Homemade Pedal for Inverter TIG

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I just bought myself an inverter TIG off Ebay to get a bit of practice until I can afford a "proper" AC/DC unit.It's just a cheap Chinese machine, but it seems to work okay so far, it even has HF start, which I wasn't expecting.Question is: it has the usual control on the front panel to change the amp output, could I wire this potentiometer (rheostat) into a foot pedal and vary the output during welding without damaging the unit? The manual sort of suggests (usual colorful translation) you can vary the amps during welding, and I tried turning the knob with one hand while holding the torch in the other - it worked and nothing exploded, but would doing this constantly fry something?J.
Reply:Originally Posted by JDHI just bought myself an inverter TIG off Ebay to get a bit of practice until I can afford a "proper" AC/DC unit.It's just a cheap Chinese machine, but it seems to work okay so far, it even has HF start, which I wasn't expecting.Question is: it has the usual control on the front panel to change the amp output, could I wire this potentiometer (rheostat) into a foot pedal and vary the output during welding without damaging the unit? The manual sort of suggests (usual colorful translation) you can vary the amps during welding, and I tried turning the knob with one hand while holding the torch in the other - it worked and nothing exploded, but would doing this constantly fry something?J.
Reply:Hi Zapster,Yeah, I just tried the "twisting the knob with the other hand" thing to see if it would work while I had the arc going....... I don't want to waste time building a foot pedal and wiring it up if it fries a circuit board when I first use it.Basically what I need to know is: will varying the amps under load cause damage? J.
Reply:There's no reason it shouldn't work.  The welding amperage knob on an inverter actually alters the duty cycle (frequency) of the inverter itself.  There's nothing that should or would break while you're varying the frequency of an inverter.  In comparison, a welder with a tapped transformer could actually short out the transformer if it's changed while welding.If you want a remote foot pedal, there's no reason why you couldn't hook up a pot with the same value as the one that's in the welder.  You take the leads going to the internal pot, hook up a DPDT switch and use that to switch between the internal and the "remote" pot.  If you're really crafty, you can do the same thing with the lead going to the contactor and run that to a remote switch in the foot pedal as well.-Heath
Reply:To add to what Heath said about transformers vs inverters...hes totally right,  but add this...NEVER ever adjust the heat on any transformer machine while you are welding...on any transformer.  The only exception is the remote control can be altered...but never off the panel.  This will destroy the machine.  I cant speak much on grounds of inverters, but transformers of anytype, tapped or the other type lol, you will ruin.  Youre in good shape as far as I can tell on this inverter though.IF it Catches...Let it Burn
Reply:Originally Posted by JDHI just bought myself an inverter TIG off Ebay to get a bit of practice until I can afford a "proper" AC/DC unit.It's just a cheap Chinese machine, but it seems to work okay so far, it even has HF start, which I wasn't expecting.  Can you post a link or an image J?Question is: it has the usual control on the front panel to change the amp output, could I wire this potentiometer (rheostat) into a foot pedal and vary the output during welding without damaging the unit?
