WOW A lot of reading and arguing I don't currently have the link but there is another phase converter no one has mentioned it uses a single phase transformer with a 220 volt primary (or 240 volt as you want to call it) and a 3 wire center tapped 120-0-120 secondary and the secondary side is hooked to make a high amperage 120 volt secondary that has 1 lag tied to the primary in a way that produces about 360 volts at the open end of the 129 volt secondary and the other end of the primary that power is then fed through capacitors (calculated to the amperage requirements of the 3 phase load) the rating of the transformer to the motor HP was about 1 KVA per HP Nothing rotating and FULL rated starting torque I bought the book but have not made that type of converter yet although I have accumulated all the parts to do so I bought the book on AMAZON Gary
Where was it "shown above" for the connections you describe?
You would connect a single, SINGLE PHASE line to two of the motor terminals (A-B OR B-C OR A-C) of a three phase motor. It doesn't matter if it is a star wired motor or a delta wired motor as long as the applied voltage corresponds to the motor rated voltage.
All the RPC designs I have seen are similar with respect to one thing. After the idler motor is brought up to speed they all connect a single phase voltage of an RMS amplitude that corresponds to the motor nameplate voltage rating to two out of the three idler motor terminals. If you have a 3 phase, 240 volt rated idler motor you apply a 240 volt single phase voltage and can generate a 3 phase 240 volt supply. If you want to generate a 415 volt three phase supply you would need to apply a 415 volt single phase voltage to a three phase idler motor wired for the 415 volts. If you only have a 240 volt single phase voltage available you could step the 240 volt single phase up to 415 volts single phase to generate the 415 volt three phase supply with the 415 volt three phase idler motor. For some reason old kodger and nhengineer believe the 415 volt single phase needs to be 480 volts single phase to apply to the 415 volt idler motor. You could also take the 240 volt three phase output of the 240 volt idler and use a three phase transformer to get a 415 volt three phase supply but transformers cost money, especially three phase ones or three single phase ones wired in a three phase bank.
The first diagram I uploaded:
shows the error in applying a 480 volt single phase voltage to a star wound 415 volt three phase idler motor.
This is the post where nhengineer claims to have studied power distribution.
Based on nhengineer's "design calculations" so far, I wonder exactly what they teach there.
Almost ever one that has had single phase dream of just using a transformer
The close it can get is simple three phase motor converted to single phase and using the third leg for the three phase (rotary type transformer)
This why most MFG of converter use a simple start cap and relay The converts a three phase motor to single for few seconds now you have a rotary type transformer
Good luck
Dave
Junker2,
I guess I was referring to the diagram in your post #146 where you clearly show two 240V phases with a ground at their common point. You show these two adding up to 480V but you do not show any transformer. And they are connected to two terminals of a three phase motor in that diagram. My point was that if a building had only single phase, 240 Volt service, as a person in Australia would typically have, then there is no way to get 480V (or was it 415V?) from that without using a transformer. And those transformers apparently are prohibitively expensive. Perhaps I misunderstood, but you seemed to be suggesting that a single 240V, single phase feed could be hooked up in that manner to produce 240V.
I personally think this discussion is getting a bit ridiculous. We are, or at least we originally were, discussing the use of nhengineer's design in Australia. But I and apparently most of us have never even seen his plans or even a circuit diagram of the design. So we have no idea if it is or is not possible to use it there. He seems to think that it is not suitable.
Paul A.
Here is where nhengineer realized there needs to be two hot leads (out of phase with each other) with reference to earth ground for his present design to work.
Somewhere around here is where old kodger suggested using two phases of 230 volts 180 degrees apart.
And here is where nhengineer confirmed that old kodger would need two phases of 230 volts 180 degrees apart.
Now why would you want to buy an expensive transformer to get the two 230V outputs a half phase apart that would create (kind of) a 230V 3-phase (supply) suitable to run your 230V, 3-phase motors with reduced horsepower output (83.3% of the nameplate rating) when all the other RPC designs use a 230 volt (240 volt) idler motor to generate a "full" power 240 volt 3 phase supply?
I assumed they wanted the "480" volts to generate a 415 volt supply from a 415 volt star wired idler motor.
