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  1. #21
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    Quote Originally Posted by Rob F. View Post
    The single phase motors I linked to above are 230/460v for 30& 40hp and 50 to 100hp are 460 only. 100hp has FLA of 170. Specs are only 2x load for starting. Here is spec sheet for the motors:
    100 HP Single-Phase Motor
    I wonder who has 460 vac available that's only single phase ?

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    Quote Originally Posted by Aryan165 View Post
    Hi all,
    I've been wondering if it's possible to drive a 3-phase generator with a suitably sized single phase motor, to provide 3-phase for a shop? I'm thinking a ''motor-generator'' set up, but to get 3 phase from single phase. I remember reading the Monarch 10EE had a motor generator, where a 3 phase motor turned a DC generator that powered the DC spindle motor.
    Is it possible to buy 3-phase generators on their own, without them attached to an engine, and spin them at rated speed? I realize this would be complicated with a single phase motor, and possibly require mechanical transmission to spin the generator at correct speed to have standard line frequency out of the generator, but say you could do that. Is this done anywhere commercially? Has anyone done such a thing? I'm thinking if you have a powerful enough single phase motor, and you could spin the generator at the right speed, you'd have a much quieter 3 phase generator that you could keep inside the shop, and power moderate loads with it (say 3 hp motors?)
    If you have the amperage to run the motor that will run the generator, that will run the 3 hp motor, is there really a good reason that you don't just buy a VFD?

    I spent a lot of years around a dozen or so different motor generator rigs providing various voltage, amperage, and frequencies for aircraft power running off 3 phase wall plugs. the equipment was big, heavy, expensive, and noisy, but I wasn't paying for any of it (other than the wear and tear on my body).

    If someone tried to sell me on the idea of generating my own 3 phase power, to run a paltry 3 HP motor with, I'd think they were bloody stupid.

  3. #23
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    Quote Originally Posted by digger doug View Post
    I wonder who has 460 vac available that's only single phase ?
    They have some customers and uses listed on the website, mainly large rural industry and small municipal users.

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    Thank you all for your input in this thread. After thinking about it, I realize it was mostly a theoretical day dream, of walking in the shop, flicking s switch to a single phase motor, and having ''real'' 3 phase out of a quiet running generator to power a few machines in the 3 hp range. Considering the cost of all the pieces required, and the hassle of putting it together, and the very real problem of the drive motor bogging down under load and causing the output frequency to drop (I am not an electronics wizard, so hooking up any smarts to compensate for constant speed is beyond me right now, although I'm willing to learn).

    I don't know why I had such a bad perception of RPC, thinking they put out unbalanced power and kill machinery, but thinking about it, after Jim Rozen's post, and considering likely machines will be in the 3 hp range, I think I will give a hard look to an RPC, and also keep VFD's in mind, as both are valid options when I buy any 3 phase machines.

    There is actually a used 11kw 3-phase motor locally going for about $125 USD. I might buy it for the RPC.

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    Quote Originally Posted by Aryan165 View Post
    Thank you all for your input in this thread. After thinking about it, I realize it was mostly a theoretical day dream, of walking in the shop, flicking s switch to a single phase motor, and having ''real'' 3 phase out of a quiet running generator to power a few machines in the 3 hp range. Considering the cost of all the pieces required, and the hassle of putting it together, and the very real problem of the drive motor bogging down under load and causing the output frequency to drop (I am not an electronics wizard, so hooking up any smarts to compensate for constant speed is beyond me right now, although I'm willing to learn).

    I don't know why I had such a bad perception of RPC, thinking they put out unbalanced power and kill machinery, but thinking about it, after Jim Rozen's post, and considering likely machines will be in the 3 hp range, I think I will give a hard look to an RPC, and also keep VFD's in mind, as both are valid options when I buy any 3 phase machines.

