# ROTARY PHASE CONVERTER WITH TWO IDLER MOTORS ?



## Brain Coral (Nov 5, 2017)

Hello all,

I recently bought a rather large lathe with a 10hp motor on it. It is a 575v 3 phase motor that I will have to replace with a 10hp, 220v 3 phase motor.

I presently have both, a 5hp RPC and a 10hp RPC. Both work very well. I think that a 15hp RPC would run this lathe, as it has a clutch. 

My question is, can I utilize my present 10hp RPC, along with the 5hp pony motor to achieve a 15hp rating, without actually purchasing a new 15hp RPC control box, as well as a 15hp Pony motor?

Brian


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## Karl_T (Nov 5, 2017)

I've built a couple RPCs now each using two 3 phase motors. For larger HP converters its an advantage because the starting current is much less.  I start the small motor just like any RPC then have a delay timer bring the second motor in about five seconds later. On one of the builds I used another delay timer to bring in the run caps after both idler motors were up to speed.


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## Brain Coral (Nov 5, 2017)

Well, that is encouraging, Karl  

My knowledge about electronics is limited, so I will have to do some digging around to see what I need. I might have to pick your brain for further details.

Brian


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## Brain Coral (Nov 5, 2017)

I am off for a hike in the woods, to place a couple of game cameras, but will be back later on to check in...

Brian


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## Ulma Doctor (Nov 5, 2017)

Hi Brian,
like Karl said, you can use multiple motors for your function.
you'll spin each motor up individually, then use the entire strength of the combined generative effect to power the 15 hp requirement.
the single phase supply wiring will need to be sufficient for a 15hp load (minimum)


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## xalky (Nov 5, 2017)

This is interesting.  I'd like to see a diagram of how it's done. Is it harder or easier to balance out the voltages?


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## Karl_T (Nov 5, 2017)

here's one i built for my son 
http://www.hobby-machinist.com/threads/25hp-3pahse-conveter-with-load-center.26944/#post-237760


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## Reeltor (Nov 5, 2017)

Since you will be putting a 10hp 3 phase motor on the lathe and the lathe has a clutch; I don't see any reason why a 10hp RPC won't run the lathe.  Try it as-is, I think you will find that it runs just fine.  If you have any problems then you can always add a pony motor to your setup but I don't think you'll need it.


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## Brain Coral (Nov 5, 2017)

Well...... I like that ...... I guess that I should at least try it, before going to all of the trouble of making a new RPC. I just have to find the right 10hp motor. Or, I might go the voltage transformer route, as 3 phase 220v motors don't seem to be numerous around here. The local recyclers don't bother setting them aside for guys like us.

With the existing motor at 575v 3 phase and 10hp, if I were to go the voltage transformer route, would I be looking at a 15VAC transformer ? And, do I have to look for specifics about the 575 volts, as well as do some step the voltage down, but not up?

Brian


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## Reeltor (Nov 5, 2017)

Brian,

Tells us about your "rather large" new to you lathe and how hard are you planning on working it.  You might get by with a 5hp motor on it.  5hp 3-phase motors are easier to find.  I have a 5hp motor on my Monarch, it will take as big a cut as I ask of it and doesn't seem to notice if I'm taking 50 thou a side or 250 thou a side.  Put your 5hp "pony" motor on the lathe and see how she does, Unless you have a 22" or larger swing American etc. may do better than you think.

Mike---reeltor


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## Chipper5783 (Nov 5, 2017)

As Brian says, the 10 HP RPC may be just fine. I have a 5HP RPC and it works fine to run my 5HP air compressor, but it doesn't like starting my lathe on the 5HP setting (2 speed motor, so I usually run it at the lower speed, which is 3HP). You have a clutch, it will probably be fine.

The 575V is an issue.  I am running 3 different 575V machines. I'm simply running a 230 to 575 three phase transformer. It was originally sold for step down service, but it works the same to go the other way.  I seem to loose capability through the transformer, as the 3HP mill motor does not like to start on the higher speed.  Not really an issue as the motor controls are set up such that I can start on the low speed, then punch the high speed button and it comes right up.

As Brian said, put in a little smaller motor, 5HP or 7.5HP, whatever comes your way - tell us about this new machine.


