Constant power welding machine

I found these constant power welding machines (http://www.arconweld.com /) from one of the Google sponsored links. I've used constant voltage and constant current machines, but I've
never even _heard_ of a constant power machine. It sounds like a good idea... but I'm a pretty inexperienced. The claim seems to be that constant power keeps the weld puddle more consistent.
Now that I've heard of one I'm just curious... Has any one ever used one? Is there any real benefit to going with a constant power machine, vs. constant current?
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Those are Constant Current machines. Arcon is the reborn Powcon. Founded by Goran Hedberg, the inventor of inverter based welding power supplies.
They are very very good machines, just pricey.
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The Arcon web site states there 'Work horse' series of welders to be constant power not constant current. Constant power is very different from constant current.
I am very interested in this topic of constant power welding power sources. I am a hobby TIG welder and professional electronics design engineer, and have thought about this very concept of a constant power source. I would be interested to learn of actual comparisons of welding with constant power vs. constant current. I have given some thought to building a low power constant power source just to fiddle with. Low cost digital signal processors would allow for all sorts of experimenting with closed loop power control.
I have attempted to locate technical references on the more theoretical aspects of electric welding, without success. I would appreciate any references others may have come across.
Ernie Leimkuhler wrote:

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OK I read the description on their website, and yes Constant Power would be an improvement over Constant Current for Stick and TIG because your arc length has much less effect on your puddle temperature.

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I was so impressed with the quality of custom parts fabricated by both of these companies that I wanted to share there contact information:
http://www.hobbymachine.net /
http://www.rapidcreekcutters.com/index.html
I saved over $600 by using the above shops, compared to local Seattle shops.
I have no affiliation with either shop, just a very satisfied customer.
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You *may* also wish to check out http://littlemachineshop.com/ - especially if you're out near Pasadena, CA. They specialize in replacement parts for small lathes and mills - 7x10, 7x12, 7x14 & mini mills, and I don't know if they take in custom projects or not, but they probably do. Have read some really good things about their parts and accessories for the above mills & lathes.
====== Mike wrote:

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Ernie Leimkuhler wrote:

lengthects of electric welding, without success. I would appreciate any

Can I but in and ask something technical from a non technical person, just a hobby welder. I have been led to believe that the rate of deposit for stick welders is down to the rate of current flow all other things being equal.
Therefore most welders for stick seem to use constant current sources with the voltage slope trying to compensate for the welders arc length. As the arc length increased the voltage would go up to maintain the same current flow and therefore weld deposit *Within reason". Say 100 amps setting voltage going between limits of 30 to 40 volts.
Now if the unit is a constant power source then I would imagine control would be very difficult. As arc length increased then current would have to drop to compensate for the higher voltages. Power being Voltage x current. I would therefore have thought much more difficult to control then constant current.
In a constant voltage supply it gives the welder much more control over deposit rates by allowing the arc length to vary the current.
In eather case one is always steady, what would the controllable aspect be in constant power.
Always trying to learn more about it, using big red bible from Lincon at present.
Cheers
Adrian
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Well, I'm certianly no expert, and just a begining weldor, but I imagined that the weld, *once started*, wouldn't be too much harder to control. When the electrode and base metal get hot the weld would progress about as easily with constant power as with constant current. I'm sure someone with more experience will say for sure, though.
Just a guess, but starting a weld might be more difficult, as the shielding gass is not ionized and not as conductive, and the base metal & electrode are cold and not throwing off electrons as easily. I was thinking that some sort of HF start, like with regular TIG on aluminum would help a lot to start a weld.
This might be wrong, too, but during the time* I spent tig welding, it seemed like you wanted more voltage/heat to start out with to establish an arc easier, and get a puddle faster. But, now that I think about it, with a constant power machine, the foot pedal would vary the amount of *power*, and hence the voltage, so it wouldn't be much different in that respect.
Any way, I think constant power probably wouldn't let you move the electrode as far away from the work, so you'd need a steadier hand, but it would let you have a more constant puddle heat.
* 2 hours or so
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snipped-for-privacy@rgs.uci.edu wroteionised

