CC vs CV and actual machine output

[hypothecary]

I'm trying to get a better understanding of CC and CV, the differences, how each works, why each one is better suited for specific applications, etc. I have searched the net and the forum to gain a basic understanding but I'm having trouble finding more detailed info and I figure some of you guys probably already know where to look. I'm not an engineer or electrician so I prefer something written for my demographic, just a new guy that wants to learn.

Also, is there a way to use a DMM to see what the actual output of my machine is on each setting? My Clarke Turbo Weld 150EN has 1/A, 2/3, MIN/MAX switches for output adjustment and I'd like to know more exactly what I'm doing when I flip those switches. Can I just set the DMM to dc voltage then connect the neg lead to the work clamp and the pos lead to the wire and pull the trigger (assuming GMAW, reverse leads for FCAW)?

Finally, does the output of the machine vary with fluctuations in the input? I know residential power grids are not exact or perfectly stable but will that noticeably affect welder performance?

Thanks for any input, even the "tie your welder to your foot and jump in a lake you idiot noob" ones....I lmfao reading those.

Nate

[Warpspeed]

No other takers?
O/k I will have a go at answering this.

I assume we are talking here about transformer welders ?

Constant voltage machines will have varying output voltage as the mains voltage goes up and down in direct proportion.
Constant current machines will maintain a fairly constant current regardless of mains voltage variations.

Inverter welders use electronic feedback to keep either the CV constant, or the CC constant to whatever it is set to.
The arc welding process needs to be self adjusting to maintain a steady rate of metal transfer, and there are two very different ways to go about doing that.

With constant voltage, the wire feeding into the arc determines arc current. As the wire gets closer to the work, the arc current rises and the wire melts away faster. If the wire retreats away from the work, the arc current falls and the wire melts away slower. It is a self regulating process, where the wire feed speed controls the arc current.

Constant current TIG or stick welding is also a self regulating process, but it works quite differently.

As the tip/rod gets closer to the work, the voltage falls and total arc power decreases. But the heat generated right at at both rod and work remains the same right at the arc/metal interface, because the current remains constant.

Given that the guy doing the welding can set up the machine properly, and that he can maintain reasonable control over the welding hand piece, both CV and CC can both do the job of creating a self regulating metal transfer process.

[hypothecary]

Thanks for the reply Warpspeed. I am talking about transformer welders since that's what both of mine are.

I understand the basic principles:

CV is used for wirefeed and varies amperage
CC is used for stick/tig and varies voltage
arc length affects variable in all processes

I guess what I'm after is a detailed explanation of how the electrical side of welding machines work including what individual components are doing but its a vague question seeing as how there's many different kinds of machines. I'll keep searching and reading...

[hypothecary]

As for actual machine output, I threw my DMM on as described above and came up with a range of 19 to 34 volts. I noticed that changing the wfs directly affected voltage. Lower wfs, lower voltage/ higher wfs, higher voltage.

Wfs adjustment changed voltage by up to 3 volts.

Is this normal?

[Warpspeed]

Constant voltage transformer welders just step the mains voltage down with a transformer to the required welding voltage, and the ac voltage is rectified to provide a fairly constant dc output voltage.
The voltage will always fall slightly under increasing load.

Constant current machines use a special design of transformer that has a magnetic shunt air gap located between primary and secondary windings. Usually the welder has a plunger or handle of some kind to set the welding current by moving an iron pole piece in or out of the shunt air gap.

Too difficult to fully explain here.
But basically the magnetic flux generated by the primary winding can take two alternate paths. One is through the secondary winding, the other through the shunt air gap. With no load, all the flux goes through the secondary, and output voltage is high. As more load is placed on the welder, the flux divides, and always takes the easiest path, and the output voltage falls. With a total dead short across the output, just about all of the flux avoids the secondary and is forced through the shunt gap.

The magic thing about all this, is that the current in the secondary winding remains fairly constant over a very wide range of applied loads, and the output can be fully shorted without the primary current going dangerously high.

