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  1. #1
    Join Date
    Jan 2004
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    Bellingen
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    Default Are two compressors are better than one?

    I did post this up at the end of a long thread on me fixing my air compressor....which got fixed (I don't know if I'm happy or sad about that yet).

    It's worth reposting as it opens up a few options and a bit of debate from the brains trust!

    I stumbled across an online forum with a guy needing a lot of air only sometimes. Occasional spray painting, sand blasting,bigger air tools etc but most of the time it's used as an air duster or tyre inflator.
    If your not a panel beater or pro spray painter I think that situation fits a lot of us.

    His take on it was to buy two top end single phase compressors and plumb them in together.
    Using one of the pumps to fill one or both tanks plus shop lines for general usage. If the tool required more air, switch on both compressors and double the output.

    He compared the prices of two single phase compressors against a single twin pump and twin motor set up as well as an equivalent 3phase unit and the two separate compressors come out well in front as far as price, running costs and storage (one on top of the other on the wall).
    You can take one with you if your out of the workshop. You can't really take a twin motor unit easily and three phase units are pretty much stationary.

    Their are draw backs though. It makes no sense if you use a lot of air. 3phase is cheaper to run and the quality motors are cheaper and last longer than an equivalent single phase.

    You have to check out your power board as most small shops will only have a single 20A power circuit or a mixed light/power circuit. Grab a sparky if your not sure.
    If you going to rough in new lines to your workshop, run 2 new power circuits (provided your board can take it). It will cost bugger all extra as the money is in the callout, and time to rough the line in. An extra line and safety breaker don't cost much at all and don't add much work time.

    Food for thought but a two separate single phase compressors suit my workshop better than a 3phase unit.
    That is unless you guys find a flaw in it....I haven't as yet. Maybe the noise when both are running but I'm building another room outside the shop for the dust extractor and compressor.

  2. #2
    Join Date
    Sep 2002
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    Minbun, FNQ, Australia
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    2,012

    Default

    Yup, some of us can't get 3 phase.

    Another trick is to get a second tank off an old compressor as a 2nd receiver.
    It give you more capacity & if you run a long line between the 2 tanks, it gives the air time to cool & any water in it can condense so your water traps work better.

    I have a big compressor down one end of my shed with a long hose to a smaller tank on wheels.
    I set the regulator on the first tank high.
    The second tank is close to where ever I work with a short hose & a 2nd regulator & water trap & that regulator is the one I adjust to suit whatever I'm using it for.
    Cliff.
    ...if all you have is a hammer, everything looks like a nail...

  3. #3
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    Default

    For occasional home use, nothing beats having two compressors. There are no downsides, just many many upsides.

    But for someone needing lots of air, every day, running two compressors is just not an efficient choice. There is more maintenance. And higher electricity bills, because multistage compressors are much more efficient at transforming energy into air flow and pressure. Plus larger 3 phase motors are more efficient, and more reliable than single phase motors.

  4. #4
    Join Date
    Jan 2004
    Location
    Bellingen
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    278

    Default

    Your more likely to get a discount buying two at the same time!

  5. #5
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    Aug 2011
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    Default

    Maybe a bit off topic but the conversation of not having 3 phase available comes up an awful lot. For many who live in a rural area or on larger properties it's never going to be solved but for some it may be worth simply biting the bullet, paying the extra $2000 or so and getting 3 phase to the house. My shed is about 100M from the street and I'm still considering it. Not sure what it would cost in my situation. I just know that I am now kicking myself for not doing it when we built but the builders at the time quoted me an astronomical amount to do it….. more than was reasonable IMHO.

    Sorry, doesn't really contribute to the topic does it?

    Simon
    Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.

  6. #6
    Join Date
    Jan 2004
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    Bellingen
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    Default

    I think it does as it's a consideration when setting up any shop.

    I had a carpentry/electrical business with a mate when I was in Sydney. Worked out really well actually. I ran the building jobs, he ran the electrical and we worked most of the jobs together...And I made money hanging out with a great mate! The skill sets supported each trade nicely and we both got to learn something new.

    A lot of the time with running new circuits, the cost was roughing in the lines. The cable and breakers were a small part of the money in comparison.
    I'm spoilt here on the farm and have not even used it yet! I have three phase and a single phase in the workshop but have not bothered to set it up right yet! Everything including the lights are on one circuit! Not good but I never overload the circuit. I guess it's like the mechanic having the worst car in the street scenario.
    It's something to take in to consideration though, as I have it but not really needed it...yet.
    If only one person is in the shop, two power circuits should be plenty for most people. I can only run one piece of machinery safely at a time and add a dust extraction or compressor on a second circuit and you have most situations covered.

    I will be getting on to that soon enough though. I have not needed any 3phase equipment yet but I will be taking advantage of having four 20amp circuits.
    It would be nice not having the lights dim every time I start something up.

  7. #7
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    Jan 2004
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    Bellingen
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    Default

    Simon, have a chat to the sparkie about roughing in your own line. In your situation it's still a sizeable part of the cost.

    If you get a sparkie who also has a ticket to work up the pole on the street it will work out a bit cheaper still.

    Some won't like it, most will appreciate the trench being dug ready for the cable. If it's easily seen ( to be above standard) sometimes they won't mind if you mount the board and pull the cable through as well. It depends on the tradie as in the end, they sign off on the job and are responsible for it being safe. Sparkies are constantly made to update their skills to new safety standards.
    The electronic meter costs you the same if it's single or three phase.

