Motor Phases

I'm setting up a hobby machine shop and am getting into the issue of 3 phase motors. Most of the motors are going to be in the 1 to 3 horsepower range.
For motors of this size, why would I want to have make three phase power to run these machines instead of just swapping out the motors for single phase?
Thanks. Steve.
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If you can swap out the motors for less than it will cost to get a converter...go for it. I'm sure that many others will respond and this is the place to be for converter and other power related questions.

phase
range.
to
phase?
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Well, I can tell you why I chose to put in a home-made rotary converter: one of the machines I bought had a two speed pole changing, three phase motor, and I wanted to keep that motor in place. For the lathe, I found that real three phase provides the advantage of plug (instant) reversing.
And then later, I found I purchased yet another (hardinge) machine with a similar two speed motor.
The cost of the phase converter itself was miniscule compared with the cost of changing those three motors, or installing a VFD for each machine - aside from the convenience aspects.
Jim
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Three phase motors are an order of magnitude cheaper. Machines powered by three phase motors have inherently less vibration. (Think about it - 120 times every second the power applied to a single phase machine is instantaneously *zero* ..) Many industrial motors e.g. motors that come on a Bridgeport mill are much better quality than cheap single phase replacements.
Good question!
Grant Erwin
SRF wrote:

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phase
range.
to
phase?
There are a number of answers. As others have said, industrial 3 phase motors are much better made than the cheap single phase equivalents. Used 3 phase machinery is generally cheaper than single phase stuff. You only need to make one converter instead of buying a number of separate motors so the total cost is less. A number of machines use non standard motors so replacing them is difficult. The answer quoting 120 times per second that the power is zero made me think a bit. The first reaction was to realise that you are on 60 Hz mains and we (UK) are on 50 Hz. The other thought was that a single phase motor doesn't actually rely on single phase as such but it makes another phase by use of an inbuilt capacitor. This second phase is frequently of a lower power than the primary phase though hence 3 phase is generally a better motor.
John
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    Amen!
    Again amen.

    Correct -- or you can set up a VFD (Variable Frequency Drive) to generate three phase at the machine, which offers you the advantage of being able to fine-tune the motor speed (while it is running) to eliminate chatter.
    I would suggest that for machines which have only steps in their speed selection (e.g. gears or belts and step pulleys), the VFD is preferred, while for those with variable speed pulleys, and for running multiple machines at a minimum initial investment, a home-built rotary converter (built around a larger three-phase motor, some capacitors, and some voltage-sensitive relays) would be the better choice.
    For long-term operating cost, the VFD will put more of your energy budget directly into the motor, but the initial investment is greater.
    *My* choice is VFDs. I have two machines which currently have three-phase motors, and a third three-phase motor ready to go into my lathe to replace the existing single-phase motor.

    Well ... that depends on the motor. There are some single-phase motors (capacitor-run motors, and hysteresis-synchronous motors (which would be found on audio turntables and tape recorder decks, not on machine tools)), but most found on machine tools are only capacitor *start* motors -- the manufactured second phase is present only when the motor is at a standstill, or very low speeds, just to get it started in a desired direction, and more quickly. If you are starting in under load, it is possible to spin a motor by hand, then switch on the power, and do entirely without the starting capacitor. And once the motor is up to speed, the starting capacitor and winding are disconnected automatically, so you are back to the once per 120th of a second (or once per 100th of a second in the UK) zero power point.
    For surface grinders in particular, the three phase motors produce a much better finish than the single-phase ones -- thanks to the vibration introduced by the zero-power points.
    Enjoy,         DoN.
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At the face of it this would seem to be the case, but the really odd part is, folks who have some machines like the monarch 10EE, or the lathe with the variable speed drive that everyone dislikes (I think this is either a rockwell, or a delta, or maybe it was both) seem to say, the varispeed drive is a major pain, and they always retrofit with a VFD. But the folks with step belt machines like southbend or the older hardinges, seem to get along fine with step belts.
Where the VFD really shines though, IMO is in a drill press. Just *so* handy for getting the right speed.
Jim
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    I've seen a lot about the problems with the hydraulic variable speed lathes produced by Clausing. It seems that they are just getting to be old enough to have problems with the hydraulics by now.
    My Clausing is a 1957 one with the step pulleys. And there are times when I would like to be able to reach out to a knob and tune the speed without interrupting the cut. I also would like the ability to reverse the spindle without having to wait for the motor to coast down to near a stop (when I'm tapping with the turret), hence the desire for a three phase motor, and a VFD (with the reversing being done by commanding the VFD to reverse, not by switching the motor windings. I can get away with that with the vastly oversized (e.g. 30A) VFD which is currently running the 1HP motor on the Nichols horizontal mill, but I could not do so with a VFD which is a closer match to the motor's horsepower.
    As for the Monarch 10EE -- that is because the electronics for the older ones is getting to be rather expensive to keep going (replacing the big old thyratrons to drive the motor), and some of the newer replacement electronics is showing up as rather fragile. Probably the best in terms of long-term service is the old motor-generator style, which I used to use at work.
    A friend in the local metalworking club (CAMS) has recently done a marvelous job of marrying a three-phase motor to the original gearbox in his 10EE -- to be driven from a VFD, of course.

