# Need Help On Converter Choice.



## Zachp (Jun 23, 2015)

Ok I bought a leblond 15c lathe a few weeks ago. It has a 7.5 hp motor on it. My question is what is the best way to get 3 phase to this machine? I have 100 amp service in the garage. Static converter? RPC? Change the motor out for a smaller one? I have found a 25 hp RPC for a good price but I'm afraid that it will be too much to start on my 100 amp service. What kind of startup amperage will this draw? I may purchase a compressor, or a bandsaw somewhere down the road so that has me leaning toward a RPC. Suggestions?


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## T Bredehoft (Jun 23, 2015)

Investigate the term VSR, it seems to be the latest improvement in converting single phase to three phase.   I'm a tool maker, not an electrician, and this is new since I retired 15 years ago.


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## Zachp (Jun 23, 2015)

The vfd for this size motor is out of my price range. I put a vfd on my Bridgeport since it is only a 1 hp motor. The affordable vfd's only go to 3 hp I believe. Thank you for the suggestion though.


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## Ulma Doctor (Jun 23, 2015)

you can make a RPC pretty cheap i wrote a thread on how to do it and it has plans too!
click the link below!
http://www.hobby-machinist.com/threads/rpc-simple-design-unbalanced.12712/


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## Firestopper (Jun 24, 2015)

Your lathe has a 7.5 HP motor, so your minimum Idler (RPC) motor size will need to be 7.5 hp.  No need to run a giant RPC, the cost of operation is fairly low for what it provides.   
Static phase converters are not (at least back then) that great as they convert three phase motors to single phase resulting in loss of power and run hot.  

VFD's provide the ultimate control and options but as you know come with a price for larger units. 

I have been using RPC (balanced) for 15 years now. The current set up is wired in conduit thoughout the shop and provides power to nine machines. I'm a one man shop, so running more than one machine at a time is not common, however I have run (no load) two mills, lathe, cold saw, band saw, iron worker at the same time with excellent  balanced (+/- 3 volts) readings. In essence, each machine becomes a RPC for the next (I believe).

Check out Phase Craft on ebay, I purchased his control panel for a 7.5 HP Idler for $200 free shipping. It came prewired and balanced. The motor I used is the same motor from my old shop's RPC and runs quiet and efficient. You send him the information on your idler (size,RPM,service factor.etc) and he builds the panel accordingly and balances the legs.

As you can see from the photos, the machines are decent size and run fine on a 7.5 HP RPC. The largest machine (iron worker) is a 5 HP unit. The RPC is on a 40 amp circuit on a 200 amp sub panel. 

I recently  added a VFD (with the help from a fellow member MJ) to the plate roller for more control. The VFD allows for POT, hour meter, ramp up/down, braking, as well as torque values to be adjusted. This VFD does not convert the power to 3 phase in this case as I use the RPC for that.

I hope this helps.


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## Zachp (Jun 24, 2015)

Thank you both for your replies.

I had a friend that has a home machine shop tell me to double the idler motor size to the size of the load. Is this not true? If i have a 7.5 hp motor on the lathe, then a 7.5 RPC will be big enough? If that is the case I should be fine. I may opt for a 10 hp unit to allow a larger compressor down the road. Can anyone confirm this statement for me? I hate to keep asking stupid questions but this is all new to me and im trying to get everything set up as soon as i can so I can start using the equipment. I have some small parts that a friend is wanting me to make and I am sure it is going to take some practice to figure it out. 

Just to clarify:
The Leblond lathe has a 7.5 hp motor
The bridgeport has a 1 hp motor with a VFD on it
Need to know the minimum size of RPC I need to run the lathe.


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## Firestopper (Jun 24, 2015)

It's been a very long time since the research was done on the original RPC, but I tend to remember key items. If memory serves, your idler must be the same or larger, but never smaller. It was never an issue for me as the biggest load comes from the iron worker at 5 vs. 7.5 RPC.
If you have the option to go 10 HP, then thats a better match imo. I'm sure someone else will chime in to add more information.


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## Doubleeboy (Jun 24, 2015)

Ideally you want a idler motor twice the size of largest motor that will be used.  Talk to the guy at Phase Craft, he builds good stuff, and responds to questions.  He is on ebay and has lots of models.

michael


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## Zachp (Jun 24, 2015)

I guess I should add to my question a bit. While picking up some parts for the lathe and mill yesterday, the sales guy looked in his manual and the machine originally had a 3 hp motor on it. Someone has put a 7.5 hp motor on it somewhere in the past. Would this have any affect on the RPC sizing? Or do I need the double size still?