I have been pondering on this constant heat thing for some time since my last posting and still can not think how constant power would mean a constant temperature of the puddle.
I have this vision of the ionised gas in a colum a bit like an electric bar from a fire.
If you put 1000 Watts of energy in to a bar a foot long and 1000 watts in to a bar an inch long which one would be hotter, the one at an inch in length. Therefore as I visualise it, if you wanted to keep the bar at the same temperature you have to supply more energy as the bar gets longer and less as it gets smaller.
From what I can see the temperature of the puddle is from the heat of the ionised gas. so to keep a similar temperature in the arc colum you need more energy the larger the arc gap and less the smaller gap. Constant power would in tend to give less controll over this.
I need someone to describe the mechanics better to me if I have the wrong idea. It may not help me weld but it is nice to understand sometimes.
Adrian
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Adrian Hodgson wrote:

P=I*E Power (in watts) = Current (in Amperes) * Voltage (in volts)
Look at P (power or watts) as your constant. Thus the other two would have an inverse relationship to each other. As the voltage goes up the current comes down and visa versa.
Summary: If the same wattage gets to the puddle you'll probably maintain very close to the same temp.
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Al Patrick wrotvisualisationAdrian Hodgson wrote:

OK but what about the rest of my post, which is on the lines of heat per unit volume of arc. We are only taking of moving the arc length about 1/8" or so to double the length of the arc. If the power input stays the same but the arc length varies then I still say the temperature has to vary. The heat generated in the arc is not all at the puddle of the weld. I still see it as being a colum of heat going from the tip of the electrode down to the metal. When you increase the volume of the arc by increasing its length then the heat must be dissipated over a greater distance and therefore get a lower temperature.
If the books I have been reading said that all the heat of the arc was in the base metal then I would agree, but then stick electrodes would not melt. TIG tips would not need water cooling and welds would never happen!
I know there are temperature differences between DCEN and DCEP and AC welding One provides more heat at the work, one more heat at the electrode and AC is the mid way situation where both tip and work have the same.
But where is my visualisation of the electric fire bar going wrong.
Adrian
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Here is an attempt at a partial explanation. I have a good understanding of the electrical principals involved, the area I am still trying to understand is the physics of the plasma, ionized particles and there mass and how this is converted to heat.
1) Energy is the ability to do work. So for example a welder connected to the power grid has the ability to melt metal.
2) Power is the rate at which work is done. Again with a typical welder the operator controls the current: more current = more energy per unit time = more work per unit time = metal melts faster ( higher temperature)
3) A constant current source will have a defined voltage compliance. In order for the welder to maintain X amps in the circuit the welder must be able to both increase and decrease the voltage measured at the welders terminals. For example if you connect a length of steel between the two terminals on a welder and set the current control to 20 amps the welder will have to impress a voltage V = 20 amps * Resistance of the steel in Ohms ( Ohms law ). At some point the resistance will be low enough and or the desired current high enough that the welder will not be able to increase the terminal voltage in order for the desired current to flow. Example: Lift the TIG torch away from the work and eventually the arc stops, because the welder could no longer increase the terminal voltage in order to maintain the arc, for the set current.
4) So as the arc length varies the resistance in the circuit varies (increases for longer arc length decreases for shorter arc length), which causes the constant current source to vary the voltage applied to the load ( the load in this case is the welding cables, the arc, and the work piece). Power = Voltage * Current, if current is constant, and voltage changes to maintain the constant current then the power dissipated ( converted to heat, light, and sound ) changes.
5) A constant power source will modify BOTH current and voltage in order to maintain a constant power dissipation.
6) For welding most of the power is dissipated as heat, the small amounts of light and sound generated by the arc are negligible.
7) So for a constant power source as the operator moves the torch relative to the work, and the welding machine has sufficient current and voltage compliance the power dissipated as heat will remain constant, therefor the weld pool temperature will be constant, even if the operator changes the distance between the torch and work. All within the limits of the machine.
Adrian Hodgson wrote:

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Mike wrote:

power
welding
to
cost
theoretical
I was thinking the exact same thing, that it would be fairly easy to cobble together a constant power machine... Of course, I also have a fairly poor understanding of electronics. Not much beyond the basics, so I could be totally wrong.
It just seems that it would be possible to grab some components from the cheap automotive inverters and, maybe by running a few in parallel, get a substantial DC output. That, coupled with some components out of an old welder, and some junk from the scrap pile, should get you fairly close... Of course, I'm not talking about an industrial strength welder or anything, but it would make for some fun mad-science-type experiments.
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