    If it were not for the turret tapping work, I could probably do without the upgrade, but I must admit to not always selecting just the right speed for a given operation, thanks to having to squat down to access the motor lever and belt for the changes. :-)

    That is something which I need to do some of these days. But I also have a hefty permanent magnet DC motor and a matching speed controller, which I may use for the purpose instead.
    Enjoy,         DoN.
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phase
range.
power to

phase?
Here's a site with some info. http://www.processcontroltechnologies.com/Phaseinverter.htm My only experience is with the Toshiba S7. A very cool product, but probably in the $800 range. This is the best I could do for a picture http://www.lbelec.com/toshiba/drives.html It's the one shown in the palm of a hand. Contact TK Electric at 702 293-2310 if you need more info. Why would you want one? Smaller wire sizes, variable speed, variable torque, slow startup, safety cutoffs, etc. Not really needed for woodworking I don't think, and you wouldn't be able to make use of most of the sophisticated programming anyway if you were running multiple motors. Although if you have enough motors, perhaps adding one new device would be easier than swapping them all.
Wayne
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I have been hearing about VFDs and other types of solid state controls. The Phase Inverter seems not to offer variable speed, but lots of features. I presume similar units are available with variable speed.
However, it would seem to me that you would need a specific variable speed drive for each tool, that you would not want to walk to the corner to adjust the speed. That could get pricy.
To me the most practical (cheapest) thing would be to have one convertor for the whole shop, asuming that you might eventually have multiple devices with 3-phase motors.
The way I understand it, the alternatives go something like this.
1. Static rotory converter, simple, only gives 2/3 power, probably costs around $100 for under 5 hp. Probably could be shared by several machines.
2. Rotary converter - full power, could be cheap if you use an old 3 phase motor to make your own, or more expensive if you buy one new. Could be noisy. Often shared by multiple machines.
3. Phase inverter - solid state, I think that you said $700. I think that you said that they could be shared, but you lose some of the sophisticated features in that case.
4. Variable Frequency Drive - the top of the line solution, provides electronic variable speed control. I would assume the top price. I would guess that with some machines, you might want to run part of the machine with the VFD, while running other parts with straight 3-phase power, like the controls. It would seem unlikely that one would share the VFD, but maybe some people do.
What is the price range here? Which of these solutions can be shared between multiple devices? Am I wrong about what I said above? I am trying to make sure that I understand.
Richard
wmbjk wrote:

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you can get a VFD drive for anywhere from around $400 to any large number you care to mention - my wood turning lathe has one built into it. You can get some basic information at Minarik (did I spell that right? they have a web site, www.minarikcorp.com ) and look at their offerings. You can find the things surplus cheaply, if you know how to work on electronics.
http://www.phase-a-matic.com/ is a source for static and rotary inverters - I'm told that their static inverter is around $100

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A lot (if not all) VFD's can use remote speed setting. A 2 or 3 core flex to a potentiometer will do the job. This can then be taken to the machine in use on it's long lead. Remote stop/start/reverse controls are also incorporated into many VFD's. As a thought, I suppose that a VFD could be coupled to a lathe Digital Read Out to set the speed according to the diameter of the work. That way, the linear cutting speed is kept constant as the workpiece diameter is reduced. Very handy for facing cuts. Lots of you will no doubt tell be that this is already the case somewhere.
John
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In principle one *could* run low voltage control lines to each machine, and switch them so whatever machine you are running has the active lines. Sounds like a major nosebleed to me though.

