Choosing a welder that my generator will support

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Hey guys! I joined this friendly forum because I am about to get into some limited welding and need a little advice. A little background first - the real questions are right at the end.An experienced & competent, hands-on contractor friend is helping me build a 21' bridge (16' actual span) to access my property. Me, I just do the non-skilled and repetitive work: I have done a lot of grinding  . He has done the engineering design and and will do the structural welding with a heavy duty unit we will rent. Then, I will have to weld 50 pieces of 2" OD pipe across the six 14" tall I-beams to make the deck (like a 21' cattle guard : that is 600 welds each about 8" wide As I have not welded before, this is going to take a while. I figured that it will cost me almost as much in equipment rental as a new 7000 watt continuous duty (8250 surge) generator (240v/30amp output). It should just power my friend's portable 240v 30 amp input SMAW inverter which we anticipate we can use for the pipe (perhaps depending on the choice of rod), so I snapped up the almost "free" generator (I could not justify the cost of a larger one which would be MUCH more expensive). We will test the combination in a few days to ensure the genny provides enough power to avoid damaging the inverter, using a suitable rod (it HAS to work, to justify the generator purchase)! I am quite glad for this opportunity to learn the very basics of welding rather late in life, as I have a few little welding jobs I would like to do: mostly welding things onto my backhoe, trailer & truck, like hooks & toolboxes and modify loading ramps. I would like to buy an inexpensive portable SMAW welder with the highest output the generator will support. It seems an inverter type is preferable. My needs will be simple and infrequent: I'll seek help for any major welding challenges.I know that the type and thickness of rod, the thickness of steel to be welded and other factors affect the draw on the welder. Given the limited capacity of the generator (it does have an overload cut-off), it is important to understand how to avoid underpowering the welder, and what its limitations in terms of welding capacity may be. This leads to the main question - what might be a suitable and affordable portable welder for me (considering I don't HAVE to own one)? The best deal I have found is Harbor Freight inverter arc/tig welder # 66787, input: 240 volts, 16-25 amps (couldn't find a 30a model), single phase, 60 Hz, electrodes up to 3/32, capacity 1/4" steel, currently $230 (about my budget). I don't know if 3/32 electrodes are large enough for most applications I am likely to encounter.Now I'll admit that "portable" is a relative term: I can't lift the generator without the help of forks on my tractor, so we might agree that I don't need a truly portable welder, but I do want one I can run off my generator if need be. I can also buy a cheap, ancient, very heavy and moderately powerful unit (Lincoln I think - I suppose this would be a transformer welder), and run it off a house 240v circuit; perhaps it would be as "portable" as the generator, although I'm not sure this type of welder can be run off a generator at all. It certainly would have to be set to a limited input amperage, by plugging the leads into the appropriate sockets to avoid overload problems. I have little idea how to calculate that (one would need to know the inefficiency ratio of the welder and estimate the load from the work being welded, I suppose). I did find some amp. data on popular sticks.Sorry, I have rambled on a bit: in doing so I have raised a number of issues I have not found clear answers to. I will be very grateful for any comments and suggestions. Thanks!CrankySeeking Knowledge - Hoping for Wisdom
Reply:buy a used generator and a used transformer welder. a 7kw genny at 220 v makes a little over a 30 amp circuit, should be enough to run a buzzbox at the max 125 amps you will need for this job, i guess..but the surge might be a problem..spend a lot of time practicing..you've never welded, and 2" pipe is a lot harder than a straight flat weld..and youre gonna drive trucks over it..dont attempt this job  until you know you are comfortable and consistent with the welding involved..better not to run an inverter off a genny...hf is good for hammers, nothing more technical than that..
Reply:No offense, but you really need to get a professional second opinion on the engineering aspect. This is a bridge designed to support the weight of a tractor?  Contractor does not equal experienced, trained, licensed civil engineer. Your friend may not be aware of the specific building codes in your area concerning bridges, especially if they're intended for more than foot traffic. Codes exist for a reason. They may require a licensed engineer to sign on a project like this. Nearly all welds on a bridge should be considered "structural"  meaning bad, expensive things can happen if they fail under any circumstances. The design and construction of abutments is more critical than the design of the bridge superstructure itself. poorly built abutments will render even the best welding job to be pointless. This may not be news to you, but I think it bears mentioning. All waterways are subject to erosion and flooding.  You may be wise to simply buy a large, corrugated steel conduit, or several if necessary. Then backfill, compact, and grade the road over it. This is a hell of a lot easier to maintain and repair in the long run. (Since I've never seen the site you'd be the person to tell me if that would work or not.)If you still consider a steel beam bridge to be your least expensive option here's what I'd suggest:Talk to an electrician and ask about wiring up some 220v cable to run down to the work site from your house. Then you can buy a little Lincoln or Hobart "buzz box" stick welder which will save you a at least a thousand in fuel and equipment rental. Those things are known for being bulletproof. (this cannot be said of anything bought at harbor freight.)Last edited by Joshfromsaltlake; 06-11-2012 at 06:59 AM.
