View Full Version : Amps, Volts, & Wire Feed Speed

11-08-2007, 04:02 PM
In the thread "Run time before overheating unit?" on this section of the forum, Sundown III posted as a part of his reply - "What I find interesting is that it seems that all manufacturers rate their machines based on amp output, yet the machines only have voltage taps (or voltage adjustment) and wire feed speed (wfs). I guess they expect the user to go to the graphs and figure out how many amps they're really pulling out of the machine." Aye, lads, there's the rub.

Sundown, which graphs do you refer to, where a MM251 is concerned? This is an issue that has just aggravated the snot out of me. Page 31 of the MM251 O&M Manual would seem to indicate that amperage is solely a function of wfs. Various values are assigned, with no indication of where those values derive from, for inches per amp for a specific wire size. That is, .023 wire = 3.5" per amp. .030 wire = 2" per amp. .035 wire = 1.6" per amp. So, according to the book, if 125 amps are required then 1.6 X 125 A = 200 ipm (wfs) for .035 wire. Using that equation, Amps could be derived from any give wfs.

According to this same page in the O&M, voltage only controls the height and width of the bead. Forty years of stick welding before I sat down with a mig welder I worked in a world of amps. I cannot get my head wrapped around volts and wfs.

To the questions at hand. Given a mig welder with voltage adjustment, or voltage taps, and adjustable wfs:

1. Is amperage solely a function of wfs (ipm X constant for a given wire diameter)?
2. Where does this constant originate which is to say, how does one determine xx in per ampere for .045 wire?
3. If amperage is solely a function of wfs, then where and how does voltage come into the mix?

Before I go to my just reward shoveling coal I would really like to finally, completely, understand the function of voltage, and wfs, and the calculation of amps on my mig. I have searched long and hard on the net, but have failed to find the answer. If any of you can educate me, or point me in the direction where I can find it in the literature, I would appreciate it.

Sundown has a very valid point here. You buy a welder and find that you have a duty cycle of 40% at 250 amps. Then crank the machine up and weld at 18.0 volts and 280 ipm wfs. Eh? Ello? Whot? Does that equate to 175 Amps? If so, that seems really hot in my little pea stick welder brain for welding on 3/16" steel.

11-08-2007, 07:44 PM
The Voltage is Constant so the Current has to change to keep the Arc going to burn off the wire.

With Stick the Current is constant and you have to vary the Voltage-distance to work- to maintain the Arc to burn off the Stick.

The wire is the resistance.

I believe the Constant is derived from what the resistance is but I can't explain it any deeper than that.

Hopefully SundownIII can answer that:)

11-08-2007, 09:01 PM
The wire feed speed is in direct relation to the amperage at a given wire stickout (length of wire from the contact tip to the arc). The voltage is in the case of a CV (wire welder) the constant and is the length of the arc from the end of the wire to the weld pool, as you change the wire stick out the amperage changes to maintain the weld voltage. A normal wire stick out for short circuit mig welding is 1/4".

The following example may help you understand this with .035 ER70S-6 wire and C25 shield gas set at 20 SCFH flow.
1/4" wire stickout, volts 17 and wire feed speed 150 IPM = 100 amps
3/8" wire stickout, volts 17 and wire feed speed 150 IPM = 50-60 amps due to the resistive heating of the wire between the tip and the arc the weld current drops to the level required to maintain the set voltage.
If you were to reduce the stickout to 1/8" the weld current would increase to approximatly 150 amps to maintain the set voltage.

Typical min and max ranges of each wire diameter for ER70S-6

.024 minimum 30A 15V 105 IPM WFS, maximum 150A 21V 710 IPM WFS
optimum vert. setting 80A 18V 310 IPM WFS
optimum horiz. setting 110A 21V 465 IPM WFS

.030 minimum 50A 17V 95 IPM WFS, maximum 200A 23V 600 IPM WFS
optimum vert. setting 100A 18V 235 IPM WFS
optimum horiz. setting 150A 20V 385 IPM WFS

.035 minimum 50A 18V 75 IPM WFS, maximum 225A 25V 500 IPM WFS
optimum vert. setting 150A 18V 185 IPM WFS
optimum horiz. setting 215A 22V 415 IPM WFS

I hope this helps more than confuses you.

11-09-2007, 12:39 AM

Sorry, wish I had a more definitive answer for you. I mentioned the V/ws issue in the other post because it was something I've never been very clear on. If you look at the graph on page 11 of your owners manual (MM251), there is a broad range between minimum and max volts with a resultant decrease in volts as the amps go up. Still not enough to determine duty cycle for a given volt/ws setting.

I did go to the owners manual for my HH187. A little clearer there as there is a plotted graph for each tap setting (total of 7) but it is still not clear as to the amps being provided at any particular v/ws setting.

For DrIQ. I appreciate all the info (not sure I've figured it all out yet though). I do understand that stickout affects amperage along with WFS but still find it difficult to try to ascertain what amps I'm pulling from my machine at a particular v/ws setting.

