Thread: Rotary Phase Converter (RPC) wiring questions and idler motor uses

First, let me say that I have read many threads here and articles or other information elsewhere regarding phase converters. My problem, especially reading the threads here, is sorting out the different approaches and understanding the functionality of the different parts. Many members here are far more knowledgeable and educated in this area than I, and what is simple terminology for most folks here is almost Greek to me.

I ask for your patience in reading and replying to my questions.

My goal: Build a "low cost", simple yet effective converter that can also use the idler motor for mechanical work in addition to its generator duties.

Here is what I have so far: 15 hp 208-230v/460v motor (used), 1750 rpm, 40.5 amps, max amps at 208 is 45. I also have ordered five 270-324 MFD 330 VAC motor start capacitors.

I still plan to purchase: run capacitors; switches, starters, buttons, contactors, relays, coils, etc. that are needed to start, run, and stop the RPC. I also plan to purchase a 3 phase load center with individual breakers for each machine I will run from the RPC. I plan to come out of my single phase sub-panel load center with one single phase breaker that will feed the RPC.

My current machines: 1944 K&T 2K Plain horizontal milling machine, 7.5 hp, 220v/440v, 20 amp on 220v, 1750 rpm; Mid 1940's(?) U.S. Machine Tool Co., Model "V" vertical milling machine, 1 hp, 220v/440v, 4.8 amps on 20v, 1200 rpm. The distance from the planned 3 phase load center to each machine will be approximately 15 to 20 feet.

Question 1: Can I use the idler motor for powering a water pump with a power requirement of 5.5 hp? Distance from the load centers to the "desired" idler motor/water pump location is approximately 100 feet. The water pump may run for as much as 12 (maybe more) hours per day to run a water aeration system for a 1/4 acre pond near the workshop. I know this may be unusual, but it seems like the idler could be used to do some type of work beyond acting as a generator for 3 phase power.

Question 2a: What do I need to order to most cost effectively (read that cheaply and reliably) turn the idler motor on and off and to energize then "drop out" the starter capacitors? I assume I will need several components, but I am not sure which ones will allow me to start and stop the idler motor AND be safe when using the capacitors.

Question 2b: Suggestions on the best place to order or purchase these components (e.g., Grainger, Surplus Center, etc.)? Specific part name and number would be really appreciated!

{Edit} Question 2C: Any opinions regarding the kits offered by WNY Phase Converter & Supply? I was informed of these kits by a member here. The kit seems like it might be a good choice for me since I can either buy the components and do it myself OR buy a complete "box" already put together.

Question 3: How should I wire up those compenents in non-electrician terminology and what and how will these components work together, i.e. function of each part and how they integrate into the whole system? I'm trying to learn, but I'm not an electrician.

Question 4: What size single phase breaker should I use coming out of my workshop, single phase load center? What size wiring should I use with the set up above.

I want to say "thank you" to everyone who posts well-meaning advise. Let me say that I know the responsibility for wiring my RPC and workshop correctly is my responsibility, not yours. I'm trying to learn and learning by doing usually works out pretty good for me.

gkbikers

If you are interested in a kit contact American Rotary-many people will tell you to stay away from WNY Supply.

Originally Posted by racer55

If you are interested in a kit contact American Rotary-many people will tell you to stay away from WNY Supply.

Thanks racer55. I'll do some searching on WNY here at PM and also investigate American Rotary.

I don't necessarily have to go with a kit. I've already ordered my start capacitors. However, there is not a RPC For Dummies book which is what I seem to need to purchase and wire up my RPC components!

Originally Posted by racer55

If you are interested in a kit contact American Rotary-many people will tell you to stay away from WNY Supply.

Unfortunately for me, American Rotary does not appear to offer kits for a panel. Basically, they offer turnkey units. I already have a 15 hp 3 phase motor, but I need all the other components. WNY Supply offers the solution, but I'm still reading others' experiences on PM.

