Here is the schematic for SCR control of my arc welder

[Mike W]

This is what I used on my Linde buzz box when I converted it to TIG using the Lincoln HF unit. The pot in the foot control has a small pulley attached to it. A larger pulley is turned by a rod on the pedal.

A 1/4" belt connects the pulleys. They are sized so the small pulley will turn the 270 degrees needed by the pot.

[Timinmb]

This circuit works great. Thanks Mike.

[Mike W]

Thanks for the feedback. I was starting to think that nobody cared.

[Silverback]

We care, I think that there is just a feeling of "well, how likely am I to electrocute myself with this thing" going on.

In my case I just need to regulate the input to a 12VDC field coil and I pretty much get any output I want, makes things fairly simple. Tomorrow I'll see if I can snag an old sewing machine pedal for a TIG pedal.

Actually I think I just asked a question about a schematic hinted at having in another old thread… I'm building an HF box and am looking for ideas… (once you light yourself up with 5-10KV once or twice you don't seem to worry as much about it as you did before, I think it's the brain cells sizzling )

[Timinmb]

Originally posted by Silverback
We care, I think that there is just a feeling of "well, how likely am I to electrocute myself with this thing" going on.

I think this sense of caution is wise. My setup is all enclosed in steel cases and grounded. I believe I am familiar enough with good construction techniques from having worked in the repair field.

There are some circuits out there for high frequency high voltage arc starters. There are some bits to construct that you can't just buy off the shelf, like the air couple coil to get the HF into the workpiece lead and the spark gap assembly. Neither of them beyond the determined.

Let us know how you make out. I took the easy way out and purchased an old Airco HF unit. I'm glad I did, as it has gas and water valves, timers, various start options.

[morpheus]

Originally posted by Mike W
Thanks for the feedback. I was starting to think that nobody cared.

Not the case at all Mike, still working on gathering the parts. I will definitely use your diagram. hey, I sent you a PM first of the week over on the WW board ...

- jack

[Mike W]

I don't think I got it Jack. I will go look.

[doctane]

You could probably look on ebay or a used music store for an old guitar volume pedal. Most of the cheaper units I have used have a rack and pinion
setup, Replace the pot with the apropriate unit and you would have a durable pedal.

Doc,

[doctane]

You could probably look on ebay or a used music store for an old guitar volume pedal. Most of the cheaper units I have used have a rack and pinion
setup, Replace the pot with the apropriate unit and you would have a durable pedal.

Doc,

[Mike W]

Mine will take a licking and keep on ticking.

[morpheus]

Originally posted by doctane
You could probably look on ebay or a used music store for an old guitar volume pedal. Most of the cheaper units I have used have a rack and pinion
setup, Replace the pot with the apropriate unit and you would have a durable pedal.

Doc,

Good idea Doc, there's one guy who made a TIG pedal out of a wah pedal since it already had a pot in it.

- jack

[Silverback]

I snagged an old sewing machine pedal today… looks like it will be perfect.

Anyone know when the shielding gas is turned on in a tig machine? I was originally thinking of using a transistor wired to the output of the pedal (again, in my case a simple 12V circuit) to trigger a relay for the gas valve, but after seeing this thing I may skip that whole deal and just mount a microswitch on the lever coming off the pedal…

[Mike W]

On my Lincoln HF, the gas flows for .5 sec before the HF comes on.

[Silverback]

What triggers the HF comming on?

[Timinmb]

Originally posted by Silverback
What triggers the HF comming on?

Depends on the settings. If not set to touch start (to initiate HF by shorting the electrode to ground), then the HF starts when triggered, by either a switch or pedal. When welding DC, the HF runs until an arc is initiated, then drops out. When welding AC, the HF continues (until the arc is broken). You can sense the arc starting or breaking by the large change in voltage of a constant current power supply. The OCV might be say 70 volts and the welding voltage around 20 volts. This can be rectified and run into a 24 vdc relay. A resister is used to drop the voltage to a level that triggers the relay on OCV. A timer is often used to run the gas for a number of seconds after the start signal. The gas shuts off unless the arc is initiated. After the arc stops, the gas runs for the length of the timer then shuts off. I have mine set at 10 seconds postflow. This is gas to shield the red hot puddle and protect the still glowing tungsten from oxygen.