Reply:Just a tip on welding your pipe to the I beams. Welding the pipe to the beam makes for a hard weld to do and get a strong weld to booth the pipe and the beam.I redid a cattle guard that was put in that way and most of the pipes were broken loose from the beams. Well these were pipes in place of beams but same problem, all the pipe has is the weld to keep it from rolling.When I put the new pipes in I used a piece of channel under the pipe makes it easier to weld and much stronger. Hope that makes sense. Attached ImagesTrailblazer 302Hobart Stickmate AC/DCLincoln SP 135 TSmith torchSpoolmatic 30A
Reply:I read your post last might and was going to say "go for it" but then thought that your parade despereatly needs to be rained on.There is very little metal in 3/32 rod, you will need a lot of filler to anchor the 2" pipe to the flat deck of the  I Beams.  The inverter welder you described is just not up to the job. If you persist with the purchase of the HF Welder, sppennd a few bucks for their policy, I strongly belive you will be taking it back to the store,ShortArc seems to have it together.  The lack of time today keeps me from dumping even more rain on your parade, but you need it.GailLast edited by nadogail; 06-11-2012 at 09:08 AM.Reason: spellingI offer three choices: Good, Fast, & Cheap. You may pick two.Hobart AC/DC StikMate LXHarbor Freight AD HoodHarbor Freight Industrial Chop SawDeVilbis 20 Gallon, 5 HP Compressor
Reply:I should have noted the welding on the ones I posted were done with 5/32 7018 @ about 160 amps.Trailblazer 302Hobart Stickmate AC/DCLincoln SP 135 TSmith torchSpoolmatic 30A
Reply:Thank you Weldbead and JohnyfromSaltLake and others for your comments, and certainly no offence to the cautonary remarks: I understand there are a lot of issues in this project that require careful planning (one reason I posted).  While my questions were ostensibly about welding equipment, concern about abutment design and support are important issues we have given a lot of thought to.Let me first address the equipment issues, then I will comment on the design and its rationale. My contractor friend (actually a commercial project supervisor) is very experienced in a wide variety of commercial construction fields and technologies; he is also an experienced welder and will do all the critical welding. I would not be contemplating this project without his help and expertise. It is too far (1/5 mi) to run cable for 240 volts at 30-50 amps from my home to the bridge in order to run a buzz box. So we will have to rent a trailer-mounted Lincoln gen/welder for the structural welds for sure.I will only weld the pipe decking to the I-beams’ flanges, welds that are not intended to be structural. That is 600 8” welds – I can’t expect my friend to do that, so I will have to practice until I can do it adequately: he will train me. These welds are seen in section like so: .O.  .O.  .O., where the periods indicate the welds (2" x 1/8” wall pipe on 5" centers welded across 8" I-beam flanges). I am well aware that drive wheels can rip the pipe off the I-beams if not adequately secured, but a failure of one of those welds would not be fatal.  Of 12’ of pipe (the deck width), 4’ will be welded on both sides to the six I-beams. Do you think that is insufficient to secure them, Shortarc? Why is it a bad idea to run an inverter off a genny, Weldbead?  If my friend cannot obtain adequate welds (I don’t know what size stick he can use) with his quality 240/30 amp input inverter run off the 7000 watt generator, then we will have to rent the more powerful trailer-mounted Lincoln generator/welder for as long as it takes for me to make the 600 welds; this will require a considerable amount of money I had hoped to put to better use by buying the 7000w genny which I could later use for other things. Also, the genny and inverter would let me take my time on this job: I am too old to work 12 hour days at 100+F in order to rush the rental unit back.I evidently confused the issue by asking about the Harbor Freight (yeah, I know!) inverter. I don’t intend to use it on the bridge, but for misc. lighter jobs around the place I would like to do later; I was weighing it against a small buzz-box for about the same price.Regarding design: Let me clarify some points. This bridge is on a dead-end driveway to my house.I am actually replacing an existing wood bridge built 25 years ago that is supported by 4 enormous transmission poles up to 2' dia,  (who knows how old the transmission poles are). These beams and wood decking are showing signs of aging and I am replacing them now, partly out of an abundance of caution. There will be 6  21' long, 14” webbed I-beams with 8” flanges on a 16’ span. These will be adequately anchored into a headwall and crossed-braced to resist lateral and torsional forces. This will be much more secure than the previous structure ever was, partly because the materials will not deteriorate, it is designed to resist torsion, and the load it will support is greater (est. 30,000 pounds). The arroyo is subject to severe flash floods every several years, and six years ago one