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how to make a decent welder?

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Inducktion

Thu Aug 25 2011, 11:40PM

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

Seems I've come into need of a welder...

I've heard of the two microwave trick, but that draws a lot of excessive current when not even under load!

Not to say, that you have no reliable way of changing the power output.

I know you can make a SMPS sort of welder, and I already tried this... using a KA7500. and a FAN7392 for the output driver.

But the High side driver, as always, did not work properly. I made it a variable duty cycle output by changing the voltage reference to the dead time pin on the KA7500. The output signal is NOT a complement to itself, where say, the signal is on 60%, off 40%? The other signal was the same, just, different phasing. I thought it was supposed to be exactly the same just 180 degrees behind the other signal, where one is on, and the other is off.

Because of the nature of the output wave, I don't believe a GDT would work properly. And, the high side output would not work either on the FAN7392. (I tried with the power on, current limited by a light bulb) and the high side gate signal did NOT change, and I double checked the connections. Everything was as it was supposed to be.

The output transformer from the half bridge (made by two Fairchild power IGBT's) was a 15 turn litz wire primary, with a 5 turn secondary.

Input voltage to the bridge was 170 vDC.

Is there some other way to make a welder with modifiable duty cycle? I could try to use a buck converter output stage, using just ONE of the outputs of the KA7500, but I'd still need a high side driver.

Appreciate it!

Ash Small

Thu Aug 25 2011, 11:56PM

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

Ebay, for example, $10....

You can always turn it into a TIG welder if you need to. Plenty of shematics for HF, etc on here.

EDIT: The other option is to modify an automotive alternator. Shematics also online.

EDIT EDIT: I've also been looking into building an inverter welder, primarily so I can run it from a generator.

I've found a few papers on the subject, I'll try and find them. There are Î¼C's and IGBT's specifically designed for this application.

EDIT: International Rectifier application notes for welding inverters:

Dr. ISOTOP

Fri Aug 26 2011, 09:30AM

Registered Member #2919 Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652

A standard (DC) TIG welder is just a regulated DC SMPS, a job that is perfect for our beloved TL494.

Daedronus

Fri Aug 26 2011, 01:08PM

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

What kind of current control should be used for the smps type welder?

Ash Small

Fri Aug 26 2011, 04:58PM

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

bwang wrote ...

A standard (DC) TIG welder is just a regulated DC SMPS, a job that is perfect for our beloved TL494.

The (now discontinued) HIP2030 supposedly privides a lot more control that the TL494, allowing more control over things like ramp up and ramp down, etc. (I'm certainly no expert on μC's)

Most welders enable DC electrode negative, DC electrode positive and AC welding modes, although DC electrode negative is probably the most versatile of the three.

Dr. ISOTOP

Fri Aug 26 2011, 05:19PM

Registered Member #2919 Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652

Ash Small wrote ...

bwang wrote ...

A standard (DC) TIG welder is just a regulated DC SMPS, a job that is perfect for our beloved TL494.

The (now discontinued) HIP2030 supposedly privides a lot more control that the TL494, allowing more control over things like ramp up and ramp down, etc. (I'm certainly no expert on Î¼C's)

Most welders enable DC electrode negative, DC electrode positive and AC welding modes, although DC electrode negative is probably the most versatile of the three.

But its discontinued, and there's nothing wrong with using a TL494 for this purpose (its not like you need to regulate to within mA's or anything).

Inducktion

Fri Aug 26 2011, 06:11PM

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

What about a buck converter SMPS?

dude_500

Fri Aug 26 2011, 06:52PM

Registered Member #2288 Joined: Wed Aug 12 2009, 10:42PM
Location: Cambridge, MA
Posts: 179

Inducktion wrote ...

What about a buck converter SMPS?

Commercial welders usually use half or full bridge based converters with an output transformer.
On an AC welder, the setup is input->rectifier->bridge->transformer->rectifier- >bridge->rectifier, where the second bridge is made of high-current, slow IGBTs with low Vce.

Weston

Sat Aug 27 2011, 04:10AM

Registered Member #1316 Joined: Thu Feb 14 2008, 03:35AM
Location: Cambridge, MA
Posts: 365

What welding process will this be for? The supply requirements really depend on the welding process. I am going to guess SMAW (stick welding) as that is the type of welding with the least amount of equipment required.

SMAW is a constant current welding process, so take that into mind when looking for SMPS designs.

For a cheep welder I would go with the option of the rewound MOTs. Its cheep, easy to build, and more reliable then the majority of DIY SMPS. You can add additional primary winding to reduce the no load current draw. Not that it makes much of a difference given the low periods of time a welder is used for.

Power control can be achieved by using a additional rewound transformer with a variable air gap as a variable inductor in series with the AC line or with a SCR based phase controller similar to a light dimmer.

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