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3-phase for home shop

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  • 3-phase for home shop

    Hi folks. I'm in a bit of a dilemma here and could use some suggestions.

    I'm starting out with a 1967 BP with 1 HP 3 phase and was planning to buy a small VFD to run it.

    I am about to be the recipient of a really nice collection of machinery. My BIL has a customer (manufacturing) that is getting rid of a lot of their older maintenance equipment (they're changing locations) and it looks like I can get the stuff for pennies on the dollar, well under scrap iron prices. Too good of a deal to pass up.

    I am looking at adding a lathe, horizontal band saw, vertical band saw, cold saw, hydraulic press, and a surface grinder. I haven't seen the stuff yet, but everything is supposed to be in decent, running condition.

    Problem is that everything is 3-phase and I really wasn't looking to put VFDs on all the equipment. I have a new 5 HP, 3-phase motor I bought surplus from my company a while back and was wondering about the feasability to build a rotary converter from it and have a dedicated 3-phase circuit in my shop.

    Hobby shop only and so I will probably only be running 1 machine at a time, maybe 2 if I've got something on the surface grinder and want to run the mill while I wait for that to finish.

    Any suggestions would be VERY helpful.

    Will post pictures and details as I get the equipment. I've got several trailers full to go get.

  • #2
    Sounds like a really good reason to build a 3 phase distribution, althou it might better be served by a slightly larger 3 phase generator then a 5 hp motor


    • #3
      sounds like quite the your own RPC with that motor. Lots of guys will tell the benefits of VFD's but i went RPC because i didn't want to buy many VFD's as machines are added. Seven 3 phase machines currently. the variable speed advantage of vfd is there I guess, I've never missed it as each machine as an adequate range via their gearboxes....I need a vfd for the monarch though but will input 3 phase into it so i don't need as large VFD

      you'll get opinions on both, but with a motor in hand vs half a dozen VFD's isn't the decision already (mostly) made?
      in Toronto Ontario - where are you?


      • #4
        My shop is a one person home shop also. My Roto-Phase says max motor size is 3 hp max. Total load 9 hp max. It works very satisfactory. I never run the Mill and the Lathe at the same time, but I could. From a functional standpoint the Power saw is the most likely to be run with something else. Sounds like you gat a super good deal on the machines.
        Byron Boucher
        Burnet, TX


        • #5
          The first one I used was a 3hp 3phase motor to pull a 1 1/2hp BP. I wired it up, wound a rope around the shaft, gave it a pull, then hit the power...Presto
          3 phase power to my Bridgeport.
          Yep, I'm a redneck. d:^)


          • #6
            I am a huge fan of VFDs, but your application is the perfect example for rotary converters. I would take the above suggestion and wire the shop for three phase distribution. The only thing to consider is the size of the motors on the machines and size the rotary accordingly. Another thing to keep in mind is that many machines really don't benefit from variable speed (saws, shapers, surface grinders etc), while the lathe and milling machine would benefit and you always can add VFDs to those machines when the need and funds permit . If you already have three phase power from the RPC then the vfds can simply be added with no concern about single phase input. This may save a few bucks in the future.


            Happily working on my second million Gave up on the first


            • #7
              Can't beat a rotary converter for YOUR application.
              Check the HP of the other equipment.
              5 HP is overkill and will waste energy UNLESS one of the
              machines has a 2 speed motor.
              If they all are 1 .5 HP or less, I would go with a 3 HP to reduce noise and
              electric bills.
              If you decide to use the 5 HP unit, by kicking the shaft to start
              You will not need the capacitors either, Although they do help
              Kicking over the shaft and powering up, is the absolute simplest and cheapest way to get 3 phase in the shop

              Green Bay, WI


              • #8
                Let me explain myself why I suggested a slightly larger motor for the 3 phase generator

                I have a 7 1/2 hp Ronk Rotophase. Its a good unit and I can run multiple machines on it with ease. The problem is "Starting Current". My cnc mill has a relatively small motor at 2 hp, but when it starts you can hear the rotophase grown under the "Starting Load". Which as you know can be 400-700% of motor load.

                Other then that the 71/2hp unit works flawlessly and has been doing so for years


                • #9
                  I was in the same dilema.., 5 VFDS, more machines appearing... have a nice 5hp rotary converter - but it won't run my 4hp lathe in the upper two speeds - the lathe motor starter will thermally trip because it's taking too long to spool up.

                  So... screw it - I'm putting in a 15 hp converter, three phase distribution, and some of the larger VFD's will be run from the three phase (oh... easy to buy used or new "cheaper" larger vfds that are three phase..). In addition to speed control, VFD's also provide excellent soft-start and motor protection (if programmed correctly)...

                  Single phase -> three phase -> VFD... Inefficient? Don't care...
                  Last edited by lakeside53; 12-31-2009, 07:43 PM.


                  • #10
                    You have found a gold mine there. Your right in that since your a one man shop you only need an RPC and even if you run 2 or 3 machines the 5 hp RPC will run them.

                    This is the wiring diagram for my RPC and I have been using it for over 15 years. The VFD's are only needed if you want to vary the rpm of the motor and can only be used on one machine at a time as you well know.

                    It's only ink and paper


                    • #11
                      I'd be looking at a vfd powered motor-generator, but then again I'm biased to that route because I took it.

                      Total cost for 24hp output capacity of TRUE BALANCED 3 phase was $1800; with the advantage of running the whole works off a 98% efficient vfd.

                      Of course I did it because I needed the phase angles to be perfect for the servo drives on my turning center, but it does make for a good solid power source for anything else down the road.


                      • #12
                        Ditto most of the above.