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## 4GSR (Nov 5, 2017)

I wouldn't put a motor any smaller than 10 HP on the Lodge & Shipley lathe Brian has.  It's not a big problem on start up, but it is trying to get it into the higher spindle RPM's.  I ran my L & S on the 10 HP motor that it came with on a shop built static phase converter.  Had it balanced with oil filled capacitors on the generated leg along with the other two, too.   I'm sure some of the loss power had to do with not having full 3-phase power.  Using the static converter, I had a bank of four 375-450 mFd capacitors in parallel providing juice for startup.  And it took every bit of it, too.  Of course, the old 1950's 10 HP frame motor on that lathe would be like a 30 HP motor today!

If I remember correct, the motor pulley is about 8" in diameter with 5 or 6 "B" section grooves and the pulley on the input shaft is about12" OD.  That much belting takes a lot of power to get it up to 1800 RPM on the motor.  So a 5 HP pony motor may not be large enough.  7-1/2 HP, maybe.

Ken


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## xalky (Nov 5, 2017)

Karl_T said:


> here's one i built for my son
> http://www.hobby-machinist.com/threads/25hp-3pahse-conveter-with-load-center.26944/#post-237760


Hey Karl, so I read the thread, and watched the video. You start the 5hp to make the 3 phase power to start the 15hp then they both run together, is that right? Are you using start caps to start the 5hp? Do the 2 motors share run caps?


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## Brain Coral (Nov 6, 2017)

I am late in getting back to reply, but Ken has described my lathe. As he said, it is a Lodge and Shipley 16" (really 18" ) swing and 8' between centers and weighs in at around 9000 lbs.  I have started a thread on the L&S forum. I agree with Ken, about keeping the 10hp motor capability. I like to keep things as original as possible.

So, as I am intent on keeping the 10hp capacity, can anyone guide me to a schematics diagram dealing with a 10hp and a 5hp combination RPC set up ?  I have done some digging, but haven't found anything conclusive so far. As well, I don't trust my limited knowledge.

Brian


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## Karl_T (Nov 6, 2017)

xalky said:


> Hey Karl, so I read the thread, and watched the video. You start the 5hp to make the 3 phase power to start the 15hp then they both run together, is that right? Are you using start caps to start the 5hp? Do the 2 motors share run caps?



I had to re read my own thread. First tried to get away with no start caps (just run caps only, brought in at startup) and that did not work out.

Motor 1 comes in with start caps. these caps drop out on a timer after one second.

Motor two comes in at about three seconds. The system runs real ruff until the run caps for the entire system come in at about five seconds.

watch the video, you cans see the second motor come in, then smooth out. there's a quick shot of volt meters showing great balance.


I had wanted my son to put a loose pulley and belt between the two motors. if this was done, I think you would never even see motor 2 come in. And you would not need the delay timer for the run caps, just bring them in with motor 2


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## Karl_T (Nov 6, 2017)

Brain Coral said:


> So, as I am intent on keeping the 10hp capacity, can anyone guide me to a schematics diagram dealing with a 10hp and a 5hp combination RPC set up ?  I have done some digging, but haven't found anything conclusive so far. As well, I don't trust my limited knowledge.
> 
> Brian



If I understand correctly you have a 10 HP converter running already...

I also have a big lathe, a Mazak M4 (machine weighs 16,000 lb has a 22" swing by 72" long). I learned that you need considerably more total HP in the RPC than the lathe motor if you want to keep any decent starting load and voltage balance..

Anyway, I'd use the 10 HP to build from. Add a second motor making the RPC total HP near twice what your lathe motor is. All you need is a motor, delay timer relay and motor starter. Personally, I'd suggest a loose belt between these two motors so motor 1 spins motor 2 up. If this is done, I'm almost positive you could bring in your balancing run caps along with motor 2. 

The amount of run caps has to be done by trial and error; build your caps box with plenty extra installed and make it easy to add/remove run cap connections. Permanent voltmeters are cheap make balancing trivial.

I'll be glad to help with the wiring step by step when you get there. For now, get yourself a big electrical enclosure, a large used 3 phase motor, a motor contactor, a delay timer and about 70MFD  of run caps per total HP of your system.  if you don't belt the motors, get a second delay timer and motor contactor.

