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Thread: Rotary Phase Converter (Create 3-phase power from a single phase source)

  1. #131
    Paul Alciatore's Avatar
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    Oh for gosh sake! The electric Voltage in the US has been specified, stated, and generally assumed to be anything from 110/220 to 130/260 Volts or even more. It is not and never has been any exact figure and I have seen various specifications put forth by different power companies in different regions/states. Many people simply say 110/220 Volts. Nameplates on appliances generally show a number between 110 and 120 VAC but they can show other values. 230 Volts is a commonly used number for motors: I can not remember seeing even a single nameplate that used the 250 Volt number but I would not be surprised if there were some. For a time 117 VAC was a commonly used number, probably a compromise due to the confusion. And 117 is approximately half way between 110 and 125 and that range is generally assumed to be where most power lines and most appliances will exist. Most, dare I say all appliances and devices sold in the US WILL work just fine on any Voltage in the range from 100 to 130 Volts or perhaps more.

    I have measured the line Voltage on many occasions and always get a different figure. And it can vary during the duration of a single day. Just for fun I cranked up my best digital meter and measured the line here at my desk. It was 126.4 V. So what? It will be different tomorrow morning or at midnight or next week. It is probably different for different houses on my block that are on the same pole transformer as the copper losses will be different to each one. I would likely get a different reading if I took that same meter to my bedroom or garage/shop. Oh, and in one location where I had line Voltage monitoring equipment I have seen the line Voltage go as low as 85 Volts or so. An aluminum processing plant had their furnaces on the same feeder and when an additional one came on line, the Voltage really dropped until the local utility was able to bring more capacity on line. Sometimes that took as much as a half or even three quarters of an hour. And that was in a major metropolitan area, not out in the countryside. This was an unusual situation, but it did happen and not just once, but often two or more times in a week. What I could not understand was why the local power station, which was in the same general area, did not take more effective measures. I also do not understand why it took so long to slowly come back up to normal.

    I choose to use the numbers 115/230 V as a way of more easily saying "whatever the local line Voltage presently happens to be, somewhere between 110/220 V and 125/250 V" which is rather lengthy. But if you really want to be completely precise, then please feel free to go over my post and substitute that language for every place where I simply said 115/230 V. Personally, I think my post was long enough already.

    You say the rest of my post is also incorrect. In what way? You do not say. I have had some struggles with understanding the fine points of deriving three phases from what is called single phase and I have read a lot about it as well as giving it a lot of thought. I would appreciate a clarification. And don't worry, I won't be embarrassed.



    Quote Originally Posted by nhengineer View Post
    Paul, the first incorrect assumption you made is that electric service in the USA is 115/230V. Wrong. If you want 115V (I cannot imagine why you would) you would need a buck transformer. 125/250V is pretty much standard from generating stations in most metropolitan USA locations. By the time it gets to your house or shop, losses could have taken away as much as 10% giving you 112.5/225V but that is highly unlikely unless you live way way out in the boon-docks.

    Intending no disrespect but the rest of your manifesto is equally inaccurate. I only mention this, not to embarrass you, because there are some folks out there the may believe it and that could be dangerous for them.

    Thank you.
    Paul A.

  2. #132
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    Are you in Australia? And have you actually measured the potential (Voltage) on the two pins of a 220 Volt outlet with respect to earth ground? I am not trying to be funny, I would be highly interested in that measurement as I could not find any definite information on the actual relationship between the two lines and earth/ground in the Australian power system. Although I did see some references that seemed to be saying that it was much like the US system but they just never or at lease very rarely actually ran a neutral conductor to any outlets.

    Apparently some outlets in Australia do have a safety ground connection. I would greatly appreciate it if one or more Australians would take three measurements on such an outlet: L1-L2, L1-G, and L2-G. and post the actual numbers.