[Silicon-based]

This link may help you :

http://www.esabna.com/EUWeb/AWTC/Lesson1_1.htm

particularly the first 2 chapters. Lincoln and Miller also have books available on their sites covering basic electricity for welders. They can be downloaded or purchased as hard-copies.

Note that the voltage of constant-voltage welders is not truly constant, nor is the current of constant-current welders. The variations are responsible for the arc characteristics(e.g. crisp vs. soft arc) of different machines. Voltage measurements need to be made under load to be useful.

John

[morgaj1]

Warpspeed, that is the most concise explanation I have heard to this question. Great job!

[hypothecary]

Thanks for the replies. I know I'm being difficult but I don't have time/opportunity to discuss this stuff in my weekly welding class. I'll read up using the link and suggestions from Silicon-based. Thanks again guys.

[hypothecary]

Originally Posted by Silicon-based

This link may help you :

http://www.esabna.com/EUWeb/AWTC/Lesson1_1.htm

John

I spent practically all my free time in the last few days reading these ESAB lessons, very good stuff and thank you John for sharing. I hate to admit it but I think I got more out of the lessons on SMAW electrodes than anything else.

I'm still confused about output ratings...

With a CC machine you change amperage by knob/tap on machine and change voltage by varying arc length.

With a CV machine you change voltage by knob/tap on machine and change amperage by wfs.

So why is output rated in only amps for both types of machines? Are they rating CV machines as a range of amps at a given voltage? That would make no sense to me since the machine is capable of a range of voltages. Why don't they specify the voltage range of the machine?

For example, I prefer the Millermatic 252 for GMAW at my local welding class. The machine has a knob that adjusts voltage in 0.1V increments and the digital display shows voltage output.

Then when I go to millerwelds.com to look at the machine's specs the site lists "rated output" using 2 different amperages at the same voltage to demonstrate duty cycle and "welding amperage range" from 30-300amps but no spec for voltage output range.

I know this stuff is superfluous to learning how to lay good beads but I really want to understand and my confusion with this one is driving me nuts. I'd discuss it at class but there's just no time for that - too many students and I'm the only one who'd care.

Also, how would I measure voltage under load without frying my dmm or welder? Pos lead on work and neg lead on ground clamp insulated from work seems hazardous to me.

[lotechman]

You can easily measure voltage on any machine by putting one volmeter lead on the work and the other in the electrode holder with the stick or the welding power cable to the wire feeder. You are only working with 30 volts so you will not do the chicken dance but you definitely can give yourself a good tingle. Amperage is much more difficult since you need a special clamp on DC meter that clamps around the cable and measure the field produced. If you have meters on the machine it is nice.
Most manuals give you some sort of volt amp curve. The constant voltage one is more like a flat line.
The slope of the volt amp curve changes the characteristics of the arc. The droop or slope of that volt amp curve is designed into the machine.
Inverter machines work similarly however digital controls create the volt amp curve making the machine much more versatile.

[hypothecary]

Originally Posted by lotechman

You can easily measure voltage on any machine by putting one volmeter lead on the work and the other in the electrode holder with the stick or the welding power cable to the wire feeder. You are only working with 30 volts so you will not do the chicken dance but you definitely can give yourself a good tingle. Amperage is much more difficult since you need a special clamp on DC meter that clamps around the cable and measure the field produced. If you have meters on the machine it is nice.
Most manuals give you some sort of volt amp curve. The constant voltage one is more like a flat line.
The slope of the volt amp curve changes the characteristics of the arc. The droop or slope of that volt amp curve is designed into the machine.
Inverter machines work similarly however digital controls create the volt amp curve making the machine much more versatile.

Thanks, that method of measuring voltage makes sense. I was thinking the full current of the circuit needs to pass through the dmm to get an accurate measurement but I guess that's not the case. Like I said before, I'm not very knowledgeable about electricity but I'm learning. My electrical experience has been limited to automotive applications and simple residential repairs.

I have no manual for my machine and since its a 10+ year old Clarke I doubt I'll ever see one. That's most of why I'm trying to measure and record output and in the process I've come to see I lack understanding and want to fix that.

[Warpspeed]

Originally Posted by hypothecary

So why is output rated in only amps for both types of machines?