If the manufacturers want us users to be aware of duty cycle, maybe they should provide a machine which measures amp output along with volts/ws.

Although a mig machine is classed as a Constant Voltage machine, the graphs I'm reading (for the MM251 and HH187) show a drop (somewhat minor) in volts as the wire speed (and amps) increases.

The fact that the manufacturers warn the user about not exceeding the duty cycle of the machine, they do not make it clear how to determine when you are approaching it while welding (ie what amps are you really welding at).

I have never received a clear answer to this question.

11-09-2007, 08:22 AM
Amp meter for MIG welder is easy. Put clamp on amp meter on ground lead. Have someone read it while your welding or use high reading hold.

11-09-2007, 10:45 AM

Great suggestion. I've got a Fluke AC/DC clamp on meter. Will have to give it a try and see how stickout affects amp draw.

11-09-2007, 04:24 PM
Aaaaa Haaa! The haze is beginning to clear.. The fog starts to lift.

Thanks Broccoli. And a special thanks to you, DrIQ. Nowhere in my research did I come across wire stickout as having an effect on amps. And quite an effect on amps. This begins to explain some of the things that I see in out of position welds and having to use a long stickout. Very interesting.

Roger. Kudos! It amazes me the things that would never enter my mind. Like Sundown, I have an amp meter with a high reading hold. Would have gone to my grave and not thought about using it on the ground lead to read amps. Now I am hot to get out to the shop and see what is really going on with amps, stickout, etc.

There may be hope. I may finally understand this. I really appreciate the informed responses. Thanks again.


11-09-2007, 05:10 PM

Great suggestion. I've got a Fluke AC/DC clamp on meter. Will have to give it a try and see how stickout affects amp draw.

Most meters I've seen only go to 10amps, I guess you could shunt it with a tiny resistance, but I'm not sure where you would get a fractional ohm resistor from.

11-09-2007, 06:45 PM

Shouldn't be a problem since the Minimum Amps are about 25 for a HH140/HH187 and 30 for bigger machines.


11-09-2007, 08:42 PM
thank you DrIQ for that informative response, the best explanation i've seen yet. i have a couple of questions for this thread.

1. would the parameters you gave hold true for a MM 212 as well as a MM 251?

2. if my MM 212 has a wire feed rate range of 50 - 700 ipm, and my WFS dial goes from 0 - 100, am i correct in assuming that a setting of 35 on the WFS would mean 35% of the way from 50 to 700, or 228 ipm?

3. does anyone know where i can purchase a reasonably priced clamp on (induction type) amp meter that will go up to 200 amps?

this is such a great forum! thanks for everyone's input.

11-09-2007, 09:00 PM
one more quick question. i see some amp meters (clamp on) on ebay. one is for HVAC use. its specs state it is rated for 600 amps AC. does this mean it can be used to measure DC amps, such as for a mig welder, and would the amps reading be the same, AC or DC? TIA.

11-09-2007, 09:08 PM

I suspect you're thinking about a standard volt/ohm meter where amperage is checked with the leads being placed in line with the current flow.

My fluke clamps around the wire carrying the current, and will measure AC or DC amps in the 0-600 A range. I went with the AC/DC meter vs the AC only since I sometimes have to measure pretty high amp draw DC motors (diesel starters, bow thrusters, windlasses, etc).

Tigster, You will need a meter that measures DC in order to check the amps on your welder. A good AC/DC clamp on meter will set you back a couple hundred. I got mine from an electronics store. I think Sears sells an AC/DC meter for less but is a little less accurate. Probably fine for this purpose.

Hope this helps.

11-09-2007, 09:45 PM
The ranges I listed above are for the respective wire diameters regardless of the welder you are using.

The simplest way to check your wire feed speed is to select a given voltage range and WFS setting, clip the wire flush at the contact tip, then simply trigger the mig gun for 6 seconds. The amount of wire measured from the contact tip to the end of the wire multiplied by 10 will give you the inches per min. for example if you measured 19" of wire the WFS would be
190 IPM (make sure that the wire doesn't touch the ground or work table).

11-09-2007, 11:16 PM
You might look at some of the charts in the back of this guide.
There is a lot of stuff in here if you're will to look for it.
Dave P.

11-10-2007, 10:22 AM

You are looking for a "Hall Effect" type meter, which will read AC and DC amps with no problem. Amprobe makes a good unit, which is a clamp on type AC/DC Amp meter. Mine has a capability of up to 300 Amps. Also has a set of probes with it for use in reading AC voltage up to 600 Volts. Digital. I ran this down for you which will give you a more complete explanation - http://en.wikipedia.org/wiki/Clamp_meter. While you are there, type ampere in the search box and learn a LOT more about measuring amps.

FM117 thanks a lot for that link. That is a lot of information in one place. Wouldn't you know that I would find more information about what is going on with my Miller Mig in a Lincoln publication that I ever have in everything that I have downloaded from the Miller site. Really good info.

11-12-2007, 06:17 PM
More reading for ya:D


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