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## Ulma Doctor (Jun 24, 2015)

IMO, if you were to get a 10hp RPC you could easily run the lathe and the BP at the same time as long as the lathe was started first, then the BP.
care should be taken to make the single phase load lines to be heavy and have the proper size breaker.
i have started 10 hp motors with a 7.5 hp rpc, i'm not recommending the practice , rather giving a point of information.

your 7.5 lathe motor won't be working hard to power the lathe.

have you considered downsizing the motor???- you can get away a lot cheaper in wiring and other ancillary supplies necessary to install and run


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## Zachp (Jun 24, 2015)

I have considered downsizing the motor. I have also considered running a single phase motor. Both are more expensive than what I can purchase the 10 hp rotophase for. It is $400. I have been told I need at least a 10 gauge wire to the converter. Is this wire big enough? How many wires will it take? I have someone who knows what he is doing that will wire it but would like a head start on supplies. What size breaker? Is 50 amp big enough? Is it best to keep the converter close to the panel or the machine. What size wire from the converter to the machine?


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## Ulma Doctor (Jun 24, 2015)

the choice seems rather simple from where i sit.
if i were in your shoes, i'd bite the bullet, and get the 10 hp rotophase and not look back.
but i'm not like most guys you'll meet.


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## Zachp (Jun 24, 2015)

That's good Ulma, as I'm not normal either! I plan to jump on the 10 hp and get this thing up and running so I can start tearing things while I learn!


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## Ulma Doctor (Jun 25, 2015)

Zachp said:


> I have considered downsizing the motor. I have also considered running a single phase motor. Both are more expensive than what I can purchase the 10 hp rotophase for. It is $400. I have been told I need at least a 10 gauge wire to the converter. Is this wire big enough? How many wires will it take? I have someone who knows what he is doing that will wire it but would like a head start on supplies. What size breaker? Is 50 amp big enough? Is it best to keep the converter close to the panel or the machine. What size wire from the converter to the machine?




i'd use 8 gauge for the short single phase 50 amp input wire run to the RPC, then you can use 10 gauge everywhere else as long as you aren't making long runs


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## Firestopper (Jun 25, 2015)

*Sizing For Load Types
1.*

*Motor Loads *

*A...
TYPE 1 Motor Load:*

May be used up to the HP rating of the converter.* For _instant_ reversing (as for rigid tapping), size according to* TYPE 3 LOADS *
*Many restrictions apply. Most applications require sizing the converter a
minimum of 50% larger (see all load types). 


*B.
TYPE 2 Motor Load:*

These include domestic & European lathes without a clutch, some pumps, wheel balancers, paper cutters, flywheel driven equipment, air conditioners, blowers, woodworking band saws, dough mixers, meat grinders, motors rated below 1000 RPM, etc. Use a converter with HP rating of at least 50% larger than HP of the motor. *.*

*C.
TYPE 3 Motor Load:*

These include Design "E" motors, Taiwanese, Chinese, Brazilian, Mexican motors, pumps starting under load, etc. Use a converter with twice the HP rating of the motor. *.*

*D.
TYPE 4 Motor Load:*

These include laundry extractors, hoists, elevators, etc. For these start-up loads use a converter with three times the HP rating of the motor. *.*

*E.
TYPE 5 Motor Load:*

Often hydraulic pumps, which come under a momentary load during use will be loaded well beyond their rated HP for the brief period of maximum PSI. Examples includes bailers, compactors, paper cutters, shears, pumps, etc. The HP of the converter must be at least as high as the actual HP developed by the motor. To calculate the HP developed, you must first find the actual amperage drawn during maximum PSI. This is different from the rated amps of the motor. Next you would divide the maximum amperage by 2.8 to find the actual HP being developed by the motor. That figure is the minimum size of converter to be used. Example: A 10 HP compactor with a motor rated at 28 amps but draws a peak of 40 amps momentarily at maximum compression. Divide 40 by 2.8 = 14.3 HP being developed, use model R-15 Rotary Converter.

*2.*

*Resistive Loads *

Resistive loads must use the Rotary type converter, the Static type should never be used because it would be damaged. There are two methods to determine the HP of the converter to be used. One method is to take the amperage rating of the equipment and divide by 2.8 to find the equivalent HP. The other method is to take the KW rating and multiply times 1.34 or divide by .75 to find the equivalent HP of the equipment.