With both transformer type CC and CV welders, it is the transformer winding temperature rise that determines the maximum allowable welding current, and maybe the rectifier current rating too, if there is a rectifier.

The current rating of the transformer is determined by the temperature rise of the transformer windings. There will be a continuous current rating, normally expressed as 100% duty cycle. That is unrealistic for most welding processes, so higher current ratings with cool down periods is another common way to rate welding transformers.
You may see something like:
100 Amps at 100 % duty cycle.
200 Amps at 25% duty cycle.

Why 25% and not 50% at double the current?
That is because twice the current actually generates four times the heat and temperature rise inside the transformer. At 200A the transformer windings heat up four times as fast as it would with 100A, so it needs one period of operation, and four total periods to cool down to keep the thing within it's max rated allowable temperature rise.

In all of this, voltage is irrelevant, it is the current flowing through the resistance of the copper windings that heats things up inside the transformer.
So it is logical to rate a transformer welder for output current, because that best measures what it can do in a real world welding situation..

[lotechman]

One exercise done by many welding instructors is to hook up a light socket with a 110 volt light bulb. One side goes to workpiece and one side goes to the electrode holder. Your open circuit voltage should be under 75 volts and the bulb will glow moderately.
Now strike up an arc and watch the light bulb as you increase or decrease the arc length. You will clearly see the bulb glow brighter when you pull a longer arc. ( voltage has gone up) When you go to a tight arc the voltage drops and the bulb will not be as bright.
The light bulb is easier to see for a group of students gathered around the instructor.

[hypothecary]

Originally Posted by Warpspeed

With both transformer type CC and CV welders, it is the transformer winding temperature rise that determines the maximum allowable welding current, and maybe the rectifier current rating too, if there is a rectifier.

Thank you, Warpspeed. That was a big piece missing from the puzzle in my mind and makes it easy to understand why everything is rated in amps. I feel kinda stupid not having figured that out myself.

[Warpspeed]

Nate,
You are a lot like me, trying to get my head around how all this works.
And that is good.

Understanding what is actually happening is probably a rather important part of welding.
I just wish my own welds looked a lot better than they do.

Seeing the welds some of the guys here make is a truly humbling experience.

[SundownIII]

Think you'll find that an excellent explanation of CV vs CC is covered in the Miller GMAW Handbook. You may be able to download it from their site under the resources tab.

[hypothecary]

Originally Posted by Warpspeed

Seeing the welds some of the guys here make is a truly humbling experience.

Very true. Thanks again for your time and help.

[hypothecary]

Originally Posted by SundownIII

Think you'll find that an excellent explanation of CV vs CC is covered in the Miller GMAW Handbook. You may be able to download it from their site under the resources tab.

Silicon-based mentioned this earlier but I didn't see an option to download the book, only one to purchase a hardcopy for $50+shipping. A bit much for 128 spiral bound pages IMO. I saw a copy on ebay for $29 shipped and been thinking I'll probably go that route.

They do have a free download for GMAW but its a very basic pamphlet and doesn't cover CC/CV.

[con_fuse9]

Originally Posted by hypothecary

I'm trying to get a better understanding of CC and CV, the differences, how each works, why each one is better suited for specific applications, etc. I have searched the net and the forum to gain a basic understanding but I'm having trouble finding more detailed info and I figure some of you guys probably already know where to look. I'm not an engineer or electrician so I prefer something written for my demographic, just a new guy that wants to learn.

On systems that 'maintain an arc' there is a relationship between shielding gas, and gap that more or less specifies what the voltage must be. Its actually very similar in your car. Everyone assumes that when you put a ignition system in that is rated at 40K V, you are getting 40K Volts. Nothing could be further from the truth. The reality is the voltage, in a car, is determined by the gap on the spark plug and the air/fuel mixture. Same with stick and TIG welding. To put more power in, you must increase the current. So CC machines will deliver whatever voltage is needed to maintain the arc (note some have what they call open voltage - when the gap is too large, no spark, the maximum voltage). To control the power, you increase the current. (not to confuse things too much, but if you increase the gap, the power goes up as well).

