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ARC WELDER MACHINE - CONCEPTUAL

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Newton Brawn

Fri Jan 18 2013, 12:50AM

Registered Member #3343 Joined: Thu Oct 21 2010, 04:06PM
Location: Toronto
Posts: 311

Hi All !

For long time I was trying to design a arc weder machine that can weld stell using commom arc welding electrodes.
The basic specifications could be;

Power supply available : 230V, 60Hz
No load output voltage at the welding electrode: 50~60V
Arc on output voltage: 20~30V ac or dc
Welding current (arc on current): 30~80A
Short circuit current whem the electode is touching the work: 40~90A

My first idea is:
to make a full wave rectifier that deliver 325V dc to a inverter ,
the inverter ( or any suitching device) will provide 20kHz or more to a transformer,
the transforner will receive 325V and deliver 50~60V to welding electrode.
the current will be regulated and ajusted by a simple inductor in series with the transformer secondary.

Any suggestion, schematic for the switching circuit, or even the "apparatus circuit" ?

I have built welding transformers in the range of 60~240A using 60Hz transformers and inductors as ballast, also transformers with magnetic shunt to control the arc current

Thanks for any comment,

Newton

Dr. Dark Current

Fri Jan 18 2013, 12:09PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

The most simple an unoptimal solution is to use a bridge (half, full) of transistors at maximum duty cycle, which drives a transformer through a series inductor. It is recommended to put the inductor on the primary side of the transformer. On the secondary you just have a full wave rectifier with fast diodes. The pros are - no feedback loop, simple control of transistors. The cons are - high reactive power in the transistors, higher losses, control of output current basically possible only by varying air gap in the inductor (frequency control is also possible, but efficiency of such solution is questionable)

Ash Small

Fri Jan 18 2013, 12:51PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

I'm also interested in building an inverter welder, to run from a mobile generator (you can't run a 'normal' welder from a mobile generator, for reasons that were once explained to me by the designer of my generator over the phone, which involved phase angles or something when running inductive loads).

Is it possible to limit current using series capacitors, either on the primary or secondary, or would this cause other adverse effects?

StormInABottle

Fri Jan 18 2013, 01:04PM

Registered Member #9252 Joined: Fri Jan 04 2013, 06:27AM
Location: Andromeda
Posts: 253

You can always re wind a MOT For the voltage and current you want.

And that is a really nice tutorial on how you do what he did.

It covers everything. Please be safe and have fun :D

EDIT: if you are interested in mad ass current

EDIT: Video of it working..

EDIT:Another tutorial

Someone messing with it

I think you might be interested in it

Newton Brawn

Fri Jan 18 2013, 11:29PM

Registered Member #3343 Joined: Thu Oct 21 2010, 04:06PM
Location: Toronto
Posts: 311

Hi Arcingnoob:

Thanks for the videos, they are realy goood and guive a precise procedure to dis assemble a MOT.
Also the project with the 2 mot running a arc werder is a good one.
However, as posted in the first place, the concept is a metal arc welder using a inverter.
Thanks again
Newton

Newton Brawn

Fri Jan 18 2013, 11:37PM

Registered Member #3343 Joined: Thu Oct 21 2010, 04:06PM
Location: Toronto
Posts: 311

Hi Ash !

The generator arc welder is still working in the farms, and matches very well with the arc V/A characteristics.

But I am interested in a very simple inverter supplying AC and DC to the welding rod.

Thanks

Newton Brawn

Sat Jan 19 2013, 01:26AM

Registered Member #3343 Joined: Thu Oct 21 2010, 04:06PM
Location: Toronto
Posts: 311

Dr Dark Current:
Yes, your arquitecture match with my conceptual.
Assuming that the output welding current under short circuit at the electrode may be limited at 100A, the aparent output power could be 100A x 60V = 6000VA. ( 60V is the no load voltge at the electrode)
Assuming the converter efficience as 90%, the converter input could be 6000/.90 = 6700VA
The 230V input after a full wave bridge rectifier and input capacitor filter will be 325Vdc.
The load at rectifier, 6700VA/325V = 20.6A
The R load at rectifier, 325V/20.6A = 15.8 ohms

If a capacitor of 5000UF is input, a ripple of 10% may be on the dc bus.. .

Time to sleep, I continue tomorrow....

Ash Small

Sat Jan 19 2013, 01:28AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Newton Brawn wrote ...

Hi Ash !

The generator arc welder is still working in the farms, and matches very well with the arc V/A characteristics.

But I am interested in a very simple inverter supplying AC and DC to the welding rod.

Thanks

Hi Newton. I think you mis-understood me. I didn't mean to recommend using a welding gen. set. I meant I tried running a buzzbox from a generator and it doesn't work.

I'm also interested in building an inverter welder, and the question I asked is 'would a series capacitor on either the primary or secondary of the inverter transformer work to limit current, or would other problems arise?'....My idea would be to vary the capacitance, either using a variable capacitor, or switching several parallel ones in and out of the circuit, in order to control current.

Another simple idea might be to vary the switching frequency, which I think could work, maybe also with a series capacitor to prevent saturation of the core at low frequencies.

I'm still a relative newbie when it comes to designing high frequency transformers, so maybe someone with more experience than me could advise on either of these ideas, and whether they could work or not?

AwesomeMatt

Mon Jan 28 2013, 07:46AM

Registered Member #4454 Joined: Sun Feb 26 2012, 12:47AM
Location: Western Canada
Posts: 74

wrote ...

And that is a really nice tutorial on how you do what he did.

It covers everything.

Why thank you for the kind words. Some day I will finish the actual project videos that were supposed to come after them :)

Steve Conner

Mon Jan 28 2013, 08:32AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

I would add a rectifier and filter inductor after the transformer, for the following reasons:

If you weld with high frequency current, the inductance of the long welding cables will prevent you from getting the welding current you want. The current will vary a lot depending on how the cables are laid.

Likewise for the inductance of a large steel workpiece.

Even the thickest cables will get extremely hot from skin effect.

Stick welding electrodes are designed for use with DC (AFAIK)

The filter inductor ensures a continuous current, helping keep the arc lit, and allowing you to regulate the current with PWM.

Last of all, this is what's inside an inverter welder, I've examined the guts of a few. They are basically a SMPS minus the output filter caps.

Some of them feature an AC output for welding aluminium. They actually use a rectifier followed by another inverter to produce a low-frequency square wave output. This explains why they are considerably bigger and more expensive than DC-only machines.

You can get fast rectifier modules with multi-hundred amp ratings from Digikey.

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