    In any case, if an isolation transformer with a one to one turns ratio were used then even a 220 V feed with one side grounded could be rearranged to have the 110V-0V-110V configuration of the US system. This could be done in Australia or any other location in the known universe where a 220V, grounded power exists. So it CAN be done in Australia, it just may cost more.



    Quote Originally Posted by old kodger View Post
    junker2,

    "is the single phase motor in Australia any different?"

    The motor, no; but the power supply IS.
    Since this thread is about single to three phase conversion, single phase motors are really not under discussion. So, one more time, I don't know your location, but I would guess that you're in the USA. I the states you have the capability to split 220 volts into two single phases of 110 volts thereby enabling you to maintain the speed of a 3 phase motor with 2 phases, IN AUSTRALIA WE CANNOT DO THAT single phase is one hot line (L1) and ground (no L2).

    Rob.
    Paul A.

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    paul,

    Please get off of the grass, I tire of this, I LIVE in Australia, please don't presume to tell your granny how to suck eggs! I've just measured the line voltage and it is 236.5 volts most often referred to as 240volts (not 220), I used the 220 reference so as not to further confuse the issue for Americans
    Across the two "hot" lines I can measure nominal 240 volts, between one hot pin (in the socket) and the ground (safety) pin I can measure 240 volts, BETWEEN THE OTHER "HOT' PIN AND THE GROUND, THERE IS NO POTENTIAL DIFFERENCE, i.e neutral is bonded to ground.....NO L2!

    With respect to transformers, Nhengineer and I have discussed this, the cost here for a transformer to produce two phases 180 degrees apart, and incidentally they have to be 240 volt phases because there are NO 120 volt motors of any sort, in this country, (the nearest we get to 120 volts is in walking machines which are 180volt DC single phase motors) is in the order of thousands of dollars. It would be far and away cheaper to buy a 3 phase generator, and most likely more reliable in the long run.

    Rob.

    Rob.

  4. #134
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    Quote Originally Posted by old kodger View Post
    paul,

    Please get off of the grass, I tire of this, I LIVE in Australia, please don't presume to tell your granny how to suck eggs! I've just measured the line voltage and it is 236.5 volts most often referred to as 240volts (not 220), I used the 220 reference so as not to further confuse the issue for Americans
    Across the two "hot" lines I can measure nominal 240 volts, between one hot pin (in the socket) and the ground (safety) pin I can measure 240 volts, BETWEEN THE OTHER "HOT' PIN AND THE GROUND, THERE IS NO POTENTIAL DIFFERENCE, i.e neutral is bonded to ground.....NO L2!

    With respect to transformers, Nhengineer and I have discussed this, the cost here for a transformer to produce two phases 180 degrees apart, and incidentally they have to be 240 volt phases because there are NO 120 volt motors of any sort, in this country, (the nearest we get to 120 volts is in walking machines which are 180volt DC single phase motors) is in the order of thousands of dollars. It would be far and away cheaper to buy a 3 phase generator, and most likely more reliable in the long run.

    Rob.

    Rob.
    Rob,

    I could not have created a better response myself. Thank you for saving me the time and effort.

    Paul,

    As with Rob, I tried of this exercise also. In addition, the time I spent learning power distribution at Franklin Institute of Boston (Massachusetts, USA) cost my parents a fortune. You could enroll there yourself ( Home - Benjamin Franklin Institute Of Technology ) or you could listen to Rob; your choice. Regardless, I do not have the time or inclination to provide free education. I have other projects to work on. Anything you would need to know regarding this subject you should be able to find using proper Google search phrases.

    Best regards,
    David Lee

  5. #135
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    I think you will most of the world is slowly switching to 115 volts over the old 220 volts for home and small shop use.
    If think about if you touch 220 volt it will be bad this close to USA 480/277 v witch not found in smaller shops offices and homes
    The 115 to 120 volt is safer to use for that one day you come in contact with power side

    I agree this is thread is on running three phase motor on single phase
    Today most motors can run on 50 or 60 Hz and has wide voltage range from 208 to 240 volts.
    Back in 70's we just ran the motor that was on 50 Hz 220 on 60 Hz 240 work just find for over 30 year and still ran the day I sold the tool

    Dave


    Quote Originally Posted by old kodger View Post
    paul,

    It was not until I had answered junker2 that I read your post. Whilst I have not read all of your post, the misconception is contained within the first paragraph.