    There is actually a used 11kw 3-phase motor locally going for about $125 USD. I might buy it for the RPC.
    I have two VFD's that cost me less than that, that will run a 3phase motor at either fixed or variable speeds, with single phase power in, and whatever frequency I want out, rated for 3 horsepower. I can wire them to simply turn on and off, wire in a pot to use to vary the speed, or even, if I really see the need, wiire the VFD to be operated by a computer so as to provide a constant surface speed or continuously variable speed for CNC use. With a fan on it smaller than the one on your laptop.

    Back in the day when you had to lay out full on actual industrial grade money to buy a VFD, many hundreds, up in to thousands of dollars, scrounging up the parts to make a Rotary Phase Converter made a bit more sense, esp. if you were essentially tripping over the major components (3 ph motors) and had ready access to the minor ones (3 ph switches, assorted surplus capacitors, cabinets, etc., etc.)
    Maybe you are having to step round three phase stuff at curbside every garbage day, but the last free three phase anything I was offered here, was a seized up 100 HP submersible pump that was about the size of a anti-submarine torpedo. Not a very useful scrounge!

    Every Rotary Phase converter I have seen so far, has been anything BUT silent! Most lived outside the shop area, for that reason. The aircraft power supplies that I dealt with at work, were all noisy to the point that wearing hearing protection was a real requirement.

    If you can get parts for free, materials for free, and don't mind dicking around building the stuff for fun, sure, but buy the motor, buy the gen head, buy the assorted switching and interlocks to turn it all in to a working assembly, you have to really start figuring out where the money could better be spent.

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  7. #26
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    Quote Originally Posted by Rob F. View Post
    They have some customers and uses listed on the website, mainly large rural industry and small municipal users.
    I would think their total customer base would be quite small.

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    Prior to getting the commercial motor-generator set, that former employer had a 5 HP induction motor and a generator hooked up with dissimilar pulleys to run the generator at the right speed.

    That worked fine also, but was too small, and was not suitable to be wired to all the offices and labs. When the company was bought out, I nabbed the then "surplus junk" motor-generator set, which I still have taking up space. (one day it will become a backup genset when I connect the 8 HP Kohler to it).

    So handwringing about the induction motor speed is not entirely justified.

    However, I think the RPC is a much more sensible approach.

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    Quote Originally Posted by JST View Post
    Prior to getting the commercial motor-generator set, that former employer had a 5 HP induction motor and a generator hooked up with dissimilar pulleys to run the generator at the right speed.

    That worked fine also, but was too small, and was not suitable to be wired to all the offices and labs. When the company was bought out, I nabbed the then "surplus junk" motor-generator set, which I still have taking up space. (one day it will become a backup genset when I connect the 8 HP Kohler to it).

    So handwringing about the induction motor speed is not entirely justified.

    However, I think the RPC is a much more sensible approach.
    I don't think 8 hp is enough. 16 to 20 hp.

    Tom

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    Generator head is only about 3500W.

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    I have a nice old Winpower FM4V2-D/4, 3ph generator at about 3500 watts ouput.
    It has winding provision to supply 28 Volts for excitation and engine starting battery charging.
    So, five wires out.

    Pulley driven , I've thought to build a skid and pto drive powered by the Bolens lawn tractor. "Just in case" I needed to power a machine tool during a power outage ;-)

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    The generator I have is a Winco. Not 3 phase in my case.

  13. #32
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    Quote Originally Posted by trevj View Post
    Every Rotary Phase converter I have seen so far, has been anything BUT silent! Most lived outside the shop area, for that reason. The aircraft power supplies that I dealt with at work, were all noisy to the point that wearing hearing protection was a real requirement....
    .
    Probably the aircraft supplies were 400 cycle. That's a whole 'nother thing. The converter shown above is in a tiny crawl space off my basement
    shop, wood door to seal it in (was an old root cellar I suspect). I've considered putting a red lamp alongside the knife switch which is in the shop,
    to remind me it's on. So quiet, I've forgot and left it running.