CV machines tend to be short circuit orient. What I mean in short circuit MIG. That means the current levels fluctuate widely. From a dead short to essentially an open. Much easier to maintain voltage. Note that slight variations in voltage makes a big difference. 18V vs. say 20V. But it still easier building a machine that maintains voltage.

Originally Posted by hypothecary

Also, is there a way to use a DMM to see what the actual output of my machine is on each setting? My Clarke Turbo Weld 150EN has 1/A, 2/3, MIN/MAX switches for output adjustment and I'd like to know more exactly what I'm doing when I flip those switches. Can I just set the DMM to dc voltage then connect the neg lead to the work clamp and the pos lead to the wire and pull the trigger (assuming GMAW, reverse leads for FCAW)?

You can simply put a volt meter across the leads of a welding machine, but you CANNOT read current that way. If you want, they make inductive clamps to read higher current. You basically put the clamp around one of the welding leads and typically read off the mV scale. Keep in mind that all welding machines have a voltage level at rest, and a different one when welding (under load). Bigger machines tend to fluxuate less than smaller ones. On a MIG machine, the voltage curve and how fast the voltage/current reacts is what makes one welder seem different vs. another Faster reacting machines tend to spatter more. Machines with more inductance less etc.
On CC machines, its again, all about the arc length. Typical for TIG is about 15V (normally slightly less). My understanding is stick normally around 25V. OCV (open contact voltage) typically 90V or on some machines as low as 50. The OCV sometimes affects how easy a machine starts an arc. I'll let the pros debate if higher or lower OCV is better.

Originally Posted by hypothecary

Finally, does the output of the machine vary with fluctuations in the input? I know residential power grids are not exact or perfectly stable but will that noticeably affect welder performance?
Nate

Sure, a little. But it depends on the machine. Most machine adjust and regulate internally. To make the same power off of less input voltage, the machines must draw more current. That reduces duty cycle (things get hotter/faster) and makes regulating typically more difficult. Invert type machines typically see less issues. My understanding (talk to the pros) is that some generator based machines are extremely affected - meaning you need a steady/smooth engine driving everything. Most of the modern ones seem to have an inverter behind the generator - so maybe not a problem anymore.

[hypothecary]

Originally Posted by con_fuse9

On systems that 'maintain an arc' there is a relationship between shielding gas, and gap that more or less specifies what the voltage must be. Its actually very similar in your car. Everyone assumes that when you put a ignition system in that is rated at 40K V, you are getting 40K Volts. Nothing could be further from the truth. The reality is the voltage, in a car, is determined by the gap on the spark plug and the air/fuel mixture. Same with stick and TIG welding. To put more power in, you must increase the current. So CC machines will deliver whatever voltage is needed to maintain the arc (note some have what they call open voltage - when the gap is too large, no spark, the maximum voltage). To control the power, you increase the current. (not to confuse things too much, but if you increase the gap, the power goes up as well).

You're right, it is much like the ignition spark in an engine where resistance in the gap determines actual voltage needed to send predetermined current across said resistance. That's why lots of guys increase plug gap to increase ignition voltage (even though its not actually an ideal way to get more complete combustion).

Originally Posted by con_fuse9

Faster reacting machines tend to spatter more. Machines with more inductance less etc.

So inductance is basically buffering a CV machine's rapid current fluctuation for a smoother arc?

Originally Posted by con_fuse9

Sure, a little. But it depends on the machine. Most machine adjust and regulate internally. To make the same power off of less input voltage, the machines must draw more current. That reduces duty cycle (things get hotter/faster) and makes regulating typically more difficult. Invert type machines typically see less issues. My understanding (talk to the pros) is that some generator based machines are extremely affected - meaning you need a steady/smooth engine driving everything. Most of the modern ones seem to have an inverter behind the generator - so maybe not a problem anymore.

Being that I have an older low-end machine, I doubt mine has high inductance or much internal regulation to offer. Despite a new ground clamp, tedious prep and trying every setting available I've noticed it's arc is unstable and noisy compared to the Millermatic 252 at school which is smooth with a nice steady buzz even over millscale.