Reply:Hi Jim,This is the unit, but don't forget its's Ebay Australia, not US.. Sounds like everyone agrees I can add the foot pedal without damaging the circuit boards, so I'll get the front panel off this weekend and see what value pot I'll need. Quick trip to the electronics store for a switch, connector and the pot. Then I'll just have to figure out how to fabricate the pedal.I think I'll make it myself rather than go for the musicians foot pedal Jim, good practice for me plus I can make it around the pot mechanism. As Halbritt suggested, I will try and add the contactor switch to the pedal.Thanks for the advice, I'll post some picks when I'm done.Justin
Reply:Took the cover off the TIG this weekend and started hacking into the wiring. I've got the internal parts wired up......Drilled a new hole in the front panel for the 3PDT switch to select between the internal pot and the one thats going to go in the pedal. Looks like it has always been there, I even mounted it slightly off center so it matches the rest of the assembly accuracy!Spliced 2 wires into the contactor switch socket down the bottom and wired these into a 5 pin socket in the rear panel.I've used 5 core trailer wire for the wiring and lead. Basically 'cos it conveniently has 5 wires and is of the right gauge.I've got the other electronics to make the foot pedal, now I just have to figure out how to turn the pot 300 deg with only about 45 deg. of foot movement. The two ideas I'm toying with are A). gears and B). a small chain drive of some sort. Will post an update when I finish the pedal......... Attached Images
Reply:Very nicely done.  Please keep us apprised of how well it works.  If it does work well, I may actually consider purchasing a similar unit.I noticed that you used a DIN style connector on the back panel, which should work fine.  If you would rather use one of the mil-spec style amphenol connectors, I know that they are sold by Newark Electronics in the US.  They aren't particularly cheap (~20USD for each connector) but they are very durable.I have a PowCon Inverter that I built a pedal for.  I used a musician's foot pedal that worked quite well.  It came with a set of plastic gears that works with any standard Pot.  I also put a voltage divider on it to adjust the range of the foot pedal.  I found a schematic for an original PowCon cable that had this feature, so I followed it with some minor modifications.  If you'd like to try this, just do a google search for "potentiometer voltage divider" to get some hints.  For the cable, I purchased some 5-conductor SO (SOJ/SOOW) cable from a dude on ebay here in the US.  It was the best deal I could find on anything greater than 4-conductor without having a commercial account at an electrical supply.-Heath
Reply:Thanks Halbritt, I've been fiddling with electronics since I was about nine so I learnt the hard way how much frustration can be caused by one dry solder joint, one loose wire or a tiny short circuit, so now I try and do it right the first time. Oh, and a big thankyou to the guy who invented heat-shrink tubing! I actually picked up the amphenol connectors when I was in the store, not mil-spec but still AU$20 each. Seemed like putting $4000 mag wheels on a $200 jalopy, so I opted for the cheaper DIN connectors, I can always upgrade later if it all works out. As is always the case I nearly bought a whole box of mil-spec locking connectors on Ebay a while back, but I've been trying to cut down on buying stuff I don't really need right now. If only I'd known!Will post more pictures when the pedals finished and I've tried it out...............Justin
Reply:Nice work Justin.Should you decide that the 45° to 300° ratio mechanism is more than you want to accomplish, here is a website with 'universal' footpedals of various resistances.But it looks like you are well on your way.http://www.ssccontrols.com/homepage-...otcontrols.htm - Jim
Reply:Originally Posted by halbrittThere's no reason it shouldn't work.  The welding amperage knob on an inverter actually alters the duty cycle (frequency) of the inverter itself.  There's nothing that should or would break while you're varying the frequency of an inverter.  In comparison, a welder with a tapped transformer could actually short out the transformer if it's changed while welding.If you want a remote foot pedal, there's no reason why you couldn't hook up a pot with the same value as the one that's in the welder.  You take the leads going to the internal pot, hook up a DPDT switch and use that to switch between the internal and the "remote" pot.  If you're really crafty, you can do the same thing with the lead going to the contactor and run that to a remote switch in the foot pedal as well.
Reply:Originally Posted by JDHHi Jim,This is the unit, but don't forget its's Ebay Australia, not US.. Sounds like everyone agrees I can add the foot pedal without damaging the circuit boards, so I'll get the front panel off this weekend and see what value pot I'll need.
