Remotor or Rotary Phase Converter

[SmithDoor]

Never seen that I have run single and three phase lathes.
If have bad bearings out of balance motor may give you a bad finish but this true with both phases

Dave

No one mentioned the fact that on (especially belt) lathes, you get a better finish with 3 phase.

 

[Gordon]

From my experience having an idler motor is the key to having a smooth 3 phase experience. I have read that you only have about 2/3 of the HP using a phase converter. I do not know if that is true but for most home shops we are not using anything close to the maximum HP. We are not trying to do heavy duty production work. Taking three cuts on a lathe instead of two is not an issue in the home shop. Perhaps with some of the smaller machines others are coming close to maximum. I doubt that my South Bend lathe and Excello mill are anywhere near capacity the way I use them.

 

[mu38&Bg#]

Static(solid state) phase converter or a 3PH motor running with capacitors on 1PH results in less power output than nameplate rating. (phazpak and others as mentioned above)

A 3PH motor running from a rotary phase converter(idler motor) or VFD will make full power when properly sized and configured.

Someone mentioned VFD's with 230V input with 380V output. There also exist VFD listed as 115V input with 230V output. While they do work, cheap ones do not output full 230V so you lose some power.

 

[Chiptosser]

Robert Murphy
First off, in your situation you first need to check your motor for wiring options.
If you can not change wire configuration, you will have to change the motor or use a transformer.
Look at the spec. tag on the motor for available wiring options.

I am in the same situation as Gordon. multiple horse powers on multiple machines. from 3/4 hp to 15 hp.
I have capacitor bank for the very large loads, to no caps. for the smaller motors.
The capacitors are to balance the loads between the 120v per line feed.
Yes, this is a 220v single phase system.

This is always a big decision for someone starting out.
If you do not plan on getting any more machinery, VFD's can be very nice, especially a drill press where you want to vary speed for different drill sizes.
One thing that you need to know about VFD's is that older motors, it all depends on the use, don't play well together. You can get humming and over heating. The VFD can over load if you don't size it properly. You do have to set parameters in the control for it to work properly. If you don't like to mess with that sort of thing, you will have to get somebody who understands what is needed.
It is fairly easy but if that is not for you, so be it.
All the formation is on line and you can check it out for your selves and decision.

fltenwheeler
Is your lathe a Delta Rockwell, variable belt speed lathe? The one with the variable speed lever on the lower left.
Or is the v/speed near the gear changer?

 

[Paul_C]

It is a 2HP on a Rockwell 14"x30" lathe.
Tim

Unless you already have a 2hp single phase motor that would fit I would recommend a single to 3 phase VFD. It will cost less and would be perfect for that application. A few things to consider. A VFD will allow the motor to make full power. A single phase motor of the same rated power will not have the same start torque as a 3 phase. Unless you have a monster rotary phase converter the machine motor will only produce 2/3 to 3/4 of it's rated HP.

I ran a 1 hp Bridgeport and a 10" South Bend lathe with the original 3/4hp for years on a rotary converter. I never had a problem bogging down the Bridgeport but the 3/4hp on the South Bend certainly was weak. Now I can make some serious chips on the South Bend. So many advantages to using a VFD such as adjustable acceleration, deceleration and DC braking.

 

[Robert Murphy]

I have a 240-V VFD connected directly to the original Brooks Crompton motor, with no disconnect between the VFD and motor. The rotary forward/off/reverse switch controlled by the red ball handle above the headstock is wired to the VFD remote control inputs. The coolant pump motor is abandoned in place. The worklamp is powered separately via a normal wall receptacle.

I have two mills that were originally 575-V. On one, I removed the 575-V motors and replaced them with 240-V 3-phase motors driven by separate VFDs. On the other, I built a 575-V step-up transformer system to power the mill from my 240-V phase converter. That mill has kept its original electrical system.

Unless you foresee more 575-V machines or have a strong yearning to keep the Chipmaster all-original, if I were in your shoes, I'd swap the motor to a 240-V, 3-HP, 3-phase, 4-pole motor and drive it with a 240-V VFD wired directly to the motor, and reconfigure the switches to control the VFD. YMMV.

Many thanks for the information...I was wondering about the feasibility of consolidating the f/r switch with the vfd remote
Controls. Knowing that pushes me toward new vid+motor combo. Was the step-up transformer difficult to build?

 

[Robert Murphy]

Robert Murphy
First off, in your situation you first need to check your motor for wiring options.
If you can not change wire configuration, you will have to change the motor or use a transformer.
Look at the spec. tag on the motor for available wiring options.

I am in the same situation as Gordon. multiple horse powers on multiple machines. from 3/4 hp to 15 hp.
I have capacitor bank for the very large loads, to no caps. for the smaller motors.
The capacitors are to balance the loads between the 120v per line feed.
Yes, this is a 220v single phase system.

