Scored a welder. Is it any good?

[2manyrocks]

The logical first steop is to open it up like tommu56 suggested and check the internals. Electrical wiring is one place where it's a good idea to be sure things are right before it can burn your place down.

Also, watch out for welding sparks. I think Miller warns that they can fly about 30' and start a fire in places you wouldn't expect.

If it works and doesn't cost you anything more in parts $60 is a good deal.

 

[rus_geek]

Disclaimer: "Technical" limitations are one thing. Code (local/state/national) always trumps reality to protect you from yourself :-/



For a safe wire run, you need to look at voltage drop, which is a function of the current and the wire size. NEC says no more than 5% voltage drop to the outlet.

Using LD1's example of 600v @ 20a and 220v @ 40a, let's see what we can run over 12 AWG:

100 feet of 12AWG gives these drops:
20amps: 6.53V
40amps: 13.06V

600v @ 20a -> 1.08% voltage drop
220v @ 40a -> 5.94% voltage drop

220v would have a maximum allowable voltage drop of 11V (5%). In order to run 220V @ 40A over 12 AWG, you could drop your length to 84 feet. (10.97V or 4.98%)

I believe most of the voltage drop is wasted as heat. Turning 5% of 220v @ 40a into heat would be a 440watt space heater...

 

[LD1]

rus geek: If I understand you correctally, you are saying that 40amp on a 220v circuit would work if under 84feet????

Don't get me wrong, I'm not trying to suggest to anyone to do anything unsafe or not to code.

But, the question I have never got a straight answer to is why wires are rated in amperage and not watts??? Maybe theres an electrical engineer on here who could help us out.

It is my understanding of electricity that watts are what does the work/creates the heat. Wires are rated on how much current they can carry without getting to hot. Heat being the limiting factor. They have to stay under a certain temp to keep the insulation intact. Watts are what creates the heat. More watts =more heat.

The widely used amperage ratings of common wire sizes kinda assume a set voltage. Lower the voltage and it should be able to carry more amps right?? Given the automotive 12v systems as an example.

Doing some searching I found an interesting artical that kinda sums up the mind boggling questions that I have. Wire Capacity Chart

And as far as having 2 hot wires on 220v to "share the load" not being an acceptabe argument puzzles me too.

Again, I'm not trying to be argumentative or unsafe, I just don't understand the logic of the code. If someone could shed a little light on it for me please am all ears.

BTW My powercord for the welder is not tucked behind any walls, and I don't feel the least bit unsafe running my welder to max with it's 12ga powercord plugged into a 40amp breaker. Call me crazy

 

[LD1]

I also just found this nifty calculator Wire Size Calculator

And it says for 240v 40amp with a 30ft cord that 12ga is fine

 

[Midsouth]

A good weld with 7014 will hold better than a bad weld with 7018.


I would think that a good weld with any rod would hold better than a bad weld with any given rod

 

[LD1]

A good weld with 7014 will hold better than a bad weld with 7018.


I would think that a good weld with any rod would hold better than a bad weld with any given rod

Exactally. Thats why I weld with 7014 and leave the 7018 to the "pros".

7018 is just too difficult to get a good weld with IMO

 

[jsborn]

Quote from LD1 But, the question I have never got a straight answer to is why wires are rated in amperage and not watts??? Maybe there's an electrical engineer on here who could help us out.



Try this , a 14 gauge NM insulated wire is Rated for approx 15amps the insulation is good for say 240 volts . By your reasoning that would be 3600 watts if you are considering DC or if AC you discount the power factor. With that assumption you are saying that if you lowered the voltage to a car battery IE. 12 volts and keep the watts constant (3600) you will be pulling 300 amps. DO YOU REALLY think a 14 gauge wire will carry 300 amps????

As you should be able to see watts is not how wire is rated or how much it can carry.

 

[LD1]

Quote from LD1 But, the question I have never got a straight answer to is why wires are rated in amperage and not watts??? Maybe there's an electrical engineer on here who could help us out.



Try this , a 14 gauge NM insulated wire is Rated for approx 15amps the insulation is good for say 240 volts . By your reasoning that would be 3600 watts if you are considering DC or if AC you discount the power factor. With that assumption you are saying that if you lowered the voltage to a car battery IE. 12 volts and keep the watts constant (3600) you will be pulling 300 amps. DO YOU REALLY think a 14 gauge wire will carry 300 amps????

As you should be able to see watts is not how wire is rated or how much it can carry.

On a 12v system a 14ga wire could carry 40amps.

Maybe neither amps or watts is a good measurement.

What about the flip side. A 10ga wire is rated for 100amps in a 12v car system. Would you want to run the 100amp power to your garage on 10ga wire????

Also, a 240v system has 2 power wires to share the load at 7.5 amps each

Like I said, maybe watts isn't the best, but there has got to be more to it than just amps.

I just used watts because watts seem to always be a constant. The power supplied.

Think of it this way, you run juice through a transformer. The volts and amps change. If volts go up amps go down and vice versa. But the total wattage (or Power) is still the same.

 

[Transit]

LD1, you can spin it any way you like, however MBURL is correct, the current capacity of the wire is tied to the circuit breaker. The rule for sizing the wire is a 2% voltage loss at the rated current for one conductor, for the length of the run. If the loss is greater then 2% you must go up to the next larger gauge.
BTW, if you are protecting a 12ga circuit with a 40 Amp breaker, don't let your insurance company ever find out. You don't have fire insurance.

 

[jsborn]

On a 12v system a 14ga wire could carry 40amps.

Maybe neither amps or watts is a good measurement.

What about the flip side. A 10ga wire is rated for 100amps in a 12v car system. Would you want to run the 100amp power to your garage on 10ga wire????

Also, a 240v system has 2 power wires to share the load at 7.5 amps each

Like I said, maybe watts isn't the best, but there has got to be more to it than just amps.

I just used watts because watts seem to always be a constant. The power supplied.

Think of it this way, you run juice through a transformer. The volts and amps change. If volts go up amps go down and vice versa. But the total wattage (or Power) is still the same.

If a 14 ga wire is good for 15 amps @ 120 volts it will only be good for 15 amps at any voltage. voltage rating on wire is a measure of the insulation not the wire. it is how much voltage the insulation will withstand before it breaks down and shorts out.

Current is the amount of electron flow a wire can stand before it breaks down due to heat.

You can do a lot of things with wire but to be safe you should always stay below the current rating of the wire no matter what the voltage is.

Your reasoning about 240 having 2 legs is flawed some what since you are not taking into account that for a fixed load the current will be somewhat divided between the two legs but not at a 50% rate. i can give you more information on how this works but I can say that if a wire is rated for 240 it will not carry twice as many amps as the same ga wire that is rated for 120volts.