How is the circuit made between the welder unit and torch/tungsten?

[jcorallo]

Hi,

Sorry if its a daft question but how is the circuit made between the welder unit and the torch/tungsten?

I cannot see any obvious wire or dedicated connection between the two. I can only assume that there is some sort of conductor in or around the gas supply pipe?

The gas supply pipe has brass nuts at each end, but is sheathed in a cotton-like material. Does a wire run down the middle of this or something?

http://img.photobucket.com/albums/v727/jcorallo/tig/IMG_3218.jpg

Jules

 

[TonyWilk]

The welding circuit is from the brass hose connector, there is a wire inside the gas pipe.
(I know 'cos I overcooked my torch lead and the inner wire melted thru the pipe - mind you, 'twas a cheapnese job).

The small connector is the trigger switch only.

Yours,
Tony Wilk

 

[mishka]

The gas pipe has a metal braid covering over the flexible tube. This is what carries the current. In water-cooled torches it is the water that carries the current (apparently).

 

[astro_al]

Mishka - it can't be because I was recently using my water cooled torch without the water cooler connected...

...which led straight to me doing what Tony did and melting the pipes near the handle.

(Thought it would be ok on low amps for a bit of light testing).

Cheers, Al.

 

[malcolm]

Yes, I need to fix the water supply on mine. There's a big wire up to my torch, but not as big as it would need to be if it didn't have water cooling. Hence the melting.

 

[mishka]

Mishka - it can't be because I was recently using my water cooled torch without the water cooler connected...

Mmmm.... thought I read somewhere that the water is used as the return path. May be mistaken.

 

[shenion]

Water would have too high resistance and the current would introduce hydrolysis. Not a good idea to have hydrogen and oxygen passing through the system

The better torches have a braided sheath around the gas tube. On mine, the gas line screws onto a copper block that is bolted to the output terminal on the welder. There is a fitting for the gas input that runs up to the gas valve.

Tony, sounds like a real cheap torch. Have seen some Chinese "WP-17" torches sell for $23 new on ebay. Seems all they copy from Weldcraft is the model number and the consumable thread sizes

My WP-26 hose is almost 3/4" in diameter and stiff as hell. Must be a lot of copper in there

I have an off brand WP-17, works well but is supposed to be rated at 150A. I notice it starts smelling funny at about 80A (the cable seems fine as it is coaxial.) I saw the Heiarc WP-26V on ebay for $20 shipped and decided I needed it in case I wanted to do anything serious

 

[TonyWilk]

... Tony, sounds like a real cheap torch. Have seen some Chinese "WP-17" torches sell for $23 new on ebay. Seems all they copy from Weldcraft is the model number and the consumable thread sizes ...

Yep, it was a real cheap torch 'til I beefed it up a bit, some pics are in this older thread

The right-hand part of the first picture shows the thin copper "welding circuit" braid which ran down the middle of the black plastic gas pipe.

... good that they copied the thread sizes tho

Yours,
Tony Wilk

 

[jcorallo]

I suppose mine must have a piece of wire running down the middle of the gas pipe then - as mentioned the sheath is not metal - its a cotton like material.

Cheers for the replies - wasnt a daft question after all!

Jules

 

[astro_al]

Mmmm.... thought I read somewhere that the water is used as the return path. May be mistaken.

I guess I'm confused about what you mean, but isn't the 'return path' the earth lead attached to the thing you're welding?

Would have been a neat system to use the water though - if it were practical!

Cheers, Al.

 

[mishka]

Sorted: water-cooled torches have three connections:
1. Gas In
2. Water In
3. Copper Conductor / Water Out

The idea being the cooling water also cools the copper conductor. See, for example, the Parweld WP24W (PDF) torch. Nicer picture here Bolton Community College lecture slides (PowerPoint) on page 17.