                        I found myself in the same situation: I started out with one 3-phase machine, a small lathe that I bought already converted with a VFD. I'd already known of them before that, but this was my first hands-on example of just how handy they are, especially on a lathe.

                        Shortly thereafter I picked up a small horizontal mill that came with a 3-phase motor, and moreover, was one of a unique configuration that would have been troublesome to replace with a more common frame-size single phase. So I bought another VFD for it.

                        Before that one was done, I lucked into a large (12"x2" 2HP) pedestal grinder for fifty bucks. Also 3Ph, so I bought a third VFD. Then shortly after that, I bought an older Wells bandsaw- again, 3ph, and with an oddball motor mounting that would have made it difficult to swap.

                        I was starting to run out of money to buy VFDs.

                        The tipping point came when I decided to convert my other lathe to 3-phase (to get the speed control and additional torque, mainly) and then at about the same time, happened across a nice surface grinder. The grinder included a vacuum/coolant module, so had three 3-phase motors all by itself. That would have been some $700 just in VFDs...

                        So I wound up using one of the VFDs I already had, which I'd been using as as sort of portable power source for the pedestal grinder and the saw, and put it in the lathe.

                        Then I bought an American Rotary prefab control box- it was everything but the idler motor, and ran $225. Yes, a good scrounger can assemble an RPC for less, but I had no stash of caps and I'm not what you'd call electrically inclined. It was worth the cost to me to have a tested, ready-to-go, and better yet, warrantied controller.

                        I wired it up using one of the two 5HP motors I had laying around, and now I use it to power the pedestal grinder, the surface grinder (and it's vac module) and the bandsaw. It works great, easy to use, no problems.

                        The 5HP idler gives me something like 3HP of capacity, which is plenty for any one or even two machines. But as others have mentioned, I'm also a one-man shop, so it's rare that any two RPC-fed machines will even be on at the same time, let alone drawing anything close to full-load amperage.

                        So that's the solution I'd recommend: Put a VFD on the machines that can best use the VFD features- namely mills and lathes. Then put together one fair-sized RPC setup, and use it to run the machines that don't necessarily need variable speed, or programmable ramp-up/ramp-down, etc., like the cold saw, hydraulic press and surface grinder.

                        I'm just using cords and a single wall outlet for my RPC. All the machines it feeds are in the same corner of the shop, and two of them are immobile. Short lengths of cord were cheaper and simpler than running conduit past doors and around other fixtures.

                        But if you're industrious, running dedicated wiring, junctions and outlets is pretty easy.

                        Doc's Machine. (Probably not what you expect.)


                        • #13
                          the way we did it in my shop was to build a rotory phase converter ran that to a 3 phase breaker box then wired the machines like a 3 ph system. that way if i ever bite the bullet and get 3ph all i have to do is hook it into the panel box and i am good to go.


                          • #14
                            How many machines can you operate at one time? If they are manual machines, that number may be close to 1. Which means that one VFD could run all the machines and give them all the benefit of variable speed.
                            It is a trade off between cost and convenience and depends on your usage patterns, etc.

                            There are a few issues, though.

                            Parameter sets: if you don't use the same parameters for each machine, you need multiple parameter sets. Some VFDs can do this. Baldor is an example. A computer can also reprogram a VFD with a communications port. Many of the parameters you might change from motor to motor are for protection or tuning that a rotary phase convertor isn't going to offer; others, like PID settings could depend on what motor you are driving especially with different sized motors. Some can change the PID parameters based on external input, even when other parameters can't.

                            Distribution: Longer wires between VFD and motor can increase voltage spikes. Stubs distributing power to unused machines may also. In a small shop, though the distances may not be too bad.

                            Control: if the VFD is centrally located, you need to go to that location to control or have a remote head.

                            Safety: there can be some unintended consequences depending on the wiring configuration you use.

                            One option is to carry or wheel the VFD from machine to machine, plug it in and plug the machine into it. If you move work between machines a lot, this is a pain but if you spend a lot of time on one machine between changes, not so big a deal. Another is to wire a remote head (with shielded control wire due to proximity to power wire) to the end of a three phase extension cord. Carry the cord end to the station and plug in.

                            Another option is contactors/relays can distribute power and control wiring to different machines if you have some cheap ones available. Push a button to select one machine, then power and control are routed to that station.
                            Using circuit breaker panels, you may be able to use mutually exclusive circuit breakers. Like you might use to select between mains power or a generator but not both. Easy to do with two, basically a slide between two breakers on opposite sides of a panel that will not let both engage simultaneously. Selector switches are another way to ensure mutual exclusion. You want something that is low in cost compared to the VFD itself, otherwise you might as well use multiple VFDs.

                            If you can use the same parameters, one centrally wired VFD with no remote speed control is in a sense no worse than a rotary phase converter. At worst, you set it for 60hz and leave it but you can change it if you really need to. But do not disconnect machines while the VFD is running as that is potentially bad for the drive/motor (spikes). Have at least gang wired VFD start/stop buttons. Be careful you don't have any machines that start up unexpectedly when you turn on the VFD because you left them on.

                            You can have each motor/machine plug into an outlet on a rotary phase convertor to run fixed frequency yet be able to unplug a machine and plug it into a VFD to vary speed.

                            You can physically lay out the machines to facilitate sharing one or more VFDs. One VFD could run the "background" machines: surface grinder or horizontal bandsaw. Another run the lathe or mill. Other machines connect to one or the other as convenient. With two machines sharing a VFD, it can be located between them, in some cases maybe even close enough you don't need to run extra stop/start buttons.


                            • #15
                              I don't think it's that easy. It seems to me someone said the VFD's adjust to the motor they are running and that changing them from motor to motor causes problems. I think they have to be dedicated to one motor.
                              It's only ink and paper