    "it would appear that in some installations the Australian 230 Volts can also be split to two 115 Volt "phases" by the addition of a neutral wire"

    Not so under ANY circumstances. Single phase here is ONE hot line and ONE neutral bonded to ground, and cannot be split except with a 1:2 center tapped transformer where you will get the high end of the transformer putting out 220volts, and the low end of the transformer putting out 220 volts 180 degrees apart.

    Incidentally, 3 phase here is three separate phases of 220 volts 120 degrees apart.

    Rob

  6. #136
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    Rob,

    OK, apparently some of the things I saw on the internet were not correct. This is why I asked for an actual measurement by someone who is actually there. I wasn't trying to be difficult, I just wanted to have it clear in my mind.

    On the subject of transformers, 50 or 60 Hz transformers that can handle any serious amount of power can and will get quite expensive. This comes from the physics involved and there is just no way around it. Unfortunately steel and especially copper is expensive. So the transformers are also expensive. As I already said, there is no way around it - at least no legal way.

    But, I did say 50 or 60 Hz transformers. The way people get around this is to use a higher frequency instead of 50 or 60 Hz. Then the size of the transformer shrinks and so does the cost. I can't say anything about the cost of them in Australia. I could only suggest that there must be some surplus places there. But even so, they will also know the value of copper so their prices may also be quite high. In any case, it wouldn't hurt to look.

    Many, dare I say most of the modern, switching power supplies used in electronic equipment use transformers that operate at higher frequencies, often in the 10KHz or even the 100KHz ranges. These supplies take the raw line Voltage and rectify it. Then it is filtered with a capacitor and that DC drives a power oscillator circuit which operates at the higher frequency. This goes to a transformer, usually a toroid, which has a secondary that produces the needed Voltage level(s). This is again rectified and filtered to produce one or more DC outputs. This is the way that most VFDs are made in order to save money. They omit the toroid transformer and the DC output of the first rectifier goes to a switching circuit that generates a pulsed version of the three phases that are needed by the motor or other three phase device. These three phases are further filtered so they approximate a sine wave. This is how a VFD can be made in an economic manner: they save on the copper, plain and simple. It has the further advantage that by controlling the frequency of that generated three phase supply you can be easily control the speed of a three phase motor. I am sure a VFD would be a viable option for those of you who are in Australia.

    Line - Rectifier - Filter Cap - DC - Power Oscillators/Choppers - Filter Caps - 3 Phase Outputs.

    I am not talking against the sale of the OP's plans. In fact if I had the details of those plans I may be able to suggest a way to use them in Australia. I am going to investigate another possibility and will post it if it seems to work out.

    I apologize if I have offended anyone here. That was not my intent.

    Paul A.



    Quote Originally Posted by old kodger View Post
    paul,

    It was not until I had answered junker2 that I read your post. Whilst I have not read all of your post, the misconception is contained within the first paragraph.

    "it would appear that in some installations the Australian 230 Volts can also be split to two 115 Volt "phases" by the addition of a neutral wire"

    Not so under ANY circumstances. Single phase here is ONE hot line and ONE neutral bonded to ground, and cannot be split except with a 1:2 center tapped transformer where you will get the high end of the transformer putting out 220volts, and the low end of the transformer putting out 220 volts 180 degrees apart.

    Incidentally, 3 phase here is three separate phases of 220 volts 120 degrees apart.

    Rob
    Paul A.

