VFD on a PM 949TV OXYMORON???

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Gersh42

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I ordered a PM 949TV single phase on Friday. Being a head case and letting my anxious personality get the better of me hah, I am second guessing the single phase decision. I have done some initial searches but cant find info for my exact scenario.

I do not want to go down the road of a rotary phase converter, that leaves me with the static phase converter or a VFD. Right off the bat I don't like losing 1/3 of my HP to a static converter, so I have been leaning towards the VFD option. I guess my actual question is what is the TRUE benefit of possible changing my order to a 3 phase version? Also like the title says is it a oxymoron to run a VFD on a 949TV machine? any problems you foresee?

A few things that don't come into play for me, being a TV model I'm not looking at the VFD for speed control only to convert to 3 phase power. Also I'm not worried about the lack of efficiency of single phase motors.

The benefits I am interested in, is a 3 phase motor is said to be more durable and longer service life. Also increased performance out of the machine itself i.e. better surface finishes. Just wondering how true that is and worth the trouble of installing a VFD

Thank you in advance!
 
I think the surface finish issue is not nearly as big a deal on a milling machine as on a lathe. Single phase is fine, and easier to hook up
The variable speed is nice to have but not essential. Again, more useful on a lathe IMO

The main concern with a vfd is that the motor must be permanently connected to the vfd output with no switching or contactors in between.
Any existing 3-phase motor switching controls on the machine would be bypassed, and control panels may need to be rewired or re-built, in order to have variable speed and/or reversing functions in a convenient manner without having to scroll thru vfd menus.

You can use a vfd as a fixed frequency power source, but it's kind of a waste since they can do so much more.
 
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markba633csi said:
I think the surface finish issue is not nearly as big a deal on a milling machine as on a lathe. Single phase is fine, and easier to hook up
The variable speed is nice to have but not essential. Again, more useful on a lathe IMO

The main concern with a vfd is that the motor must be permanently connected to the vfd output with no switching or contactors in between.
Any existing 3-phase motor switching controls on the machine would be bypassed, and control panels may need to be rewired or re-built, in order to have variable speed and/or reversing functions in a convenient manner without having to scroll thru vfd menus.

You can use a vfd as a fixed frequency power source, but it's kind of a waste since they can do so much more.
Click to expand...
Its very easy to rewire existing controls to make the VFD do forward reverse start stop E stop ect.
 
You are doing the same stuff as me.
In principle, VFDs need not much care about the motor type, They accept whatever power is available, rectify AC to get a DC bus, and then make artificial AC out of that, but of a special high frequency pulsed sort, to allow control of the energy in the output. Most motor drivers I have seen allow choice of single or three phase inputs, and all had a U, V, W output, good for three phase, but the kit could be configured to use only two of them to connect single phase motors. Basically, they can be very versatile, and highly efficient, but you do have to check carefully what are the options available on the VFD you might be considering.

Three phase compared to single phase? Three phase has three poles spaced 120°, so the torque tugs are even, and regular at three per rev. Modern motors can have more poles, like 4, 6 or 8, but I am thinking here of using VFDs on old style motors. Single phase motors have two poles, set at 90° to each other. The AC is traditionally directly connected to one pole set, and a nearly 90° phase-shifted version of the AC is contrived by putting the AC through a capacitor, to use on the other pole set. One finds various other capacitor arrangements for START to get it turning in the right direction, or reversible.

The nice thing about VFDs is that you can throw away the capacitors. VFDs are able to make very satisfactory versions of 90° phase-shifted, energy adjustable, artificial outputs to directly drive the pole coils of a single phase. Three phase motor is better, in my view.

About the motor voltages.
In principle, a VFD can accept energy at some voltage, and make outputs for any style motor. This is where you find those that use 235VAC or 240VAC inputs are lower cost and perform better. An AC 3-phase motor, wired in "star" connection, in a place where the single phase is 240V would expect 415 volts AC between phases. In USA, 3-phase voltages are lower, but the math is always the same.
Line Voltage = √3 × Phase Voltage

Changing the connections on an old 3-phase motor to "delta" recovers the 1.73x power, and allows it to run on the lower available bus voltage the VFD can get out of a 240V input. It's useful to know if you are trying to use an older 3-phase motor.

VFDs that can hike the voltage.
These are types that have a built-in front-end inverter. They suck more current from a lower voltage, and deliver normal currents, but at the higher voltage. You can use a separate inverter. Boost-type switched-mode power supplies at machine powers are bound to be expensive, and most VFDs are not. A simple use of delta connection can save money. Some folk like changing out the old motor for a modern multi-pole permanent magnet motor.

I go for VFD artificial 3-phase, but single phase is OK
I don't know what the latest available lower power VFD technology does now, but I expect single phase with VFD will do just as well. I was into inverter-driven servo motors at the 70kW level. I loved that they could deliver full torque forwards, even when stopped, or being driven backwards. These things had a separate small motor strapped onto them just to keep a cooling fan turning. When it came to my own modest vintage lathe stuff, the South Bend 9's had 1/3 HP and 1/2HP single phase. Given their low power, they were big, and heavy, and one had a capacitor kaput! Available VFDs seemed to be much cheaper, simpler things, and one I borrowed for a while had poor torque at low revs, and made huge RF interference.

I am not so intent on "keeping it original" that I won't consider a motor upgrade. Line voltage in UK is 235VAC anyway, so I would replace with a 3-phase driven by artificial, speed-controlled AC . Being cheapskate, I have recovered a used old servo drive, and that will be re-purposed into use as a VFD. I also have a couple of servo motors, but they are too good to be used just for speed control of a lathe motor.
 
