Can one shift a (sine) wave up or down like on osciloscope?

bluesrocks

bluesrocks

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I'm about to do some experimenting with a portable camping economy welding device from an additional alternator. Concerning an analogue sinusoidal waveform, in this case from an automotive style alternator (but 24v),, can those waveforms from the 3windings be "moved" up or down so that the waveform becomes unsymmetrical to the horizontal zero-voltage reference? What I hear (Mr Tig, Weld.com) is that for aluminum welding 30% positive allows for some cleaning, but the 70% negative emphasizes penetration and heat energy toward the puddle making it easier to start and maintain. (I think I said it correctly..) I understand that the AC waveform is bridge rectified into DC.

Again, my main question is, can one move the waveform toward positive or negative side, and if so, how?
thx
 
Yes. Add DC to it in the polarity you want it to "move" to.

If you are rectifying it into DC anyway, just add that to it at that point, or using a transformer to boost the average voltage while it's still AC.
 
Could you just use DC and swap it back and forth? 70% of the time this way, 30% the other.
 
I'm about to do some experimenting with a portable camping economy welding device from an additional alternator. Concerning an analogue sinusoidal waveform, in this case from an automotive style alternator (but 24v). Can those waveforms from the three windings be "moved" up or down so that the waveform becomes unsymmetrical to the horizontal zero-voltage reference? What I hear (Mr Tig at weld.com) is that for aluminum welding it's helpful to use the AC +/- "balance" control, to set the waveform roughly 30% positive allows for some cleaning action, but the 70% negative emphasizes penetration and heat energy toward the puddle making it easier to start and maintain. He says that 50/50 causes too much splatter, not as good as 70/30. Forgive me if I got the polarity incorrect.

As for the alternator, I understand that the AC waveform is bridge rectified into DC. I might also be ok by blocking the lower more (potentially) powerful portion of the crest of the waveform... So if I can't lower the entire waveform to around 70/30, then perhaps I can limit that part of the waveform, accomplishing nearly the same thing..

My question is, can one move the waveform toward positive or negative side, and if so, how?
thx
 
amberwolf said:
Yes. Add DC to it in the polarity you want it to "move" to.

If you are rectifying it into DC anyway, just add that to it at that point, or using a transformer to boost the average voltage while it's still AC.
Click to expand...

Great! And perhaps some DC could be a good thing mixed in with the AC, saw a show where they tig welded aluminum with DC using helium instead of argon, but the recommended method is argon w/high frequency AC at 70/30 (neg/pos) "AC balance". I want the option to weld aluminum (& magnesium) on AC, the rest on DC. So I assume I'd need to use an oscilloscope (and practice welding) to see how much effect introducing X amount of negative DC current has in pulling the waveform toward the negative scale.
Does that sound accurate?

I figure might need smoothing (buffer) caps between the alternator and the welder to protect the alternator from whatever electronic feedback damage might occur. I'm hoping capacitors are kinda like diodes in that they only allow electric flow one direction..

I can control the RPM speed on the alternator for power control that doubles as my main frequency (hz) control too. Double the hz from 60cycles per second, and it's a tighter arc and puddle, reduce hz for wider spread for thinner material.

Out of my 24v alternator welder project, I'd hope to satisfactory control AC balance and hz cycle frequency, otherwise Im saving up for a $700 160amp tig & stick welder and plasma cutter (<-nice bonus feature, but costs extra) with pulse frequency control, percentage of + and - for AC cleaning/penetration targeting around 30/70, but it varies on different kinds of material/alloy, material quality, weathering etc. Todays HF (high frequency) interter tig machines, getting above the 60hz cycle limit, and sharpening the tungsten tip, produces a nice tight arc flare.

Question
How would I best introduce the negative DC to the AC signal as I dont want to send DC backwards into the alternator which could easily cause extra heat and other problems. Was thinking about running two power cord leads to the tig/stick gun/stinger, one for AC and the other for DC. Cant really put a diode on the AC line as that would turn it into DC,, stopping AC from occurring, so the question rises about the unintended consequences on the alternator from DC current (guessing 25v @5-10amps into AC 50v 100amps) trying to run backwards thru it while AC is being created, or would the bridge rectifiers take all the heat from the DC?
 
I went through this process years ago, attempting to build my own machine. Best to save up for a decent TIG machine if you need the capability. Nothing beats a commercial machine. I'm running a Lincoln Squarewave 275. I have welded tinfoil pie pans with it for kicks to 1/2 inch plate.