  7. #137
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    Not what I was talking about in my last post, but this may be a way to cut down a bit on the cost of transforming the Australian single phase to a split phase. The idea is that a single transformer that only handles half the current and therefore half the power would be less expensive than one that handles all the current and power. In fact, in theory it should be half as large so only cost about half as much. The trick is to jump up to double the Voltage or 460 Volts. It uses the 230 Volt line for one half of that 460 Volts and the output of a 1::1 transformer for the other half. With twice the Voltage you can use half the current to get the same HP. It is kind of a do-it-yourself auto-transformer. Here is the circuit.



    This, of course, depends on getting a three phase motor that runs at twice the Voltage and I realize that may be difficult to find. Perhaps a dual Voltage motor. Anyway, it's an idea. And I see no reason why it should not work with nhengineer's plans or at least an upgraded version of them: Twice the Voltage but half the current for a given HP rating. But then, as I said earlier, I have not seen those plans so I can't be sure.
    Last edited by Paul Alciatore; 03-01-2017 at 12:55 AM.
    Paul A.

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    Gee, I really don't know where to begin correcting all the erroneous statements made since my last post. Most individuals experienced with connecting electrical power equipment know that a single phase power connection involves connecting 2 wires. So to Mr David Lee AKA nhengineer, you do not have to have a pony motor to start the 3 phase idler motor rotating. You can also use a simple pull rope as stated by Dave, AKA smithdoor, or use a capacitor to shift one of the incoming single phase line voltages line voltages and temporarily connect it to the third phase (L3) of the idler motor until it comes up to speed , then disconnect it.
    There is a diagram of the power distribution transformer as used in the US at this web address: https://www.allaboutcircuits.com/tex...power-systems/. It has the polarity markings on the transformer. Anybody familiar with basic transformer theory should realize that the voltage you are applying to the three phase idler motor is actually a SINGLE PHASE voltage. So my point in questioning the difference between a motor in the US and a motor in Australia is this: There is no difference. Unless the plans you are trying to sell use some control voltages that use the neutral reference point that exist in the US ie somewhere between 110 volts to 120 volts, I don't see why the Australian voltages will not work even if one side of the output voltage is connected to ground. You still have the nominal rated voltage across one winding of the 3 phase idler motor. All you would have to do is modify the plans to use a control voltage that is readily available (like 230 VAC) or use a small transformer to convert the available 230 VAC to the control voltages that the plans call for.

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    Originally Posted by Paul A
    An unloaded three phase motor, AKA a phase converter, CAN be powered from a single phase in both the US and in Australia. There will be some capacitors involved that will generate a third phase for the third input wire on the motor.
    Capacitors generate the third phase? What about the induced magnetic field on the rotor that is now producing a time varying magnetic field on the other two windings in the idler motor as it rotates? I believe the capacitors are used to condition the line voltages to resemble the "two" phases at something closer to 120 degrees apart as opposed to the 180 degrees apart as referenced to the neutral point on the split phase source here in the US.

    Originally Posted by old kodger
    With respect to transformers, Nhengineer and I have discussed this, the cost here for a transformer to produce two phases 180 degrees apart, and incidentally they have to be 240 volt phases because there are NO 120 volt motors of any sort, in this country, (the nearest we get to 120 volts is in walking machines which are 180volt DC single phase motors) is in the order of thousands of dollars. It would be far and away cheaper to buy a 3 phase generator, and most likely more reliable in the long run.
    Well if you applied two 240 volt phases that are 180 degrees apart to two of the input terminals of a three phase motor you better hope the motor is wired for a 480 volt input because that is what you are applying. I have no idea who proposed this idea much less who agreed with it but if the rated voltage of your motor is 240 volts, I suggest you apply only a 240 volt RMS voltage.

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    nhengineer,
    I couldn't help myself!

    Junker2,
    It might be a good idea for you to go back and read all the previous posts. this particular part of the discussion is referring to AUSTRALIA, stop thinking America. We have a minimum of 240volt motors, and three phase motors are ALL 415volt (read Paul's post about vector maths) two 240 volt phases 120 degrees out of phase will produce 415 across L1 and L2, jeesh!

    Rob.

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