This is always a big decision for someone starting out.
If you do not plan on getting any more machinery, VFD's can be very nice, especially a drill press where you want to vary speed for different drill sizes.
One thing that you need to know about VFD's is that older motors, it all depends on the use, don't play well together. You can get humming and over heating. The VFD can over load if you don't size it properly. You do have to set parameters in the control for it to work properly. If you don't like to mess with that sort of thing, you will have to get somebody who understands what is needed.
It is fairly easy but if that is not for you, so be it.
All the formation is on line and you can check it out for your selves and decision.

fltenwheeler
Is your lathe a Delta Rockwell, variable belt speed lathe? The one with the variable speed lever on the lower left.
Or is the v/speed near the gear changer?

The lathe is a Colchester Chipmaster with a variable speed (mechanical unit )called a variator 35-3000 rpm. The motor drives the variation via flat clogged belt which then in turn drives the headstone. I would like to keep it original but want to keep cost below $1k. The motor Is 550v so the only other option is two-fold, phase converter & step-up transformer. I would build a rotary phase system but the used motor market sucks in my area!

 

[rklopp]

The transformer setup was not difficult to build, but I have experience with code requirements and running conduit. The hardest part was lifting the heavy transformers onto the wall mounts! Beware you are dealing with lethal voltages, so use wiring, switches, and other appurtenances rated accordingly. I have attached a diagram of my setup. The RPC shown in the diagram has been replaced by a PhasePerfect unit. That makes no difference to the open delta transformer setup. More info here.

Key safety aspects include (but are not limited to): (1) grounding one corner on the high side, or else the three phases could theoretically float to higher voltages and might not blow a fuse in case of a ground fault; (2) having no fuse in the grounded leg, or else in the case of certain phase-to-phase faults, the fuse in the grounded leg might open while leaving the "high" leg fuses intact and therefore leaving the "high" legs live and dangerous.

 

[Gordon]

I am wondering if there is a problem with using a VFD which is oversize. In other words if I am running a 1 HP motor would it be a problem using a 3 HP VFD?

Also is there a proper way to run multiple motors from one VFD? Size the VFD based on total HP of all motors or just the largest if there is a possibility of running more than one at a time? Run an idler motor and size the VFD on the idler motor size?

 

[Robert Murphy]

Sorry about typos as I was using a tablet that I had just flattened and spell check was running rampant...I meant "Variator" not variation and 'headstock" not headstone! Had a chuckle over that one!

 

[rklopp]

"I am wondering if there is a problem with using a VFD which is oversize. In other words if I am running a 1 HP motor would it be a problem using a 3 HP VFD? "

There can be a problem dialing down the current limit for motor protection, depending on the VFD. I have a 3-hp Teco VFD for which I am unable to set the motor current limit down to the nameplate current rating of a 3/4-HP motor. I suggest you check the motor nameplate full load amps (FLA) and the manual for the VFD you have in mind.

 

[Paul_C]

I am wondering if there is a problem with using a VFD which is oversize. In other words if I am running a 1 HP motor would it be a problem using a 3 HP VFD?

Not at all, in fact you are better off oversizing a bit. I got two 3hp Hitachi VFD's for my lathe and mill. I have never seen a VFD where you can't set the motor ratings, but I guess they can exist.

Also is there a proper way to run multiple motors from one VFD? Size the VFD based on total HP of all motors or just the largest if there is a possibility of running more than one at a time? Run an idler motor and size the VFD on the idler motor size?

It's possible, you just add up the motor ratings or size the VFD for the largest motor But is it worth it. What VFD's don't like is a load switched on. You also won't benefit from sensorless vector which requires the VFD to be autotuned to a particular motor.

Many of the newer VFD's have a second motor parameter so you could program them for different machines. But by the time you build some complicated scheme to switch the output and controls your money would be better spent on a dedicated VFD for that machine. Then you can program all the custom parameters such as accell, decel, braking, jog for that machine. On my Bridgeport I set the first motor data for 60hz with a fast acceleration and maximum deceleration so I can instant reverse. Then I set the second motor parameter for 90hz with a mild acceleration and deceleration. Not all motor parameters such as jog speed can be set to a second motor profile. I even fiddled with the carrier frequency to get rid of the ringing a certain speeds.

 

[David Shealey]

This is an old wives’ tale, Snopes-worthy.

No. I have a JET 13X40 gear head lathe, when I got it was surprised at the finish I was getting, read a few things on line about this being a problem with a single phase motor. Did not change the motor, but changed the belt to a Fenner "link belt", finish improved greatly. This was mentioned on a few forums as being almost as good as switching from a single phase motor to three phase. In my case, it was good. The belt on this lathe is pretty short, so the stiffness of it transmits the vibration of the motor very well. The Power Twist belt has enough stretch to even it out. I may one day put a three phase motor on the lathe as I have a rotary phase converter on my milling machine.