Building a multi-purpose welder

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There are quite a few DIY and other projects on the net for building one's own welder. Most of them involve getting a few MOT's (microwave oven transformers) and rewinding them to be stepdown transformers, then I assume putting a bunch of them in parallel for lots of amps and some limited amount of volts. I have even seen claims that 3-4 volts at some specific amperage was sufficient to spot weld. Is there a table somewhere of what voltage and amperage is necessary for each size of electrode and or material?Does a 'multipurpose' welder exist? By this I mean that you have a box that generates your current, and you either hook up an electrode holder, or wire gun, or spot weld pinchers, or spot weld gun or whatever? Or is it really necessary that each style of welding have its own differently operating power source?Is it best to get down to DC in each case or are some methods better suited to AC where others are better suited to DC?
Reply:I have even seen claims that 3-4 volts at some specific amperage was sufficient to spot weld. Spot welders don't really use an arc; intense clamping pressure across a small area and a lot of amps are the key - so yes, 3 to 4 volts may be enough to push hundreds of amps through the small area - momentarily melting the metal to form a nugget weld.Is there a table somewhere of what voltage and amperage is necessary for each size of electrode and or material?Here's a table... with stick the main controlling factor is the electrode size, not the thickness off the metal although that has some influence.Does a 'multipurpose' welder exist?Welding circuits tend to be of two different types:Constant Current (CC): Stick-arc welders (23 - 36 volts) and TIG welders (15 - 22 volts)Many transformer based arc welders can perform TIG welding too - their voltage is a mite higher than necessary but it works OK.  Many inverter-based welders are marketed to do both stick (24 volts) and TIG (18 volts).  However once the voltage drops below 20, it is difficult to maintain an arc.  e.g. The Millar Diversion series of TIG welders does TIG only.For a transformer-based welder, the output filter section (after the diode-rectifier bank) consists only of a choke (inductor = coil of wire around iron core).  This device serves to maintain the current constant.Constant Voltage (CV): MIG welders (18 - 28 volts)For a transformer-based welder, the output filter section (after the diode-rectifier bank) usually consists of a large capacitor followed by a choke (inductor = coil of wire around iron core).  Working together this dual-element filter serves to maintain the voltage constant.There are several 'multi-process' welders on the market but these tend to be large amperage industrial units.  Look at the Lincoln and/or Miller web sites.For home/hobby use, I am aware of only one combination MIG/Stick welder on the market.I do wonder why there are not more of these (and there may be).  A triple MIG/Stick/TIG unit is possible because all that may be necessary is a simple switch to have the capacitor in the circuit before the choke (CV = MIG) or to have the capacitor out of the circuit leaving only the choke (CC = Stick/TIG).Is it best to get down to DC in each case or are some methods better suited to AC where others are better suited to DC? In general, DC works better for everything.  The sole exception being TIG welding aluminum where AC is favoured for cleaning purposes.  However, even there, DC- TIG welding with high-purity helium as been used for many years in the aerospace industry.Rick V 1 Airco Heliwelder 3A/DDR3 CTC 70/90 amp Stick/Tig Inverters in Parallel1 Lincoln MIG PAK 151 Oxy-Acet
Reply:What are you guys on about? there are countless CC/CV power sources that do Multi-process.   The Powcon's I have are all multi process power sources.Tiger Sales:  AHP Distributor    www.tigersalesco.comAHP200x; AHP 160ST; MM350P,  Spoolmatic 30A; Everlast PowerTig 185; Thermal Dynamics 60i plasma.  For Sale:  Cobra Mig 250 w/ Push-pull gun.  Lincoln Wirematic 250
Reply:Originally Posted by soutthpaw What are you guys on about? there are countless CC/CV power sources that do Multi-process.   The Powcon's I have are all multi process power sources.
