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HF Mig-mag welder

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LAN_403

Dr. H.

Wed Feb 04 2009, 06:49PM

Registered Member #931 Joined: Mon Jul 30 2007, 05:25PM
Location: Bulgaria
Posts: 486

Good day guys

I have been working on this project for a few weeks now (when I have time) and I finaly got it working. It is a just HF inverter based on the sg3525. It consists of a full bridge of irg4pc50ud IGBTs, the transformer consists of 18 primary and 2+2 secondary turns. The electronics is as simple as it gets - just variable puls width, no feedback, the output is boosted with UCCs, few seconds delay to charge the filtering caps up to voltage and a OCP (something like the one used on DRSSTC - it shuts the whole thing down if it exceed the current in the primary).

Here few pics:)

...

Wed Feb 04 2009, 07:02PM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

Wow that looks really nice!

You know that you are getting good when making a smps mig welder is just a simple project done in your spare time

Proud Mary

Wed Feb 04 2009, 07:03PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Good work, son!

Dr. H.

Thu Feb 05 2009, 06:01AM

Registered Member #931 Joined: Mon Jul 30 2007, 05:25PM
Location: Bulgaria
Posts: 486

Thanks for the kind words guys :)

Arcstarter

Thu Feb 05 2009, 07:49AM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

Wow, very nice! If only there where less gangsters and rapists in the world and more smart people like you and the rest of 4hv :P. When i have more electronics knowledge, i think i might try this.

101111

Thu Feb 05 2009, 12:39PM

Registered Member #575 Joined: Sun Mar 11 2007, 04:00AM
Location: Norway
Posts: 263

I really enjoyed this project, everything with it is just so damn neat.
Would be great if you made a good and thorough project thread about this.

Dr. Dark Current

Thu Feb 05 2009, 12:42PM

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

Very nice.
-what do you use for the transformer core?
-how do you limit output current? (leakage built into transformer/external inductor?)

Dr. H.

Thu Feb 05 2009, 03:24PM

Registered Member #931 Joined: Mon Jul 30 2007, 05:25PM
Location: Bulgaria
Posts: 486

Good day guys

again thanks for the kind words !

Dr. Kilovolt - for core I use three sets of E80 cores (a bit of an overkill but they work great).

About the current limiting - if I directly short the output of the SMPS the over-current detection kicks in (the leakage inductance is not enough). Mig-mags are a little bit fifferent from stig welders. The current is limited by the resistance of the thin wire that comes out from the nozel -it's speed and thincknes - bigger the speed and thikness bigger the current. Afcourse in big deal it depends from the output voltage of the inverter.

(I don't know how to explain it better).

Cheers :)

ConKbot of Doom

Thu Feb 05 2009, 05:45PM

Registered Member #509 Joined: Sat Feb 10 2007, 07:02AM
Location:
Posts: 329

Very nice, I take it by HF you just mean the inverter, and youre outputting DC? or is your inverter a pulse arc type mig welder?

What kind of voltages/currents can you output?
Did you buy a wirefeeder?

Pulsearc mig is really nice to use.

For those who dont know about regular mig, it just holds a constant voltage across the terminals, and the constant voltage keeps the arc length constant, as the wire feeds, arc length drops and current increses, melting the wire back and transferring the metal.

As far as welding technique, as you move move the tip in circles, similar to drawing an inductor symbol (the loopy style, not the one with just humps), like this

Slow down as you get to the bottom of the loop, and speed up as you get to the top where the lines cross. Doing it like that will give you the "stacked coins" appearance since youre advancing, slowing down, advancing... The side to side movement of looping helps get a proper fillet on the edge of the bead. Though the whipping doesnt have to be pausing at the bottom and advancing at the top like the symbol I posted, whatever works for you.

Also, you can 'push' or 'pull' the puddle as you weld. Pushing is having the gun pointed so that youre 'pushing' the puddle forward, and then obviousley, pull is pulling the puddle forward, both work, most people have a preference though. Just make sure you can see the puddle however. :)

Nice work, cant wait to see some other stuff made with it :)

On the two samples you posted I would also turn the 'heat' up a bit and definitely whip more as you move.

Dr. H.

Thu Feb 05 2009, 09:42PM

Registered Member #931 Joined: Mon Jul 30 2007, 05:25PM
Location: Bulgaria
Posts: 486

Good day guys

Really good article ConKbot and thanks for the explanation. About the welding - I am not a welder - my father is. I was just demonstrating high and low powers on the two pics.
Yes I am outputing DC.
I was getting around 130amps but the input voltage was dropping below 200vac so I will test again when i get the wire feeder home.

About the wirefeeder - it came from a scrapyard - the motor needed new bearing and all the magnets have detached from the case (they are glued to it). New roler was made, the electronics came from an old welder - needed repairing. (here a pic - it is on my big heavy transformer mig-mag - you can see the cable coming from the left going to the inverter)

Cheers

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