volts vs. amps

Anybody got a clear way to explain to an educationally diverse group of
students how amps and volts are different in arc welding ?
Reply to
ben carter
Loading thread data ...
Yes, just hold the end of this one, and lick your fingers and.....
..Stick to water flow analogies - amps is volume flowing, volts is pressure.
Steve
Reply to
Steve Taylor
I would add, voltage is directly related to the arc length in processes such as GTAW, SMAW, GMAW. As the GTA torch is pulled further from the workpiece, the voltage goes up.
In arc welding, current is adjusted for the disired weld size and metal thickness. Thicker metal and larger welds require more current to melt more metal.
Reply to
Ipeak
"ben carter" wrote: Anybody got a clear way to explain to an educationally diverse group of students how amps and volts are different in arc welding ? ^^^^^^^^^^^^^^^ Are you trying to explain what volts and amps have to do with arc welding, or are you just trying to explain the way current flows in a circuit as a result of voltage difference?
Reply to
Leo Lichtman
Ayup..thats the one I use too.
Gunner
"If I'm going to reach out to the the Democrats then I need a third hand.There's no way I'm letting go of my wallet or my gun while they're around."
"Democrat. In the dictionary it's right after demobilize and right before demode` (out of fashion). -Buddy Jordan 2001
Reply to
Gunner
Suggest you research (Google or otherwise) drooping generators, drooping volt amp curves, CC (constant current), desired volt amp curves for SMAW vs GMAW, CV constant voltage, also effect of arc length on drooping volt amp curve power generator or welding power source.
A good way to explain the concept is with a good illustration of a volt amp curve as produced by a drooping welding power source. The best will be to obtain power curves for all the ranges of a classic Lincoln type DC generator and demonstrate how the arc characteristics will differ for a similar heat setting on separate ranges. This can lead into a discussion of the whipping technique used to make a root pass in pipe with 6010.
Reply to
Private
First off, I'm an electronics engineer and not a welder. I also don't know if the following explanation is any clearer than anyone else's.
But I know that welding requires heat. Heat represents power dissipation in the metals. This heat has to come from the electricity.
Power is amps times voltage (P=I*E) in electrical circuits. To increase the power (heat), you either have to increase either the amps or the voltage. Either will do, but high voltage can kill you, so welding is usually done with low voltage and high current (amps).
The reason high voltage kills is that it can overcome the resistance of the skin and conduct current through your body - enough to stop your heart maybe. There's a whole lesson here someplace on safety and watching out for 110/220v from the line. It's ac, but it's high enough voltage to perhaps cause damage.
Voltage can be used to model water pressure. Think of the high pressure coming into your house. Resistance to water flow can be modeled by an electrical resistor or throttling device (hose bib). This is why having too long a delivery wire to the work can cause problems. It has too much distributed resistance that will cause a voltage drop at the weld, much like having a really long hose or a hose with a kink in it will drop water pressure.
Amperage can be modeled by water flow. A large diameter hose can carry more water per minute than a small diameter hose can at the same pressure difference. So amps are essentially gallons per minute in the analogy. A large diameter wire will have less resistance than a small diameter wire, so welding cable has a large diameter to reduce its resistance.
This is probably not as clear as you'd like, but I'm old and it's late :-)
Regards, Larry
Reply to
ldg
It seems to me that what is really of interest and use would be understanding from a use point of view. What happens to a weld when you use the wrong type power supply (what does the right one do for the arc)? Why is the type of power supply different for different welding processes? This is the sort of understanding that I suspect would be most useful.
Spend a couple of minutes on the water analogy to start, then get to the real point of the talk. I really dislike the water analogy, but I don't know of a better one. The problem is that electricity is so abstract--unlike water, for instance.
Steve
Private wrote:
Reply to
Steve Smith
"Steve Smith" wrote: (clip) The problem is that electricity is so abstract--unlike water, for instance. ^^^^^^^^^^^^^^^ That is exactly why the water analogy works so well--anyone can visualize it. A gallon of water is a coulomb. A gallon per second is an amp. PSI translates into volts. Small pipes or long pipes have more "ohms." It works.
Reply to
Leo Lichtman
I agree with "the water analogy" for explaining electicity, to answer Ben's question - current is like how much flow of water there is and voltage is like what pressure it is under. I teach in a technical college and I know this explanation would work just fine with your learners.
I had my own separate interest in this statement:
"This can lead into a discussion of the whipping technique used to make a root pass in pipe with 6010."
My question - are you doing something to the arc volts and therefore heat input when you are whipping the rod?
Richard Smith
Reply to
Richard Smith
I am new to this group and am not a tech school instructor so am hesitant to be too opinionated on the subject of teaching because I have little experience with what works as explanation to varying levels of background and knowledge. As a general and personal opinion, I am usually opposed to the search for excessive analogy to describe physics. IMHO the actual science makes more sense to me than stretched comparisons or forced analogy. I am certainly opposed to the current drive to dumb everything down to the point of insult. I think we need to challenge ourselves to rise to the real knowledge.