Reply:A simple look at Miller or Lincoln Electric would show several multiprocess power sources. Another simple search here or with the googles would get you some basic information of electric resistance welding including those using an open arc. But hay why look when you can ask? You will find that aluminum and steels both can be efectiave welded using AC and DC+-. http://en.wikipedia.org/wiki/Weldinghttp://en.wikipedia.org/wiki/Weldinghttp://www.millerwelds.com/products/multiprocess/http://www.lincolnelectric.com/en-us...s-welders.aspx
Reply:Thanks Rick! That was more information than I even hoped to come up with. From what I understand from power supply building technology is the capacitor is used for smoothing. The output of the rectifier is a variable DC wave based on the Hz. When you put the properly sized capacitor in the circuit it 'smooths' it to where it simply has a 'ripple' of about 10%. If that is acceptable I can stop there, but otherwise I assume I will need a regulator to make it a very constant voltage. I have to look a little deeper because once the amperage gets > 90 the size of the smoothing capacitor starts to get pretty big. (Almost 300,000 uF) I assume it will overall be easier to use multiple transformers, rectified and smoothed and possibly regulated to a nice DC voltage/current and then series or parallel them out to control effective voltage and current. So it would seem the controls need to be:set Max Amperage for nugget/spot weldset Specific amperage and relative voltage for either stick or tigset Specific voltage and relative amperage for migGot it! Thanks for the info. I think you just saved me about 6 days worth of searching
Reply:Not sure what your time is worth but for what u have spent on your HF welder, getting and tearing apart a couple of microwaves, trying to reinvent the wheel etc.  you could have returned the welder and taken some of the good advice given you and been off and welding for hours already.    Oh well,  as the saying goes. Some things you can't fix.Tiger Sales:  AHP Distributor    www.tigersalesco.comAHP200x; AHP 160ST; MM350P,  Spoolmatic 30A; Everlast PowerTig 185; Thermal Dynamics 60i plasma.  For Sale:  Cobra Mig 250 w/ Push-pull gun.  Lincoln Wirematic 250
Reply:Hi southpaw! The HF welder is working fine now that I adjusted my technique. Thanks for asking. I am also looking into the DC mod, but the calculations I have done for the smoothing capacitor suggest that I need a bigger one than the ones I have. However, it seems to be well enough that I am not sure I want to mess with it. Seems to me, I now have a 'stick welder' with a really thin and long stick  Thanks for chiming in here, I am sure you can have something good to add. The microwave thing is an ongoing project, that will probably begin with a small spot welder. I think I can achieve that with just one of the two transformers I have so far. However, with the things I was looking at for making the DC mod, as well as the other research I was doing, it seems that with enough umph behind it, such a beast can be built that could serve multiple duties. I am still about 6-8 microwaves shy of what I want to do, but who knows, I might end up with something useful. The little HF welder is doing its job of giving me something to learn on, but soon I will have my O/A stuff back in service and Sparky might just find himself on a back shelf for emergencies only. I just don't find the electrical stuff as fun as the O/A..As for my time, this is much more of a hobby than a paying gig. So I am enjoying it. It is finally giving me a chance to use my electronics hobby for more than blinking lights and screeching noisemakers and such. I assume, that you are a professional and that you do this as a livelihood. I can certainly understand how you might find my hobbyist endeavors to be a waste of time. And certainly if there were a paying gig involved that you could charge $125 / hour welding, and write off a welder of any amount with an ROI of some number of hours no question there would be neither enjoyment nor justification for building anything such as a welder. But I am not a welder, and there is nothing I will ever weld that anyone will ever pay me for. I am not a founder and there are no castings that anyone will ever pay me to pour. As a matter of fact, I am not really an electronics engineer and it is doubtful that anyone will ever pay for any circuit I wire up. I do these things for my own use and purposes. I do them because I enjoy them. And if any of these projects fail or succeed it will not affect my mortgage or car payments or my next meal. But I will learn something and enjoy the journey to get there. I may build my own forge, or welder or any of those countless Gingery projects, or so many others, just like other people build a chair for pleasure, or a child's pull toy. Hell, I might even build a chair!! Nice hearing from you again,- Abs