Firebrick43 said:
Its very easy to rewire existing controls to make the VFD do forward reverse start stop E stop ect.
Click to expand...

Is there any sort kit on the market (VFD + control panel) figured with as common as these style of machines someone would have developed something by now.

I have to say most of Graham-xrf response went over my head (ill have to read it a few more times) I do commercial refrigeration, mechanical repair and building maintenance for three ice rinks. While I do encounter three phase power and motors very often and have a decent understanding the control portion is a bit of a struggle.

This is my first milling machine and maybe down the road I can dive deeper into this but for now I would really like to find some "plug and play kit" where I can just bring 240v single phase and wire the motor to the new control panel. In a perfect world I would like to have a panel that can eliminate the direction change when using the backgears.
 
A 3 phase motor is more durable, but single phase motors can last a long time mechanically. The problem with single phase motors in this application is that the start capacitor tends to go, in particular with frequent start/stop cycles. The start capacitor will overheat with frequent start/stop cycles. The other concern is that if you try to reverse a single phase motor before it stops, it will continue in the same direction instead of reversing. So for say tapping, you need to wait until motor stops and then reverse. This is less of an issue in a mill vs. say a lathe. You can use a VFD as a fixed frequency source for 3 phase, but the on/off cycle/reverse needs to be controlled by the VFD and NOT a motor switch. The PM-949 has no contactors, the motor is directly wired to a motor switch for FOR-STOP-REV. If using a VFD this would be eliminated. On a mill, I usually recommend 3 wire control, it requires a momentary stop, run and a sustained forward/reverse selector. It is very easy and basic.

When using a Reeves drive, it is recommend to use the VFD more as a fixed frequency source and use the mechanical speed adjustment. This prevents wear in a single position on the drive and also gives you a mechanical advantage of the belting ratio. The down side is they are more expensive, noisier, they wear and can be expensive to repair (although in a hobby environment should last decades). Most individuals buying a new mill with the intent to run it off of a VFD go with a pulley head. You can use a basic VFD for use on the mill, some people install them in the body of the mill, otherwise you need an enclosure and you should have a power disconnect switch at the machine. A simple control box/switch gear is maybe $100, so not much expense if you choose to go that route. There are also mills that come with factory installed VFD's, they run as a single belt speed with a back gear.
 
I went 3-phase and VFD to get away from reliability issues of a single phase motor (cap failures especially with lots of start stop ops) and the mechanical complications associated with a Reeves drive system, and greater control flexibility (speed control, instant reversing, jog, braking, etc.), plus I'm very much at home with VFD systems, having worked with some really huge ones (plastic extrusion) in my career.
I've got my belt set to the second groove down from the top of the pulley system and I've got excellent torque and speed-range for everything I need to do at that setting, so far have never needed to change the belt settings, never even used the back gear to date. I go from drilling to power-tapping on the machine effortlessly, switching from FWD to REV without even thinking about it. My spindle ramps down to a dead-stop from any speed in 1.3-seconds and ramps up to full speed in 2-sec. I find my jog speed especially useful for power-tapping.
 
Gersh42 said:
Is there any sort kit on the market (VFD + control panel) figured with as common as these style of machines someone would have developed something by now.

I have to say most of Graham-xrf response went over my head (ill have to read it a few more times) I do commercial refrigeration, mechanical repair and building maintenance for three ice rinks. While I do encounter three phase power and motors very often and have a decent understanding the control portion is a bit of a struggle.

This is my first milling machine and maybe down the road I can dive deeper into this but for now I would really like to find some "plug and play kit" where I can just bring 240v single phase and wire the motor to the new control panel. In a perfect world I would like to have a panel that can eliminate the direction change when using the backgears.
Click to expand...
Sorry to do this to you. I will try and say it simpler.

If you already have a new single phase delivered, you can use it, with VFD, although the machine does seem to have a load of it's own speed options.

Your mill requires a 220Volt, 20Amp supply for both single and three phase versions, and one of it's features is it normally has a spindle speed range 80-2720RPM, which goes to 40-5000RPM if you use a VFD. This is stated in the specification. If you happen to use a VFD, you can automatically have the 3-phase output option, without any separate converters, rotary or not.
I was looking --> HERE

I am pretty sure you can get a full explanation from your supplier for what you need, if you explain what supply you have. I should think you need the right VFD, 220VAC to feed the VFD it, and have exactly the right 3-phase motor, with correct connection type, to suit. You can also use a 220V single phase motor, though most folk here who have the experience, seem to advise 3-phase, because the inevitable capacitors on single phase kit do not do so well when having many stops and starts.
 
Gersh42 said:
Is there any sort kit on the market (VFD + control panel) figured with as common as these style of machines someone would have developed something by now.

I have to say most of Graham-xrf response went over my head (ill have to read it a few more times) I do commercial refrigeration, mechanical repair and building maintenance for three ice rinks. While I do encounter three phase power and motors very often and have a decent understanding the control portion is a bit of a struggle.

This is my first milling machine and maybe down the road I can dive deeper into this but for now I would really like to find some "plug and play kit" where I can just bring 240v single phase and wire the motor to the new control panel. In a perfect world I would like to have a panel that can eliminate the direction change when using the backgears.
Click to expand...
Yes there is but you pay dearly for it.

Bridgeport Retrofit

I have used this kit before(at work retrofitting Series 2 bridgeports.

This is no reason other than time that you cant reuse the original buttons/switches. Its simple wiring directly off the VFD and a parameter setting depending on how you want the switch to act.
 
At the price point of that VFD kit, you might as well buy a factory installed VFD with a dedicated vector motor, Yaskawa VFD and Tach. Downside is the run controls are still primitive, the electric motor fan runs continuously unless one adds a timer.
 
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