Generator to power welder

fishman · May 29, 2007

It's been a while since I posted. Rain makes Fishman busy!

I've got a problem. I've recently acquired a Hobart ac/dc stick welder and am having a lot of fun making stuff around my place. However, some of the more interesting projects I want to do are in areas with no power. For example, I'm currently building a combination boat/rv barn out of steel. My neighbor (God bless him) has been helping out with his Miller Bobcat. However, I would like to work on some of the smaller stuff when I have time. So my question is:

Can I run my welder with the 4000 watt generator I have? I think that is it's rated capacity. It is a Generac 4000 XL has a 7.8 hp engine. I have a pigtail to convert the 240 - 20amp plug to my welding plug so that part is o.k. However, the specs for the machine state 47.5 amps at 240 volts for it's rated capacity, which I believe is interpreted as maximum capacity. Given that I'm running it at much lower than max, can it be done? My generator has a breaker, so I can try it pretty risk-free, but I thought I'd ask here first.

Now, something a little more complex. If it can't be done with a single 4000 watt generator, can it be done with two hooked together? See, I have two of them, although one has been loaned to a friend. I don't have a clue how the wiring would look, or if it could be done safely. Anybody want to take a stab at that?

I try and make my questions challenging, at least

reb · May 29, 2007

I'm sure you are not going to find a way to hook up those two generators to one load. It would take some sophisticated synchronization circuitry.

Several years ago I had an identical generator, which I tried to use with a wire welder. After several tries to strike an arc, I gave up. Maybe it was my technique, but the generator would bog down whenever the arc started and the voltage dropped, killing the arc. I figured it would take a larger generator or one with a beefy flywheel.

Soundguy · May 29, 2007

As the other poster stated.. striking the arc is where the smaller generators run into problems. Otherwise your limit on amps output will be limite dby amps input.. EG.. you'll not be able to weld at full capacaty.. but rather at pro-rated capacity. based on input amps and input/output ratio.. etc.

Soundguy

cp1969 · May 29, 2007

You could probably run a little 120V Mig welder off that generator but I doubt that even reducing the amperage of the stick welder will get you there. I was amazed when my generator wouldn't start my air compressor, which is well within the rated capacity of the generator. Not enough oomph.

If you look at the Miller Bobcat and Hobart gas welders, they have over 20 hp engines so that should give you an idea of what it takes to do stick welding.

RonMar · May 29, 2007

Power(P) equals Curent(I) times Voltage(E). 240volts X 47.5Amps = 11.4KW or VA. That generator is about 1/3 of what you need. Now you want to weld remotely on 4KW, try using it to charge batteries and do the welding with the DC current from the batteries.

fishman · May 30, 2007

So far it sounds like it's no joy in Fishman-ville. I'm going to give it a try with 1/8" 6011 and see what happens. Wish I could justify a pto generator

Mickey_Fx · May 30, 2007

As has been pointed out the figure originally give is 11.4kw and I question if this figure is correct. That would be one honking welder. What is the rated capacity of the welder? Typ stick welder one finds at home are in the range of 200-225A but that is secondry amps. These welders typ take about 5-6kW at their rated capacity.

Highbeam · May 30, 2007

It'll work fine on the low amp settings with smaller rods. Anyone who says it won't hasn't tried it.

I have tried it and done it again and again with my somewhat larger generator and similar AC225 stick welder.

You have the pigtail so give it a shot. Worst case, the breaker pops. No explosions.

The power equation Ronmar gave you is correct but the use of the equation is improper. The 47.5 amps of input power is at max load and worst case scenario to keep full welding output. What if you are only flexing the welder's muscle at say 1/3 of its max power. Hmmmm, less than 4000 watts.

Honestly though, your genset is pretty small for this so you will notice the difference. Striking the arc will take some more finesse and your limited power won't allow a good weld on thick material so do try it but don't settle for poor welds on a building just because they seem to stick.

Soundguy · May 30, 2007

I'd go for an easy strike type rod.. and as the other poster pointed out.. good metal prep.. and more passes with small rod.

To the poster witht he compressor not staring with a genny at rated specs.. well.. that's cause the motor start load can be 2x of the rated run load.. even more if it's an older unit.. etc.

Pto gensets are nice.. I've got a 12.5kw genny.. love it..

Soundguy

fishman · May 30, 2007

Mickey_Fx, I'm pretty sure the rating is 225 amps.

Highbeam: What would you consider thick material? I was thinking of welding 1/8"-3/16" thick clips to 1/8" purlin. Do you think it might be capable of 1/4" or is that "thick"?

Soundguy: An easy-strike rod. I guess you're talking about a 7014 maybe? 1/8" is what I have.