Buzzbox conversion to TIG welder

Thanks for the heads-up, Wolfgang :)

I'll be sure to check that out. As for keeping the files together, are you familar at all with Zip compression\archiving? It is relatively simple to "zip" the files together all into one archive file, using a program called "Winzip".

Very cool. Thanks for posting.

Pic. #4 shows your spark gap. I saw in the manual of another welding box that it used a spark gap as well. What on earth is this for? Why do they need a spark gap?

Intersting. I don't quite understand how the 4 diodes and 2 extra resistors fix the hysteresis problem. Do you? Can you explain it?

Digging around I found a Teccor application note that I suspect was the one you used (it had a circuit almost identical with yours).

The basic idea is that the extra parts allows the capacitor charge to be reset to the same starting conditions for each cycle so the starting condition is not a function of whether, or when, the triac triggered on the previous cycle. But I don't quite grasp how those parts do that. I guess the idea is that if there is a charge left on the capacitor from the previous cycle, it will quickly be discharged at the start of the next cycle.

Looking at it some more, I guess I do basically understand it. When the voltage reverses at the next cycle, there's an extra charge path though R2 and D1 to help quickly drain off the extra (reverse) charge from the previous cycle. And D2 clamps the voltage to the forward drop of D2 which means the extra discharge path is disable once the reverse charge on the cap is removed. But R2 seems to be too large. At 20K it's more than twice the minimum resistance of the R1/R4 set. Ah, but it is still 1/25 the max resistance. So I guess it will drain the charge quick enough to not create much delay at the start of the next cycle. And you can't have it too large because it is causing current to flow in the off cycle of the dimmer through D2/D4.

Also, you changed the schematic slightly from the app note. You attached the variable R1 before the load instead of after it. Why?

On your HF unit, did you implement a HF on start only feature or is it just on full time?

They seem to be together now.

Here's a list of the URLs to save people the trouble of finding them:

And again, thanks for sharing!

Curt,

I'm glad the pics are of interest.

If you look at the top of pic. #7, the second line from the top, credit is given to the originator of the circuit....TECCOR.

My son did the adaptation for 220 VAC and also made those changes to improve circuit performance for the welder application. As I stated earlier it works very well. I cannot explain in detail how the circuit works and why....I leave that up to junior. I just make sure he doesn't burn down the homestead, or the neighbourhood.

The HF arcstarter is either on or off, controlled by its own switch on its cabinet; there is no provision to turn it off upon arc strike. I suppose for very light welding this may be a worthwhile addition. If so it would be a simple job to incorporate a micro-switch in the foot control to turn the arc starter off upon arc strike. Automatic turn- off upon arc strike is also doable if thought worthwhile.

The spark gap in the HF arc starter is part of the high frequency oscillator (tank coil) circuit. As a kid I used to fool around with Tesla Coils, and the Tesla primary circuit is very similar to the arc starter circuit.

The circuit will not work without the spark gaps.....2 gaps are a minimum, some people use 2 or 3. Think of the spark gap as the PUT or neon bulb in a relaxation oscillator. The .008" gap seems to work best...its used in commercial units and we settled on it also, after trying larger and smaller gaps. BTW the 10,000 VAC is overkill for the arc starter. 5,000 VAC is probably enough to work reliably. We found the spark much too fierce at 10KV and placed a 2:1 step-down transformer into the primary circuit of the ignition transformer. The spark also seems to jump much easier through the argon gas, than through air.

Numerous solutions are available for producing the high voltage, ranging from automotive spark coils, lawnmower spark coils, or television fly-back transformers; we picked what we were comfortable with and had the material on hand for.

Wolfgang

Thanks to the moderator for joining the files.....I'll try to do better next time. w

Ok, I'll do some research on these types of circuits and learn something new. I don't currently know how Tesla Coils work....

I do have a nice high voltage neon sign transformer somewhere in the basement that makes a very nice Jacob's ladder. But all it does is step the voltage up with a transformer. I guess the HF circuit needs not only high voltage, but also a circuit to generate the high frequency. Though if it's only used for arc starting with DC current, I don't know why you would need the high frequency. It seems to me you would only need to use high frequency to balance the A/C.

Thanks.

Hi Curt

You probably wont want a neon sign transformer. It is too dangerous. The beauty of the tuned RF circuit is its high output impedance. That makes it capable of burning you but (probably) not killing you.

You dont need the HF for TIG with DC, but it sure makes starting the welding arc alot easier/cleaner

Jerry.

HF is used because it travels on or very near the skin rather than thru the body. If you "get a little on ya" it burns a little but doesn't shock. If you get bit by a 60Hz oil ignition or neon xfmr it will be a very shocking experience and hurt bad.

The sparkgap excites the resonant primary of a (often) air-core HF transformer, whose secondary is heavy wire or strip in series with the welding lead. This xfmr is typically 1:1 or even stepdown. The resonant frequency is typically about 8 MHz. It's basically a Marconi radio xmtr, but there is specific provision in FCC regs for use of these in TIG welders. Only HF is coupled to the welding lead. There must be a capacitor in shunt with the leads between the HF HV and the welder's rectifers and/or xfmr.

Oil ignition and neon transformers are not the best sources of HV here because they are designed to be current sources and sustain arcs at 30 mA or so once a spark happens, and they typically have far more open-circuit voltage, short-circuit current and power than is needed (or wanted) here. The 8KV xfmrs from electrostatic aircleaners are a much better choice.

Curt,

If the neon sign transformer is AC output it'll probably work fine. If DC then not. The spark gap / capacitor / coupling coil circuit form a tuned high frequency oscillator. The high voltage is to jump the welding arc gap to provide a conductive path for the arc current to flow without having to touch the tungsten electrode to the work, ie. striking the arc the way you would with stick electrodes.

On high quality work arc strikes are a no-no and require repair and endless NDE. Also the tungsten electrode becomes contaminated when it touches the parent material, ruining the tip for fine work. On low current welding jobs it is difficult to strike and maintain the arc, especially with AC, and DC with small or absent series inductance. Here the arc starter helps to maintain the arc.

The high frequency (HF) component is to keep you alive; high frequency current travels on the surface of conductors and over your skin. Sensitive people sometimes feel a tingle. But no shock or danger, unless you have a pacemaker!

Wolfgang

I got myself across one of those when I was a teenager. Knocked me on my ass when I brushed the terminal.

Joe Gwinn

Ah, that makes sense.

Hum, something else to research. Yeah, I remember reading the use of spark gaps in those old radios.

I've been reading about Tesla Coils since my post and I understand this now. At least to some extent. I don't really understand the full dynamics of how the nonlinear effects of the spark gaps helps the L/C circuit resonate however.

I just went on a hunt for the one I have in my basement. It's 12KV at 30 ma on the secondary (110 V input). I didn't intent to actually try and use this for a welder. I just mentioned it in passing.

But I notice in the web sites I was reading about Tesla Coils that it's typical to use such a beast to drive the resonating circuit in a home made Tesla Coil. That sounds like a fun project as well. :)

I just recently started two welding class. One is for stick, the other in inert gas and covers Tig and Mig. Because of this I've become interested in the technology of welders.

I've already felt the "sting" of HF on tig - right through my tig gloves. Don't make the mistake of letting the filler rod hit the tungsten as you pull away from the work. :)