Looking for some help understanding OCV's
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  1. #1
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    Looking for some help understanding OCV's

    The way I understand it, OCV is what allows you strike an arc when stick welding. But what happens after you strike an arc and start welding? Does the voltage drop down? Does the voltage have any effect on the arc itself? I ask because watching one of our machines at work today, I noticed that the voltage on the display stayed around the mid 70's range (miller pipe pro 304). Guy was running 5/32 6010 5p at around 80 amps. Would like to better understand OCV's and it's effect while welding.
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  2. #2
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    Re: Looking for some help understanding OCV's

    Here's a good background

    Dave J.

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  3. #3
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    Re: Looking for some help understanding OCV's

    From the Lincoln Handbook of Welding and Design:

    Name:  Lincoln VA curve arc force 1.jpg
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    Name:  Lincoln VA curve arc force 2.jpg
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    Lincoln SA200 manual:

    Name:  Lincoln SA 200 OCV description settings.jpg
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  4. #4
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    Re: Looking for some help understanding OCV's

    OCV or Open Circuit Voltage is what the volts are before you strike an arc. If using CC (constant current) then voltage will drop when welding. If using CV (constant voltage) then volts wont drop much if any but current will fluctuate.

    You said its a MILLER and I guess it has a CC and CV mode. Was it in CV when welding with 6010.

    BTW, hows the new job? Im sure as beautiful as it is driving thru the Sierras, it gets old.
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  5. #5
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    Re: Looking for some help understanding OCV's

    Quote Originally Posted by MinnesotaDave View Post
    Here's a good background

    I wonder if he is using the correct word. When he says amperage is exactly the same using high amperage with low voltage, as it is using low amperage, with high voltage, does he mean watts?

    In incandescent loads wattage affects heat. We can have a 100 watt light bulb at 12 volts 8.3333 amps, another bulb might be 120 volts, .8333 amps Their light output and wattage would be equal.

    I believe a flat weld can be near equal with 20 volts, 200 amps as it would at 80 volts, 50 amps. Wattage is equal

    I'm not clear about the science of having an easier time weaving uphill with lower voltage/higher amperage. Can anyone enlighten me?

    Willie
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  6. #6
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    Re: Looking for some help understanding OCV's

    Willie, your uphill question is explained on the right hand page of oldendumb's first picture.

    The low OCV vs high OCV affects the shape of the volt/amp curve.
    This change affects the arc characteristics when you pull a long arc momentarily during a whip and pause.

    In the volt/amp pics you can see one changes the amps more than the other as the arc length (voltage) changes.

    For your first question on watts, he isn't referring to watts, he is referring to the overlapping amperage ranges on the engine drive.

    Selecting a higher gear (coarse range setting) and reducing the fine dial can get you the same amps as a lower gear with the fine setting increased.

    Both of your questions are actually related to each other.

    The overlapping amp ranges are also described in the last pic he uploaded.
    Last edited by MinnesotaDave; 03-10-2018 at 07:07 PM.
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  7. #7
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    Re: Looking for some help understanding OCV's

    I was an annoying kid, "Why Daddy, Why? Now, I'm an annoying old man, "WHY?" If amps remain the same, and voltage increases, we get more heat. Longer arc length gives more resistance. In a series circuit, any point of resistance gets a bigger share of voltage. I've never been clear if a long arc, meaning more voltage means less amperage. Either way, more volts, longer arc will compound into much more voltage.

    Thinking out loud, I don't pretend it is fact; Does the short arc used with lower voltage also push a bigger share of the heat into the weld joint for more penetration? If burn off of electrode rate increases, deposit rate must increase. In the sense that dabbing filler, converting solid to liquid consumes BTUs, does this chill the weld metal already deposited?

    I envy those of you with SA-200 and similar machines. You control voltage with governor speed. Can this be controlled on a Miller Bobcat 250? I suspect higher range, with little fine amperage does this. I have no crisp, or soft control like Fieldres shows on his modern Lincoln.

    Willie
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  8. #8
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    Re: Looking for some help understanding OCV's

    Quote Originally Posted by Willie B View Post
    I was an annoying kid, "Why Daddy, Why? Now, I'm an annoying old man, "WHY?" If amps remain the same, and voltage increases, we get more heat. Longer arc length gives more resistance. In a series circuit, any point of resistance gets a bigger share of voltage. I've never been clear if a long arc, meaning more voltage means less amperage. Either way, more volts, longer arc will compound into much more voltage.