  8. #8
    Join Date
    Jul 2010
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    Melbourne
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    Do It Simon. If only to update my prices. I had a chat with a sparkie mate over 10 years ago, he started with "you'll need two new panels at $700 each+ + + +". I've since heard stories about having to lie to the supplier about fitting a 3 phase air con or they aren't interested(and who can blame them?).

    Stuart

  9. #9
    Join Date
    Apr 2013
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    adelaide
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    293

    Default 3 phase conversions

    Cheaper to run, but how much would it cost to convert lathes, mills, etc, to three phase.

  10. #10
    Ueee's Avatar
    Ueee is offline Blacksmith, Cabinetmaker, Machinist, Messmaker
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    Why would you want to convert machines to 3phase. Look at all the threads about using vfd's, just imagine being able to buy any machine and plug it in. No worrying about star points, 2 speed motors etc.

    Stu, I fit in to the 3phase air con con category......

    Ew
    1915 17"x50" LeBlond heavy duty Lathe, 24" Queen city shaper, 1970's G Vernier FV.3.TO Universal Mill, 1958 Blohm HFS 6 surface grinder, 1942 Rivett 715 Lathe, 14"x40" Antrac Lathe, Startrite H225 Bandsaw, 1949 Hercus Camelback Drill press, 1947 Holbrook C10 Lathe.

  11. #11
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    Quote Originally Posted by th62 View Post
    Cheaper to run, but how much would it cost to convert lathes, mills, etc, to three phase.
    Though I doubt the "cheaper to run" would mean much with my usage. Speaking for myself. Pretty much all the machines I own are 3 phase(11 motors the I can think of). Just lathe*, compressor and a few of my bench grinders are single phase.

    Stuart

    *the laths single phase days are numbered. Though at the rate I work it might be a big number lol

    p.s. lol air con con
    Last edited by Stustoys; 19th May 2014 at 02:44 PM. Reason: p.s.

  12. #12
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    Quote Originally Posted by th62 View Post
    Cheaper to run, but how much would it cost to convert lathes, mills, etc, to three phase.
    Wrong question. Very, very wrong question.

    Industrial machines *come* with 415V 3 phase motors. The cost & aggravation is converting them to run off a single phase supply. See endless threads here WRT star-delta conversions, 240V VFDs etc etc etc ad nauseum.

    I paid *once* for my 3 phase supply. I have it forever, effectively. I *never* have to consider if I can run anything I can reasonably haul home.

    As for costs, variable feast. A sub board without breakers costs less than $100. I know, because I recently added a 13 slot one. A 32A 3 phase breaker is around $60, you need 2, one for each end. 6mm2 5 core cable costs around $6.60/m, how many metres do you need? Add other breakers to the sub board as required - I run a high amperage 5 core cable then pick off my workshop single phase circuits from the sub board, using RCDs on that board. Cuts down messy cable runs and keeps the workshop stuff off of the domestic power supply assuming you run a line from the main board.

    Trenching to standard is a site specific cost but you can hire baby excavators for less than $400 for a weekend where I live.

    Electrician's costs really shouldn't be more than 4 hours if you do all your own cable runs to their standard and satisfaction. I've yet to meet one who actually *likes* running cable.

    In over 30 years of building my own workshops and arranging for power connections, I've yet to have any problems getting 3 phase power connected. IME the difficulties are just a myth. Cost is there but - this is an expensive hobby, if you want to own & use big machines, bite the bullet and pay.

    PDW

  13. #13
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    Default

    Quote Originally Posted by PDW View Post
    A sub board without breakers costs less than $100.
    Things have moved on I see. Pity I no longer have a friendly sparkie(with the required paper work).
    Couple of questions.
    What does the supplier charge to connect 3 phase to the main board and new meter?(or is it free and they assume they will get their money back over the next 20 years)
    What(if any) is the increase in supply charge of 3 phase over single phase?

    Stuart

  14. #14
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    Jan 2004
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    Bellingen
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    Default

    You will have to pay to get it to your board from the power pole on the street. But the 3 phase meter costs the same a single phase. The supplier (soon to be china) pays the extra for the meter as they own it. From memory the three phase meter was $60.... That was about 6yrs ago when I upgraded my workshop in Sydney.
    Things could have changed.
    All they wanted to know is if I was wanting to run 3 phase machinery... That was another sparkie mate so he could have fudged the paperwork so I could get it.

  15. #15
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    Jun 2008
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    At the start of last year (2013) I bit the bullet and had mains 3phase installed, I was sick to death of phase converters and vfd's. And with the amount of 3phase stuff in my workshop it was a never ending battle. That and the 240v supply that I had was questionable to say the least....

    It cost me little under $5400.00 To get the 3phase from the power pole out the front to the house, Then run 40 meters from the main board on the house to a sub panel in to shed. The a 16mm cable from the house (thickest cable I have ever seen) At the time I had 1 32amp outlet installed because the sparky wanted $350.00per outlet and wouldn't use the ones I had purchased prior for $20.00 each brand new ( o I had a mate install 5 more points a week or so later (he is a sparky also, and it only cost me 2 sabs)

    So like PDW said, I made a $5,500 investment that is a once off. Unless sell the place.

    Matt
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