- Thread starter Jan
- Start date
AC is generally only used to weld aluminium and magnesium. DCEN is used for virtually everything else because around 2/3 of the arcs heat occurs at the +ve electrode i.e. DCEP melts the tungsten and so only has a very few specialised applications. As an aside due to the temp/heat polarity difference you can weld tungsten with DCEN using TIG
The AC waveform can vary quite a bit depending on the machine as inverters use witchcraft to 'chop up' the leccy and rebuild it. Because they switch so fast HF (high frequency) is only used to initiate the arc and they can do all sorts of things like different waveshapes (sinusoidal, squarewave, triangular), different AC frequencies and some even let you independantly adjust the amps for both the EN and EP phase or 'mix' AC with DC.
With transformer based machines, even modern squarewave examples, continuous HF is used with AC to stop the arc going out (or relight it) everytime it crosses zero. Frequency is fixed at what comes out of the wall but many (most under 30 years old?) have AC balance either manually adjustable or automatic. As Scott said, AC balance varies the EN to EP ratio. Unsurprisingly inverters can tweak the ratio about more than transformers
This goes into a bit more detail about why you'd want to mess with waveshapes, AC frequency and the like... http://www.mig-welding.co.uk/forum/threads/waveshapes.37420/#post-412262
Scratch TIG with an AC buzzbox won't work, at least properly, due to the HF thing. HF add on boxes exist but AFAIK most of them are designed to provide HF start and gas control to a DC stick welder. Probably wrong but i don't think AC or AC/DC versions are made anymore and when they were they were more likely to be machine specific i.e. designed as a modular set up rather than a universal add on?
The AC waveform can vary quite a bit depending on the machine as inverters use witchcraft to 'chop up' the leccy and rebuild it. Because they switch so fast HF (high frequency) is only used to initiate the arc and they can do all sorts of things like different waveshapes (sinusoidal, squarewave, triangular), different AC frequencies and some even let you independantly adjust the amps for both the EN and EP phase or 'mix' AC with DC.
With transformer based machines, even modern squarewave examples, continuous HF is used with AC to stop the arc going out (or relight it) everytime it crosses zero. Frequency is fixed at what comes out of the wall but many (most under 30 years old?) have AC balance either manually adjustable or automatic. As Scott said, AC balance varies the EN to EP ratio. Unsurprisingly inverters can tweak the ratio about more than transformers
This goes into a bit more detail about why you'd want to mess with waveshapes, AC frequency and the like... http://www.mig-welding.co.uk/forum/threads/waveshapes.37420/#post-412262
Scratch TIG with an AC buzzbox won't work, at least properly, due to the HF thing. HF add on boxes exist but AFAIK most of them are designed to provide HF start and gas control to a DC stick welder. Probably wrong but i don't think AC or AC/DC versions are made anymore and when they were they were more likely to be machine specific i.e. designed as a modular set up rather than a universal add on?
BrokenBiker
Member
- Messages
- 11,290
- Location
- Newport, South Wales
I was about to say I thought scratch start and AC wouldn't go together due to the wave crossing zero would surely end the arc, but hotrodder beat me to it
Jan
Member
- Messages
- 884
- Location
- Rotherham, South Yorks
Much as I thought. Whether the arc might want to fail as the voltage goes through zero would depend on conditions as an AC arc can be maintained if they are 'just right'. How you might weld effectively on true AC is doubtful if the heat tends to occur at the positive end of the arc.
I'll just have to get hold of a 100 amp or better bridge rectifier and a decent array of capacitors and have a play.
I'll just have to get hold of a 100 amp or better bridge rectifier and a decent array of capacitors and have a play.
wheresmejumper
Banned
- Messages
- 2,626
There is an english company still making ac hf boxes I think.a yellow one rated at 190 amps.bout 3-400 pounds.think its for sale on ebay every now and then
Jan
Member
- Messages
- 884
- Location
- Rotherham, South Yorks
'Only' £300-£400? I'll have a dozen!
