I am putting this up in case anyone needs to do the same – I have a SIP P178 HF welder and wanted to get lessons in precision TIG welding from Jason McDougall, who said that without a foot pedal control on the current and stop start I wouldn’t get very far! Welders with foot controls don’t come cheap, and I didn’t want to scrap my almost new SIP, so I had a look around to see if I could fit a pedal control. No info on the web that was relevant, although there were a few pics of pedals, and unfortunately no circuits available for that model. Under the hood I found the current knob was a dual gang potentiometer of 1K Ohm resistance, which was a bit of a problem, as I would have to substitute my pedal for this potentiometer – I couldn’t find suitable 1K slide potentiometers to make my pedal from, so ended up with a bit of a Heath Robinson arrangement with a cord running round a drum that sat between two 1K rotary potentiometers moved by an arm on the pedal – after a bit of messing about I put in a sprung idler pulley to keep tension on the cord and a microswitch that operated right at the top of the pedal movement – doesn’t quite cover the full range of the pots but probably goes to 120 amps – so far so good….
