Anyone interested in a RPC build?

Jeff Horton

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FINALLY getting to start building the Rotary Phase Converter tonight. Just mounting the components in the enclosure. Had not planned on documenting this but I plan on posting some photos as I go. Just wondering if anyone else is considering building one?.

Being my first I am certainly no expert. Just stumbling through this but I think I finally have a grip on it how it works. I have been looking at the drawing for a couple of weeks now.

For those unfamiliar with the term, it is method of generating 3 phase power from standard single phase house hold current using a 3 phase 'idler' motor to generate the 3rd leg of electricity. Well something like that anyway. :)

Photos to come. To tired to walk down the stairs to the Lab tonight.
 
Document away! I don't plan to make one in the foreseeable future, but I still would like to see the details.
 
Jeff,

I definately plan on making one in the future...probably early next year...but really interested in the hows and whys right now. Look forward to your project.
 
That would be great information for a guy to have in his back pocket in case he runs across what he thinks is a good deal on a three phase machine. knowing how much trouble it is and how much it cost would be necessary to know if it is really a good deal or not.
 
I'd be interested, too. I'm having a heck of a time wrapping my head around it and i'd like to know what kind of draw it has...

Does the current draw on the line equal a combined total of amperage? I mean ... if it's 5a per leg, is it 7.5a per leg on the 220? That's the part i am still confused about (obviously)
 
Absolutely interested. I was going to ask you how you do this and where you got the plans and components.

I really like the threads that show progress of a project. I always learn something or get an idea from reading.
 
What, not EVERYONE has 3-phase in their workshops :dunno:

:D

I'd be interested in a RPC build, your rebuild threads are always interesting and I usually learn something new, so please do!! :thumb:
 
OK, guess I better get in gear today. Made a list of wire I need and expect to pick that up today and start wiring it up tonight. Will just start a new thread on this.

Jason, not sure I understand what your asking. But if you have a motor that draws 5 amps and you can rewire it 220v it then draws 2.5 amp on 220v. It's all about Ohms law.
 
Hey Jeff,

I'm glad you are going to do this. I am not ready to put a RPC together now, but I will in the (hopefully) near future! Thanks!
 
I'd be interested, too. I'm having a heck of a time wrapping my head around it and i'd like to know what kind of draw it has...

Does the current draw on the line equal a combined total of amperage? I mean ... if it's 5a per leg, is it 7.5a per leg on the 220? That's the part i am still confused about (obviously)

Jason, current draw of an RPC will be the rated current of the idler motor (I think :D ). If the idler motor's draw is 5 amps, it will be drawing 5 amps from each leg of the 220 single phase line (at different times of course), and I believe generating somewhat less for the third phase - 30% less sounds about right, but I can't remember now where I read that. That may be where your confusion is coming from though -- you'd need about a 7.5 hp 3 phase idler to run a 5 hp 3 phase machine. Maybe I should have picked different hp numbers -- they're the same as your amperages in your example -- unfortunate but un-related.

Clear as mud?:wave: Just wait till the discussion gets to balancing the single phase with the generated phase. Stuff gives me a headache.:huh:
 
Jason, current draw of an RPC will be the rated current of the idler motor (I think :D ). If the idler motor's draw is 5 amps, it will be drawing 5 amps from each leg of the 220 single phase line (at different times of course), and I believe generating somewhat less for the third phase - 30% less sounds about right, but I can't remember now where I read that. That may be where your confusion is coming from though -- ........

Maybe John should be writing this instead of me!! :)


......I made a cover for the motor shaft. I really didn't want it spinning out in the open, to get hung up on.

Good idea! I am tempted to just cut the shaft off but that ruins the motor of course.

I saw a really slick set up somewhere. They had built a metal frame and mounted the idler motor up at ceiling height out of the way where nothing could get caught in the shaft. But since I am in a basement I don't want the sound carrying upstairs.
 
Maybe John should be writing this instead of me!! :)

Not me man, I just know enough to be dangerous!:eek:

I can usually figure out why the lights went out after I flipped the switch, the tricky bit is looking at the mess of wires and realizing the lights are GOING to go out!

A friend of mine has an RPC thats mounted on a handtruck, works really well for mobile installation, and you can get a good one from HF for about $35 when they're on sale. The motor is mounted to the horizontal plate of the truck, and the box with all the fiddly bits is screwed onto the truck frame above the motor.
 
Sorry, according to sub-paragraph B section IV of the workshop electric code, only "dungeons" come equipped, standard, with 3-phase. The rest of us are out in the cold.

But we do get to have windows.

You forgot the part about bing in an insulated concrete area for at least 1 mile in all directions. No substantial amounts of tree,s grass or other greenery.
 
Jason, current draw of an RPC will be the rated current of the idler motor (I think :D ). If the idler motor's draw is 5 amps, it will be drawing 5 amps from each leg of the 220 single phase line (at different times of course), and I believe generating somewhat less for the third phase - 30% less sounds about right, but I can't remember now where I read that. That may be where your confusion is coming from though -- you'd need about a 7.5 hp 3 phase idler to run a 5 hp 3 phase machine. Maybe I should have picked different hp numbers -- they're the same as your amperages in your example -- unfortunate but un-related.

