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nasukaren

Tue Jan 05 2010, 04:40PM

Registered Member #2607 Joined: Tue Jan 05 2010, 04:28PM
Location: Southern New England, USA
Posts: 4

Hi -

I'm a new member here. Just signed up today.

By day, I'm an anthropologist but by night I'm a crazy mad scientist. Or that's what my partner and my dog think.

RIght now, I'm working on an EV conversion of a 1971 Piaggio moped. It works on a big brushless motor designed for RC helicopters (4000+ watts!) and a 43.2 volt 13 Ah pack made from Prius NiMH batteries. It's always in various states of assembly and disassembly.

I have a MIG welder (flux core only) and want to learn how to TIG weld so I can make things out of aluminium. Much lighter for my EV conversion. But AC TIG welders are expensive. So I was scrounging around ways of making my DC MIG welder in an AC TIG welder by square waving the output and adding a high-frequency, high voltage arc starter on it. That led me to this site.

Nice to make all your acquaintances.

I'm sure you'll see me around from time to time.

Karen

Renesis

Tue Jan 05 2010, 04:56PM

Registered Member #2028 Joined: Mon Mar 16 2009, 08:13PM
Location: Norway
Posts: 319

Welcome to 4hv.

nasukaren wrote ...

So I was scrounging around ways of making my DC MIG welder in an AC TIG welder by square waving the output and adding a high-frequency, high voltage arc starter on it. That led me to this site.

Seems right up our alley. A powerful H-bridge should do the trick. But you should start practicing with DC TIG on steel, because aluminium is tricky to weld.

With a powerful MIG, pure argon gas and alu wire you can succesfully weld aluminium, but that takes some practice. The trick is to use much heat, enough to break through the aluminium oxide layer (scrape off as much as possible first) without burning a hole in the workpiece. Thus this tecnique is difficult with worpieces >5mm thick.

If i were to modify a welder into a TIG i would leave my MIG behind and buy a second hand SMAW (electrode or "stick" welder). They are pretty much DC TIG as is, you only have to modify the output signal.

doctor electrons

Wed Jan 06 2010, 03:26AM

Registered Member #2390 Joined: Sat Sept 26 2009, 02:04PM
Location: Milwaukee Wisconsin
Posts: 381

If you want to do some tig, or GTAW, make sure to add a circuit to control the n cycle and p cycle!
That way you will be a able to control weather or not your arc is better suited for low penetration and high cleaning,
or high penetration and low cleaning properties. If you get this working make sure you have the ability to leave the high freq on!
Also investigate the trifecta! Lanthanated, thoriated, and ceriated tungstens! The percentage will depend on the material.
The diameters of the tungsten will depend on your amperage. For SMAW the rule of thumb is, DIA of the rod, say .125 will
work perfectly at 125 amps. This follows suit through all the diameters. Feel free to pm any questions! I have been a navy certified
master welder since 1995!

Steve Conner

Wed Jan 06 2010, 11:56AM

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

Welcome to the forum!

This site

describes an IGBT H-bridge add-on to convert an ordinary stick welder into an AC TIG. This is the only such project I know of.

nasukaren

Wed Jan 06 2010, 09:28PM

Registered Member #2607 Joined: Tue Jan 05 2010, 04:28PM
Location: Southern New England, USA
Posts: 4

Thanks! That was exactly the site I was looking at. Instead of using TTL discrete components, I think I'm going to base mine on either a PIC chip or Arduino, so I have finer control over input parameters.

I still have a lot to learn though and I'm in no great hurry to electrocute myself. I've had 120 volts pass through me a few times, and 240 volts once (back when I was young and stupid)-- and they hurt like bejoogles. I can't imagine what 60,000 volts would feel like -- most likely the last thing I feel!

Karen

Mads Barnkob

Wed Jan 06 2010, 10:36PM

Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968

nasukaren wrote ...

Thanks! That was exactly the site I was looking at. Instead of using TTL discrete components, I think I'm going to base mine on either a PIC chip or Arduino, so I have finer control over input parameters.

I still have a lot to learn though and I'm in no great hurry to electrocute myself. I've had 120 volts pass through me a few times, and 240 volts once (back when I was young and stupid)-- and they hurt like bejoogles. I can't imagine what 60,000 volts would feel like -- most likely the last thing I feel!

Karen

If you zap yourself with 60kV, it is likely to be a a high enough frequency for it to block your nerves receptors thus blocking the pain reception, id rather take 50kV zaps from a flyback transformer than 230vac from the wall, any day :)

50/60Hz is just too dangerous

Myke

Wed Jan 06 2010, 11:44PM

Registered Member #540 Joined: Mon Feb 19 2007, 07:49PM
Location: MIT
Posts: 969

The frequency doesn't change how dangerous the power is. It just affects if your nerves will trigger or not. Personally, I wouldn't want to take the output of a flyback connected to a ZVS flyback driver. There would be lots of burning due to the temperature of the arc and who knows what it will do to anything that isn't burned (muscles and such).
The current is the dangerous part because it can cause muscles to contract where the current flows (your arms, legs, heart...).

Mads Barnkob

Thu Jan 07 2010, 06:30AM

Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968

Myke wrote ...

The frequency doesn't change how dangerous the power is. It just affects if your nerves will trigger or not. Personally, I wouldn't want to take the output of a flyback connected to a ZVS flyback driver. There would be lots of burning due to the temperature of the arc and who knows what it will do to anything that isn't burned (muscles and such).
The current is the dangerous part because it can cause muscles to contract where the current flows (your arms, legs, heart...).

Only if the current is a good way below 20kHz, there is a study paper on this somewhere on the internet.

I have taken my share of wall socket shocks, and there is a considerable distinct difference in the muscle pain, even many hours after, from 230vac 50hz to high frequency high voltage.

IntraWinding

Thu Jan 07 2010, 01:05PM

Registered Member #2261 Joined: Mon Aug 03 2009, 01:19AM
Location: London, UK
Posts: 581

Hi,

Always nice to meet fellow mad scientist

This is a great forum (that's why I joined!). Hope you like it too!

Renesis

Thu Jan 07 2010, 02:33PM

Registered Member #2028 Joined: Mon Mar 16 2009, 08:13PM
Location: Norway
Posts: 319

To the above, i dont know where the high freq entered the discussion but we can pretty much all agree that a low impedance line at 60kV will most likely destroy tissue and probably relieve you of spare limbs even at frequencies in the kHz range, thus "sting" a bit more than 230Vac. Personally i prefer to avoid them both.

And in the debate wether high freq currents are safe or not, i will keep saying they are not until i can see definitive evidence that confirms this myth. It is true that the skin effect will consentrate the bulk of the current around your skin, but with skin and flesh being a relatively poor conductor it is possible that the skin depth is dangerously deep. And the fact that my pain reseptors cannot register what is going on is scary as hell, cause if my body is conducting alien currents i would really want to know about it, even if that includes a lot of pain. (I say alien because our bodies naturally create its own weak currents).

I have heard many tales of nast RF burns from people playing with their SSTC's. I cant confirm these tales, but i find it safest to assume they are true. I might remind you all that people die from lightning strikes too, which have rise times of mere microseconds.

There, im done ranting for today.

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