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Thread: Single Phase? Three Phase?

  1. #1
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    Single Phase? Three Phase?

    I’m getting pretty close to ordering a fair amount of equipment to set up a semi-professional shop and have a question about single and 3 phase. Which would be preferable? Many of the machines I’m seriously considering come either way for the same price. The only thing I would need 3 phase for is a belt sander If I decided I needed one at a later date. Any pros or cons?

    Terry

  2. #2
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    A lot of the professional machines as 3-phase. For most hobbiests it is not an option as 3-phase power is rarely available in urban housing communities.
    Ken

    So much to learn, so little time.....

  3. #3
    Three phase is a simpler motor less troubles it is said. Also I believe I heard less to operate. But I don't think it is worth mentioning at the small shop level. When you go to sell off 3 phase equipment to up grade or whatever you can expect less return in most cases due to less demand because people do not have access to 3 phase power. So you pay the same get less back.

    Tony

  4. #4
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    3 phase is more efficient because the armature in your motor is "pushed" three times more frequently compared to single phase. You'll find that three phase gear is generally more powerful (in terms of horsepower) because of this.

    It's pretty unlikely that you'll be able to get 3 phase service installed at your home--well, at a reasonable enough cost anyhow. I'd say that it's overkill for most hobbyists, but if you really need/want it, you can buy phase converters. Just search around online. You can also build your own out of a three phase motor if you're feeling handy and want to manually start it with a rope each time you need 3 phase power.
    Last edited by jeff begin; 02-07-2009 at 1:06 AM.

  5. #5
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    Thanks for the input

    I didn't think of the lesser re-sale value of the 3 phase equipment. Getting 3 phase isn't a problem since I will be operating in an industrial area and 3 phase is readily available. I think from what I've seen is I'll stick to single phase and get a converter if I do need a piece of equipment that only comes in 3 phase.

    Terry

  6. 3-phase electricity is already a rotating field and this means the motor does not need to artificially create one, which makes the motors start smoother. However, they are not necessarily cheaper to run, nor provide more power. 3-phase motors are preferred when 3-phase power is available, but I fear that some people reading this discussion will take that too literally and seek out 3-phase motors when they do not have 3-phase available.

  7. #7
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    my shop is 3 phase I would not have it other wise. pro machines are 3 phase most often, and 36" and larger wide belt sanders are almost always 3 phase. I don't buy the resale argument. if you are running cabinet saws, fine, get a single phase one so if you have to sell it, you can to joe hobby guy. BTW - a 208 Y will also give you single phase as well for those machines that are not 3 phase. you are going to find a better selection of good used 3 phase machines on the used market if you are looking at industrial machines

    lou

  8. #8
    I agree with Lou - three phase is the way to go for large motors.

    There are some costs involved if you don't already have the service, even if it is available in your area, primarily in the area of wiring your shop for three phase. But if you don't already have the shop wired, doing it in three phase is not much more expensive than single phase.

    You will need single phase in the shop in any case for smaller equipment.

    Jeff's comment that three phase is more efficient and powerful is not correct. A three phase motor is wired so that it only has one rotating magnetic field (not three). And the efficiency (power in to power out) is about the same for three phase and single phase motors of the same size and design (large motors are generally more efficient so you can't compare a 10HP 3-phase to a 1HP single phase).

    The big advantage of three phase is simple design (no starting circuit - less to break) and better starting torque than capacitor start single phase motors.

    Mike
    Go into the world and do well. But more importantly, go into the world and do good.

  9. #9
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    I have 3-phase

    My old shop was in an industrial building and it was pre-wired with 3-phase. When I moved, the projected cost of adding 3-phase was $25,000. Now I have a 3-phase converter. Figure the converter, assorted control units and electrician cost over $1000. A converter isn't as good as having 3-phase from the power company, it can breakdown, it has to be turned on (get remote start, if you do a converter), etc, etc.

    Unless someone could convince me that 3-phase is better, which hasn't happened so far, I would go with single phase. The kinds of machines I have and you are talking about, will run very well either way.

    Have fun.

  10. #10
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    In my area, I can only get 480 volt 3 phase, not 208. In the case of my Felder saw, I'd have to buy a step down transformer because it could only be used with 208 volt. Make sure that the motors can use your available voltage. One more thing to check out. I do live in a very rural area, and we use 3 phase for our 100hp irrigation motors, so that is why the company only supplies 480 volt.

  11. #11
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    IIRC,you have to have something like 15 or 25 electric motors in your shop,IN USE OR NOT,to get 3 phase.I knew an old guy who sold a few machine tools out of his home machine shop. He told me that,but it was long ago.I could be wrong about the figures,or it could be different on other areas.

    I wouldn't be concerned about 3 phase for wood working. In metal lathes,surface grinders,and some other such machines,they run smoother with 3 phase,and it definitely shows up on turned and ground finishes. These surface flaws from single phase are on the order of 1/250 THOUSANTHS of an inch- .0000025". It shows up quite a bit on reflective metal. You'll never see it on wood.