This is what I do, with a simple idler motor setup:
<
http://www.metalworking.com/DropBox/_2000_retired_files/Conv.jpg
<http://www.metalworking.com/DropBox/_2000_retired_files/conv.txt
(the text should be annotated to include the *real* current draw when idling, which is about 200 watts)

The static converters are special sized for each machine, you can't run a large machine with a small converter, or a small machine from a large static converter.

Cost for mine: free, except for the wire and wiring devices. It's so quiet I can forget that it's running and accidentally leave it on.

I haven't seen any phase inverters that don't also incorporate variable speed options. At least for the smaller ones I've seen. YMMV.

Zero to hundreds of dollars, depending on size of load.

All of them to some degree or another. Easiest seems to be the single point idler motor setup, for this factor.

You pretty much understand the issues.
Jim
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You can buy NEW VFDs for reasonable prices. For example dealers electric sells a Teco 2HP for $246. Price is dependent on size. www.dealerselectric.com
I have a Teco 1HP on my surface grinder and 2HP on my lathe. I have a Boston Fincor on my mill. VFDs are the way to go. chuck
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    Yep -- and if you have a single machine which can seriously benefit from the variable speed, put a VFD on that one item. That can be powered from a rotary converter, or from a single-phase line, with the possibility that you will want a slightly higher rating (depending on the manufacturer and model) to run it from single-phase.

    Static and rotary don't belong in the same breath. A "static converter" is (usually) a set of starting capacitor and a voltage-sensitive relay which uses the capacitor to only start the motor spinning in the proper direction, and then switches it out. (There are some versions which have tapped inductors as part of the system which is a bit more flexible, but a *lot* more expensive. The static converter's drawbacks are:
    a)    Only gives you 2/3 of the motor's nameplate horsepower         as you have already noted.
    b)    The voltage-sensitive relay and the sizing of the         capacitors is right for only a narrow range of         horsepower, and may also have problems starting a motor         under load. If you have multiple tools with differing         horsepowers, you may not be able to use a single static         converter for all of them.
    One advantage is that is is probably the least expensive bought     purely at *new* prices.
    Another is that it can be used as part of a rotary converter     built from an old motor -- used to start the motor.

    There are techniques for starting them other than the one     mentioned under "static converter", including:
    a)    "self-starting": where the tuning capacitors are a         compromise value which gets the motor spinning without         any switching at all.
    b)    "Pony motor": A smaller motor is connected with belt         to the converter motor, to get it started spinning, and         then the belt is thrown by raising the pony motor to         slack the belt.
    c)    A pull rope, used to start the motor spinning, just         before switching on the power.
    Note that a rotary converter is better made self starting, either     from the inclusion of the parts of a static converter, or from     self-starting capacitor balance. One reason for this is that if     you walk out of the shop leaving something running (even just     the rotary converter), and power drops for long enough for the     converter to spin down, when it returns, the motor will sit     there humming and drawing excess current. If the circuit     breakers are properly sized, it will pop the breaker.     Otherwise, it might fry the motor without a self-starting mode.
    Note also that a rotary converter can be made better (for a     given size) by "tuning" (the addition of run capacitors -- not     the starting capacitors) to optimize the balance of voltages and     currents in the generated phase to match the other two.
    An additional step beyond tuning is a power-factor correction     capacitor across the line power leads coming into the converter,     best done *after* the rest of the tuning. This minimizes the     out-of-phase current which flows into the idler motor, which may     not affect your electricity costs with home power, though it can     if you are being charged commercial rates. However, it *can*     trip circuit breakers if you are close to the rating, which can     be a nuisance.     

    Hmm ... not sure about this -- I think that it is the same as a     VFD, and the prices need not be that high -- unless you are into     the serious horsepower range. That is probably a brand-new     price for the current model -- which is more than you need.

    I have shared one VFD -- but it is an oversize one for my shop.     It is a 30A one (7.5 HP running from single phase). However, I     now have individual VFDs on a per-machine basis.
    One way to avoid running to the corner for each change is to     remote the controls. Most VFDs have terminals which offer you     the ability to stop it, start it in forward or reverse, and     adjust the speed with a potentiometer. These wires should be     run in a shielded cable -- especially if the reach is more than     just a few feet. Just make the cable long enough to reach to     the worst-case location machine.
    Note that you *don't* want to switch the motor leads at the     machine when running from a VFD, as the spikes created can zap     the output transistors. Instead, you command the VFD to start,     stop, and reverse -- ideally from controls mounted on the     machine.
    If there are electronics on the machine (e.g. a CNC machine, or     one equipped with a DRO, you do *not* want to power those parts     through the VFD, as they may not handle the variable frequency     gracefully -- let alone the variable voltage which comes with     the slower speeds.