Seriously: I've been spending way too much lately so I have to start drawing my horns in and being much more frugal until my finances are on a better footing. My old stick welder has done everything that I've thrown at it for the past 20 years or so and should have no trouble powering a 100 amp bridge rectifier plus some capacitance to give me sufficient DC current to make it into a scratch start TIG machine. In future I may consider a stand alone unit, but not at this time.
Seriously: I've been spending way too much lately so I have to start drawing my horns in and being much more frugal until my finances are on a better footing. My old stick welder has done everything that I've thrown at it for the past 20 years or so and should have no trouble powering a 100 amp bridge rectifier plus some capacitance to give me sufficient DC current to make it into a scratch start TIG machine. In future I may consider a stand alone unit, but not at this time.
wheresmejumper
Banned
- Messages
- 2,626
Thats damn cheap for what it is. A better known brand would be +£1000
http://www.ebay.co.uk/itm/AC-DC-190...845?pt=LH_DefaultDomain_3&hash=item1c40fb3f45
http://www.ebay.co.uk/itm/AC-DC-190...845?pt=LH_DefaultDomain_3&hash=item1c40fb3f45
KemppiFrog
Member
- Messages
- 4,298
- Location
- Aquitaine
Funnily enough I saw another one of those on the bay today, still more money than an inverter DC HF TIG, or am I missing something?
shenion
Tool Pack Rat
- Messages
- 7,586
- Location
- Stone Mountain, GA USA
But it is less than an AC HF TIG.
KemppiFrog
Member
- Messages
- 4,298
- Location
- Aquitaine
Yes, except there are a few on the bay at low prices (or at least low bids) if one has 3-phase. Usually older transformer based kit. Perhaps I was misled by the talk of big rectifiers.
I have just been welding a couple of ally tanks, one from scratch (excuse pun
) the other full of pinholes, so an AC TIG is looking very attractive. ( I was using my MIG with Argon).
wheresmejumper
Banned
- Messages
- 2,626
It is reliable welding of ally on a budget for someone with an air or oil cooled plant.there are fancier ones with amps output, upslope, downslope, pre and postflow,2t4t and more, but you are getting close to the price of a complete unit
wheresmejumper
Banned
- Messages
- 2,626
I never looked too far into it, but heard that generated ac and aluminium welding is not an ideal scenario.not a very stable or nice arc,with sub par weld integrity.
it could also be pure BS.but I do remember seeing some caveat on a lincoln engine drive so it mightnt be?
fact and fiction are getting harder to discern these days
it could also be pure BS.but I do remember seeing some caveat on a lincoln engine drive so it mightnt be?
fact and fiction are getting harder to discern these days
Greetings Jan,
In post #7 you consider adding a rectifier and capacitance to a stick welder so you might be interested in seeing such an outfit operating but without any capacitance.
I remember reading a discussion on this video where the advantage of adding capacitance was the main concern but am unable to reference it.
A wedge of carbon from a motor brush or brazing torch laid on the job allows an easy start to the arc and transfer to the job.
Dave
http://www.weldingtipsandtricks.com/homemade-tig-welder.html
In post #7 you consider adding a rectifier and capacitance to a stick welder so you might be interested in seeing such an outfit operating but without any capacitance.
I remember reading a discussion on this video where the advantage of adding capacitance was the main concern but am unable to reference it.
A wedge of carbon from a motor brush or brazing torch laid on the job allows an easy start to the arc and transfer to the job.
Dave
http://www.weldingtipsandtricks.com/homemade-tig-welder.html
Jan
Member
- Messages
- 884
- Location
- Rotherham, South Yorks
IIRC it was that video and a couple of others that influenced my decision to have a go at a cheap TIG conversion for my old stick welder. As I'm still in the process of erecting my new workshop and moving all my crap from the old shed it could be a while before I go any further with it, but at least I've already got a TIG torch virtually identical to the one in the vid.
zardoz
Old school Socialist
- Messages
- 2,217
- Location
- Chetser, UK
I sold one for 40 or 50 of the queens pounds on here several years ago. You can still get them for that on fkeabay if you are not in a rush and don't mind second hand.
