Volts vs. Amps when welding

[joshuabardwell]

I just watched this video.

I was surprised to hear him say that, in general, a low OCV is more desirable. I have heard that a higher OCV is needed to run 6010 properly. Maybe this is a case of "Goldilocks"--not too little, not too much, but just right? The other thing that surprised me was that a higher OCV is conducive to sticking the electrode and snuffing the arc when short-arcing, whereas a low OCV is more conducive to "digging" and keeping the arc going. This just seems backwards, since I would think high voltage = more energy.

Thinking about the second point: I = P / V. If 40 in gear 2 and 70 in gear 1 produce the same current output, then:

I = P2 / 40 = P1 / 70
P2 / 40 = P1 / 70
P2 / P1 = 70 / 40
P2 / P1 = 1.75

This 1.75 number is not actually correct, since 70 and 40 are not actually voltage values, but are an arbitrary representation of voltage on a 1-100 scale. Nevertheless... 40-in-gear-2 produces more power (heat / watts) at the same current (amperage) than 70-in-gear-1. This helps explain why the arc is harder to snuff, but then why does the lower-voltage setting produce a faster-solidifying puddle? It seems like putting more heat into the puddle would cause the puddle to be more liquid, not less.

Can anybody help me make sense of this?

 

[CNC Dan]

As the arc length changes, the voltage accross the arc changes.
Longer arc = higher voltage.
Shorter arc = lower voltage.

So at a lower overall voltage from the machine, the change in voltage from the change in arc length will be of a greater proportion. This is part of what some call 'dig', or 'arc force', or 'soft/crisp' arc, etc.

As far as how this effects how the puddle solidifys, I'm not sure.

 

[Arc weld]

Shield Arc posted a good explanation from an SA 200 manual. As far as open circuit volts for shop machines, it depends a lot on the individual machine. A lot of inverters only put out about 60 OCV yet strike and hold an arc 100 times easier than an AC buzz box. If a buzz box only put out 60 OCV it would be very hard to strike and maintain an arc. The 7018AC rods are listing as being for low OCV machines yet buzz boxes often have the same or higher OCV volts than other machines. Volts don't give heat, amps give heat. Maybe it's like HP and torque, High OCV is like high HP low torque and low OCV is like high torque low HP and the high torque is what keeps rods from sticking? Lincoln figured this out eons ago but it can be complicated to understand. I don't have my book from school anymore but it had a whole chapter on Lincoln Dual Continuous Control machines such as SAE 300's and 400's. The Lincoln manual goes into some detail on the affects of varying the OCV volts while keeping the amps about the same.

 

[Mark @ Everlast]

Actually neither volts or amps give heat by themselves. Wattage is translated as heat and that is VxA.

 

[Arc weld]

For welding, heat is generally referred to as amps because the voltage isn't nearly as adjustable. A machine like an SA 200 will have about 55-95 OCV but 40-300+ amps. A shop machine won't adjust the voltage anywhere as much unless it's an old generator. Voltage is the flow and amps is the push. It's kind of like the debate over how you get electrocuted. Some people say high volts kill you and some people say high amps kill you. It is the right combination of both that will kill you.

 

[CNC Dan]

Voltage is the flow and amps is the push.

Um.... I think you got that part backwards.
Amps is flow (a certain number of electrons per second), and volts is the pressure (push).

Ampere - Wikipedia, the free encyclopedia

 

[DXN1EL]

Can people get killed by a welding machine?

 

[joshuabardwell]

Can people get killed by a welding machine?

Yes, but not exactly how you might think. Generally, the OCV is low enough that you might feel a tingle, but you probably won't get electrocuted. The way people get killed is if, for example, you are laying on the ground, and the ground is wet, and your stinger lead is frayed, so you get shocked. It's important to remember that you need to insulate yourself from the stinger, but also the ground, to avoid any stray currents accidentally going through your body.