    Thinking out loud, I don't pretend it is fact; Does the short arc used with lower voltage also push a bigger share of the heat into the weld joint for more penetration? If burn off of electrode rate increases, deposit rate must increase. In the sense that dabbing filler, converting solid to liquid consumes BTUs, does this chill the weld metal already deposited?

    I envy those of you with SA-200 and similar machines. You control voltage with governor speed. Can this be controlled on a Miller Bobcat 250? I suspect higher range, with little fine amperage does this. I have no crisp, or soft control like Fieldres shows on his modern Lincoln.

    Willie
    You should play with this a little on the bobcat 250. Use a higher coarse range, and lower fine setting that gives the same amperage as the next lower coarse range at its corresponding high fine setting.

    Measure the welding voltage reading and compare how the weld puddle changes. Using a clamp meter you can also measure how much the amps change during arc length changes.

    This is how the sa200 gives different arc characteristics, not the governor.

    Note the volt/amp curve diagrams start at different heights in his pics - as a result, weld amperage changes more for one than the other during arc length changes. More amps, faster burn rate.

    Pay particular attention to how much the amps change over the same 10 volt difference.
    Last edited by MinnesotaDave; 03-11-2018 at 09:23 AM.
    Dave J.

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  9. #9
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    Re: Looking for some help understanding OCV's

    Quote Originally Posted by Willie B View Post
    ...
    I envy those of you with SA-200 and similar machines. You control voltage with governor speed. Can this be controlled on a Miller Bobcat 250? I suspect higher range, with little fine amperage does this. I have no crisp, or soft control like Fieldres shows on his modern Lincoln.

    Willie
    On the SA 200's, you control voltage (fine adjust) with a rheostat. The govenor and engine rpm are fixed for 115VDC at auxillary. Some older LINCOLNS do control volts with RPM but not the SA's.
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  10. #10
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    Re: Looking for some help understanding OCV's

    Also think of it like a car battery. A small one and big one will both sit at ~13 volts, but when you start a car, the small one has it's voltage sucked down a lot further while starting, and a big one will maintain voltage easier, but they both do gets sucked down. Not uncommon for a battery to be pulled down to 10 volts while cranking.

    A transformer machine is like a car battery in that the potential power of the transformer field is finite, it's defined by the turns ratio and the primary input current. This dictates the amount of "energy" present in the secondary side. With no load, voltage is at it's maximum. When you give the circuit a path to flow current, the voltage drops as current increases. This curve is not straight due to ohms laws, etc. more power needs more current, but the total energy potential of the transformer is limited so it starts to drop volts. Volts is often called potential in the electrical field. Voltage isn't action, it's just potential that allows action (current). Voltage will always be at it's maximum in a transformer machine with no current flow (open circuit), same as a car battery.

    I don't know how this is designed in an inverter machine because electrically they can make it do whatever they want with the right design, but they probably make it follow a similar curve. Voltage doesn't' weld, current does, so they probably make it emulate the transformer. Voltage allows the current to initiate, and to sustain arc, so it does need to be considered.
    Last edited by Chad86tsi; 03-11-2018 at 12:17 PM.

  11. #11
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    Re: Looking for some help understanding OCV's

    Cbad86tsi - Inverters have a generally vertical line unless "dig" is involved.
    https://www.millerwelds.com/resource...ining-purposes

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  12. #12
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    Re: Looking for some help understanding OCV's

    Having voltage adjustment on the miller is definitely something I miss. Lincoln definitely had it right.
    Last edited by Burnt Glove; 03-12-2018 at 09:10 PM.
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  13. #13
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    Re: Looking for some help understanding OCV's

    Quote Originally Posted by Insaneride View Post
    OCV or Open Circuit Voltage is what the volts are before you strike an arc. If using CC (constant current) then voltage will drop when welding. If using CV (constant voltage) then volts wont drop much if any but current will fluctuate.

    You said its a MILLER and I guess it has a CC and CV mode. Was it in CV when welding with 6010.

