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I want to use an H-bridge to turn my DC tig welder AC for light welding

jpoopdog

Member
Ok, so heres the jazz;

I own a transmig 175i, and a tig welding extension.
I want to do some fine/light/small welding on aluminium which requires AC
The reason AC is needed is because, ac prevents oxidation building around the immediate arc area, aka where it counts. DC however is apparently like trying to solder on oxidized copper without flux.
I want to use some sort of an H-Bridge setup with heavy duty transistors or if possible/practical, (mos)fets, to turn my roughly 17vdc at the recommended amperage, to reverse rectified AC, aka, square wave, for the function of making it possible to weld aluminium to some degree not attainable with DC

As for the actual welds themselves, it will be very light duty, on small parts, models, custom heatsinks and such. Ill be using an innoculation chamber (mycology) to maintain an oxygen free environment to the best of my powers,
Im not sure exactly on the required amperage, but it certainly wont be a full 170A, thats for sure.

Ive seen these sorts of welds done before what i have in mind, on dc, open air (normal welding), on DC, on aluminium, for the exact same purposes, welding model car chasis parts on and some other weird blocky things i didnt quite recognize as stuff.


Anyway, point being, its already possible, but i want to turn the dc to ac regardless for better welds. Otherwise ill have to make do with dc.



So, what i want to know is, is it possible? Ill be working in short bursts so temp management is already taken into consideration. But is it practical, given that the idea of spending thousands on another welder to do an unjustifyably small amount of work, is out the logic window. Furthermore these arent 100% neccesary jobs but if it all works out, ill be able to start some new projects prior to winning bags of money to toss willy nilly.

Asuming simple rectification is not practical what would i need to do?
Also consider that im not looking for anything fancy, just basic enough that utilizes the cleaning phases cleaning properties during the welding, making it better/easier. In my mind simple rectification at a low frequency should do but i dont know, hence why im asking here.
 

tcmtech

Banned
Most Helpful Member
Have you considered tapping to your units already available AC power that is ahead of the DC rectification circuits inside your machine?
 

jpoopdog

Member
hmm, i did not consider that! Although it is called an inverter welder so the case may well be that it uses some heavy duty switchmode setup or something.
Are there any risks associated with doing that? As in to the machine?
or should it not really matter if its just passing through a heavy duty rectifier?
 

rumpfy

Active Member
JPO,
I'm fairly sure that you will NOT be able to do what you want to do.
The output transformer usually has a primary running at 320 volt, (230 volt mains) switched at about 150 kHz, and the LV side is rectified. There are current and voltage feedback arrangements attached to the secondary and to interfere with this part of the unit will cause you to come to grief. I dont know the transmig at all but I have worked on a couple of 130 amp stick welders, and my comment is based on these types. My experience is that the current control loops on these welders makes them SO easy to use and to try to modify your transmig will result in tears.
Hope this helps.
 

tcmtech

Banned
Most Helpful Member
I didn't know it was an inverter type so in that case, take it to the nearest cliff and toss it as hard and far as you can.

As a former welder technician I can assure you you wont regret it later.
 

ClydeCrashKop

Well-Known Member
Most Helpful Member
There is some good info here: http://www.gowelding.org/TIG_Welding.html

It looks like it would be easier to TIG weld with a stick welder with a TIG torch and Argon. But they are talking about DC. Will that also work with my old AC arc welder?

When I bought my Plasma torch, they were selling combination Plasma / DC TIG. Why is that? What will it take to make an H bridge output AC TIG voltage and apmperage?
 

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