The newer inverter machines are so compact, but the old warhorses work forever too. Good luck either way. As said, a DC bias will accomplish what you seek. I have heard of folks using the alternator method in series with a car battery or two for DC bias. Just mind the sparks near the batteries and their potential hydrogen issue.
 
I've considered using two electrodes to form one combination arc. One for AC and the other for DC. Position the two rods at 35 degrees from each other, and position the rods so they focus about 3/16" away from their tips. Grind to an angle, not like a pencil tip, then place so grinds help point inwards to help tighten the arc form. This should allow different amounts of AC and DC power without worries about DC backing up into the AC supply. The AC arc should go first cleaning the material just before welding, breaking up ("cleaning") some of the exterior oxides, then the negative DC (or -AC) finishes the task by focusing heat to the metal. I recently saw a vid where tig welder company did something like this, mixed some DC into their AC welding which allows for lower power consumption and seems like more control over the arc and puddle, less heat to get the same job, and a smaller tighter weld puddle/bead is easier to deal with.

So, I need to either convince myself to buy an alternator ($225), variac ($225), 3-4 AGM-SLA 12v batteries ($200) wire & connectors ($50), is better than $700-800 on a multi process tig and stick welding, plus plasma cutter. If I buy the welder, the battery bank will do double duty for my bike for power assist! So the alternator would charge those batteries and that would become my much needed transpo power source. But that plasma cutter sure would be nice to have now and then... LOL I've downloaded some weldenator schematics, but no one is doing 24v, Im thinking of going 48v, and I want the options of doing AC or DC, and of changing the AC balance between pos and neg. However, I am encouraged by the suggestion of combining AC and DC together, or maybe run a standard tig AC with a negative heavy AC signal before the electrode or using different electrodes!!!

Wow, so maybe just introduce them together right before the tungsten,,, or,, just keep them separate including separate tungsten rods, and then you control each power type separately for infinite "balance" control. Call it an AC/DC hybrid welder! :wink:
 
Friendly1uk posts another good idea to make it happen. Time swapping the same electrode with AC then DC, and then just vary the amount of time each type of power dwells compared to the other. I figure high power and high frequency are not easily combined and swapped like that. But, if it can happen, I am interested in finding out. 8)
 
Why do I want to build a DIY welder out of an alternator/generator?

1) I am getting ready to build couple projects where welding is needed. I have constant sometimes severe back pain so I am pursuing a DIY recumbent bike or all wheel leaning trike. I need a general capability welder (on a limited income budget) that can also weld aluminum. Under 1/4", mostly 1/8 or less. Im no welder, but want to learn, general rule says one needs AC for aluminum and magnesium, and DC for everything else.

2) I am assembling a workshop around a 26hp gas B&S v-twin engine power plant recently purchased deal on '08 used riding lawn mower. Came with 2(!) 54" mowing decks, one brand new, the other tore some metal about 1/4" gap 4" long near a deck mount, but blades all spin freely and properly aligned. So I figure on transforming the ripped mowing deck into a pulley transmission platform to help get the output RPMs for several different applications.

Although I am keen for alternative energy, this power-plant is primarily for backup power in case of AC outage. The latest change in my plans is hoping to turn my old 4.5kw generator (head, broken engine) into a welder power supply, doing so would save me the cost of one or two high output alternators. But I need to separate the engine from the head and then adapt it to pulley driven.

The power-plant will be powering a
-7.5kw generator head for AC power
-air compressor
-4.5kw generator head power supply, adapt for use:
----battery charger
----hybrid-wave AC or DC tig/stick welder
----HHO gas generator power supply (youtube "HHO" or "hydroxy" (produced on-demand locally, not tank storage, for more info as welder and engine fuel enhancement)

Check out following vid for some amazing welding demonstrations. There is more, but this HHO torch can weld/braze/plasma fuze/heat treatment and cut, all from one torch!!! When piping HHO into petrol engine, this can extend your miles per gallon and improve HP and performance. Tends to clean out carbon build up inside engines.
8)
http://www.youtube.com/watch?v=J9yHoAm74LM

I am wondering if I used an alternator, concerning the hardware modification, couldn't I just
open it up and cut each of the three leads just "before" and just "after" the bridge rectifier
then connect a new wire lead to each end of each cut
run all wires to 3way blade switch for each the pairs functioning as,, ON DC--OFF--ON AC,, for each of the three leads
house all these switches into a nearby control box.

