Homemade Pedal for Inverter TIG

[JDH]

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.

[zapster]

Originally Posted by JDH

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.

I SUPPOSE IT CAN WORK...oops caps lock...i'm not yelling

turning the knob on the welder with one hand..holding the torch in the other hand = no hands left for filler rod...

but if you can make the rheostat work then i see no problem...

unless it grounds out when you have it in water or something
then you'll be

...zap!

[JDH]

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.

[halbritt]

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.

[TxRedneck]

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.

[MotoFab]

Originally Posted by JDH

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. 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?

Which inverter did you buy on Ebay? I did not see any with HF start either.

An 'external' control for the inverter will work perfect J. Simply use the same potentiometer value as is used on the front panel.

Be sure to use connectors so that the new pot is in an either/or configuration with the original pot. i.e.: Only one pot is connected at a time.

Try looking at musician's foot pedal controls.

- Jim

[JDH]

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

[JDH]

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.........

[halbritt]

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.

[JDH]

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

[MotoFab]

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

[gnm109]

Originally Posted by halbritt

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.

What Halbritt says is the way to do it. In fact, that's exactly the way my Lincoln TIG works. It has a switch for current control "at the machine" or "remote" (foot pedal). As he says, you need to find out the value of the potentiometer inside the machine and, once you have the remote switch in place, use the external pot to control your welds. You would have to have some sort of foot pedal or control at the torch to mount the pot but those are available.

Good luck.

[wizard]

Originally Posted by JDH

Hi Jim,
This is the unit, but don't forget its's Ebay Australia, not US.
Attachment 3403.

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.

Looking at the picture of the unit, it looks like it has an auxiliary input connection. Could this not be used for remote control? The picture is a little shrunk down with detail missing so I'm not sure what I'm seeing.

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. Even if this will be a sole TIG machine I'd have a hard time with this approach, what would you do if a TIG project came up where you didn't have the capability to position a foot switch?

What I would do first is to verify wether or not it has a remote input funciton. If not I'd open up the machine and take a look inside for an auxiliary input connection that was never taken to the outside and hope that that works.

If none of those work I'd go out and buy a milspec circular connector and wire up the machine so that the internal pot is bypassed when the external is plugged in. Nomrally this would be done with a jumper plug that is installed when remote operation is not needed. One really BIG CONCERN here is that you have to know how the machine will behave if no pot at all is connected to the controls.

Now for the bad news, you have to hope that you can get easy access to the pots terminals. A lot of these cheap machines are cheap not because of quality but becase of manufacturing techniques. The pot could easily be soldered to and part of a display / control board. If so things become very difficult for the technique descrbed in the paragraph above.,

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.

Actually the first thing I'd do is tear the machine apart and wee what you have to work with. Deterimine if it is feasable first, then the pot size and characteristics. Then go shopping.

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.

Pics are always nice, hopefully osme internal shots. You final electrical schematic would be nice too.

Justin

Best of luck.

Dave

[awright]

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

[orphan68]

I found this, thought you might like:
http://www.smidgie.com/928/machineshop/footpedal/

[awright]

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

[JDH]

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.

GNM109
I'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.

Wizard
Thanks 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.

TIG is all this machine will be doing.
I actually bought it with one job in mind - welding thin SS.
But even without the foot pedal, I've found it useful on other jobs, including making the pedal itself.
As I mentioned in the first post, I don't have high expectations of this welder, it's just to get some practice and keep me going until I can afford a full spec AC/DC unit.
I have a reasonably heavy duty arc/stick welder, so won't be using this unit for stick.

Even if this will be a sole TIG machine I'd have a hard time with this approach, what would you do if a TIG project came up where you didn't have the capability to position a foot switch?

Flick the switch I installed to the "internal pot" position (photo above somewhere in my earlier post) and make do with fixed amps.
What do other TIG users do if they can't use the pedal?

One really BIG CONCERN here is that you have to know how the machine will behave if no pot at all is connected to the controls.

Hmmmmm..............good point. I hadn't thought of no connection.
I have wired a 3PDT switch in, so theoretically one of the two pots will always be connected.....unless some clumsy oaf trips over the cable and pulls the plug out.
But then again if the plug is pulled out, the contactor will also be disconnected so welding current will stop.
If the pedal works OK I will upgrade the connectors to keep us all happy!

Oh yeah, at this point I should add that I have included a micro switch into the foot pedal as Halbritt suggested.
So now I have the 'contactor' built into the pedal as well.

Now for the bad news, you have to hope that you can get easy access to the pots terminals. A lot of these cheap machines are cheap not because of quality but becase of manufacturing techniques. The pot could easily be soldered to and part of a display / control board. If so things become very difficult for the technique descrbed in the paragraph above

I think you might have missed my earlier post with the photos..........
It's already done and was quite an easy job.
I was actually surprised by the build quality, not bad at all.

AWRIGHT:
Again, good point on accidental disconnects.
The DIN connector is quite a snug fit, but if all goes well I will replace it with a locking connector.
I don't think using extra pins to disconnect the power is necesary. The contactor is N/O (normally open), so if the cable was disconnected whilst welding the power would be shut off the same as if you released the footswitch.
I don't think anything would happen if the cable was disconnected when the unit was ON but not welding. Would it????

Orphan68
My pedal will be "Heavy duty", but the one in that link is over the top!
I too was getting carried away with ideas for pulleys, belts and gears to turn the pot, but I've realised that simple is better.


I did some more work on the pedal tonight, hoping to have it all finished this weekend, so stay tuned for more pics and a performance review......

Justin

[awright]

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

[halbritt]

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.

[awright]

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...

Thanks

awright

[JDH]

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.

Yeah, this is really important.
Using a slide pot would have made this project a WHOLE lot simpler, but they're hard to find in linear at the required value. Even in log there doesn't seem to be much available. Understandable I suppose, when was the last time you saw a piece of equipment with a sliding control?

I thought about building a foot pedal, but it seemed too much of a hassle.

I'm starting to agree! But I'm past the point of no return..................

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.

I know what you mean. I used to fiddle around with electronics when I was a teenager, could build all sorts of gadgets for less than you could buy them in the shops.
Now components are getting harder to find and more expensive.

I have most of the pedal assembled now, should have some finished pictures to post by tomorrow.

Justin

[gnm109]

Originally Posted by awright

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...

Thanks

awright

Yes, it's true that the electronics outlets are dwindling. It is certainly true in Sacramento. There are only a couple of them left. Even Radio Shack is drying up. I understand that they are closing nearly 7,000 outlets nationwide. That may be a sign of the times as far a home-built electronics equipment is concerned. Most young folks have little interest in building electrical devices in general. They would probably rather just upload and download songs for their I-pods.

Oh well.

[JDH]

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

[MicroZone]

Looks good and that is surely a heavy duty unit that will last for years and years. Good work!

[gnm109]

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!