 

[Mark @ Everlast]

Yes, but not exactly how you might think. Generally, the OCV is low enough that you might feel a tingle, but you probably won't get electrocuted. The way people get killed is if, for example, you are laying on the ground, and the ground is wet, and your stinger lead is frayed, so you get shocked. It's important to remember that you need to insulate yourself from the stinger, but also the ground, to avoid any stray currents accidentally going through your body.

Or use one of our new digital units with VRD.

 

[DXN1EL]

I read somewhere the reason for using amps was to prevent that?

The other day I was welding scrap, I had one hand on the table but I am not sure if I was touching the stinger (I accidentally broke the back side the metal is exposed) any way I felt a little current.
Was that the welder or do I just felt something and the welder has nothing to do with it?

Like I said i read somewhere that that why amp are used so people don't get electrocuted?? :confused3:

 

[ThomasH]

"Or use one of our new digital units with VRD."

Huh??

 

[CNC Dan]

"Or use one of our new digital units with VRD."

Huh??

Voltage Reduction Device.

Instead of having the welders output on all the time, it switches to a low sensing voltage. When a good connection (metal to metal) is detected, the welder switches to welding power. This can keep you from getting shocked in less than ideal conditions (wet).

 

[Arc weld]

Um.... I think you got that part backwards.
Amps is flow (a certain number of electrons per second), and volts is the pressure (push).

Ampere - Wikipedia, the free encyclopedia

I might have it backwards but it still requires a combination of both amps and volts but arc voltage doesn't change a whole lot at different amperage's. Bigger rods don't require more volts, they require more amps. On a CV machine, volts remain pretty constant but turning up the wire speed increases the amps and can drastically increase the heat. The same watts with different volts and amps can drastically affect the arc characteristics. That's why better machines allow for changing the OCV to suit the application.

In perfect conditions a welder could kill you but generally they have to meet ULC and other codes that limit the OCV volts to under 100. The highest I've ever seen was about 93-95 OCV on an SA 200. Most machines are in the 60-80 OCV range.

 

[jaotguy]

lower voltages don't break the skin barrier ( point at which it conducts electricity ) but adding moisture makes it possible ( don't weld in the rain unless you are well insulated)

you can safely put fingers across a car battery ( 12v and 500 amps ) and not feel a thing ..... but 1000V at .25 amps can kill you .....

put a 9volt battery on your skin and ... nothing, ..... put it on your tongue and you will feel it.....

 

[joshuabardwell]

you can safely put fingers across a car battery ( 12v and 500 amps ) and not feel a thing ..... but 1000V at .25 amps can kill you .....

You're mixing terms here. 500 amps may be what the battery is capable of supplying, but it doesn't actually supply that when you touch it. Resistance is the thing that always gets left out of these discussions. It all goes back to Ohm's Law, which says that Current (Amps) = Potential (Volts) / Resistance (Ohms). A 12 volt battery doesn't put much current through a person because the resistance of the skin is high enough that the current is kept below what you can feel. Resistance is why a car battery can weld a wrench to the terminals, if you short-circuit the battery with the wrench. The wrench's resistance is so low that the battery can push 500 or 1000 amps through it. 0.25 amps at any voltage will potentially stop your heart. Higher voltages are dangerous because they are more likely to successfully push that dangerous amperage through you.

 

[CalG]

Volts push amps

Amps do all the work

But it's I^2R (dissipation) that makes heat!

 

[jaotguy]

notice the reference to "skin" .... extremely high resistance unless wet ... and it's the reason for keeping voltages low and amps high for welding, or we would have a lot of electrocuted welders on job sites ..... also the reason for low 48 Voltage in Phone systems , so the line technicians don't get zapped ( unless someone calls and the voltage jumps to trigger the "Ring")

not knocking the explanation about wrenches and car batteries ....

 

[Mark @ Everlast]

VRD is recognized as </= 35 Volts. Ours run somewhere around 20-25 depending upon the machine with VRD engaged. It is required on some jobs sites these days. They sell external VRD's but I've personally never seen one used other than the ones built into a machine.