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    Quote Originally Posted by jim rozen View Post
    Probably the aircraft supplies were 400 cycle. That's a whole 'nother thing. The converter shown above is in a tiny crawl space off my basement
    shop, wood door to seal it in (was an old root cellar I suspect). I've considered putting a red lamp alongside the knife switch which is in the shop,
    to remind me it's on. So quiet, I've forgot and left it running.
    A lot of it was 400htz 120v, but mainly we were using 28V DC at some pretty serious amperages. Varied by aircraft. Most took in the 28VDC and had onboard rotary inverters to produce the other stuff they needed.
    3Ph 550v at the wall in a 100x300 foot hangar floor. Enough copper wire laying about the place to give a tweaker palpitations!

    In this neck of the woods, finding 3 phase stuff is a rarity. At least, in sizes useful to a home shop type. With prices for VFD's what they are, and my needs being relatively lightweight, not having accumulated a bunch of 3phase machines, VFD's are MY most reasonable option.

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    Quote Originally Posted by trevj View Post
    A lot of it was 400htz 120v, but mainly we were using 28V DC at some pretty serious amperages. Varied by aircraft. Most took in the 28VDC and had onboard rotary inverters to produce the other stuff they needed.
    3Ph 550v at the wall in a 100x300 foot hangar floor. Enough copper wire laying about the place to give a tweaker palpitations!

    In this neck of the woods, finding 3 phase stuff is a rarity. At least, in sizes useful to a home shop type. With prices for VFD's what they are, and my needs being relatively lightweight, not having accumulated a bunch of 3phase machines, VFD's are MY most reasonable option.
    Quite probably the oriignal poster's as well. I keep my rotary because I have hardinge machines with two speed motors, and I also like plug reversing the other lathe to a stop
    while working. But at ths point I've got three machines with single use VFDs - drill press, small milling machine, and a small lathe. For older flat belt machines, the VFD
    is a life saver allowing variable speed.

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    I have been using a simple RPC for over 8 years since I Retired and sold my large shop with 3 phase power. Plus have been helping others make RPCs for over 20 years. They work great and get the job done. I use the slower 6 or 8 pole motors. Delta wound motors seem to work better than Wye wound. Also the slower motors are not as noisy as the faster ones and are easier to start. I get motors cheap at HGR Surplus, I search their listings for the slower motors, they have a watch list option so I add those I'm interested in to my watch list. HGR will lower the price as time goes bye if item is not sold. If I'm not in a rush or simply want to buy an extra motor cheap I wait until price gets down to a steal! Many items at HGR is buying a "pig in a poke" so I look at the photos carefully, have gotten new or rewound unused motor but have not get got a bad motor. HGR will ship the motors and anything else though I feel their shipping cost is a little high. Will refund the purchase price if item is returned BUT not the shipping either way!
    As for simple connection I only use a start Capacitor, no run or balance cap since no set will work for operating motors of different sizes in addition to multi motor operation as often I have more than one machine running in my shop at the same time. My shop is wired so that the created leg is used only for the motor power and no single phase items like control transformers or machine contactors. I have yet to have any motor burn out, motors are old and in lathes built in the 1950's nor have I had to replace the RPC motor yet!

  17. #36
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    Thanks for the post, it is encouraging to hear you've had success with RPC for such a long time.

    I just bought a 10 hp 4-pole 1500 RPM (50 hz) for an idler. Nameplate says 380-440 Delta, but the back of the connection box cover has cast-in wye and delta symbols and connection graphics. I dob't know if the cover is a generic item that the factory installed on all the motors, or if the motor can truly be wired both ways (i.e dual voltage), because the nameplate (photo attached) makes no mention of any other voltage or wye symbol, just 380-440 delta.

    motor-nameplate.jpg

    img_8678-1-.jpg

    Can I wire the motor for delta and put 240 single phase across one winding (i.e 2 corners of the delta triangle) once the motor is spun up by the pony?