I am not an electrician OR an electrical engineer, but I do not believe that you can place a load on an idler motor. Remember, the idler is running on single phase power, or single phasing. I am not sure what amperage would be drawn by a load placed on this idler motor, but simple physics dictates that it would not be efficient, or durable. There is an entire forum here that has detailed plans and options for a phase converter. You can build it simple or bells and whistles, but I don't think that you can put a load on the idler motor. Regards, Clark

On question #1, you can use the idler as a motor, or as a phase converter, however, you cannot get power for free. I believe a single phased 3 phase motor puts out about 2/3 of the power, so say 6 hp for your 10 hp motor/phase converter. If you are pulling 5.5 horse for your pump, you have .5hp to run anything else in your shop. So, pretty much one or the other, not both.
Joe

gk,

You and I are thinking along similar lines. I always thought it might make sense to use an oversize idler motor to run a dust collection system as well as generating the missing leg. I concur in general with what Joe posted directly above, but for me this is pure conjecture and I do not have any hard factual basis to back it up. I only differ in one sense, and that is the numbers that Joe quotes. I agree that a three phase motor that is single-phasing will deliver no more than 2/3 nameplate horsepower. I also agree that you can't get something for nothing here. But remember that not all loads are consistent and consuming full power all the time. If you are taking light cuts with your K&T, you won't be drawing anywhere near 5HP worth of electricity. In an instance like this, I suspect the milling machine becomes a de facto idler, too, and improves the efficiency of the real idler motor when it is being used to drive a load. The K&T should have a clutch, unless it's a newer one, and I suspect it will be a fairly easy starting load, so starting currents should not be too excessive.

It is my GUESS that the 15HP idler motor should be adequate for what you want to do UNLESS you are seriously hogging with the K&T or you are running all three motors at the same time. The problem i see is a geographic one, the pump is too far away to be run by the idler motor, at least as a practical matter.

btw, this assumes that the pump load can be brought on line AFTER the idler is up and running. Starting the pump under load will be more difficult than starting the 15HP motor alone.

Here's an idea, why not set up the pump with is own 5HP motor, and turn it on and off as needed? 5 Hp three phase motors are generally falling out of trees and should be available for little money.

Steve

on edit: the 1944 K&T will have a clutch, allowing ou to start the motor without driving all of the machinery inside.

To expand on what I said above, if you go the idler motor/pump route, the cost of wiring is what will probably become the deal breaker, however attractive any other elements may be, unless you have access to dirt cheap wires. Maybe you can find some overhead power drop wires and run your lines overhead, but you'll need to find three phase drop cable.

Skip all the potential relay's and all things associated with it and just buy a PhazPak unit. Solid state controls for all the starting circuitry part of a RPC, takes up little room and only has 3 wires to worry about hooking up.

Mine works like a champ and gets my idler to snap to life with a very short inrush of current.

Originally Posted by Mr.Green

Skip all the potential relay's and all things associated with it and just buy a PhazPak unit. Solid state controls for all the starting circuitry part of a RPC, takes up little room and only has 3 wires to worry about hooking up.

Mine works like a champ and gets my idler to snap to life with a very short inrush of current.

Is this a capacitor?


PhazPak Product 1

Putting a mechanical load on the idler is NOT a good idea... basically takes away it's ability to act as a rotating transformer. Better to run your pump load with a dedicated 3phase motor... this actually improves your system balance, rather than cripple it.

Originally Posted by Shawn Ghormley

Is this a capacitor?


PhazPak Product 1

The concept behind them is solid state controls for your starting circuits, relays and such.

Here is all that is in my RPC panel:




You could just order this part, for the correct size idler motor and skip all the relays, potential relays and such. That tube with the 3 wires takes care of all of that.

Thanks everyone, great information.

I'll drop the idea about using the idler for additional "work". However, the idea of using another 3 phase motor for the pond pump sounds workable. I'll also be checking out the PhazPak equipment.

Other thoughts or ideas?

Again, thanks to everyone. PM is "made" by its members.

gkbikers

If you look at the connection topology, sizing table and derating comments shown in the technical documentation, you'll see that the Phazpac gadget is nothing more than a static converter module. Same concept as a Phase-a-matic.

The concept of both is simple... a 3-phase motor will not START on single phase power by itself, but if you apply capacitance between one of the 'hot' legs, and the 'unused' leg, the motor will 'kick' itself off in the right direction, and once running, will carry full load amps per leg, on two of the three legs (hence, advertised ratings of around half to two-thirds power, and the note to use a 'smaller pulley').

TO make your own version of the gadget, you just need an appropriately sized capacitor, and something that will 'shut it off', either after some particular timeperiod, or when the third leg voltage naturally rises above a certain threshold, or after a certain amount of time expires. Judging by their 3-second comment, I'd bet that if you cut one open, you'd find a typical paper-electrolyte type motor-start capacitor wired in series with a 3-second timer circuit. Since they indicate 'solid state', I'd guess they used a thyristor (a TRIAC) that's bleed-charge gated (rising voltage defeats the gate) after about 3 seconds. The non-explosion-proof note reinforces this suggestion.

