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  1. #1
    Join Date
    Jan 2006
    Location
    Blue Mountains NSW Australia
    Posts
    408

    Default More phase converter questions

    Hello all,

    I have decided to bite the bullet and get 3 phase going in my workshop.
    I have 7 machines that now have single phase motors. I plan to change these over to three phase, and to sell of the single phase motors to help fund the changeover.

    I have a 10hp 3 phase motor to use for the idler, and I also have several smaller 3ph motors lying around from 2 to 5hp. My workshop has 4mm/sq active and neutral supply, to a sub board with earth stake at the board. I presume I have the required 40amps single phase at the sub board, as the supply easily starts my biggest single phase motor, being a 4hp 4 pole on a large stroke sander.

    So...... my questions after plenty of reading about this stuff on mainly US sites:

    Do I need a step up transformer to get 415 single phase, before conversion to 3 phase, or am I reading correctly that the idler motor will generate the required 415 3 phase from 240v single all by itself?
    If it will, do I need to spin up the idler motor first, with a smaller single phase motor to get it all working, or will the idler motor start and produce 3 phase without initial external rotation?

    Has anyone here actually built one of these with Australian 240v 50hz single phase supply?

    Reason for changing over??

    1. I used to have a larger shop which had 3 phase. Since moving about ten years ago, I haven't been able to run my spindle moulder, which would require a 7hp single phase motor, which is too big for my available power. I have been using a router table for that time, and I am sick of it, considering the moulder has a 2hp feeder as well.

    2. I have plenty of 3 phase motors laying around, and can get what I don't have very cheaply from my brother.

    3. I have been offered a nice wide belt sander that needs 3 phase as well, and I can sell my stroke sander for a couple of hundred less than getting this nice wide belt sander fro a fiend who has now retired.

    I hope I have explained this well enough.

    Thanks in advance for any assistance.

  2. #2
    Join Date
    May 2003
    Location
    Kuranda, paradise, North Qld
    Age
    62
    Posts
    65

    Default

    Fossil,
    there's some people living nearby who have an unwanted rotary phase convertor at their place, I could enquire about it if you're interested. However, I believe it's a 2 phase model ( 2 seperate phases in, 3 phases out). If there's 3 phase power running past your door you may find it cheaper to get connected rather than building/buying a convertor. When I ran the power for my shed from the house board I ran an extra cable for a third phase (had two already). The cost of connecting the third phase was minimal: a new main switch, connection box on fascia, a few metres of cable and of course all the three phase breakers and outlets, which you'd have anyway if you were using a convertor. The power company fitted a new 3 phase meter for free as well as a new ABC (aerial bundled cable). I did the work under supervision of my neighbour (sparky and electrical inspector ) and this was perfectly legal. Cost me a couple of hundred dollars all up for all the bits and pieces.

    Mick
    "If you need a machine today and don't buy it,

    tomorrow you will have paid for it and not have it."

    - Henry Ford 1938

  3. #3
    Join Date
    Apr 2002
    Location
    Brisbane
    Posts
    429

    Default

    Just a couple of things.
    Why would you convert perfectly good single phase machines when you have a single phase supply?
    I can undarstand that you want to run your 3 phase machines, that is a seperate issue.

    40 amp single phase isn't a hell of a lot of power, I reccon ,by the time you account for conversion losses, you will be pushing slimy stuff up a very steep hill with a pointy stick to run your 7 HP motor.

    In this day and age I'd be looking at an electronic convertor, they are a far better prospect.

    better still I recon you need a supply upgrade, 40 amps 3 phase minimum.

    step up transformer .... no.

    three phase works like this.

    there are three phases,
    If you are running single phase, you have one of them. between the pahse and neutral measures 240v aprox. neutral is the same potential as earth.
    all 3 phases measure 240 v to neutral.
    By magic (or sequebtial phasing) there is 415v measured between any two actives.
    from there is gets complicated.

    I think you are barking up the wrong tree.
    I think you are dreaming if you think you are going to home brew a phase converter to do 7hp.
    I know you have no chance at all of getting it to pass inspection.

    sorry but thats the way I see it.
    cheers
    Any thing with sharp teeth eats meat.
    Most powertools have sharp teeth.
    People are made of meat.
    Abrasives can be just as dangerous as a blade.....and 10 times more painfull.

  4. #4
    Join Date
    Jan 2006
    Location
    Blue Mountains NSW Australia
    Posts
    408

    Default

    Thanks for the replies guys.

    Mick.. thanks for the offer, but I don't have dual phase here.

    Soundman,

    I think you are barking up the wrong tree.
    I think you are dreaming if you think you are going to home brew a phase converter to do 7hp.
    I know you have no chance at all of getting it to pass inspection.

    sorry but thats the way I see it.
    No need to be sorry, I like to hear it straight, so thanks for your advice.

    I'm not giving up though.

    I hope to move bush again in a year or two, and plan to use a phase converter in new premises, so It won't go to waste, even if I can't use it here. 3 phase supply connected to front of present property is just under $4000, and I have ongoing charges. I would also have to dig up present supply to workshop from front of property and cough up more loot for that to be upgraded to 3 phase.

    When I originally referred to 40amps supply at present, It was within context of article that I read that suggested 40amps as satasfactory supply for the idler that I have. The power to workshop is single phase by way of 4mm cable over 30m that is taken off a 16mm supply cable. It starts a 3kw single phase motor, without the lights in the shop dimming, and I estimate it draws over 60 amps at start up. The 10hp / 7.5 KW idler should draw 18 amps when running based on calc of 7500/415 = 18amps

    So.... I plan to start the idler with a spare single phase 2hp motor, which should reduce the amp draw way down nearer the 18amps on startup of the converter. Once running, I hope to be ok.
    If it doesn't work so well, I can drop the moulder motor down to 5hp. I think I have a spare 5hp up in the back shed, or mabey it is 5kw???? will have to check.

    If needed, plaese call me stupid, however that has been done before, and I generally come out on top with a bit of effort.
    I would like to give this thing a go, and post my efforts as I go for constructive input, insults or donations.

    Thanks again.

  5. #5
    Join Date
    Jun 2006
    Location
    bendigo. vic
    Posts
    0

    Default three phase from single

    Suggest you "Google up" Ferrarasano system. Also Plough Books have some interesting stuff on this project.Good luck with it.

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