Scored a welder. Is it any good?

[patrick_g]

Does changing the voltage ONLY change the watts and not the volts????????

Look at the formulas some of us posted?

Especially those for power such as:

P = I*E or P = E*E/R Where P is watts, E is Volts, I is in amps, and R is resistance.

For a simple example to make a point and ignoring the small change in resistance with change in temperature and any other minor effects...

Lets look at two simple examples with the same resistance (load device) but different voltages and see what the amps and watts do, OK?

How much power is dissipated in a circuit with 12 volts and 24 ohms?

P = 12*12/24 or 144/24 or 6 watts

I = E/R so I = 12/24 or 1/2 We get 0.5 amps.

Now we increase the voltage to 120...

I = 120/24 = 5 amps P = 120*120/24 = 600 watts.

Looks to me that when the voltage went up by a factor of 10 so did the amps AND the watts.

By the way the typically quoted voltage of an AC circuit (120 for exapmpe) is root mean square voltage and with a resistive load (lights or heater element or...) so that the current to voltage phase angle is 0 degrees (power factor of unity) the AC voltage quoted is the voltage that is equivalent to a DC voltage of 120 volts.

It DOES NOT matter that the voltage is a time varying value or that the actual peak voltage you can measure is about 169.68 volts. in a 120 vac circuit. Use the RMS voltage and the listed equations and you will get the right results.

The two legs of a 240 VAC circuit do not take take turns supplying voltage. The instantaneous voltage difference measured between the two legs varies in a sinusoidal manner at the rate of 60Hz and if your meter could follow the rapid changes AND our eyes and our brains could see and interpret the meter fluctuations we'd see the voltage between the two 240 volt legs vary smoothly from about +339.36 to about -339.36 and all values in between. (Easy to see with an oscilloscope.)The current in the two legs is at all times equal in a 240 vac circuit (sans malfunction) and each "half" of a double pole breaker sees the same current (again sans malfunction such as a short to ground or whatever.

Hope some of this helps some of us.

Pat

 

[Egon]

Hope some of this helps some of us.

Yes, it takes me back to a time of utter confusion!

 

[aczlan]

The two legs of a 240 VAC circuit do not take take turns supplying voltage. The instantaneous voltage difference measured between the two legs varies in a sinusoidal manner at the rate of 60Hz and if your meter could follow the rapid changes AND our eyes and our brains could see and interpret the meter fluctuations we'd see the voltage between the two 240 volt legs vary smoothly from about +339.36 to about -339.36 and all values in between. (Easy to see with an oscilloscope.)The current in the two legs is at all times equal in a 240 vac circuit (sans malfunction) and each "half" of a double pole breaker sees the same current (again sans malfunction such as a short to ground or whatever.

Correct, except that a 240 VAC circuit is made up of two 120 VAC legs, not two 240 VAC legs.

Aaron Z

 

[Transit]

And the beat goes on. I see many replies are in agreement with mine.
The NEC limits the voltage drop in any single conductor at 2%, meaning a 4% total for the round trip at a set current load equal to the breaker rating protecting that branch. Need to go a longer distance by a few feet, than you must go to the next larger gauge wire.

Think about this; wire a circuit with #14 wires [15 amps] and connect it to a 30-amp breaker. How so? Go to the last receptacle in the circuit and splice in another # 14 wire, then run that wire back to the 30-amp breaker. What you have effectively done is parallel the first wire with a second capable of carrying another 15 amps. 15 + 15 = 30 amps.
Of course, you have busted a bazillion sections of the NEC by paralleling the circuit.
Parallel circuits do work. DO NOT EVEN THINK ABOUT DOING IT.

Patrice g, now you are talking about the maximum voltage of a Singe wave in relation to its effective value, RMS voltage. The conversion factor is 0.707. 120 /0.707 = 169.3 volts. This is a story for another time.

 

[Transit]

Correct, except that a 240 VAC circuit is made up of two 120 VAC legs, not two 240 VAC legs.

Aaron Z

Not always true.

 

[aczlan]

Not always true.

As I understand it, in the context of this discussion (a single phase US residential electrical service), you will always have two 120VAC legs which are at opposite "ends" of the phase from each other (+120 and -120) in a 240VAC circuit.

Aaron Z

 

[patrick_g]

As I understand it, in the context of this discussion (a single phase US residential electrical service), you will always have two 120VAC legs which are at opposite "ends" of the phase from each other (+120 and -120) in a 240VAC circuit.

Aaron Z

Aaron you are correct of course, I mistyped. 240 volts is comprised of two 120 volt circuits 180 degrees out of phase. Typically the transformer supplying you with 120-240 single phase power has a center tap on a 240 volt winding. The center tap is neutral and each end of the winding is a separate 120 volt leg 180 degrees out of phase with the other.

I think MOST of us are in agreement, nearly violent agreement in some cases and some of us are a bit misinformed and or mistaken. There is always lots of bad advice available.

Pat

 

[Transit]

Right, residential. I've been chasing a 240 v circuit, not center tapped, problem at one of our stations. I'll be putting a power analyzer on it with voltage and current probs Monday or Tuesday.
With all the bad weather this past few weeks everything is falling a part. Thursday morning there was a roadway overpass that collapsed on our Gladstone line before rush hour. Lots of fun.

 

[Sully2]

You can quote that "X" amps requires "Y" wire gauge all day long...but it DONT APPLY to ELECTRIC WELDERS! The thermal breaker in them kicks out L.O.N.G before the wire feeding it can ever go "poof".

Dont believe it? Go to Hobarts or Millers websites...download a manual ( PDF file) for any decent size3d welder made by them..and READ and see what size wire they RECOMMEND for wiring TO the outlet...and also for the size wire recommended for any EXTENSION CORD one might need!

The duty cycle being so "short" with an electric welder is how they "get by with it"

 

[RWolf]

When in doubt hire an electrician. Pat has said it about as clear as anybody. I've been in electronics/electrical work for most of my life and it never ceases to amaze me when anybody has an electrical discussion. My 2 cents are Power (watts) are capacity generated or used. Volts and amps are the medium used to get the job done. If your welder requires 50amps at 240volts then you will need x-sized wire. Because of duty cycle you "may" get away with something smaller. But like I said you "may"....... To wire your shop best advice and to keep you legal and safe is to have an electrician perform the task. Then all you have to worry about is going from the wall outlet to your welder.

LD1 your on the right tract to understanding but keep in mind that when dealing with electrical circuits there isn't a one rule fits all. DC circuits are done differently than AC circuits. Keep on learning. I've been at it for around 50 years and I still find something new each time I work on something that deals with electricity. Here's a challenge derive an AC circuit to get 3phase power out of a single phase line.

Good luck.