Tig welding tips, questions, equipment, applications, instructions, techniques, tig welding machines, troubleshooting tig welding process
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Dalzani
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    Sun Jul 30, 2017 7:46 pm

I built my own TIG pedal this weekend. I've tested it and it's working as it should. My concern is about insulation versus compromising the machine.

Explaining: The pedal I built is entirely made of metal. The electrical insulation between the pedal housing is the standard, meaning, wires and the normal insulation between the pot and its terminals.

There is no electrical contact between the circuit and the housing at least at low voltages.

I am worried about what would happen in the event that the pedal somehow comes in contact with the part to be welded and this part is not grounded with the cable of the machine. Could HF (high voltage) go beyond the normal insulation of wires and the pot and return to the machine?

I have two welding tables and eventually when I change tables I forget to reground to the working table. If the pedal were touching the table we would have this situation described above.

I've never seen a commercial pedal internally and I do not know how this problem (if it exists) is solved.

I already asked in another forum and I was told that wires and other components would have a standard 600V islolation and also make a choke in the cable as a trap for the HF. But I would like some more opinions.

Thanks all.
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noddybrian
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    Thu Jan 24, 2013 12:13 pm

Nice build - I've had a few pedals apart to repair & they have all been similar to yours with regard to insulation - only possible difference is most ( but not all ) had an earth wire so the body of the pedal was earthed to the machine chassis so I think if the HF did try to jump to the pedal in a situation such as you describe it would use the mains supply earth to go to making the pedals metal body effectively a Faraday cage for the pot & low voltage wiring inside - it's a valid question you have but I never heard of this happening so possibly your over thinking it - I do think adding an earth would be a good idea as letting the pixie smoke out of a something as a Tig is never good !
MFleet
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The schematic for an old Lincoln that I needed to test shows the cable shield grounded to the metal connector at the machine. That sends HF interference straight to earth ground through the machine chassis. However, it doesn't show that the pedal chassis is grounded. I don't see a ground on the old metal Miller or the aftermarket metal SSC pedal. They may be using the same scheme as Lincoln.

Nice work btw! What is the secondary pot for?
Miller 350P w/Python
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Dalzani
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Thanks all. Yes grounding the cable shield is a nice idea. I am doing some modifications. This will be one of than for sure. I am doing a heavy insulation for the internal components and wires also. Better safe than sorry :x

The second pot... My machine (and many others) disable current pot when it "feels" a pedal attached. Have no ideia why!
So, the second pot is to set the max current.

I'll post some pictures soon.
Dalzani
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    Sun Jul 30, 2017 7:46 pm

Redone engineering.

-All moving parts are bearings.
-Weight (pressure) on the pedal is 4.5 pounds at the end of the movement (max current).
-Electric insulation with milled nylon blocks.
-Sliding pot rather than rotary pot (easier mechanic and higher resolution).

I looked at several pedal pictures on google. None of them had a sliding pot. I do not know if there are any drawbacks for this type of pot but it works as it should.
I did not have any spring light enough for this kind of pot so I just used a rubber band.
I believe I made a good electrical insulation and the cable shield is grounded only on one side, on the side of the welder.

Tomorrow it will come into real use. Let's see if it was worth the effort.

Thank you all.
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Looks nice, what will the retail price be?
Richard
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Dalzani wrote:I looked at several pedal pictures on google. None of them had a sliding pot. I do not know if there are any drawbacks for this type of pot but it works as it should.
Risk of dust and metal particle ingress making the response jumpy or give bad spots in the travel.

Rotary pots can be pretty much completely sealed (IP68) and especially if you go for a hall effect type (needs a little more circuitry though) that's pretty much fully water and dust proof.

For hobby-use the sliding pot should work just fine, but for a commercial product that's expected to be used in very bad conditions they likely would not use this style but use a sealed rotary pot.

Bye, Arno.
Dalzani
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Looks nice, what will the retail price be?
I did not intend to commercialize it. Also I'm not sure if I will adapt myself to using it. I've been welding steel for at least 2 years and recently started welding aluminum boxes (1.5mm sheets) and I started to think that a pedal could make my job easier (especially near the edges). I ended up adapting myself to use the down slope of the welder in these cases. We also make several overlaps with weld beads up to 50cm in length. Without a pedal to control the amperage I started slowly (waiting for the heating of the box) and after a few inches I had to go fast to avoid melting away the corner of the upper sheet.
Risk of dust and metal particle ingress making the response jumpy or give bad spots in the travel.

Rotary pots can be pretty much completely sealed (IP68) and especially if you go for a hall effect type (needs a little more circuitry though) that's pretty much fully water and dust proof.

For hobby-use the sliding pot should work just fine, but for a commercial product that's expected to be used in very bad conditions they likely would not use this style but use a sealed rotary pot.

Bye, Arno.
Important information. But in our use I think dirt will not be a problem, at least in the short or medium term. Any sanding/grinding work or operations that generate dust or dirt in abundance is restricted to another room. For welding we have a small room dedicated only to this activity and it should always be clean. But as I said, if I adapt to the use of the pedal and consider it an important tool, I will do another project, probably with gears and rotary pot.

Thanks all.
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FWIW, I converted an ooold foot pedal to "modern" standards:

http://weldingweb.com/showthread.php?45 ... foot-pedal

-c-
 
 
 
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Dalzani
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FWIW, I converted an ooold foot pedal to "modern" standards:
Cool!!!!

I find this system using gears one of the best. Great job.
I'm already using the pedal I built. It works perfectly. My doubts are how long it will work before showing any problems and if I am using it correctly, since I have never used a pedal before.
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