Newbie welding questions

[RedRock]

I'm wanting to buy a welder for projects on my land where I have no grid power. What I do have is a generator "7000 Surge Watts, 5500 Rated Watts"

Based on the amp output of the generator, I'm told this welder will work with the generator, it has Amperage output of 20 - 75, 90+ peak

My questions are these... Does the welder buffer up amps in a capacitor giving me the full range of amp output(75a) or am I always limited to 20 amps of output? ...and if I'm limited to 20a output is my duty cycle continuous? ...or if I get up to 75a output, am I simply losing the amount of duty cycle? Unfortunately, I'm not a EE or electrician so pardon my ignorance.

I should also add that based on the metal pipe size I need to weld I prefer to use the largest electrode the welder will accommodate which is 3/32 E6011 (if this has a bearing on my earlier questions)

 

[Shield Arc]

Boy that's not a whole lot of amps! I don't think you'll be very happy with 3/32-inch 6011! I can't even remember the last time I ran 3/32-inch 6011 or 6010.

The link to your welder didn't work for me.

 

[k0ua]

here is the deal with welders, the 20 to 75 amp rating is the output current not the input current. Your welder link would not open for me, so I could not see anything about it, but I am guessing that welder is a 120 volt welder for input voltage.. Now when we say the welder is set for 75 amps, that DOES NOT mean the welder is drawing 75 amps at 120 volts from the input circuit. As you can see that would pop a typical 20 amp 120volt breaker real quick. but the 75 amps is the welding current at the welding voltage of the arc. So my experience says the welding arc voltage is maybe 20-25 volts. So lets do the math, at 75 amps welding current, at lets say 20 volts is figured this way...... Amps X Volts =Watts. so about 75x20= 1500 Watts. So lets assume the efficiency of the welder in the conversion of the 120 volts down to the 20 volts is pretty high.. so lets lets leave that to one side of these figures.. Now we have 120 Volts at the AC input that much we think we know, and we want to know how many amps will be pulled from from our 120 volt circuit if it has to supply 1500 watts the welder is going to consume. So Amps X Volts=Watts.. lets plug in the things we know and calculate the thing we don't know which is the amps.. So Amps X 120=1500.. OK so far?.. this is called algebra but don't let that intimidate you. Now we wind up with Amps= 1500 diveded by 120 so AMPs= 12.5 This is how much current the welder would consume from the 120 Volt circuit to make 75 amps of welding current.. Now,.. remember the thing I said to set aside for now? the efficiency of the welder..? We need to think about figureing that back in.. I am sure it will not make the conversion at 100% efficiency.. Maybe 85% by my estimate would be a better number. so we are going to need a little more that 12.5 amps at 120 Volts to make that 75 amp weld.. SO... 12.5/.85 =14.7 Amps.. this is a more realistic figure of what the welder needs to make that 75 amp weld at a welding arc voltage of 20 volts. So now we know (isn't this fun) that at 120 volts we will be pulling about 14.7 amps so again Amps X Volts=Watts.. so 14.7 X 120=1764 watts pulled from the source of the voltage, in this case your generator. Now all this said.. I have made some guesses here. As for duty cycle, That is complex engineering subject and best thing is to go off of what your published specs are.. I am guessing here again that the duty cycle of your little welder is around 20%.. which means you can only weld 20% of the time.. so weld a bead.. for 10 seconds clean off the slag... do any setup for the next one, and let some time elapse, and go again.. So if you spend 60 minutes on the project from start to finish, your actual weld time can be no great than 12 minutes.. Now, at the lower current settings of the welder you duty cycle will increase, at the higher settings, your duty cycle will decrease. With 3/32 electrode you are going to want to be around the top end of the little welder at that 75 amp setting.. That means you are going to have to keep your beads short, and let it cool off a lot between beads.. Don't get in no hurry. Your welder is very small, you will have to baby it to get the job done, but it can be done.

James K0UA

 

[Shield Arc]

you will have to baby it to get the job done, but it can be done.

Not by me! I'd quit and go back to the house if I had to work with those conditions! :laughing:

 

[Gary Fowler]

Not by me! I'd quit and go back to the house if I had to work with those conditions! :laughing:

Same here. I would look for a welding machine that had a bit more duty cycle and run it off the 220V circuit on the generator. I would look for something in the output side at 85-100 amp / minimum of 50% and 100% duty cycle range preferable that will run on your generator at full power.

 

[RedRock]

sorry about the link, here it is again. I'm just trying to find something that will get the job done with the gennie I have. Here's the link again st80i from Northern Tool + Equipment

Thanks guys, based on this response, my first intuition on this was accurate .... barely enough generator and minimal welder = not the right tools for the job. Not sure my back would hold up to the duration of this welding project. 32 x 48 foot cattle pen with crappy saddle cuts on rusty posts.

As bad as I like to do things myself, I'll need to enlist my neighbor's help with his giant welder, hire it out or pay the big bucks for the right equipment

* special thanks to k0ua for the quick lesson in fundamentals, I'll use it in the future

 

[Shield Arc]

That's not much of a welder! Wonder how far $180.00 would go towards renting a portable welder? Wonder if your neighbor would loan you his welder? Saddling the pipe should not be a big deal if you have a drill press.

 

[k0ua]

sorry about the link, here it is again. I'm just trying to find something that will get the job done with the gennie I have. Here's the link again st80i from Northern Tool + Equipment

Thanks guys, based on this response, my first intuition on this was accurate .... barely enough generator and minimal welder = not the right tools for the job. Not sure my back would hold up to the duration of this welding project. 32 x 48 foot cattle pen with crappy saddle cuts on rusty posts.

As bad as I like to do things myself, I'll need to enlist my neighbor's help with his giant welder, hire it out or pay the big bucks for the right equipment

Well, how much time and patience do you have?.. the loose fit-ups of the joints is going to take a while to fill in with that 3/32.. at 75 amps maximum. And I did look in the manual.. yep 20% duty cycle at 75 amps.. so no more than 12 minutes out of an hour welding. spaced through the hour....gonna take a good long while. Yep probably best get some help. A good engine driven welder is what you need for this.. but I am not telling you anything you probably don't already realize by now. I am not saying the little inverter welder is a bad welder, but the key word is "little".. as in "very little welder". My Everlast PA160 is not much larger, but it is a 230 volt welder @30 amps input, so 160 amps output maximum and a 60% duty cycle.. more guts by far than this one, and I would like something a little larger before tackling your fence job. Good Luck

James K0UA

 

[k0ua]

Not by me! I'd quit and go back to the house if I had to work with those conditions! :laughing:

Patience!.. he might have a long beard by the time he is done. but hey, he wanted to know if it would weld it... well sort of, kinda, almost

 

[RedRock]

That's not much of a welder! Wonder how far $180.00 would go towards renting a portable welder? Wonder if your neighbor would loan you his welder? Saddling the pipe should not be a big deal if you have a drill press.

I'll check into the rental, and the neighbor did offer to loan his welder, he tried to scare me though with how much gas it used, surely $180 worth of gas would do the job. My saddles were done using a cutting torch on used oilfield 2 3/8 pipe already set in concrete. I think I can make them ok after grinding a bit. For the horizontal rails, I'm going to try some 30 degree cuts with my chop saw for the saddle cuts. Those pictures using the drill press explain the perfect fences I see around.