Ideas for modifying a TIG welder

Discussion in 'General Electronics Chat' started by Jimmeh30, Apr 26, 2012.

  1. Jimmeh30

    Thread Starter Member

    Mar 4, 2011
    Just looking for some general advice from anyone who has better knowledge of how TIG welders work.

    My problem : I recently bought a cheap Chinese 3 in 1 job (TIG/PLASMA CUT/MMA) which came with a "foot control". The pedal however, only utilizes the micro switch and not the pot... IE: it's useless (only starts and stops the arc, no current control)

    Inside the welder itself, the DIN socket that accepts the cable from the pedal, has only two wires connected of the 7 available.

    Schematics for these welders are impossible to get.

    I've read through all the other posts I can find regarding these welders and I'm sorry if there's one that I've missed that answers this question but....

    What I need to know is, 1: when a given pedal control on a given TIG welder is implemented, does it only control the "Peek current" or does it also effect the "background current" limit.

    And 2nd: has anyone ever managed to dig up a schematic for these welders?
    My particular model is a "Proweld CT250P" but looking at the pictures supplied by another contributor for a C250D (I think it was, or maybe it was C500D) it's identical in construction aside from differences in the HV arc start) also, the unit was built by CHIRY (as they all seem to be) or at least, all the boards have "CHIRY" and model numbers for the boards.

    I can supply more info and some pics on request, and any info/advice anyone can give would be greatly appreciated.

    Last edited: Apr 26, 2012
  2. shortbus

    AAC Fanatic!

    Sep 30, 2009
    Not familiar with these machines but, is there a potentiometer on the machine that controls the amperage? If not your stuck with just the "set" amperage. If there is an adjustment you could possibly go inside the machine and change the wiring to put a pot on the foot pedal. Do these machines have high frequency start or just 'scratch' start?

    The usual thing about multipurpose machine like this is they don't do any of the things very well.:)
  3. KMoffett

    AAC Fanatic!

    Dec 19, 2007
    Does your TIG have a pulser? From my experience only pulsers have a "background current". With a pulser, the foreground current is a % of the maximum current set by the dial, and background current is a % of the foreground current. So with a foot control, it controls both foreground and background current.

    Last edited: Apr 26, 2012
  4. gerty

    AAC Fanatic!

    Aug 30, 2007
    If you do manage to get the foot control working, you'll have to disconnect the pot on the front panel. In other words, the controls will try to read both pots at the same time and who knows what the results will be.
  5. Jimmeh30

    Thread Starter Member

    Mar 4, 2011
    Yeah I realize that Gerty, thanks though.

    Problem is trying to find a way to switch the pedal in, in series with the current limit pot, but only in TIG mode (and not in MMA/plasma cut mode... same control pots for all three modes).

    If I had a schematic, it'd be a crap load easier as there's not really any way to make any measurements while it's turned on and assembled, and no way to lay it all out and have it all interconnected without a lot of temporary wiring.

    perhaps I should just buy another 7pin DIN and wire it up to short the pedal pins when not using any remotes.

    I'm not getting any hits on this, so I guess I'll do a bit of plug and pray :)
    Last edited: Apr 30, 2012
  6. Jimmeh30

    Thread Starter Member

    Mar 4, 2011
    More, info...

    Yeah, it's a pulse welder upto 200 Hz, AC/DC, balance control, main current (limit), background current, lead in & lead out times. Just hasn't been designed such that the pedal can control the current. And, yes it's a HF start in TIG and CUT modes, scratch start stick. Also the pulse, bkground/foreground and balance controls work in stick mode too. (strange I know, but confirmed with my scope)

    I think I can simply wire the pedal pot via the socket on the machine, in series with the foreground current pot on the front of the machine?

    The simplest way I can see to do it is to do just that for the TIG plug, and modify the plug on the plasma cutter so it shorts the two pins for the remote pot effectively returning the welder to "standard" wiring. The only problem with that approach is that I'd need to make a 7 pin plug to install when using the stick welder, that shorts the same two wires.

    I'd much rather set up a relay that operates off the function switch and kicks in only in the TIG mode, in order to avoid having to have a shorted plug for the stick welding function.

    I'll take some photo's for plug locations and pull it all down tomorrow and see if I can figure something out. Really my question was "has anybody ever found a diagram for one of these"

    I'm open to more suggestions, and thanks to all who've responded. I'll post the pics and let you know what I've figured out, for anyone that's interested.
  7. Jimmeh30

    Thread Starter Member

    Mar 4, 2011
    Thanks Ken,

    You've answered one of my main questions about the welder and confirmed for me what the background current setting actually does.

    The major lesson learnt, if you don't know how to use a machine, don't buy a Chinese knock off... spend the money and get a real one with a REAL MANUAL ;P

    Thanks again.
  8. lindolo2

    New Member

    Aug 22, 2013
    In order to install a foot pedal to an old or even a new welder, you must open the welder and determine the oms for the front potentiometer that is in the front panel which controls the amperage. The foot pedal potentiometer should have the same oms. You would have to buy and install a 3P2T (triple pole, double throw) switch. If your welder already has a 5 or 7 pin input for the pedal but only 2 pins are used for the on-off, you can use 3 unused pins to route the potentiometer cables from the foot pedal up to the welder. You must unsolder the potentiometer cables from the welder and those cables should be welded to the middle 3P2T switch pins. From one set of the outer terminal of the switch, solder new extension cables and solder their ends back to the potentiometer in the exact same locations. From the other side of the 3P2T switch, solder cables to the pins selected for use on the 5 or 7 pin input. Make sure the cables run exactly to the same positions on the foot pedal potentiometer as the front panel one! Now drill a hole on any available space on the front panel as per the new switch dimensions. Install the new switch with its locking nut. Label the switch "Up-Welder, Down, Foot Pedal". WARNING: Since you are not using a standard to install this pedal, the pedal should be used ONLY with this welder since the pin-outs change from welder to welder! A certified technician or electrician should perform and verify the usefulness of this information and wether it will or not work with your particular welder.
    Last edited: Aug 22, 2013
  9. Rbeckett


    Sep 3, 2010
    Need to make sure that your machine is actually capable of variable amps on a pedal. Some of the import welders do not employ that feature because they utilize scratch start DC only tig which will NOT be usefull for aluminum. Ufortunately I would recommend against plundering around inside of an import welder because they are super easy to let the magic smoke escape from them and cheaper to replace than repair.If you could include the brand and model number of the machine and any specs you have on it I will look in my library and tell you if it is even possible to make that modification even work. Sorry to sound so negative, but they are often best left alone and a welder more suited for a specific application obtained. You can easily spend way too much money trying to get it to work and end up with poor results even after all the work and engineering. Been there, done that with a Lincoln Buzz box 225 Amp machine that never worked as good as it should despite massive time and investment to get it going. I would have been better off to just buy an AC Tig welder from the start and just ended up having two working machines. Sorry.

    Wheelchair Bob
    Last edited: Aug 23, 2013