Extra bonus:  I found 3 phase load centers are cheap in ebay. One of these makes it great to fuse each component and make future equipment additions easy.

EDIT ON 2017 11 07 There is a typo above. get about 20 MFD run caps per hp in your converter


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## Brain Coral (Nov 6, 2017)

Hi Karl,,
Yes, I already have a 10hp RPC up and running. Based upon what you wrote, should I be looking for another 10hp motor for a total of 20hp in the RPC ? Or is an additional 5hp enough ?

WNY Phase Converter sells a complete 20hp RPC panel for $300.00 USD shipped. Would this be another avenue?

Brian


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## Karl_T (Nov 7, 2017)

You are going to get differing opinions on if 15 hp is enough. More HP here will improve voltage balance and starting load on big motors. But you can try what you have, if you want.  

that's a complete 5hp converter, correct? its worth more than just a surplus 10hp motor. You need to find a surplus motor jockey, ask around, they exist.

that 20 hp panel leaves you looking for a 20 hp motor. And starting 20 hp will really dim all the lights on your place if you have the typical home 200 amp service.


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## Brain Coral (Nov 7, 2017)

Hi Karl,

Yes, the 5hp motor is a complete RPC unit that I bought from Elimia converters in Kentucky. My residential service is the typical 200 amp service.

Brian


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## Reeltor (Nov 9, 2017)

I don't know anything about your lathe, I will say that my 16" (really 18" swing) Monarch runs well with a 5 hp motor.  Could it do better with a 7-1/2 or 10hp motor?  Yes, most likely but I wouldn't test it and the 5hp does well enough.

I'm convinced that your current 10hp RPC can run your lathe just fine, even if you replace your current high voltage motor with a 10hp 240V 3 phase one.  In the event that you do have any issues starting your lathe with the 10hp RPC then just start another machine on the circuit first.  The HP of the RPC plus the HP of the second machine will allow you to start your 10hp lathe.

Here is Keith Rucker talking about his RPC system


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## Brain Coral (Nov 10, 2017)

Hello Reeltor,

It's certainly worth giving it a try. I have often wondered how to wire my machines to achieve a higher overall RPC hp rating by turning on an additional machine. I do happen to have a 3 phase breaker panel, that I have yet to hook up, but if I do hook up my 10hp RPC to the 3 phase breaker panel, and then feed my machines with separate feeds and breakers from the panel, would I achieve the desired effect?

Brian


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## Reeltor (Nov 10, 2017)

Brian,

I don't think so.  If you are on separate circuits (breakers) I don't think you get the desired effect.  I am not the electricity expert to ask.  There are many here on the site who are real experts and can give you the benefit of their knowledge.  I have all of my three phase machines daisy chained from my RPC.  Breaker at the panel box and fuses or breakers at each machine.  From the get-go I put in a large RPC (15hp) box from WNY phase convertors and a NOS locally sourced motor.  In your case, I'd try to make what I have work and not re-spend money already spent, at least try to use what I have until conditions prove unsuitable.

Mike


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## Karl_T (Nov 10, 2017)

Brain Coral said:


> Hello Reeltor,
> 
> It's certainly worth giving it a try. I have often wondered how to wire my machines to achieve a higher overall RPC hp rating by turning on an additional machine. I do happen to have a 3 phase breaker panel, that I have yet to hook up, but if I do hook up my 10hp RPC to the 3 phase breaker panel, and then feed my machines with separate feeds and breakers from the panel, would I achieve the desired effect?
> 
> Brian


Using that 3 phase panel would be a great idea. and yes, all the motors help generate 3 phase. For many years, I started my drill press and left it running to start my big lathe.

There is no exact rule for how much 3 phase motors are needed to generate the 3 phase circuit. everything depends. Just remember if you are undersized and start too heavy a part in your lathe at too high a speed, lots of majic smoke will come out.


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## Brain Coral (Nov 11, 2017)

Well, I found a 10HP 3 phase motor to replace the high voltage one on the lathe, for a start. I just got home with it, so I haven't checked if it runs,  without issues. It is a dual voltage Baldor motor 208-230/460V , 1725 RPM and the same 215T frame size as the one on the lathe. The 10HP 3 phase motor on my RPC is a Canadian made Leeson motor with exactly all of the same specifications. Although, the Baldor motor lacks the cast cooling fins, it still looks like a TEFC motor.