Paul,
Yes, the 480 volts is generated from a transformer configured as they are discussing above. I uploaded the diagram in post #146 to show that if the 480 volts was connected as shown in the diagram the actual voltage across the motor winding would be 277 volts, NOT the 240 volts that the motor windings are rated for.
This post:
shows how to connect a 240 volt single phase system to generate a 240 volt three phase supply WITHOUT THE NEED FOR ANY TRANSFORMERS.
I agree Paul, At this point, this thread appears to be a big circle jerk.
The one thing that caused this thread to travel down the road top perdition is the fact that there are folks all around the globe with differing electrical power services available to them, plus the fact that not everyone understands that when something is written up or explained it can mean the nominal voltage, as with the term of single phase. In the USA single phase 220/240 volts requires 2 hot lines of 120 volts (nominal) in other places this is done by a single hot leg and the neutral. In many places such as Europe or in particular the Middle east 3 phase power is supplied to many homes in the form of 415v across any 2 of the phases
While I was working in Kuwait we often installed overhead doors made in Denmark that were powered by small 3 ph motors but only used a single hot leg and the common. this was accomplished via a very compact box which contained a small center tapped transformer and a couple of capacitors and not a whole lot else except for maybe a few resistors and a 5 amp fuse and a reversing switch.
I do onw a set of rhengineer's rotary phase converter plans and although his method of construction differs from the way I made my RPC years ago they are a valid set of plans. But no as they are written up they do not address differing voltages or energy production methods around the world. any more than a friend of mine who lives in New Zealand on another form who a long time ago made his own buck and boost transformer would have worked as made in the USA However he later created a spread sheet calculator which if a person understood enough about how electromagnetic currents are created could build their own
I've posted a few times on this thread of how a solution to achieving 3 ph from 1 ph could be accomplished, as wqell as a couple of others who have posted as well. This is not to say that my way or another's way is better or the only way they are simply a means to reach a suitable outcome.
When it comes to a RPC for small ones I prefer to simply add the required amount of capacitors to the idler motor when the become larger say over 7.5 HP the addition of a pony motor to serve as a means to start the idler motor turning reduces the inrush current of the locked rotor condition call it reducing amperage spike. However I still prefer to have a bank of capacitors across the phases of the idler motor to smooth out the 120° 3 ph offset from the 180° of a 2 hot line single phase.
You still need a way of creating 2 hot legs though in order for any 3 ph motor to be started and run even with the addition of capacitors or a pony motor, no matter what the desired output voltage is to be. The 1 exception might be and I say this only becaus I have never had the opportunity to try it, would be a motor with 12 or 18 wires, instead of the more common 9 wire motors
Last edited by Frank S; Mar 20, 2017 at 02:01 PM.
Never try to tell me it can't be done
When I have to paint I use KBS products
Hi Frank S,
Thank you for your input. Everything you have written is correct. I have never implied it was the ONLY way to run a 3-phase motor from 2-phase service but my RPC design has worked for me running my Bridgeport, lathe and 7-1/2 HP compressor since 2012.
I have refused to get into a urinating contest with the trolls patrolling this thread and, by your writing, "...I do own a set of nhengineer's rotary phase converter plans and although his method of construction differs from the way I made my RPC years ago they are a valid set of plans..." you may now be a victim of their venom as well. Honestly, I've found their exchanges quite entertaining. It is interesting to note that they have never even seen my plans yet they freely criticize them.
For your edification, the edification of sincere contributors here and the edification of prospective owners of my plans, at the time I created them, I had no consideration of helping builders other than those in the western hemisphere. It simply did not occur to me. Now that there have been international inquiries, I intend to amend the booklet to include possible uses in former British Crown colonies (India, Japan, New Zealand and others) with the help of our Rob Candy (Australia).
In Rob's case, my research so far indicates that just the addition of a properly configured transformer would provide the required 2-phase service to the idler motor but presently I have been too busy designing and building a lift table to devote my resources to that endeavor.
Thank you again for your valued contributions here.
Best regards,
David Lee
I made a phase converter 20 years from plans I found on eBay, I used a 50 dollar 10 HP motor it worked for 10 years then I started adding bigger machines 15 HP and 10 HP. I bought a larger one with about 8 capacitors and have been very satisfied. If this book covers larger motors it is a steal at 12.50.
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