    BTW, hows the new job? Im sure as beautiful as it is driving thru the Sierras, it gets old.
    The new job is great! Thankfully I don't have to make the 250 mile commute anymore. Happy about that as well.
    Machine was set on CC. I have never been a big fan of miller machines, but it's what I'm stuck with. And only having 600 hours on it, I better get used to it as I'm sure I won't be getting a replacement anytime soon.
    We need to get in touch and meet up. I lost your number in my old company phone.
    Not sure if you know but I ended up getting a green light machine like yours. PM me when you get time.
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  14. #14
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    Re: Looking for some help understanding OCV's

    I realize now that 70 volts was to high for CV but it was the first thing I thought when you said OCV's didnt drop. The OCV may not have dropped at 80 amps if that MILLER pipe pro is a bad boy welding machine. Be happy its not a BOBCAT.

    THORTON made that video in post #2. I think he was asking questions like yours before he made it. Check out his thread with similar questions. Hes the King of old LINCOLNS.

    http://weldingweb.com/showthread.php...ing&highlight=


    I know more about electricity than about welding. Higher volts allow longer arcing without snuffing like for the xx10 type rods. Thats in part why you turn up FINE volts (OCV) on your SA for 6010. You know all about the welding so good luck with the new Pipe Pro.

    On a side note: I was playing with my INVERTEC and LN22 feeder. A weldor that was helping me dial it in helped me learn something. That is; the wire feed speed affects volts when using CC. The OCV for INVERTEC is 69volts. That would always slam the 40 volt max meter on the LN22 but with correct wire feed speed, volts on meter showed about 29 volts. I think wire feed speed affects amps on a CV machine.
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  15. #15
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    Re: Looking for some help understanding OCV's

    On a side note: I was playing with my INVERTEC and LN22 feeder. A weldor that was helping me dial it in helped me learn something. That is; the wire feed speed affects volts when using CC. The OCV for INVERTEC is 69volts. That would always slam the 40 volt max meter on the LN22 but with correct wire feed speed, volts on meter showed about 29 volts. I think wire feed speed affects amps on a CV machine.
    Insaneride, I have a slightly different take on what's happening when you run a CC-capable suitcase wire feeder with a CC power supply.

    Arc voltage is determined by two things with this equipment setup.

    One, the current set on the CC power supply will determine the voltage, based on the slope of the volt amp curve.

    Two, the amount of stick-out, will further influence the voltage of the welding arc. There is resistive heating (sometimes referred to as I2R heating) of the wire. The longer the stick-out, the greater the pre-heating of the wire as it feeds towards the puddle. This pre-heating of the wire causes added electrical resistance and this causes a voltage drop. A CV power-supply compensates for this by maintaining voltage. With a CC power supply the welder can influence the arc voltage by adjusting how much wire sticks out past the contact tip. Shorten the stickout, and effectively increase the voltage. Lengthen the stickout and slightly reduce the voltage.

    A suitcase feeder set in CC mode is also modulating wire feed speed slightly to try and maintain a constant arc. At least the Miller VS feeders work this way.

    When I use a VS wire feeder with a CC power supply, I set the wire feed speed for what I think it right for the bead size and travel speed I want. Then I check the mfg datasheet for how much amperage is needed at that wire feed speed. I set the CC power supply for the correct amperage. then I start welding and play with the stickout until I get the smoothest arc possible.

    It's been my experience that some power supplies are much better for this type of welding than others. Newer, inverter type welding power sources are much less forgiving than the old copper wound iron core transformer machines or engine drives. The volt amp curves on the old machines are much more suitable. The slope is a better match for getting the voltage in the right window and they don't respond as fast as newer inverter machines. That lag in how the old power supplies respond has a smoothing effect on the changes in arc. This in turn lets the welder respond by adjusting stickout to achieve a nice, stable arc. Couple this with the suitcase feeder in CC mode modulating the wire feed speed, and you can get a very respectable welding arc.

    The newest inverters in CC mode respond much, much quicker, and I think this leads to the welder 'fighting' the machine for control of the arc. I've seen this in practice when trying to develop a welding procedure for some FCAW-G wire on a CC power supply. The welding arc was completely worthless on a brand new inverter. The same wire and feeder on a 50 year old transformer power supply was smooth and relatively easy to maintain with some attention to the stickout used. I thought it was a lost cause when I started with the inverter power supply. Turns out I was right, until someone with more experience sent me out to use a really, old abused transformer power supply.