Reply:Motofab, thanks a lot for the link to the pedal manufacturer, SSC.  I've requested a quote from them already.JDH, one thing that I would be concerned about is the possibility of the DIN audio style cable connector being jerked out of the welder as you maneuver around the workplace (if your workspace is anything like mine) and what effect an open pot circuit might have on the machine.  This is the question raised by wizard.  Hard to know,since I assume it is impossible to get a schematic of the welder control board.  For this reason, I also recommend a MIL-type connector with a locking mechanism like a threaded ring to minimize the possibility of accidental disconnect.  An advantage of the multi-pin connector approach with extra pins is that you can use a spare pair of pins as a safety interlock, opening the circuit to the power contactor if an appropriately shunted plug is not installed.  Obviously, this would have to be inserted into a control circuit, not the main power circuit.I know it is too late now, but for others who may contemplate this mod, automatic switchover from front panel control to remote control could also be incorporated into the connector wiring if you used a connector with enough pins.  Plugging in either the remote cable or a shunting plug would effect the changeover of control.  The shunt plug would be hung by a chain to the rear panel as insurance against loss.Have fun.awright
Reply:I found this, thought you might like:http://www.smidgie.com/928/machineshop/footpedal/
Reply:Very nice job on that foot control you provided the link to, orphan68, but perhaps a tad over-engineered?  I like the idea of adapting a musician's foot pedal.  Got the pedal.  Now have to find the time.awright
Reply:Wow! Bit of a flood of posts in the last 2 days!This project has been on hold, I only picked it up again this week, so good timing.So........To Motofab:Thanks for the link, checked it out, they look like quality units but at USD90 plus shipping, it works out at nearly half the price of the actual welder, so will have to keep going with homemade version.GNM109I've figured out what pot I need and have already wired up the internal switch (see pics in earlier post), just the pedal to complete. It's re-assuring to hear another "can be done" vote though.WizardThanks for the input Dave, sorry about the low res pictures, I'm still experimenting with picture and file size..................I'll post some better ones when it's finished.There is no auxillary input connection on the front panel, but there are some empty connectors on the main circuit board. I'm not going to start messing about with them without a circuit diagram though.As to the modification you are talking about I'd suggest not doing so unless all that you expect to do with the machine is TIG with remote control. It certainly wouldn't work well with stick.
Reply:JDH, looks like you are covered on the issue of accidental disconnect.  I didn't realize that you had incorporated a contactor switch into the pedal, although it seems obvious that it is needed.  With that taken care of, I wouldn't worry about accidental disconnect except for the inconvenience.  I also agree with others that there is no risk varying power during welding with an inverter machine.One thing that people considering this kind of project should be aware of is the difference between a linear pot and a logarithmic or audio pot.  Many pots out there are intended for or salvaged out of audio equipment and has a curve of resistance vs. rotation angle that is unsuited to welder power control.  That is, if you turn an audio pot to the middle of its rotation range, you will not find equal resistance from the wiper to each end of the resistive element.  This is highly desirable for audio volume control, but not welder power control.  Just another booby trap out there.The other item to keep in mind is the power rating of the pot.  With inverter machines and others having full electronic control circuits, pot power rating is rarely an issue because there is very little current through the pot.  In older machines, it may be wise to check the physical size of the pot (a reasonable indicator of power rating), or check the maximum current through the pot and calculate the power dissipation.  Pot power requirement is one reason I have never gotten around to making a foot control for my old Harnishfager stick/TIG welder, but as soon as I find the schematic, I'll work on a pedal using a low power pot and a power transistor.Let us know how you like the economy TIG machine.awright
Reply:As far as pots go, every single one that I've seen that is used on a machine built in the last 15 years has been a 2W pot, which is the standard size.  Many older transformer-based TIG machines run a significant amount of current through a pot or a rheostat.  I've seen some examples that were designed to handle anywhere from 10 to 40 amps.  Consequently, if anyone is considering building a foot pedal for one of these machines, I could probably find an appropriately sized pot.  I'm in the silicon valley which has a plethora of electronics surplus places.  One of them has a really good selection of high-power pots for reasonable prices.I've got a 10-15 year old Powcon that I built a pedal for.  It used a standard 2W pot, but it was an odd value.  Apparently 5k linear pots aren't common any more.As I understand it, most inverters have five leads for control purposes.  Generally, that includes supply voltage, ground, and sense for current control as well as supply voltage and return for contactor control.  The current level (or voltage if running CV) is set by the level of return voltage on the sense lead.  On my welder, the supply voltage is +15VDC and the sense takes 0-10VDC to proportionally set the current.  It also uses 24VAC to drive the contactor relay, which is normally open.  Assuming that most inverters work similarly, it seems obvious to me that without a pot to drive the current control or a switch to drive the contactor the welder would simply sit idle.  Infinite resistance would cause it to do nothing.I thought about building a foot pedal, but it seemed too much of a hassle.  Music pedals can be had pretty cheaply and generally contain the necessary linkage to drive a 2W pot that is likely logarithmic.  The pot itself can easily be replaced with a linear pot of the appropriate value, which is how I built my TIG pedal.  My pedal was given to me, but others  can be found on ebay for $20-70, a new pot should only cost a few dollars.  This makes the pedals from SSC seem expensive in contrast, particularly given that some music pedals are quite sturdy in construction as they're expected to be used on stage and banged around quite a bit.For my next trick, I want to build a pulser for my Powcon so that I can do pulsed MIG.Last edited by halbritt; 06-02-2006 at 03:31 PM.-Heath