    I'll let others specify the prices of the other systems, and I will deal with the kind of prices which *can* be found for VFDs -- if you are lucky, and don't insist on new. That 30A VFD which I mentioned above cost me $100.00 -- at a hamfest perhaps five years ago.
    The other VFDs that I have cost around $300.00 each (some adjustment, as one was 3HP and the other 2HP rated running from single phase). These were when a local individual, looking for a VFD to power his own machines, got to talking with Mitsubishi USA at the right time. It turns out that the had just come out with a new line, slightly smaller footprint, and a few more features (beyond what is needed for a HSM type -- more for industrial controls). He was able to buy a large number of them for a good bulk price, and was selling them locally for equally good prices.
    Then, someone at Mitsubishi got the idea of selling the VFDs on eBay -- usually bringing in more money, though still well below the price of the current models.
    There are at least two web locations which sell VFDs -- both used, and new, for good prices. The one which I remember is <http://www.dealerselectric.com . I'm sure that someone else will point to the other source.
    A VFD from one of these sources (even eBay) can cost you less than a commercially-built rotary converter, though unless you luck into one at a hamfest as I did, it will be hard to beat the price of a rotary built from used parts.

    Most of the above *can* be shared -- with some compromises with some. For running multiple machines, a good oversized rotary converter is probably the best bet. A "static converter" is the least likely to be a good choice for this, especially if you have a wide range of horsepower ratings for your machines. A VFD can work, with the remoted control box, as long as you don't need to run more than one machine at a time, but it can be a nuisance as you move from machine to machine.
    Now to see what others have posted.
    Good Luck,         DoN.
    
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On 21 Oct 2003 23:20:39 -0400, snipped-for-privacy@d-and-d.com (DoN. Nichols) wrote:

No need to throw the belt, just switch the power off to the pony and let it freewheel.

Always use a contactor to supply power to the rotary. The contactor is activated with a momentary push button, then it is held in by auxillary contacts on the contactor. If the power fails, the contactor releases, and won't re-engage until you push the start button again. This way, if the power fails, the converter will be *cold* until you manually restart it after the power returns. You'll also want a normally closed push button in series with the contactor coil. This is your stop button.
Gary
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I remove the belt, Gary, because it reduces the noise output of the converter setup by about a factor of three. The belt and pony motor spinning makes a fair racket.

This is also excellent advice. Unless one is willing to be absolutely fanatic about never leaving a converter that is not controlled by a contactor, it's the way to go.
If a large idler motor spins down and then power is re-applied, there's going to be some smoke, someplace. If one is lucky, it will be in the fuses or circuit breakers.
Jim
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My converter uses a 15 hp idler, and the pony is a 3/4 hp single phase motor. Frankly, I can't tell the difference with the belt on or off. Most of the windage is in the big idler.
Because the running speeds of the two motors aren't exactly the same, there's a bit of a squeal when the big idler first gets power and the pony is switched off (I have the switches interlocked). But that's all.
Gary
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Folks - I'm curious, and would welcome if someone could explain something for me. I notice on this and many other threads that when the topic of making three phase power from single phase comes up, often the use of an idler motor is proposed.
My question is. If you don't need the variable speed function ( ie use a VFD ) why the use of a separate idler motor?
- I have a three phase motor on my drill press and I simply hooked it up in Steinmetz connection - single phase supply across one motor line and a suitably sized run cap ( about 50uf per hp ) from neutral to the third motor phase. Admittedly the starting torque isn't great, but most machine tools start on light-load conditions, and if it is a problem it is simple to arrange for an extra start cap to be switched in during startup.
Its not that I'm advocating one method over another, but the use of idler motors seems so general that I'm assuming I've missed a point somewhere along the way, and would like it if someone could explain the pro's and con's
Peter

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I like to plug reverse my machines' motors on frequent occasion, and using an individual phase converter consisting of another run cap, or even another starting capacitor and potential relay, does not allow that.
Each machine would have to have its electrics modified to do what you propose, whereas I can simply stick the idler motor (bought at zero expense) away in a crawl space and start it when needed. Then I can buss the 3~ supply wherever I want in the shop.
Also running motors as you suggest, with a static (capacitor type) phase converter - and that's what a commercial static phase converter is - does not allow the full hp rating of the motor to be used.
Jim
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