Advice on Tig (Heli-arc) setup?

Hi all :)
I have an older Lincoln AC 225 stick welder (220 v), that works quite well. I would like to invest in a Tig torch set, flowmeter, and bottle
of argon to do some light to medium duty heli-arc welding with, using the Lincoln welder as the power supply. It would be mostly sheet metal, and up to 1/4" max thickness for short welds. Would this be a practical setup? I can't afford a dedicated Heli-arc welder, with all the bells and whistles, so I'm wondering if this would be a do-able compromise.
All advice welcome :)
Thanks,
Allan
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Al Porter wrote:

You would probably have better luck with a DC welder using reverse polarity (IIRC) for aluminum, than AC without a High Frequency supply.
The High Frequency allows the arc to stay lit while the AC current cycle back and forth across the zero line.
High frequency add on boxes for larger welders come up on ebay, but at prices that start to make a low end TIG setup affordable.
IMO, unless you have a talent for electrical circuitry, you will waste less of your time and money by going straight to the real thing, rather than dicking around trying to make the stick welder be what it isn't.
On the other hand, at least one of the guys here has converted a heavy duty power supply to an all singing all dancing AC/DC/Pulsing/Plasma Cutting and everything else welding machine. Out of the league of the likes of me, though.
Cheers Trevor Jones
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Hock your first born, take out a 4th mortgage on your house and car but get a good TIG machine. I've got a real good Miller stick welder that came from a College welding department. I hardly ever use it now that I have the TIG. Now that I'm getting used to my Plasma cutter, the TIG and the Plasma Cutter have a permanent home and will be the last tools to leave my shop. My Acetylene torch set up is relegated to brazing and heating only.
--
Stuart Fields
Experimental Helo magazine
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Al,
What you propose is doable.....my son and I converted the same AC buzzbox into a simple but fully functional TIG welder which is used to fabricate stainless steel exhausts for the family fleet. We have tested it on aluminum and copper, using pure argon cover gas, and junior sez it works like a charm. The visual inspection and mechanical tests by me bears this out.
To do the conversion you ought to be familiar with power electric wiring, and a modicum of electronics experience. Here is why:
You will need to convert the AC welder to supply DC current. This is achieved by means of a full-wave bridge rectifier capable of handling say 220 amps at 350 volts.
The DC must be filtered by means of a choke or inductor. The size of the inductor is about the same as the welding transformer and handles the full DC welding current. The inductor is needed to keep the current flowing when the DC voltage drops to zero during the rectification cycle. This is particularly necessary for low current welding.
For light gauge welding and Aluminum (with AC) you require an arc starter. These are surprisingly simple....we built ours from scratch using an oil burner ignition transformer and broken tungsten carbide endmill shanks, among other electronic stuff.
To weld thin material, especially copper and aluminum, but handy for all thin metals, you require on-the-fly current control because the arc is started with a relatively heavy current and once the welding pool has formed the current is reduced to prevent melt-through. Not a difficult circuit to build, same for the foot pedal, but some knowledge of electronics is required.
As Trevor stated it is easier and faster to begin with known DC equipment. Conversion of AC welder to DC can be fraught with expensive lessons when you marry the HF arc starter to the welder. :-))
If you are still interested in pursuing this let us know and I can help you on your way. If you have the AC welder and are good at scrounging the costs are not too steep. Just be prepared for some set- backs manual labour.
Wolfgang

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snipped-for-privacy@hotmail.com wrote:

I'm curious. How does it regulate the current? Do you regulate the line voltage going into the box with a light-dimmer like circuit? Or do you somehow regulate the high amp current after the transformer?
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For current control we designed a triac phase control on the primary side of the transformer. The tricky part was to get regulation that was wave symmetrical (important for transformer application) and hysteresis-free for fine current adjustment. The potentiometer we put into the foot-pedal. The triac can handle 600VAC up to 40 amps, and has been trouble free. The tig torch is rated for up to 150 amps so I doubt we will exceed the 40 amps of primary current.
Wolfgang
On Feb 1, 6:13 pm, snipped-for-privacy@kcwc.com (Curt Welch) wrote:

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snipped-for-privacy@hotmail.com wrote:

Meaning that the percentage of on time for each half of the wave was equal?
How was that hard to do? Wouldn't a simple R/C timer triggered from the zero crossing do it?

Why would there be a hysteresis effect? Does the inductive load cause a phase shift and move the zero crossing reference point?

Cool. How much does one that large cost roughly?

Your posts make me think building a welder might just be one hell of a fun project. It seems like it's the type of project which you are almost guaranteed to have to fry a few big parts before you figure out how to make it all work right.
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Curt,
Let's just say that a commercial light dimmer type circuit doesn't cut it.
The uneven capacitor discharge for each half cycle has the effect of introducing a DC pedestal onto the AC phase controlled current, which transformers don't like and may, in the extreme, act as a short circuit and blow the fuse / breaker.
On many phase controlled circuits to get the load to initially turn on, the control resistance has to be turned lower than the desired power level would indicate.....a reference scale on the pot shaft would show this clearly.
While this may not matter for a light, fan, or even motor control, it is very irritating for fine current control on a welder, where you want the welding current to follow the pot adjustment - up or down - immediately and very closely. Our circuit does all this very nicely as verified by oscilloscope and actual usage.
The only draw-back is the limitation to 40 amps AC; this is the largest triac available. Cost: About $10 or so. If you need higher AC current symmetrical control there are methods of doing it with a pair of inverse / parallel scr, but we didn't bother with this since 40amps AC is fine for our purposes.
Wolfgang
On Feb 2, 1:24 am, snipped-for-privacy@kcwc.com (Curt Welch) wrote:

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snipped-for-privacy@hotmail.com wrote:

Yeah, I know that effect from light dimmers now that you mention it.

