave

Thanks, Dave, I'll remember that about the aluminum. Thanks for the info on the HF unit; I've seen one or two of those on local lists.

Jon

Gotcha, thanks Don. I might have to consider building that "welder arc stabilizer" that the fellow made the page for. I think I've probably got most of the items on the list anyway. I'll have to bug Iggy to see how his box turned out.

Jon

"Ignoramus14435"

Heya Iggy, you don't by any chance have any reference to how you built it? That sounds like what I'm trying to be able to do, and I can't even decide if I want the SCRs before the iron or afterwards.... :)

Jon

Aye, thanks for the consideration, Leon. I'm already planning on putting a dedicated service in there anyway; so I'll have the capacity.

Jon