*3.*

*Computer, Rectifier & Transformer Loads *

Transformers and electric equipment (welders, lasers, EDM machines, CNC equipment, computers, plating rectifiers, power supplies, etc.) can operate on the Rotary Converter. Use the same formula as for resistive loads to determine the proper size converter to use.

If a 4-wire wye input is required (all lines equal voltage to ground), a three phase delta-to-wye isolation transformer must be installed between the converter and the equipment to change the delta power to wye power.

*4.*

*Multiple Motor Applications *

Due to the high in-rush current required to start a motor (5 to 10 times the normal running current), most applications require sizing the HP of the Rotary Converter 50% larger, *or more* than the horsepower of the largest motor, or any combination of motors started at exactly the same time. The first motor started, *if not running heavily loaded,* generates additional 3-phase power back into the circuit. You can then run additional motors, provided they are not running heavily loaded and not all started at the same time. A maximum of up to 3 times the HP rating of the Rotary Converter can run at the same time, if not heavily loaded, and not started simultaneously. For example, a 30 HP Rotary Converter potentially could run motors totaling up to 90 HP. Contact factory for verification of sizing.



I found some interesting info on types of loads for determining Idler selection. I stand corrected on the minimum idler size. According to the type of load chart, most applications would require a Idler to be 50% larger than the highest HP in the system. 

I ran #8 wire from panel (40amp breaker) to RPC, and used #8 for all machine feeds as they are long and can be extended to add machines. All machines have cord caps and receptacles. All larger machines have internal breakers to protect the machines.  AC tends to be quite dirty and input voltage can vary thought the day. The Idler in our system is a Howell (very robust and heavy compared to other 7.5 3PH motors) continuous duty, RPM 1725, 21 amp @230 (lower as Idler) and SF of 1.15 . I have not experienced issues with this set up, even during the summer months when AC input is the dirtiest. 

If you decide to mount your RPC, use vibration isolators to mount the Idler as this will prevent horrific harmonics, ask me how I know lol.


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## Zachp (Jun 25, 2015)

Thank you firestopper for that info. It seems that maybe I should go with a larger motor but, the 10 should work fine in my application; I hope. If not, I will cross that bridge. I should never be working the machine hard to have that high of a demand for power. I will let you all know how it turns out. Thank you very much for all of the input.


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## Firestopper (Jun 25, 2015)

Your welcome, 

Is the VFD for your mill single phase input or 3 ph input?


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## Zachp (Jun 25, 2015)

It is single phase input only i believe. I will check that tonight for sure. Im pretty sure it is a Teco. Would be nice if I could run them both from the 3 phase and use the mill for additional startup power.


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## Firestopper (Jun 25, 2015)

We're on the same page. Single circuit for all equipment. VFD's are very nice to have on a mill/lathe.

Looking forward to your progress.


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## Zachp (Jun 25, 2015)

Looks like I have lucked out on the VFD. It is a teco n3-201-cs-u which appears to run on single or 3 phase and has increased hp range in 3 phase. Woohoo. Two birds one stone!


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## Firestopper (Jun 26, 2015)

Zachp said:


> Looks like I have lucked out on the VFD. It is a teco n3-201-cs-u which appears to run on single or 3 phase and has increased hp range in 3 phase. Woohoo. Two birds one stone!



The best of both worlds IMO.

 I would like to add a VFD to the lathe someday. I saw another members (mjks) lathe set up who is using a ton of parameters via VFD. He's very sharp and has helped a lot of members on this site. I am lucky to live in the same town as he has been very helpful with design, rewiring and programing a plate roller I had been struggling with for some time. One of the cool things he did upon finishing the install was Autotune using a laptop. 

Keep us posted.


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## mksj (Jun 26, 2015)

I believe the Teco VFD model specified is single phase in 3 phase out from the specs. But not really a problem, just run off a single phase 20A circuit from the sub panel, and use a RPC for the lathe. Not sure of the size of the lathe or the work envelop it will be used for, but if the 7.5Hp gives you problems,  a smaller motor in the 3-5Hp range is very reasonable. Could look at something like the a Teco 3 phase 5Hp (usually new around $200-250), and a RPC, or VFD if you need speed control.
1 HP, 230 Volts, NEMA 1, Teco, N3-201-CS-U

*MODEL #:* *N3-201-CS-U *​230 Volts 1 Phase Input, 230 Volts 3 Phase Output


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