seriously eroded the earth abutments under the bridge, so I am acutely aware of potential flood damage and abutment support & protection issues. To repair that damage I rebuilt the abutments back out with rock, concrete and rebar, and reinforced the support for the beams, adding extra upstream counter-erosion measures, so there is now no earth exposure, and less beam span. The current plan includes excavating behind the existing abutments to build reinforced concrete headwalls running the width of the bridge to help support the weight: they will tie into the existing abutments.The reason I have not adopted a culvert solution is that the rare floods bring down large quantities of cottonwood, salt cedar and rock of all sizes which quickly block even very large culverts. In fact, the most destructive flash flood completely blocked my 16’ x 4 1/2 ft. clearance bridge, which is why the earthen abutments were eroded, and it required a heavy trackhoe and lots of chaining to clear it. (I did harvest a lot of firewood!) The new bridge design will add an extra 16" clearance and so reduce the chance of blockage.Any other thoughts, please bring them on! More rain is OK.  That's how I learn.Thanks for all the responses: CrankySeeking Knowledge - Hoping for Wisdom
Reply:I dont know about your area, but 'around here' a lincoln 225 amp welder/generator is 250 for a week(welder 200, 30 for 50 ft leads). if your going to do it, for that I would just rent it for a week, get as much done as you can then check the weather and keep at it if it you can.  if you rent it for under 600 for 2 weeks your ahead, and you have enough juice to handle it without the hassle.  if your trying to do this "as you can get to it" I think your going to end up disappointed.I +1 shortarc's design for the joint, your asking for problems because of leverage and load displacement, if this was a once in a  blue moon driveway, ok, but this is your main route in and out, dont cheap out on it now, add to that your not a experienced welder, the nested joint will be way more tolerant of poor welding (it wont want to roll, ever). if the way you want to do it was ok, they wouldn't need spring mounts on trailers, they would u-bolt the spring to the axle with just an alightment bolt. broken welds increase odds of rust and lowered life expectancy. If your not competent to weld it, or cant/wont afford the cost to do it right, cover his frame with 4x6 treated lumber and replace it every 6-10 years. If your going to do whatever you want then ok, but you counting it as 600 welds at 8" isnt the right way, you will need multiple passes, grinding, prep, etc to do it right, shortarc's way requires 2 passes per side with proper fit up, yours will be at least 3 I would guess (the cups could be done close to the house with a 220v buzz box and stacked up and brought to the job when you were ready. anyway, hope you come up with a solution, please do it right or figure out another way, doing something wrong because you can't see the harm isnt going to be ok if your bridge damages someones elses car when their wheel hits a previously broken off pipe and it smacks the underside of their car.ps. if you want to do it with two welds, use heavy angle or channel instead of pipe, might be better for your desired outcome o/\oLast edited by Ryf; 06-11-2012 at 04:13 PM.Hobart Handler 190 Century 90amp on FluxCraftsman 200amp buzzbox
Reply:Why not shop around for a used Miller Bobcat or Lincoln Ranger, finish your welding project & you'll have the  machine to use as a generator plus having a  welder for future projects.Last edited by Old Skool; 06-11-2012 at 04:44 PM.
Reply:Thanks for clarifying a lot of the design issues, Cranky. I still think you'll benefit from a second opinion. You should be able to run your friend's inverter off a 7,000 watt genset. It may struggle with something like 1/8" 7018 running at 150 amps.
Reply:[QUOTE=Cranky;1253131] It is too far (1/5 mi) to run cable for 240 volts at 30-50 amps from my home to the bridge in order to run a buzz box. So we will have to rent a trailer-mounted Lincoln gen/welder for the structural welds for sure.I will only weld the pipe decking to the I-beams’ flanges, welds that are not intended to be structural. That is 600 8” welds – I can’t expect my friend to do that, so I will have to practice until I can do it adequately: he will train me. Ththis is why i suggested buy not rent..to give you time to practice. ..this could take awhile and as you mention you not gonna give it 12 hour days..good for you..Why is it a bad idea to run an inverter off a genny, Weldbead?I dont have personal experience doing so..ive read that some sophisticated circuitry is needed to adequately clean up a generators output for an  inverter, and most 7kw gennies dont have it..also read  that a transformer welder runs fine off a dirty generator..i cant picture how these 2" pipes are not structural..are they not the deck of a bridge??(i myself was thinking for 2" pipe onto the flange, 1/8 7018 at 125 amps would do..low enough in the duty cycle not tohurt anthing..)Last edited by weldbead; 06-11-2012 at 07:41 PM.