    OR:

    Can I wire it for wye, and put the 240 single phase across one winding (i.e from one corner of the wye to the centre) once motor is spun up by pony and expect to get 415 across the corners of the wye configuration, as suggested in this interesting video YouTube around 11:00 minute mark.

    Sorry for my ignorance, I am trying to learn as much as I can off the web, and have searched this forum as much as I can.

    *EDIT: don't know why photos are rotated. sorry

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    if that is a 400 volt delta motor then it won't make much of a difference if you wire it in delta and use it as an rpc conventionally (will produce 240v 3 phase)

    or if you wire it Y and connect 240 across line to neutral. (will produce 415 volt 3 phase output)

    the reason it won't make much difference is in delta, the current is shared 75% through 1 winding and 25% through the other two windings.
    in Y, connecting the motor on single phase forces 100% of the current through two windings.

    electrically the two connections are identical but, thermally, delta puts more heat in 1/3rd of the copper. this is why you can google image search "single phase burned delta motor" and compare the images with photos of single phase burned out Y motors.

    why some people say delta motors work better than Y for RPC, and others say different doesn't make much sense to me. i measured nearly identical open circuit voltages in both cases on the same motor (when corrected for the different voltages and currents).



    anyhow again if that is a 415v delta motor then connecting it in Y and running 240v across one leg.. is a good option if you have 415v motor loads. saves you the cost of finding a transformer. however, the output won't be great. the motor will be running far from saturated so you should have more margin available for current draw, because the current that would be wasted in saturating the magnetic field is no longer flowing.


    I think i replied to you on another forum but yeah, at nominal voltage, applying single phase to just 1/3rd of a motor's wingdings leaves no margin for loading it. but you would be applying 2/3rds of the nominal voltage which means you should have margin left. however, you're not going to get much power out. better than nothing. more than enough to run a 3 hp motor. also it leaves lots of margin to add capacitors to the generated phase coils. you can push the voltage up without saturating the motor.

    buy 3 ac amp meters and watch the current flowing through the driven leg of your idler motor.. and watch the current flowing through 2 of the phases of the driven motor, one being the generated leg.

    as long as you don't exceed more than 150% of nameplate amps for long periods of time you are probably good.

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    Johansen,
    Thanks for the info. I don't know if you watched the video that I linked to (11 minute mark) but I was wondering if connecting 240V single phase between the line and neutral of a wye wired motor (as shown in that video) was a done thing, or if it was an odd way of doing it. It's appealing to me to do it this way as most 3-phase motors in the UK are 415V, and I'd like to be able to run all kinds of machines that I might find locally without worrying about transformers and such. Since I will only be running a small home shop for the foreseeable future, I don't think I will drag home anything bigger than 3hp , and even if I buy say a 5hp machine, I won't be running it hard in a home shop.

    So just to confirm, 240 single across line and neutral (star point) of a idler wired in wye to give 415 3 phase will work fine?
    I can spin up the 1500 RPM idler with a 1500 RPM single phase motor, and them connect 240V across line and neutral of it's wye wired winding and go to work? I will play with capacitors after I connect a load to it, if I can get away with that.

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    i would not say it will work fine but yes you will produce 415 volts out from 240v in.

    the problem is you are pushing current into 1 winding and pulling current out from the other two.

    a traditional rpc pushes current through 2 winding and pulls it out through one of them at nominal voltage.

    get some amp meters (like 8$ each on ebay) and watch the currents and temperatures.

    you would be running this motor on 240 instead of nominal 415 so the motor will be electrically similar to a 3 hp motor. and, you're feeding one winding instead of 2, for use as an rpc.


    hook it up and let us know how it goes. starting the motor with a pony motor will simplify things.

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    Quote Originally Posted by johansen View Post
    a traditional rpc pushes current through 2 winding and pulls it out through one of them at nominal voltage.
    Most of the ones I've seen engergize only one winding. Avoid amp-clamp meters to diagnose setup issues.


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