    I still maintain that running and FCAW wire is best done with a CV power supply. But I do recognize that some FCAW wire and CC equipment combinations are practical and can produce acceptable results. But the ingredients have to be just right. One last note, if a job calls for self shielded wire and specific strength and toughness in the weld deposits, then the only way to guarantee consistent results is to use a CV power supply. But if the welding is not critical then sound welds can be made using gas shielded flux cored wires, a CC power supply, and a CC capable suitcase feeder.
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  16. #16
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    Re: Looking for some help understanding OCV's

    A DAB, thanks for your explanation. I value your take on welding. I know cv is better for volt sensing feeders but I only have cc machines. I tried my SA200 black face with the ln22 (nr202 wire), the inverter 250 and an old 1947 180 amp copper wound idealarc. The idealarc seemed to work best. The inverter second best and the sa sucked. On the sa, I turned ocv's as low as they could go on the sa (~40 volts) . From what you explained here and what I was thinking: need to turn volts up on the sa 200 and retry.

    Your opinion of inverters and cc with volt sense is understood but, the Lincoln invertertecs are made to run 6010 and tig and have suggested settings for 6010. The volt amp curve is superior to other inverters as most won't run 6010. My ahp alpha tig does have an advantage for TIG compared to my Lincoln and I am sure Miller would blow the doors off for tig. My point is, the invertec works with voltage sensing feeders but I need to retry the black face with higher ocv's.

    Thanks again.
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  17. #17
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    Re: Looking for some help understanding OCV's

    Quote Originally Posted by Oldendum View Post
    From the Lincoln Handbook of Welding and Design:

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    Lincoln SA200 manual:

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    Reproduction quality is too low for me to tell, and I'm not sufficiently familiar with Idealarc welders of the era. I believe the text infers that the Idealarc giges an adjustment for voltage.

    The old engine welders, or some engine welders allow us to adjust voltage. If control of voltage is important, why then, don't modern stick machines follow suit?

    Evidently, based on FIELDRES, and the manual Old and dumb shows, These old machines used RPM control to reduce voltage.

    In the early stages of my life I was starved for good access to the physics of welding. Those people I did know who stuck metals together said amperage equals heat. My education in electrical theory challenges that belief. Those people were using either antique Forney, or Marquette refrigerator sized machines. If they were able to adjust voltage, they weren't aware. Later, the Lincoln AC buzz boxes became standard equipment for all farms, voltage was whatever Lincoln gave you.

    To me, fieldres was the first to introduce the concept of choosing voltage to control arc properties. Unfortunately, he shows how on antique machines I don't own.

    Falling short of arc length, can it be controlled on a Bobcat? Is there a modern machine I could buy that voltage could be controlled?

    Willie
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  18. #18
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    Re: Looking for some help understanding OCV's

    Willie, welding RPM on an sa200 is fixed and therefore does not control voltage. Same for my bobcat engine.

    Although I'm sure this is likely not true of every engine drive.

    Where the volt/amp curve starts dictates welding voltage for a given amperage. It's in the diagrams.
    The manual says that using a low coarse setting, and a high fine adjustment setting gives a high OCV.
    Using a higher coarse setting, and the corresponding lower fine adjustment setting would give a lower OCV at the same amperage as above (overlapping).

    For wire feed process in general, amperage (wire feed speed) controls penetration, voltage controls bead width and height.

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    Last edited by MinnesotaDave; 03-14-2018 at 01:52 PM.
    Dave J.

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  19. #19
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    Re: Looking for some help understanding OCV's

    I checked the Bobcat manual. They show several volt amp curves. Voltage seems to not vary over a wide range. The manual makes no mention of manipulating voltage by any technique but arc length. They do say for "best results" use a low range, and high fine setting rather than a higher range, and low fine adjustment. The fine adjustment is calibrated not in amps, but in percent of the coarse range. They don't mention if either adjustment affects voltage. I believe the Bobcat too is constant speed, governed for 60 HZ tool power I believe to be 3600 RPM.

    My obsolete Twentieth Century stick machine does have three ranges. I've never experimented much. I presume they are stages of voltage. Each has a different amperage range. Now you've got me wanting to try an old machine with voltage control. It certainly is important in MIG, It seems it would be helpful in stick mode.

    The Dynasty when used as a stick machine has a dig control. that is said to increase amperage to prevent sticking, nice on 7018. I don't think it'd be all that effective for weaving uphill, except that one could run at lower amperage without excessive sticking.
    Last edited by Willie B; 03-14-2018 at 08:05 AM.
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