Reply:Heath, you say, "I'm in the silicon valley which has a plethora of electronics surplus places."  It seems to me that the plethora has dwindled to a smattering over the last decade, unless you are specifically interested in computer related stuff.Haltek, RA Enterprises, Just In Time ICs, Alltronics, C&H Electronic Recovery, Silicon Valley Surplus, Curtis Sales, all gone.  Al Boyd in Oakland (who ran a real junk shop) died several years ago.  Mike Quinn's near Oakland Airport just disappeared without a trace a month or two ago after forty or fifty years.  National Machinery in Oakland disappeared a decade or more ago.  Fortunately (or unfortunately, according to my wife), I've got a ton of interesting stuff to play with after all these years of accumulating, but my resources are drying up.The only good salvage stroes I know of these days are HSC, Triangle Machinery, Wierd Stuff, and --- and -who? I'd appreciate your posting a list of the surplus places still in existence with whatever comments and links you are motivated to supply.  I live in Oakland and used to get down to the South Bay regularly, until I mostly retired from consulting, so I have lost track of the good places.  I have to go to Southern California or Seattle with the excuse that I am visiting grandkids to do a satisfying browse these days.The control pot in my saturable reactor-controlled transformer welder is about 5" in diameter and rated at (I think) 150 watts.  No foot control could move it without a servo drive.  So I am thinking of using a small pot and a power darlington to simulate the function of the huge pot for external control.  If I could just find that darned schematic...ThanksawrightLast edited by awright; 06-02-2006 at 07:16 PM.
Reply:One thing that people considering this kind of project should be aware of is the difference between a linear pot and a logarithmic or audio pot.
Reply:Originally Posted by awrightHeath, you say, "I'm in the silicon valley which has a plethora of electronics surplus places."  It seems to me that the plethora has dwindled to a smattering over the last decade, unless you are specifically interested in computer related stuff.Haltek, RA Enterprises, Just In Time ICs, Alltronics, C&H Electronic Recovery, Silicon Valley Surplus, Curtis Sales, all gone.  Al Boyd in Oakland (who ran a real junk shop) died several years ago.  Mike Quinn's near Oakland Airport just disappeared without a trace a month or two ago after forty or fifty years.  National Machinery in Oakland disappeared a decade or more ago.  Fortunately (or unfortunately, according to my wife), I've got a ton of interesting stuff to play with after all these years of accumulating, but my resources are drying up.The only good salvage stroes I know of these days are HSC, Triangle Machinery, Wierd Stuff, and --- and -who? I'd appreciate your posting a list of the surplus places still in existence with whatever comments and links you are motivated to supply.  I live in Oakland and used to get down to the South Bay regularly, until I mostly retired from consulting, so I have lost track of the good places.  I have to go to Southern California or Seattle with the excuse that I am visiting grandkids to do a satisfying browse these days.The control pot in my saturable reactor-controlled transformer welder is about 5" in diameter and rated at (I think) 150 watts.  No foot control could move it without a servo drive.  So I am thinking of using a small pot and a power darlington to simulate the function of the huge pot for external control.  If I could just find that darned schematic...Thanksawright
Reply:Wooo hooooo!Finally got it all done.................Hopefully the photo quality has improved, I spent a bit more time resizing and adjusting them this time.First thing I realized looking at the pictures is that my stick welding has really gone downhill! The problem is, when you're an amateur like me and don't weld everyday, it take ten minutes to remember the techique and get the hang of it again when you start up. I use stick even less than O/A, so it's not my strong point. Anyway......I got everything assembled and tested it out.I works REALLY well! I was worried that the pulley setup would be sloppy and vague, but the slightest change in angle of the pedal is translated to movement of the pot. The only thing I need to improve is a notch or something just before the microswitch turns off. When you come to the end of a run and want to reduce the current to minimum, it's hard to tell when you're about to switch off.I'll post some more details of the construction if anyone is interested.I did some trial runs, then after about 5 mins ran out of gas, so no weld pictures yet. I'll get a refill next weekend, then try some more SS and thick-to-thin welding, which would be a lot more difficult without this pedal.All up, I'm pretty satisfied with the end product.I've got a TIG welder with HF start and remote foot control for around AUD350. (About USD265) Should keep me going until I can afford the AC/DC unit I really want. Justin Attached Images
Reply:Looks good and that is surely a heavy duty unit that will last for years and years. Good work!John -  fabricator extraordinaire, car nut!-  bleeding Miller blue! http://www.weldfabzone.com
Reply:Nice-looking work! My only positive suggestion would be to add some shrouding to keep out dirt. All in all, a good example of Aussie Ingenuity!Very nice job. An inspiration to those of us who have been intending to build a pedal for years.awright
Reply:Nicely done!! As someone stated, cover the thing. You don;t want any dirt to mess up anything inside.