Here's a few pics of the motor...







Here is the RPC motor...






So, now I have a choice of motors for the lathe.

Brian


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## Brain Coral (Nov 11, 2017)

I just noticed that the frame designation on this new motor is 215TC and the other two motors are 215T. I believe that the letter "C" refers to the new motor being able to foot mount, or face mount.

Brian


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## Keith Foor (Nov 12, 2017)

Things to know on multi motor RPC setups.  
First and *MOST IMPORTANT *the motor RPMs should match and motors should be of a similar design.  Don't mix winding types.

After that, it's simple.
Build your standard single motor RPC, with a starting method of your choosing.
Then you need two additional timers and contactors.
Once the first RPC is fully up to speed and running, have a contactor connect the second motor, do this with a timer that runs longer than it takes for the first motor to start.
Once the second motor is running and up to speed, have a second contactor connect the output and run capacitors for the second motor.  
Easiest way to do this is have the first timer start to second running and have it control the contactor for the output.  Wire the run capacitors to the OUTPUT of that contactor as well as the actual output to the equipment.  

Have done a couple that were in excess of 100HP total capacity off a 20 a 30 and a 50 HP motor.  
Big 3 phase motors simply can't be started with the capacitor start method.  The current draw is crazy high.  

Remember that your wire sizing will need to be rated for the TOTAL HP output of the complete RPC unit.  Meaning is you are gonna have 20 HP total output, the wires coming from the breaker box and going through to the output will need to be heavy enough for a 20 HP load.


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## Brain Coral (Nov 13, 2017)

Hello Keith,

Thank you for all of the very helpful information. I am still on the hunt for a third 10HP motor. I will be heading down to the shop soon, to check the motor that I bought, to see if it is a Wye or Delta connected motor, as well I will hook it up to my RPC to see how it runs and what voltage values it produces. I will also check my RPC motor, to see which way it is connected, as to Wye or Delta.

I am fine with those fundamental procedures, but I may have to have some help when it comes time to wire in the second motor and contactors, etc.

Just so you guys know what it's like trying to find an electric motor of this specific size, in my area, I had to cough up $250.00 for this one that I bought yesterday. If I could have found one at the scrap yard, I would have paid $200.00 for it. I had one guy answer my "Wanted" ad, who wanted $550.00 for his motor.

Brian


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## Brain Coral (Nov 13, 2017)

I have a NOS Hobart control panel, that might be of some use for the second motor, but I fear that it may not have the capacity in amps. Here's a few pics of it and the schematics...


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## Brain Coral (Nov 25, 2017)

Well, the used motor that I bought, looks like it has a bad winding. The fellow who sold me the motor, says he will refund me the money spent, but we shall see. All of the scrap yards, simply cut the motors off of equipment and toss them into a pile, so, unless you are right there when a piece of equipment comes in.... and it has just the right motor, you are SOL...

So, I called a local motor repair shop and ordered two motors. From what I understand, the Leeson motor is a re-conditioned motor, and the Ech Top motor is new.





So, now I have three good 10hp motors to work with. They are all 230/460V motors, and, I believe, all are the same winding types. The two new motors are both rated at 1760 RPMs, as well, my older 10HP RPC motor, is
rated at 1760 RPMs








So, I will go the route of using the two 10HP motors combined, to give me the equivellent of a 20HP RPC, and the third 10HP motor will go on the lathe.

Brian


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## Brain Coral (Dec 22, 2017)

Well, it's been a while since I last posted....  I ran across a thread, which gave a link to a Phase-A-Matic bulletin, which shows two identical HP RPC's wired together in parallel.

http://www.phase-a-matic.com/PDF/RMU.pdf

I am tempted to go this route, to achieve a 20HP RPC. For the price of another complete RPC panel from WNY Phase Converters, I don't think that I could source, collect, and purchase all of the parts individually for that price. In addition, down the road, I can always sell each 10HP RPC's as complete.

What do you guys think ?

Brian


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## Karl_T (Dec 22, 2017)

sounds like a good plan


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