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ZVS Welding inverter.

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LAN_403

MArked One

Sat Oct 01 2011, 07:14AM

Registered Member #3688 Joined: Mon Feb 14 2011, 07:39PM
Location: Europe
Posts: 38

Greetings.

I am looking to construct a very simple stick welder.

I am thinking of using a ZVS driver to provide low voltage, high current and this weld with the device. Sorta like a solid-state MOT welder.

The questions are: What mods (aside from HV fets) will I need to carry out on the zvs for it to run 'off the wall'? Is this idea plausible to create? What size/type of ferrite core should I use?

If anyone can answer these questions, I will much appreciate it.

Kind Regards,
Ivan Kozlov.

Inducktion

Sat Oct 01 2011, 03:10PM

Registered Member #3637 Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068

From what I've understood, so far, is the ZVS driver loves to go into a parasitic oscillation at voltages above 60- 70 volts. Why? No idea. You would need to modify it somehow to prevent it.

Doubl3 Helix

Mon Oct 03 2011, 05:33PM

Registered Member #1548 Joined: Mon Jun 16 2008, 09:22PM
Location: Ohio
Posts: 61

Has anyone done any tests to figure out why exactly this occurs?

Ash Small

Tue Oct 04 2011, 10:42AM

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

Why not go for a full bridge?

You can get IGBT's and gate driver IC's specifically designed for welding inverters.

I'll try and find some links, but I've mentioned them before in recent threads.

Daedronus

Tue Oct 04 2011, 11:01AM

Registered Member #2329 Joined: Tue Sept 01 2009, 08:25AM
Location:
Posts: 370

What's special in a gate driver for a welder?

MArked One

Tue Oct 04 2011, 05:51PM

Registered Member #3688 Joined: Mon Feb 14 2011, 07:39PM
Location: Europe
Posts: 38

Greetings.

Thank you for all the feedback so far. If anyone has a schematic or datasheet I can use as a starting point, I would much appreciate it. I was thinking of using a modified version of uzzor's multipurpose inverter to run a low-voltage, high current HF transformer. Any feedback on this idea?

Kind Regards,
Ivan Kozlov.

Daedronus

Tue Oct 04 2011, 09:30PM

Registered Member #2329 Joined: Tue Sept 01 2009, 08:25AM
Location:
Posts: 370

What I do know is that welders are constant current SMPS, half or full bridge, since a resonant SMPS is a bit harder to regulate.

I'm also working (slowly, very slowly) towards a SMPS welder.
It's built as a full bridge controlled with a UC3843. The current limit is pulse by pulse limit, sensing the current with current transformers in the primary.

It works OK right now after dealing with a lot of EMI that messed with the controller IC but I only tested it up to 40V input.

I need a variac to go slowly up to line voltage...but I'm too broke to buy one right now....so it will have to wait.

The final goal for me is a AC/DC tig welder.

Ash Small

Wed Oct 12 2011, 09:16PM

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

Daedronus wrote ...

What's special in a gate driver for a welder?

Some are designed for total control of the welding current, including 'ramping up' and 'ramping down', etc.

I'll try to find some links (I have them somewhere). I'm also interested in uprating my SGTC based HF/buzz box AC/DC TIG welder to inverter technology so that I can run it from a small generator. (You can't run a buzz box from a small generator. Something to do with inductive loads and phase differences.)

Daedronus

Wed Oct 12 2011, 10:54PM

Registered Member #2329 Joined: Tue Sept 01 2009, 08:25AM
Location:
Posts: 370

I really don't think current control/ramp is done at gate driver level.
There is probably a uC in there controlling a standard SMPS driver IC/adjusting the control loop, at least this is how I would do it.

Experimentonomen

Thu Oct 13 2011, 04:52AM

Registered Member #941 Joined: Sun Aug 05 2007, 10:09AM
Location: in a swedish junk pile
Posts: 497

A welding inverter is nothing but a regular SMPS designed for high output current.

The only difference is that it is output current that controls the pwm duty cycle, on idle it sits at 50% for maximum output voltage to easily strike an arc, then once the arc is struck, the current control or rather limiting circuit kicks in and reduces the duty cycle to say 10% or less depending on the current the thing is set to, to maintain a somewhat steady current for welding.

This mode is called Current Control while the mode used in power supplies is Voltage Control.

It may look complex at first but its really simple once you understand the basics of how a smps works.

I think there are welding inverters that are just big buck converters as well.

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