Reply:You rule Justin!  That pedal has a very cool industrial look.I wish I could remember that much about welding in 10 minutes.Maybe try a second 'staged' microswitch, to control the gas solenoid?I can't wait to see the detent mechanism you come up with.Probably just a small tab to act as a 'roof' over the pot will keep out the dust and keep the 'industrial' look.Sure, post up some more construction details.All you need now is an adjustable Pulsed TIG timer circuit with two amp levels, a ramp down(?) timer, pre and post gas timer, and a TIG tack-weld timer.  And a gas supply switchover to compressed air, to cool down the air-cooled torch cheaply. Oh yea, lift-arc start if the supply does not have it.  (I see that yours does)Trade you a pedal for one? - JimLast edited by MotoFab; 06-10-2006 at 12:31 AM.
Reply:Aww ****, now I want to build a big beefy foot pedal out of steel and I already have a good working cast aluminum one.Nice blundies.-Heath
Reply:I adapted a Roland EV-5 Expresion Pedal to a Harbor Freight TIG. Works well. This pedal has a special 50K ohm pot which is active on only about 45 deg of rotation. Lesson learned: I had to replace the cable with a shielded one. I used a USB cable with the shield tied to the pedal metal bottom plate and the welder chassis. The other three wires I used to connect the potentiometer. I am in the process of doing a Mitech now. This one has a 1k pot. Trying to find a gutar pedal which I can adapt.
Reply:Originally Posted by madjidtI adapted a Roland EV-5 Expresion Pedal to a Harbor Freight TIG. Works well. This pedal has a special 50K ohm pot which is active on only about 45 deg of rotation.I am in the process of doing a Mitech now. This one has a 1k pot. Trying to find a guitar pedal which I can adapt.
Reply:I know this is an old thread but did you wire the 3PDT switch on the front panel to control the max current, seen by the foot pedal, with the pot on the panel?  So, say you set the panel pot at 100amps the pedal can only operate between the lowest unit current, i.e. 20amps, and a max of 100amps, no more.THX, CW
Reply:Hi CW,I had forgotten all about this!The switch is wired to select either the control panel pot, or the foot panel pot, there is no max current limiting.It was done this way so I could still use the TIG on fixed amp when it wasn't possible to use the foot pedal (out of position - lying down under a motorcycle for example).In the past few years since building the pedal (I've still got it and use it regularly) I've never found the need to limit max amps on this machine, for two reasons: 1. it's only a small machine, max 160 amps I think and 2. the output is really easy to control.Unless you're a real lead-foot, it would be very hard to accidentally "floor it" and burn through, even on thin stuff. Let me know if you need any more info.JDH
Reply:JDH, THX for the response.I wasn't sure if it was really needed.  There are a couple cheap (~$80) units that have a max control pot on the on the front of the pedal.  That would be the way I go when I build mine, a very simple hook up.  I replaced the control pot on the front of my machine that has a lower range setting so I can go below 10 amps, not really sure how low I'll borrow a clamp meter and get an idea (and the rest of you looking in, I know on a DC inverter I don't need to run it low for a long time), and it has worked really well on very thin stuff.BTW, I do nothing but bikes and can't get my fat A$$ under them, I have a chain hoist and strap'em and haul them up so I can get under them ;-)THX, CWTHX, CW