    Some industrial machines are only 3 phase as the motors can be smaller,and 5 hp. is about the usual limit for 1 phase current. My shop has 6 gauge wire to my large lathe,should I want to go to 10 hp. ever.

    If you get an old industrial machine that is 3 phase,get a rotary converter,not a static converter. Static is cheaper,BUT gives 2/3 the actual power of the motor. That might be o.k. for some machines,but keep the loss in mind.Rotary units give true 3 phase power,keeping full hp. Static units only use some of the motor's windings,losing power.

    For metal machinery,the new thing,and CHEAPER,is to buy a VFD unit(variable frequency drive). It converts 1 phase to 3 phase,and varys the 60 cycle frequency so you have that benefit on a lathe,or mill.You can vary the speed of your machine by turning a knob. You may have seen Grizzly sells sells some VFD drive metal lathes. I have a VFD in my belt grinder. It is great for hand grinding of knife blades,when an accidental false touch on a fast belt can put a bad dollop on a nearly finished blade !! Especially when you are old and nervous like me!!

    You can OVERSPEED the motor,too. That could be DANGEROUS on already high speed wood working machines. Blades could come loose,bandsaw tires swell out and fly off. I had that happen once in my beginning days!! I got a powerful motor cheap,and put it on my 14" Delta bandsaw. It had such high starting torque,it caused my bottom tire to gain 2" in dia.,and fly off!! Be careful not to overspeed if you go the VFD route. If you search,certain companys make affordable rotary phase converters. I can't recall the name,but my replacement person got one pretty reasonanle,but still not a cheap item. Dempsey and Co. in Richmond make low cost units. I have 2.

    Lastly,VFD units destroy radio reception unless they are on shielded steel cabinets in use,BUT,they need to have ventilation,or burn out.
    Last edited by george wilson; 02-07-2009 at 1:28 PM.

  12. #12
    Terry,

    I prefer to stick with single phase service myself.

    Some of the tools that I've looked at that come both ways include a digital 3 phase inverter that converts ordinary single phase power into 3 phase. If a tool you want isn't available in single phase you can always buy a digital inverter yourself like the one in the picture for under $300.

    The claim made by the digital inverter manufacturers is that there is no horsepower loss as is the case with converters, which are essentially motors. The digital devices include some safety features too, such as GFI protection.

    The Powermatic 3520B lathe is an example of a tool that comes both ways. It includes an on board digital inverter. One of it's features is that in the event of a power failure it requires the lathe to be turned off and then back on before it will run again.
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  13. #13
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    The inverter is the same as the VFD as described above,so there is no confusion.Just another name. IIRC,a 1 hp. unit can be had for about $100.00. As with rotary converters,it MAY be necessary for the VFD units to exceed the HP. of the motor. I can't recall right now. I have used rotary phase converters on my present 3 phase equipment. Haven't yet put my 2 inverters to use. As I am not an electrician,I don't want to give advice beyond what I have. It should get you started on your own research.

  14. #14
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    Since your talking about a shop in an industrial building there will probably already be 3 phase available. I have both in my shop and am gradually converting all my machinery to 3 phase industrial equipment. If your doing this to make money, (which I assume you are since why else would you lease space?) the business pays for your machinery. Making re-sale much less an issue.
    Also consider that with 3 phase you can run machinery at higher voltages meaning smaller gauge wiring saving money on that end of things. But the most important thing about having 3 phase is the ability to buy used equipment you couldn't afford new. Your average home shop guy might not appreciate the difference between a $2000 20" Grizzly planer and a $10,000 20" SCM, but believe me when your trying to get work out the door and make money, there's a huge difference.
    good luck,
    JeffD

  15. #15
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    Terry, I too am in the midst of setting up a large shop and researched this question some months back. In my instance, I do not have 3-phase power available so that added another dimension to my research (generator).

    The bottom line that I arrived at was if your equipment is primarily 5HP and below, single phase is adequate. If you have a significant amount of motors in excess of 5 hp, consider 240V three phase.

    For equipment with motors in excess of 10 HP, consider 480V three phase.

    From an electrical consumption perspective, you will lose some efficiency operating three phase equipment through a rotary phase converter. I don't recall the exact amount, but it's around 15%. However, if you only operate the equipment sporadically, this may not be a big issue.

    The greatest benefit of 480V 3 phase versus 240V three phase is your wiring costs. Basically the higher the voltage the smaller the wire. This can amount to a significant cost savings if you have to install wiring for a 30hp electric motor.

    In most places, if you end up with some 240 and 480 3 phase equipment, it is more efficient to bring in 480 and step it down than to bring in 240 and step it up.

    I opted to generate 480V three phase for my shop, and to transform it down for the equipment that requires 240V three phase. This will allow me a lot of flexibility in the future to purchase and install a wide variety of equipment in the future, as most large production equipment is wired for 480V 3 phase.

    Hope this helps - good luck with your new endeavor!

    Scott

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