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DIY HF start for TIG welder.


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#1 lorenzo

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Posted 24 February 2009 - 09:26 PM

Something I found for the electronically inclined people on the board. Looks like just the thing for welding rings.

http://www.casano.co...tart/index.html

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#2 Cynake

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Posted 24 February 2009 - 11:32 PM

Yep. But not very commonly available.

You're basically 80% of the way to having a Tesla coil when you have one of these.

An easier solution, and something that's pre-made, is an oil-burner furnace transformer. They're from oil burning (and other) furnaces. Basically, a high-end ultra-reliable BBQ lighter.

If I have to, I'll go the route of the link you pasted above. Otherwise, gonna try to contact some HVAC guys who do retrofits and stuff. Maybe find one on Ebay.

http://www.google.co...snum=1&ct=title <-- Just about any of those should work, I'd think.

On my "eventually" list.

#3 lorenzo

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Posted 25 February 2009 - 03:25 AM

Here's a late night thought that may or may not make any sense. I wonder if it would be possible to initiate a spark with a third electrode not connected to the welding circuit. Something along the lines of a miniature trigatron, that would seem to be the dead simplest way to do it.

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#4 Cynake

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Posted 25 February 2009 - 04:14 AM

Hrm.

No.

Trigatrons work by having a voltage source already high enough to fly through the air. Just not fly far enough, so it needs a trigger electrode to kick off the bridging.

Posted Image

With a TIG welding setup, you're not dealing with very high voltages. How close do you have to get a TIG electrode (at the voltages we'd be dealing with) to get it to fire? A trigatron would nearly double that distance. Still a tiny amount.

Also, consider your distances. If the arc can jump 2mm... but with a trigatron could jump 4mm.. how far away is the trigger electrode? Half way, to bridge... so... 2mm.

So why have the trigger electrode at all? Why not just bring the tungsten electrode up to 2mm and have it fire on its own? Unless I'm misunderstanding you, the trigger electrode gains you nothing.

Another point, is that a mere "spark" isn't enough. Even a steady stream of HF and HV isn't enough, so says the guy feeding me advice on welding. You need a high enough current flowing for the weld current to ride the arc, otherwise it's like a fat man jumping on a tricycle.. he's going nowhere.

Now, not sure if this is where you were headed.. but.. a scratch-start might be possible. But even then, why not scratch your main electrode rather than a trigatron's trigger electrode? Either way you're melting and mucking up a nice tungsten tip.

That said... even low voltages can jump *some* distance. Brian S built himself a capacitive discharge welder (basically a junky TIG welder), and he doesn't even use the SCR to trigger it. His method is to clamp the ring on one side, and then bring the weld pencil close enough that the electricity eventually jumps. I guess voltage will jump a tiny bit, some instant before scratching to start the arc, and I guess it might be easy enough to control, if you watch your ingoing speed. Brian says it works better than using the SCR.

I think Brian's methodology is yielding inferior results, especially as he has nothing to compare it to, but, he does get welds he claims are good, so.. who knows. I wouldn't try it on a continuous TIG setup though, because you'd muck up your timing. Brian gets away with it because he's using Cap Discharge. If he's still moving fast enough to bump the electrode into the ring.. no big deal, the pulse is already gone. In TIG, that might get messy.

However, my TIG setup will be such that distance and pulse are controlled by the rig anyway. None of it is freehand. So, maybe it could work. If so, all I need is a tungsten needle and 2 minutes, and I could have a precision TIG welder. That'd be neat :)

#5 knuut

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Posted 25 February 2009 - 05:16 PM

Hrm....So why have the trigger electrode at all? Why not just bring the tungsten electrode up to 2mm and have it fire on its own? Unless I'm misunderstanding you, the trigger electrode gains you nothing.


The trigger electrode serves to pre-heat the primary electrode to 2000+ Kelvins thus increasing it's emisivity by several orders of magnitude and making for a MUCH smoother start. Nowadays, the tecnique is less common but is still usefull in situations where stray HF signels can get into delicate electronics ( Over the years, I have toasted half a dozen digital calipers by leaving them on my welding bench. Even from several feet away, the HF is plenty strong enough to do them in. )

#6 lorenzo

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Posted 26 February 2009 - 01:34 PM

My understanding of a trigatron is that it should be possible to set it to ionize the path between the trigger electrode and both main electrodes simultaneously. I believe it requires at least two trigger electrodes on further investigation but I could be wrong I can't seem to find much hard info on this. That would leave a very consistent small gap for the low voltage arc to jump and stretch the spark much farther than the voltage would normally allow.

Eric Matwe

 

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