Starting to build, testing the theory

A project log for Stick / TIG converter

An budget add-on box to convert a stick welder to a TIG welder. This project aims to produce a low current TIG welder for <£100

DannyDanny 08/20/2014 at 21:160 Comments

I've got a couple of projects on here, this TIG (very hardware based) project and a project called home cloud which is very software based.

Whilst I have actually worked on these projects it's been fair to say that I've probably spent more time at beer festivals, cider festivals, motorbike festivals, on stag do's getting drunk, getting married, watching friends get married, visiting Amsterdam and doing a whole heap of work to actually pay for the bits to get two projects up and going...

So these entry videos were a pretty rushed job, however they did force me to layout the projects in an easy to view way.

Eagled eyes people will realise that the transistors laid out during my testing are actually power MOSFET, and not IGBTs. not to worry the final solution will be using IGBTs as it's the welding current that's important, not the voltage (FETS are voltage controlled voltage devices - so good for constant voltage devices (like a MIG welder) or good for amplifiers. whilst TIG welders require a constant current, -though it'd be feasible to use either with some feedback to measure voltage and current!

I'm in the stage of really seeing if this is feasible, the rectifier will handle about 60Amps, (30 each) and the FETS will handle around 20 amps, with 8 I have enough to position 2 either side of an H bridge. with an old low power welding transformer it would be possible to do some very limited welding. -though at this time I'm just dumping the output load into a light bulb.

in the video I've said that I've developing code for both PIC and AVR (where the AVR is an Arduino - essentially the main code base is written in C)

The program simple reads a table of lookup values used to set current over time. (imagine a table with values 20, 40, 60, 80, 100, that repeat, this would create a saw tooth wave.

this table is created by the operator and represents the current that they wish to see. (where current levels would be dictated by material type and thickness desired weld penetration etc.

a further table would be generated that would turn that current desire to voltage to be applied to the IGBT base to allow the current flow.

this simple maps the current to the output -
3Amps - 1
4amps - 8
5amps - 10

This table will relate directly to the linearity of the devices used in the output stage.

This table is used essentially as a starting point, and each output measurement is based on this. (this will stop surges at power on).

Once the output has been set it is measured and the output voltage adjusted from the signal generating controller, which will set the output of the IGBT devices, (providing feedback to adjust the signal if it falls outside of parameters.)

Essentially using this system allows me to take a load (in this case a light bulb) where the resistance starts low and increases as the filament heats up allows a specific voltage to be set, and then feed back tested against the "map" - e.g. if the map of what to apply to the IGBTs is set too low for the components then this is compensated.

the video showing the components is here: