Generator sizing
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  1. #1
    Join Date
    Apr 2008
    Location
    Yuma AZ
    Posts
    2,479

    Generator sizing

    I have a Hobart Handler 175 that I'm tired of paying the stinkin electric company to run it. I already pay over $200 a month for electric (have gas stove, oven, hot water heater & furnace) that I think is outrageous. I think it may be due to the pool pump running for 6 hours a night filtering it, maybe the computers & TV's running 24/7 too.

    Anyway, I used it to weld up a couple ramps to my front/back door & it really jumped the monthly level pay. I figured a buck or two for a couple months, but wow, it's almost $35.00 more for the past 4 months.

    I was wondering if a 7.5KW generator would be enough to manage this and maybe a 200A TIG (when I finally decide which one I want). I see them on Craigslist, some are as low as 1000 watts, others I've seen (portable) are up to 8.9KW for a few hundred bucks. The difference in prices is the only reason I'm asking, that & where to store one.

    If I had the bucks, I would get a welder/generator, but that's not an option right now. I'm thinking for now I should get at least a 7.5KW genset & that would be enough for me well into the future. What do the experts think? Remember I'm no electrician.
    Mark
    I haven't always been a nurse........
    Craftsman 12"x36" Lathe
    Enco G-30B Mill
    Hobart Handler 175
    Century 230 Amp A/C stick welder
    Add a Foot Pedal to a Harbor Freight Chicago Electric 165A DC TIG
    PapaLion's Gate Build

  2. #2
    Join Date
    Feb 2008
    Location
    North of Philly
    Posts
    16,057

    Re: Generator sizing

    Mark what you need to find out is how many amps the machines will draw at 230v and then compare it to the gen set.

    From Hobarts site on the HH175. The HH175 needs 19.5 amps at 230v.

    IIRC my 4500w genset is rated at close to 19 or 20 amps at 230v so it should run it.

    As far as a 200a tig that depends on the machine. I know you could most likely run a Dynasty 200 inverter on that genset and get almost max power. You can because the inverters low amp draw.

    To run my sync 200 that needs 52 amps at max you would need at least a 12KW gen set, 15 KW would be better to run at max. It would probably run on a 10kw gen set but at reduced power.


    To figure what you need Amps X volts = Watts So... machine amps X 230v = watts from the gen set.

    Make sense?

  3. #3
    Join Date
    Jan 2004
    Location
    Northern Cal., Shasta County
    Posts
    7,044

    Re: Generator sizing

    Get a genset if you think you need one, they're good for a whole host of tasks, but don't get one to save money. You can't generate juice as cheap as they sell it to ya let alone ever recover your outlay. Even if it only consumed a half a gallon an hour and ran your whole house look at what one day would cost you. Sure you'll only be running a few hours a month but the cost factor is the same.

  4. #4
    Join Date
    Apr 2008
    Location
    Yuma AZ
    Posts
    2,479

    Re: Generator sizing

    That does make sense. I get all confused with simple calculations like this, but can do IV rate drip rate calculations in my head. This formula makes sense to me though.

    I think your correct with the max input for my HH 175 is 19.5A, that's what my owners manual says. I run it off my 30A dryer outlet, but later this summer I'm going to put in a dedicated 50A & 30A circuits in my garage. As this is a rented house, I'm going to hire it done into a subpanel. That way I know it's right. But even when that gets done, I'll still use a generator for any major welding projects. I just dislike paying the electric company their outrageous rates.

    I also would like to be a bit portable. I'm sending my son through welding school in Nebraska this fall & would like to have something for him to be able to use right out of school. He doesn't have a welder yet, doesn't even know how to put on a welding mask. But I'll learn him this summer, then when he's done with school, I plan on moving him to Yuma to work. Better to have a skill that is called for before he comes here as it's rather expensive to live here.
    Last edited by MarkBall2; 03-09-2009 at 01:08 AM.
    Mark
    I haven't always been a nurse........
    Craftsman 12"x36" Lathe
    Enco G-30B Mill
    Hobart Handler 175
    Century 230 Amp A/C stick welder
    Add a Foot Pedal to a Harbor Freight Chicago Electric 165A DC TIG
    PapaLion's Gate Build

  5. #5
    Join Date
    Feb 2008
    Location
    North of Philly
    Posts
    16,057

    Re: Generator sizing

    Mark I've gone back and forth on the gen set vs welder/generator for quite a while. I really wished I had nabbed a natural gas gen set I could have grabbed for next to nothing years ago and passed on it due to lack of space.

    I've found new, a 10Kw gen set is close to what you will spend on an inexpensive welder/ generator like a hobart or small bobcat with a 10 Kw Ac generator new.

    I keep my eye on CL and most I see are small units 3500w - 5000Kw (3.5kw-5KW) very few that are larger unless they are much larger (25KW +) and at higher prices than a new 10K unit.

    I do see used welder/ generator rather frequently in the $1500 range with 7KW-10KW AC.

    If you are thinking about your son doing welding, I would lean towards a welder/genset rather than a plain genset. You will get more bang for your buck. Most new welder/gensets give you CC/CV options for stick, mig and tig, although some older units are CC only. Generally you get more weld power from a dedicated welder/genset than you do running a welder off the AC genset. Example a Miller Legend will give you up to 300amp DC stick and 33v /300amp mig, but only 5000w of AC. If you go to the bottom Bobcat you drop to 200 amp AC/dc stick, tig and mig but at 100% duty cycle, and jump to 11.5 KW on the gen set (which would be border line to run my sync 200).