Very reasonable.

Very interesting. Thanks. Sounds like a fun project.
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Hi Curt
I have some big SCRs with heat sinks and pulse transformers that I'd give you if you get serious about building a current controller for a welder with about 250 amps max output current. I saved an article from EDN magazine by Narendra Paranjape where he shows the circuit for a SCR current controller using a fan regulator. That info is available via E-mail too
Jerry
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Jerry, there are also SCR controllers on the market that do all the hard work. PCTI is one of the manufacturers. You just send simple signals to the controller, like using a potentiometer or filtered PWM, and it takes care of the rest. I use one by PCTI in my CyberTIG.
i
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Thanks Jerry, but the odds of me getting serious and actually doing it are very small. Most likely, if I did anything, I would create something small that ran on 110 V with transformers too little to produce any real welding power just to have fun playing with the idea and not with the intent of building a welder I would actually want to use.
--
Curt Welch http://CurtWelch.Com /
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On 1 Feb 2007 19:43:26 -0800, snipped-for-privacy@hotmail.com wrote:

Sounds like you don't have a symmetry problem but I'll still note: an alternistor (Teccor) might be a bettter choice than a triac in an application like this. It behaves more like a pair of back-to-back SCR's. They are available up to 40 amps. The trigger circuit must (as you say) still provide symmetrical triggering, though.
Some AC motor controls use a full-wave bridge and a single large SCR. They are mains-voltage AC in and mains-voltage AC out but the SCR switches rectified DC. It's easy to get good symmetry in this sort of arrangement.
Note that with AC tig (aluminum) some arc rectification can occur, which may mean that the machine should be de-rated a bit for AC operation to avoid saturation. It will tell you by buzzing loudly when it's approaching a point of distress.
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http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber811
Several here have purchased this rig, and like it.
Goes on sale regularly for $199
Where are you located? I occasionally run across older tig machines rather cheaply.
Gunner
"Liberalism is a philosophy of consolation for Western civilization as it commits suicide" - James Burnham
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18:22:10 GMT, Gunner wrote:

... and some of us who bought that rig had to send it back. Mine burned out after less than three minutes of actual arc time.
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On Sat, 3 Feb 2007 11:45:33 -0500, Steve Ackman

Really? Hummmm....I kept seeing the praises..but no negatives.
What took you so long?
<G>
Gunner
"Deep in her heart, every moslem woman yearns to show us her tits" John Griffin
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21:41:16 GMT, Gunner wrote:

Hey, I can't help it if your rememberor is beginning to fizzle. On 2 Aug,
(or for the news server retentionally challenged...) http://groups.google.com/group/rec.crafts.metalworking/browse_frm/thread/8fa5eae3c48baef5/57303e9ed603d10e?lnk=st&q=&rnum=1#57303e9ed603d10e
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Hi Allan
I made two seperate "Heliarc welders" in the 1960s. I used my AC buzz box stick welder for one. The stick welder with the HF and TIG torch works very well for melting aluminum. If you are Very Good, maybe you could actually weld with a home made conversion, add -on to your Stick welder if the metal is thick enough. I used mine for "welding" thick aluminum and "light alloy" VW cases, and Corvair heads..
My observation is -- Build your own TIG if you want to laern about how to build TIG welders. Buy anything that fits your budget if you actually want to TIG weld.
I'd be happy to share any of my experiences with you if you decide to build a TIG add-on to your Stick welder.
Jerry
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wrote:
First off; a big Thank You! to everyone who replied. The depth of knowledge and experience in this NG is fantastic :) Secondly; I have decided to hold off until I can afford a dedicated rig, even a low-end one if necessary, but not necessarily a low-end unit :) I'm no electronics whiz, altho I can do basic wiring no problem. But by the sound of things, I would be further ahead to buy a proven factory-made unit rather than trying to cobble something together with my level of knowledge and experience. Once again, Thanks Everyone, for the advice!
Allan P.
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Al,
Our intent was NOT to discourage you, but to let you know what you are in for! We would be pleased to share our experience with you.
Start by picking up a 220 V transformer the size of the welding transformer in the buzzbox, or a little larger. Next you need cable to wind about 36 turns onto the transformer core, after removing the existing windings. We managed to salvage the wire we took off and, by cutting it into 4 equal lengths and putting them in parallel, wind 36 turns. The wire size you need is #4, which you can build-up from smaller dia., say 4 x #10 lacquer insulated. Next get 4 diodes, say min. 220 amps, 300 volts, plus 4 large heat sinks, say 4" x 8" each. Ideally the diodes come in pairs of positive stud and negative studs; makes mounting and wiring much easier. All this will get you a good DC welder, a start.
Wolfgang

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