Clear as mud?:wave: Just wait till the discussion gets to balancing the single phase with the generated phase. Stuff gives me a headache.:huh:


Thanks, John! I think i'm getting a bit better understanding now thanks to your description. So it sounds to me like the biggest 3-phase motor you can run is about 2/3 of your 220v 2-phase capacity, right? Running a 3-phase motor essentially draws about 30% higher current than it's 220v 2-phase counterpart of equal HP rating? (2hp 3-phase would draw about the same as a 1.5hp 2-phase?)
 
Thanks, John! I think i'm getting a bit better understanding now thanks to your description. So it sounds to me like the biggest 3-phase motor you can run is about 2/3 of your 220v 2-phase capacity, right? Running a 3-phase motor essentially draws about 30% higher current than it's 220v 2-phase counterpart of equal HP rating? (2hp 3-phase would draw about the same as a 1.5hp 2-phase?)
You have some terminology wrong, possibly, as I don't believe there is such thing as a 2-phase, it's really 1-phase. A single phase (1 phase) 220v circuit has 2 x 120v hot lines, and to make it 3 phase, you produce the 3rd 120v line. A 3 phase circuit will at any time produce 240v by using any 2 of the 3 hot lines, hence 120v+120v give you the 2 needed hots for 240v.

Some type of motors require more to start, such as a bandsaw, but typically a table saw and/or jointer, or even planer will not. Compressors require more to start up also, along with band saws that are the most common for woodworkers.

It does require more AMPs than needed for the motor to start from a 1-phase circuit, and I have heard 37% higher in the past, but that number could be wrong. In general, most people plan to have 50% more HP than the largest motor on the circuit, and for a 5HP machine would have a 7.5HP RPC (this is what I run). Once the largest motor is started, you can start 3x the rated HP, so a 7.5HP RPC would be rated to start a 5HP motor, and you could have 15HP of machines running on the 7.5HP RPC at any given time.

There is grey area since some motors do not require as much to start, and you might be able to start a 7.5HP table saw on a 7.5HP RPC for instance, but the general rule of thumb is that you need aprox 50% more HP and 37% higher amps than the 3 phase idler motor will require (23 amps is typical for an average 5HP 3 phase motor, hence you need about 31.5 AMPs to run them). I have also heard that you do not want this number to go over 80% of the rated circuit, but that is for all circuits in general and not sure RPCs. I have an idler that only sucks 19.2 amps, and run it on a 30amp 1 phase 220 circuit with no problems. My RPC is rated to require a 30 amp, but again, the amps are less for the motor and it was sold with those requirements. Do your homework, it's easy to burn a house down.

My motor has the arbor cut off. It's not a big deal to get another arbor if one wants to use the motor for something else, those are available. I believe it is safer to have it cut, although Steve's solution of building a box around it adds the same safety.

3 phase is a PITA and requires some cost up front, but once you solve it at your home, it opens up the world of 3 phase machines, and most of them are in another class of workload than the 1 phase counter parts, but not always. Much of the industrial machines are 3 phase. Having a 5HP 3 phase industrial table saw in your garage is something that most would have scoffed at when some of the machines were built, but it is reality today. Some people like that class of machine, and others shy away from them. It opens up some real possibilities on woodworking machines.

In addition, 3 phase motors are sold for pennies on the dollar since most folks getting rid of them can't use them and many production shops will not buy used motors, and specificially require a new one to replace any old motors. Truth be told, it's not too often these more industrial 3 phase motors have problems, although some occasionally do.

Good luck on your RPC build. I have one and wouldn't want to be without it, because I wouldn't be able to use either my table saw or jointer, and soon to be DC that I will build with a 3 phase motor.
 
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You have some terminology wrong, possibly, as I don't believe there is such thing as a 2-phase, it's really 1-phase.

Actually, though rare, there is 2 phase. I just learned about this recently. And there are a few 2 phase motors around. I have seen a photo of one. Very old motors btw. But yes, Alan is right in that most homes are single phase.

Rumor has it that there is at least once city that still has 2 phase running in it. As it was explained to me, it still takes 3 wires to run 2 phase and since it takes 3 wire to run 3 phase, 3 phase eventually won out.

Don't ask me any details. Thats all that I know about it.
 
I stand corrected. For some reason, I had considered "split phase" to mean 2-phase. Once I made that mistake, I'd thought about the two legs of 220v - aren't they out of phase? I thought that was why you couldn't take two 110v circuits off the same side of the main leg and get 220v. That's where my thinking got me to arrive at calling it 2-phase when I seem to be missing some further details.

Looking at motor plates, they all say 1ph or 3ph. Guess that shoulda been my first clue! :rofl:

Anyway - i'm very interested in this subject and now i'll pay close attention to the thread devoted to it! :D

Thanks for all the clarification :)
 
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