Reply:You'll need rather a large genset to run a Buzz box so i wouldn't look for any of those for this Portable Project.The Inverter will probably run just fine on a 7000watt genset- it's a HF model anyway so just return it if it burns up.Do you need a GOOD genset for back up power?yes, then spend the money on a quality unit and burn up a couple HF welders learning- if they actually do burn up.or as Oldskool suggested buy a used Engine Drive welder and be ahead on both sides of the problem.Ed Conleyhttp://www.screamingbroccoli.com/MM252MM211 (Sold)Passport Plus & Spool gunLincoln SP135 Plus- (Gone to a good home)Klutch 120v Plasma cutterSO 2020 benderBeer in the fridge
Reply:I am amazed and grateful at the amount of valuable advice I have been offered. I am still trying to assimilate it all.The most helpful thing is being shown that welding pipe directly to the I-beams is not the best way to go.  Shortarc’s suggestion of nesting the pipe in channel is a great idea. The pipe is already bought, cut to length and stockpiled on site. I don’t mind buying a small Lincoln buzzbox for the shop, chopping the channel and welding it on to the pipe. It will give me excellent basic welding practice and get half the pipe welding done without paying equipment rent, and under relatively comfortable conditions, and I can later use it for other things.The 7000w generator is also bought, so I’ll try to use that with an inverter – perhaps Shortarc’s  solution will allow me to use a smaller stick and won’t draw quite as much current.A Lincoln genset rents for $280 a week here. As we will need one for the I-beam bracing work for a few days, maybe I should try it on pipe (with channel) for the rest of the week and see how I do compared with an inverter. Of course I want to do this job right, and so I’m taking all the comments and suggestions very seriously.Taking down the old bridge is not going to begin until all the preparations are complete, all materials on site. so it will be a while before construction begins. Time to think through all the info you have given me.Thanks, again,Cranky..Seeking Knowledge - Hoping for Wisdom
Reply:http://albuquerque.craigslist.org/tls/3049890127.htmlI would keep a weather eye out for a small welder/generator.The bridge design is a whole nuther can of .....City of L.A. Structural; Manual & Semi-Automatic;"Surely there is a mine for silver, and a place where gold is refined. Iron is taken from the earth, and copper is smelted from ore."Job 28:1,2Lincoln, Miller, Victor & ISV BibleDanny
Reply:Thanks, Tanglediver: I'm watching Craigslist now. If I could get a genset like a Miller or Bobcat at a reasonable price it would be good option to consider, as others pointed out, as long as the resale looked good. I don't need to own one.The big problem is knowing enough about the different models, functions and being able to evaluate the condition and value on the older machines. I've started doing some reading, but am far from that point. I don't know enough to say if the one you pointed out is a good value.I do know Q 1: does it come with leads?   Fortunately, I have several weeks to look.Cranky.Seeking Knowledge - Hoping for Wisdom
Reply:q1a is  does it run so i can try it out?
Reply:Originally Posted by shortarcJust a tip on welding your pipe to the I beams. Welding the pipe to the beam makes for a hard weld to do and get a strong weld to booth the pipe and the beam.I redid a cattle guard that was put in that way and most of the pipes were broken loose from the beams. Well these were pipes in place of beams but same problem, all the pipe has is the weld to keep it from rolling.When I put the new pipes in I used a piece of channel under the pipe makes it easier to weld and much stronger. Hope that makes sense.
Reply:Originally Posted by weldbeadq1a is  does it run so i can try it out?
Reply:I would say look for deals on a Weldnpower or lincoln ranger 8 etc.   you will be able to sell it for close to what you pay for it.  will give you all the power you need.  if you have never Stick welded before you are going to need some serious hours of practice...Tiger Sales:  AHP Distributor    www.tigersalesco.comAHP200x; AHP 160ST; MM350P,  Spoolmatic 30A; Everlast PowerTig 185; Thermal Dynamics 60i plasma.  For Sale:  Cobra Mig 250 w/ Push-pull gun.  Lincoln Wirematic 250
Reply:Looks like previous guys have you pretty well informed. Another thought I can have for you to consider, if you buy or rent a transformer or generator machine that provides DC welding current, you can rent a 'suitcase' portable flux-core wirefeeder from the welding stores. all you need is the 2 welding power cables.  Oh, by the way, I've designed, built and installed 2 similar sized (44 feet and 52 feet) vehicular bridges a couple miles from power or anything, just the water in the creek below. The creek came in handy for the water to mix concrete for footings. Attached ImagesLast edited by dougspair; 06-13-2012 at 09:10 PM.Reason: add photosDougspair
Reply:Shortarc - I Dig the pipe in the channel welding tip."Dirty power" generators running a welder do seem to be an issue.  I've tried two of my small migs on my generac 5000 watt unit.  They both run poorly on it.  That's why I picked up a SA200 gas driven welder to work on.