I took my own advice and searched on my suggested key words
formatting link
came up with a couple of decent hits that led to more good stuff. I suspect that a more refined search will give even better results.
formatting link
looks like a good link regarding SMAW and is not really what we are looking for but it reminded me that Lincoln Electric was the source of some of the best books in my welding library. I went to their website
formatting link
with high expectations and soon found this page
formatting link
It looks like there is plenty here to keep anyone busy for a while. I found this list of available books,
formatting link
prices are higher than I remember but still very reasonable. This has always been one of my favorites
formatting link
Google also turned up this which is very close to what I was looking for
formatting link
in section 10-2 it discusses drooping power sources and arc length in detail. I failed to find an index page for this book but it seems to start at
formatting link
I think you will notice the combination to get the rest of the chapters but be careful as there are popups that may be dangerous.
You may draw your student's attention to the difference between a welding generator and one which is designed for pipe thawing (very low open circuit voltage, high closed circuit amperage and 100 % duty cycle) which is a task that has killed many good welding machines. This will probably lead to a discussion of power, watts, ohms law and duty cycle.
This is opening a big door and I do not know where to start. Section 10-2 of this link
formatting link
is a good start but is not the last word. Basically lengthening the arc causes the voltage to rise and the amperage to drop, (drooping power source) this reduces the burn off and deposition rates and can help to open up the key hole. Whipping the arc out of the puddle can allow it to fast freeze and permits us to lay the metal into the groove in the regular ripples that give 10 (and 11) welds their distinctive appearance. Shortening the arc raises the amperage and the burn off and deposition rates and fills the puddle. Whipping too far can remove the shielding gases and cause problems (and is not a good technique for low hydrogen rods which require a more subtle touch and respond more to rod angle and travel speed).
I am sure you have noticed that when welding overhead it is often helpful to turn up the heat and shorten the arc in order to soften the arc and stop the puddle from falling. With a dual control generator (like a Lincoln 300) we can raise the left (range) control and lower the right (voltage) control to give a softer arc and to change the slope of the drooping volt anp curve.
This description is not as concise as it should be. I am sure that a little prospecting on the web will find many better.
Reply to
Private
snip
snip
A further Google search on TC 9-237
formatting link
that this book is an Army training publication. I suspect that it is also available for free download online from many other locations.
Reply to
Private
You don't really need to understand volts and amps to weld - just their combined power is an adequate concept, so long as you _do_ get across the notions of "constant" and "drooping" curves. If you communicate that "manual processes vary power with length, so you have control" and "wire-feed processes are self-regulating, no matter what the stick-out", then you've got the crucial part across.
Reply to
Andy Dingley
I was an Electronic Tecnologist for our National Broadcaster( CBC) in Canada. I taught Basic Electronics in l Night School at our local High School as a hobby.
When I retired I took 2 years of Welding training, got some tickets and went to work with the Local Boilermakers.
I have been reading the posts with intrest and I must say there are quiite a few opinions on the subject. We must not forget that welding students don't care if the resistance of the rod is .1 ohm or 5 megohms. or what the particular voltage at the weldement is. They want to make good welds and pass the course.
Water is an excellent comparison to electricity. Always has been and always will be.
Unless the Politicians repeal Ohms Law!!!
Anyway that's my story keep up the good work....
Gary T
Reply to
Gary Tomada
Current - think electrons/time while Voltage is the pressure - think of pressure that drives the electrons.
Given a resistance, as the voltage increases so does the current. If one has a constant voltage machine that might have high voltage surges to arc through thin films and the current setting determines the electrons/time or current or consider the heat. More current - more heat.
Voltage allows current to flow across a gap - the higher voltage the wider the gap.
Lightening itself is very high voltage - jumps a wide gap from cloud to tree and - read that AND very high current - the bolt is white hot and wide - vaporizes the sap and water in the tree - When there is current flowing, there is power.
Power = voltage * current. If one varies the current and maintains the voltage (because the machine does) one varies the power. More power more heat more melt more penetration and so forth.
Martin A physicist wearing a different hat.
Martin H. Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net NRA LOH & Endowment Member NRA Second Amendment Task Force Charter Founder IHMSA and NRA Metallic Silhouette maker & member
formatting link

ben carter wrote:
Reply to
Martin H. Eastburn

Site Timeline

PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.