A self-starting rotary converter is nothing more than a static converter with an idler motor.

Building a rotary converter yourself, is very easy... matter of fact, many of us have, and could demonstrate building a complete, operational 4hp rotary converter in under 10 minutes, using a 240v line cord, a leftover 3-phase knife switch, three wire nuts, a 7.5hp three phase 230v motor, and a piece of 1/4" rope.

There's actually quite a few guys who use nothing more than this, to power their entire shops... zero investment, salvaged junk rocks.

Though not a convertor, here is a home brew static rig that snappily starts a 15HP. By adding run caps and not expecting it to run the lathe, it would be a RPC. It does NOT use any gizmo to drop out the start caps, and instead lifting my finger off the start button does that chore.

How To Make An Old 15HP 3 Phase Go

My point about the PhazPak is that it is an all in one, simple to wire up unit. Inside that tube is all the starting stuff, minus the cap.

All solid state, takes up minimal space and only has a couple wires to hook up. Way simple.

"A self-starting rotary converter is nothing more than a static converter with an idler motor."

Most self-starting RPCs are patterned after Hanrahan's (US Navy design, possibly from the late 1990s) which, in turn, are patterned after Habermann's (IEEE Transactions design, from the early 1950s).

Simply stated, a self-starting RPC is a three-phase motor of almost any size to which has been added a single run-type capacitor of about 30-35 µF per idler motor HP between either the A or C phases (these correspond to the single-phase L1 and L2, respectively) and the B phase (this corresponds to the three-phase L3).

Often, the idler motor is just a conventional induction motor which has been altered by turning off some of the cast-in aluminum shorting bars (which form the shorted turns within the rotor of an SCIM, a Squirrel Cage Induction Motor) and which alteration is intended to provide a higher resistance within the SCIM's rotor, thereby making it easier to start.

Alas, such RPCs have a low to very low power factor (often as low as 0.18) when unloaded, but the P.F. improves significantly as the load is increased.

The phasor diagrams of such a system can be seen ...

Three-Phase vs. Single-Phase, Illustrated

... here.

I bought an American Rotary and am very satisfied. It was shipped promptly, the manual was decent, and they answered my questions by phone whenever I had a question. They use a modified Baldor motor for the phase generator that has been designed for soft start, so your single-phase supply isn't tripped when you start it. If you design and build your own, getting a soft start feature might be difficult. To me, the soft start was worth buying a ready-to-run unit versus home brewing one.

Same here. The soft start feature and never having dealt with phase converters before pushed me to buying the complete unit from American Rotary. I have seen American Rotary box-only units on Ebay direct from AR. You supply the motor and they supply the electronics.

It might be worth a call to American Rotary to see if you can buy just the control box for use with your own motor. Even if their web site doesn't offer this version, they might still be able to supply one.

Originally Posted by BobRenz

It might be worth a call to American Rotary to see if you can buy just the control box for use with your own motor. Even if their web site doesn't offer this version, they might still be able to supply one.

I have built & installed more than 20 rotary phase conv. My favorite package is "rotogen" of missouri last contact at Smith Electric Motorworks / GWM - Phase Converters 800 326-0109. Have not used many others. You are smart to add a contactor to start the rotary and a 3 phase circuit breaker panel for distribution. Add pull a ground wire to each drop (box) & you are golden. If you continue to build your own device, as you have many parts, Always use a bleed resister on capacitors banks to prevent shock. 15 hp 3 phase breaker = 40amp. single phase supply breaker is 80 amp. If this comes from a 200 amp house circ. you will be probably ok. I use a recording multi-meter to pick up (measure) voltage drop durring 15 hp start. If V drop is to large you will brown out your place and all niehbors on that utility transformer, 1 up to 5 nieghbors. This can kill T>V, stereo, computer, refrigerator.
Many people use potential relays from refrigerator service to disconnect start caps. you can leave run caps in place all time. The goal with runn caps is to have load (voltage phase to phase, & phase to ground) become ballanced after adding most common (frequently used) load. I have found that adding more start caps with a potential relay to drop them, at each additional tool makes for snappy starting and good voltage balance to all devices. The soft start suggestion is very good. we can sometimes buy these from used tool & hardware dealers for not much. New list for a 15 hp is about $1500. I may have a recycled one on shelf. I can make diagrams & parts list. I thought about doing this as a for sale manual, but havn't talked to my attourney, (pizza & beer retainer) about liability. I have made and sold automated control specs. and parts list many times as used by industrial electricians. Plese ask me more questions.. Elmud