Reply:Glad it helped ya out. It seems like a lot of extra work at first but for strength and not having to fill that big bap between pipe and flat it really saves quite a bit of time and rod.Trailblazer 302Hobart Stickmate AC/DCLincoln SP 135 TSmith torchSpoolmatic 30A
Reply:Originally Posted by MinnesotaDaveShortarc - I Dig the pipe in the channel welding tip."Dirty power" generators running a welder do seem to be an issue.  I've tried two of my small migs on my generac 5000 watt unit.  They both run poorly on it.  That's why I picked up a SA200 gas driven welder to work on.
Reply:Originally Posted by weldbeadthis is a surprise to me.. i thought only the inverters suffered from dirtygenny...
Reply:Design update: we have run into a glitch with Shortarc's great suggestion of nesting the pipe in channel to avoid the problems of a direct pipe weld to I-beam. I am working with 2" OD pipe, not 2" ID, and there seems not to be channel available that would accommodate 2" OD. The 2" OD pipe, 1/8 wall, is technically 1.75" pipe, and will be spaced on 5" centers, leaving 3" between pipes (I realize pipe is usually specified by ID but stated OD because I was concerned with spacing.) However I have come up with a solution based on Shortarc's original suggestion. Use 3" x 1" x 3/16 channel for spacers (I think this size or something close is available) and weld 4" lengths to the I-beam BETWEEN pipes. To do this, each row of spacers is fitted and welded in place ahead of the previous row BEFORE the next pipe is placed; thus all welds can be reached on each spacer. Then the pipe is dropped in place and welded. I don't see any difference structurally from Shortarc's original idea:The pipe is still "nested", but between channel spacers, instead of inside.I will put the web of the channel UP, effectively making a box at the greatest girth of the pipe so spacers and pipe are welded together continuously along the I-beams. This should be stronger than the original design because the pipe and spacers make a continuous run and support oneanother. Does anyone think that uneven heat expansion/contraction relative to the I-beam might stress the welds? If so, I could interrupt the continuous pipe/channel run at intervals by using 1" angle instead of channel, and skipping an inch.  Any comments or criticisms on this modification? Can I get by with shorter spacers than 4" to reduce the amount of welding a little (50 pipes x 6 beams = 1200 4" welds = 400' of weld?The design is now a 12'' width driving surface composed of six 7" flange I-beams supporting 14' pipe (2' of pipe will cantilever out on the downstream side to be covered with expanded metal for pedestrians). The beams (and spacers) will be within 1.5-2.5' of one another, except for the center where the spacing will be about 3.5'. I hope with practice I can do these welds in one or two passes (if my new 7000w generator will drive a quality inverted welder using 1/8 or 3/32 stick - which remains to be seen, based on recent comments).Seeking Knowledge - Hoping for WisdomOriginally Posted by dougspair   I've designed, built and installed 2 similar sized (44 feet and 52 feet) vehicular bridges a couple miles from power or anything...
Reply:Originally Posted by Old SkoolWhy not shop around for a used Miller Bobcat or Lincoln Ranger, finish your welding project & you'll have the  machine to use as a generator plus having a  welder for future projects.
Reply:Originally Posted by Old SkoolWhy not shop around for a used Miller Bobcat or Lincoln Ranger, finish your welding project & you'll have the  machine to use as a generator plus having a  welder for future projects.  [And as Canoe2fish just reiterated]
Reply:OA will do it.
Reply:Or (swear words follow) forget  welding and bolt the pipe into the saddles and onto the I-beams.  Not much shear stress on the bolts.  might work
Reply:Or, shop weld the saddles, a great idea by the way, somewhere you have 'plug in' power.  Then the field weld the pipe, or not, into the saddles.  Your walkway decking will keep pipes in place horizontally as traffic tries to scoot them around and there's not much reason for them to jump up out of the saddles.  As much as I like melting things, we live off grid so my first answer isn't always to fire up a generator.
Reply:Originally Posted by GraywolfOA will do it.
Reply:Does it really need that much to hold the pipes down in the saddles?  Or the saddles on the I-beams?
Reply:Originally Posted by GraywolfDoes it really need that much to hold the pipes down in the saddles?  Or the saddles on the I-beams?