ThomasH
Gold Member
"Or use one of our new digital units with VRD."
Huh??
Huh??
Volts vs. Amps when welding
- Thread starter joshuabardwell
- Start date
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CNC Dan
Veteran Member
ThomasH said:
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
Veteran Member
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
Veteran Member
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.....
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.....
OP
joshuabardwell
Elite Member
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.
jaotguy
Veteran Member
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 ....
not knocking the explanation about wrenches and car batteries ....
Mark @ Everlast
Advertiser
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.