One could use two alternators for one welding system, allowing the mix of 6 different leads, 3 from each unit, allowing one to be for AC and the other for DC, or most any mix of AC and DC. You could also vary the amps and pulses by varying alternator RPMs variously controlling the amount of negative bias on the AC waveform. By varying RPMs of the alternators, you control total power/amps. Incorporate a foot switch to raise and lower the alternator(s) RPM's so you can flare soft at the end of a weld, and reduce power gradually as the parts heat up for long weld runs.

Wait, towards simplicity, how about modifying the rectification process? Can one "rectify" (chop, modify) so it's not perfect DC? Can't you leave some of the second part of the AC waveform? Im basically going to want a negative favored AC waveform, or an AC waveform with top half of the positive voltage gone, leaving less influence by the positive side of the AC waveform, but it's still there. Shucks, I guess it's better to just introduce some known amount of DC to a known amount of AC. But I am also not much of an electrician. But I did stay and Holiday Inn once, and I own two multimeters! :lol:
 
I admire your enthusiasm and "have-a-go" spirit, but I fear you may end up spending more in materials and parts on a DIY TIG welder than it would cost to be a used one in good condition, and you may still end up with something that doesn't work. A

lso, you may end up with a chicken-and-egg scenario trying to learn to weld with the thing. By that I mean, how can you test and setup your DIY welding if you don't know how to weld? How can you learn to weld if you don't know your welder is capable of welding properly?

I base this on my own experiences learning to MIG weld: A good quality welder that is set up properly is a lot easier to learn on than one without enough settings, poor wire feed and questionable quality wire/tip/earth clamp.
 
PunxOr
I am also afraid I might not succeed,, but sometimes fear should give way to creative venture. Pretty hard to advance if you just stick with the safe bet. However I surely don't have enough money to sink into a failed project. Others have done similar to what I propose before but not much detailed user friendly info, but some showed really good results, even with tig, and he was a first time tig welder. Doesn't mean I will have such good results, but I am creative and hope to make it work.

The three main modes would be look like the following:
-AC-AC-DC for aluminum with neg favored waveform
-DC-DC-AC for DC welding with some cleaning-action
-DC-DC-DC for just DC welding

Also consider when using DC welding, you could start the arc using AC for easier high-frequency starting. Maybe start out using
AC-AC-DC
then after starting puddle, switch to just
AC-DC-DC
to allow some cleaning action, or
DC-DC-DC
for straight DC, your choice.

-Welding Amps controlled via alternator RPM control and field winding (manual) regulator

-AC Frequency (even DC pulse-rate) is controlled by RPM control of alternator, one can optionally reduce power by lowering field strength via alternator regulator manual control.

-One could easily use a variable transformer (or variac) to give full control of the AC +/- balance like for mixed-AC/DC aluminum-welding.

I hope to avoid doing alternator mods, but I am new to DIY alternator welding. Anyone know if I could do what I am suggesting here, or would my concept require modification to the alternator???

I need this welder to build myself a recumbent bike or trike, and I need to do so quickly as my bike tire went flat and new bike/trike will not use 26" tires. Gonna piece together a folding bike or two to make a powered recumbent trike or bike.
 
To simplify matter, lets remove the alternator from the equation for a moment.

Lets say I have a standard AC only welder and a DC only welder.

Lets say we want to add some DC to AC for negative balance to be able to weld aluminum. Couldn't you just add the DC lead to the AC torch (and add DC ground clamp) and then control the amount of DC power to control how much negative balance is imposed on the AC arc waveform? One could weld until it's dialed in and then mark/record your settings for aluminum. Also I assume one could examine the waveform via oscilloscope,, to determine appropriate levels of AC positive to negative percentage. I hear 30/70% AC +/- balance is target starting point for aluminum.

If I could do that,,
then I could consider doing this using an alternator or two. However one could also consider doing this starting with AC like from Genset (wall outlet power), add a heavy duty bridge rectifier for pulsed DC, and add variac or variable transformers, and go from there with the setup mentioned earlier using triple place blade switches for each of several leads (AC on - OFF - DC on). So really, this project is becoming a DIY AC outlet into variac welder plus bridge rectifier to get DC, instead of a weldernator project. Thus I segway from alternator into my 4.5kw generator as power supply..
 
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