Adding foot control to tig welder

Question

I've got a simple tig welder that uses a switch on the torch to start the welding current and a potentiometer on the front panel to set the amperage. Many welders make use of a foot pedal to start te welding current and also control the amperage level with your foot for a bit more control of the welding action. This welder doesn't officially have a way of connecting a foot pedal but I think it must be possible and tried adding one.

I bought a foot pedal that has a two pin connector and a three pin connector. The two pin connecter wil connect to my tig welder as is and it will trigger the welder to start just like the button from my torch would. I've now got foot control but can't manipulate the amperage.

Inside the welder the pot meter is hooked up to the connecter circled red. The outer lobes trace to a bunch of resistors and the centre lobe traces to two pins soldered together on the unused connector circled yellow. Maybe that connecter is there for adding a foot pedal. I can't seem to find any info on this welder anywhere.

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Back to the pedal. The three pin connector is coming from two potentiometers in the pedal. Wired as follows.

I could match the potentiometer value of the pedal to the one in the panel but I would also like to be able to set the max current on the front of the panel and use the foot pedal to control the amperage within that range.

I've got it sort of working now by swapping the b103 10k potentiometer on the back of the pedal and hooking up the 1k potentiometer from the panel like can be seen here.

It is however not working as it should. I can only see and set the max amperage when the pedal is fully pressed. Also it won't go as low as it used to due to incorrect potentiometer value. I am sure there is a better (correct) way of doing it. Any help would be much appreciated!

Answer 1

I have not thought I would need to adjust the current while welding. But it sounds like a good idea. Honestly, I am only a beginner, stick welder.

Compliment to your schematics drawing skill as a welder. Soon, welders will take over EEs' job.
Anyway, this is the electrical symbol for your last try.

^{simulate this circuit – Schematic created using CircuitLab}

Firstly, "I can only see and set the max amperage when the pedal is fully pressed." is likely coming from your pedal turns the wiper (internal part of pin number 2) toward pin #3. Swap pin 1 & 3 of the pot on the pedal. And then see if that fixes

Secondly, For "it won't go as low as it used to due to incorrect potentiometer value". Use 10K (B103) for foot pedal, and see it improves. Now, along with the B103 on foot pedal, try 2K2 (B222) on the range setting, if that improves.

Now, in order to find the optimum values, and correct configurations:
a) Check the original front panel pot has pin 3->red, pin 2->blue, pin1->black, indeed as your drawing implies.
b) Measure the resistance of the original front panel pot (that you are trying to replace) across pin 1 & 3.
c) Measure that resistance of the original pot pin 2 & 3, and check if the resistance increases or decreases while turning the pot clockwise (higher current setting).
d) Post that here, please.

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Assume that the "Firstly" and "Secondly" worked, then, this is what would make it work even better (may be?). The cable is 3 wire in shield.

^{simulate this circuit}