    One thing to remember on small gensets, they frequently produce less than the stated watts on cont. power. I think my 4500w unit is 4500w peak and only something like 4000w cont power. so don't forget to look at that if you choose a generator.

    Good luck.

  6. #6
    Join Date
    Apr 2008
    Location
    Yuma AZ
    Posts
    2,479

    Re: Generator sizing

    I was just checking on Craigslist - actually used the Craigslist helper (http://www.craigshelper.com) to search - they have lots of welders listed. Most of the gen/welder sets go near new prices & some of these are close to 5-10 years old. Not that it matters on age, but some people think their stuff is gold.

    I would prefer to get my son a welder/generator, but then I would still need a generator for here. I figure with a bit of care on the genset, it should last as long as I will. I've seen the 7.5kw gen sets around $500, and they have constant output around 7kw. The ones I've looked at also have 50A 220V outlet on the side, which will work with any welder I happen to obtain. As I don't have anything that requires 50A, I figure that should be close to what I need in size.

    For the son welding, I figure a minimum of 10kw constant output & a used engine driven welder would be worth the investment for him. I've seen a couple that need new engines for around $500-$700, but then it takes some tinkering to get it up & running. Most of the others I've found go anywhere from about $2K up to $5k.......... close to new prices.

    This will probably only be used for my hobby use, maybe once a month or a couple weekends a month. I don't plan on building trailers, hitches or repairing farm equipment, but more for little jobs that I have a 'Honey-do list' for.

    Thanks guys, your input helps alot.
    Mark
    I haven't always been a nurse........
    Craftsman 12"x36" Lathe
    Enco G-30B Mill
    Hobart Handler 175
    Century 230 Amp A/C stick welder
    Add a Foot Pedal to a Harbor Freight Chicago Electric 165A DC TIG
    PapaLion's Gate Build

  7. #7
    Join Date
    Sep 2006
    Location
    NJ, USA
    Posts
    3,386

    Re: Generator sizing

    Mark,

    As mentioned, you can't make your own electricity for even close to what it typically costs to buy it from the electric company.

    You're paying what, about 20 cents per kilowatt-hour or so from the electric company?

    If you have your HH187 cranked up on the 30 amp circuit (the 19.5 amps is probably at "rated" output, which for those 'class' wire-feed machines is 130 amps output at 30% duty-cycle, I don't feel like looking the actual spec up on Hobart's website, but we'll just go with the circuit specs for now), that means you are pulling in 30 amps x 240V of power (ignoring the machine running 'above' the breaker max and relying on the duty-cycle to keep things cool enough not to trip the breaker) and that means 7200 watts incoming power. That means to run the machine for a full hour of arc-time means it costs about $1.44 (at 20 cents per kilowatt hour from the power company). That's not an hour in the shop/garage time, that's a full hour of non-stop welding at 30 amps of incoming amperage.

    A big enough generator to supply that much power is going to drink gasoline at about a gallon an hour (or more). How much is gasoline runnning by you nowadays? At $2.00 per gallon, that generator is costing you at least $2.00 per hour to run just in gas costs! That isn't including the purchase cost of the generator or any maintenance costs either.

    And a welder may or may not have a big in-rush current demand. One example is running a 'tombstone' stick welder off of a generator. You think it only needs about 20-30 or so amps of incoming power(only a 6500 watt generator), but because the transformer is not all that efficient and there is a big in-rush current, the actual generator needed is a MINIMUM 15,000 watt generator.

    http://www.lincolnelectric.com/knowl...generators.asp

    A generator is often handy. For instance in an emergency situation (but you have to have stockpiled enough gasoline ahead of time to run the generator) or in a remote situation where there is no power pole around (mobile welder, remote farm or cabin, etc).

    But they are not usually a cost effective option IF you have power available from the pole.

    The pool pump is probably a bigger cost on the electricity than your welder is.

    Unless you are doing a LOT of welding. As in hours of welding per day, almost every day.

    The TV and computer on all day could easily be the $35/month. Running a single 100 watt bulb 24/7 would cost you $14.40 per 30 days at a cost of $0.20 per kilowatt hour from the power company.

    And the same general justifications apply for an engine-drive welder/generator. Handy yes, necessary sometimes (for mobile/remote work), but usually not more cost-effective compared to plugging into a power outlet.
    The best laid schemes ... Gang oft agley ...

  8. #8
    Join Date
    Dec 2007
    Location
    Los Angeles
    Posts
    5,334

    Re: Generator sizing

    There is so much Ghost power being consumed these days it is retarded.

    Nothing is actually OFF.

    Got a couple Wall Warts- ya know the little bulky plugs for our Laptops, cell phones etc etc- if they are plugged in they are on.

    Cable box, sat box, DVD player- On-even when you turn the Power button OFF they still consume juice.
    Ed Conley
    http://www.screamingbroccoli.com/
    MM252
    MM211
    Passport Plus & Spool gun
    Lincoln SP135 Plus- (Gone to a good home)
    Miller 125c Plasma 120v
    SO 2020 bender
    Beer in the fridge

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