AC TIG welder design DIY build

[spixycat]

Goodmorning All,

I would like to investigate the feasability to be able to home build an AC TIG welder that will be very basic in the beginning and than make it more and more fancy (may be).

What I am considering is to use an older transformer basedMIG/TIG DC welder and use a very modern IGBT module as used to make a 3 phase 380V from a single power source (frequency converter or converting Solar 12V DC into one phase 220V) : this modules can be sometimes cheap and take away a lot of very complex IGBT timing issues.

I am not sure if you need to HF start every time you change the AC polarity

The idea is to use a very simple NE555 for setting the switching frequency and the AC balance will be very simple again 50/50% to begin with

Are more members interested in this or is there may be already an active thread on this? Where can I find interesting information that can help me?

I have seen and that project has been mentioned on several places of the CMOS TIG welder. I looked into it and there are a few pieces missing. But a complete design in ie CMOS that actually works is also fine.

Looking really forward getting response on this first post

Cheers!

 

[spixycat]

Dear Pdg,

Thanks for your honest input. I do see where you are comming from because I didn't describe all details : I have to start somewhere and the best place is to start working on something that almost can't fail because it is so simple and than make another itteration adding a bit more complexicity test it etc etc instead of building the ultimate welder in one go : just like an itteration approach as done in software development.

Yes you are right that a AC TIG welder combined with a MIG DC transformer welder sounds quite odd but I want to get DC power as simple as possible that is still able to provide a decent amount of current. Lator on in the proces it should indeed be replaced by a switching power supply eventually.

The baby steps of this possible project are more prove of concepts to understand unexpected behaviour that will be hard to get your head around because of the inductance nature of the welding torch cables that won't behave like a pure ideal resistor

In terms of IGBT module : you can always start of with some basic IGBT in TO-220 housing to be able to switch let's say 20 Amps and later on beef it up

It is indeed the intension to use a microprocessor for controlling the welder. That is going to be also quite a challange because of the real time aspects of the welding process that it needs to take care of which might be possible with the latest processors but than again the code is going to be quite complex

The idea is to start of using the famous KISS principle and go from there.

What do you think?

Regards

 

[spixycat]

I also consider the idea to use a defect frequency converter as the power supply at some point in time when lager currents are desirable : not sure at all if this is doable but is worth looking into this

 

[spixycat]

in other words:

my aim is to eventually use a IGBT module that I already got of 600V and 200A : the module has 3 half bridges to produce 3 phase 380V from a single source (switching time around 7nS).

The difficulty is to be able to control the current while an IGBT is in fact just a switch that is either fully on or off. That is the interesting part for me. So how do you limit the current to ie 70 amps when you have a ultra fast switch 200A current source? This is the interesting part, the really interesting part for me at least

 

[bill_gj]

Scott Henion has done this stuff, hasn't he? User: shenion

 

[Maker]

So how do you limit the current to ie 70 amps when you have a ultra fast switch 200A current source?

Pwm might work?
Sounds like a very Interesting project, keep us posted.

 

[Luke]

You need an inductor in the circuit. This will introduce a rise time to the current, which means that you can switch the IGBT quick enough to control the current.

The handy thing with VSDs that run motors is that the motor windings offer an inductive load to the inverter, this allows current control.

I'm not sure how this is achieved with a welding inverter.

 

[eddie49]

The "600v and 200A" are not necessarily what you will be using in your home-made welder - they are just the maximum specifications of the IGBT devices that you already have got.
A switched-mode power supply, or a single-to-3-phase inverter, or an inverter welder, usually starts by rectifying and smoothing the single-phase AC mains input. This gives about 325v DC, which is then chopped at up to 50kHz by the IGBTs. As Maker said, the current, voltage, and phase control is created by switching the gates of the IGBTs with PWM signals. There would also be an output transformer, with a ferrite core and a heavy-current secondary ( e.g. copper strip ), and, for a DC output, a rectifier.