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  • Trying to figure out phase converter needs.

    I need to wire up a Bridgeport mill I bought a bit ago. It has a 1½ hp 3ph motor. I also have a small shaper that has a small 3ph (<1hp) motor. I won’t run the two machines at the same time. My shop is a hobby shop. Seems I do a lot more putzing than any production work but I do have a good time.
    I have been doing a little research for a phase converters, VFD and RPC.
    My question is why mess around with an RPC when it seems a VFD is simpler and fewer parts to worry about? There looks like more hardware is involved with an RPC.

    Am I being to simplistic or am I missing something.

  • #2
    Looks like you've got it right. I've been phasing out my phase converter with VFD's, only the pedestal buffer to go. Conversion, variable speed and infinite tweaking options of braking and accelerations and even overclocking the motor speed past 60hz? It's a no brainer.

    Comment


    • #3
      Originally posted by jaybird
      There looks like more hardware is involved with an RPC.
      A motor, a capacitor, and a switch. Not a big investment; stuff you probably have lying around already.

      Comment


      • #4
        All you need is a 3 ph motor and some switched to turn the power on. It's simple and cheap and you only need one for all the machines. You'll need a VFD for each machine.
        It's only ink and paper

        Comment


        • #5
          Originally posted by Carld
          All you need is a 3 ph motor and some switched to turn the power on. It's simple and cheap and you only need one for all the machines. You'll need a VFD for each machine.
          You left out contactor, and an off switch, and the hassle of balancing the load, which is different for different HP tools and requires several capacitors. I've picked up several VFD's for well under $100, building a proper dynamic phase converter like I did 12 years ago when I moved my shop from a location with 3 phase just isn't something I would do today. Especially for a mill which is just the thing you want easy variable speed on.

          Comment


          • #6
            I chose to buy a Phase a matic RPC and install a complete 3 phase system in my shop. The Converter is 7.5 hp rated. I have a dedicated 3 phase main panel that is fed by the RPC. The Mill is hooked to that panel and I have breakers for various other machines as the single phase motors die. My lathe and drill press will get converted to 3 phase soon...

            Works for me...but you may go another way.

            The Machinist up the street from me has a 30 horse RPC and dedicated panels as well. But he has a LOT bigger machines than I. It is nice as I can walk up the street and have access to a 30" x14' lathe and a mill that can hold my lathe!

            Cheers
            Mac.

            Comment


            • #7
              I ran my Bridgeport clone (2hp) on a 3hp Transwave static converter for several years. I would have built my own static converter, but it had a two speed motor which couldn't be connected in Delta and run from 240v and the cost of a step-up converter and a phase converter wasn't that much.

              The converter also ran my Harrison L5 (1.5hp) without needing adjustment although the clutch rattle was quite annoying. It's a known issue with the L series lathes, but a phase converter makes it much worse.

              I had a small shaper (1/2hp) for a while and to run it, I would simply run the mill motor to turn the static transwave into a rotary converter.
              Paul Compton
              www.morini-mania.co.uk
              http://www.youtube.com/user/EVguru

              Comment


              • #8
                One plus for VFDs which isn't often mentioned is that machines tend to run quieter than with a converter. Yes you sometimes get a high-pitched whine especially when starting & stopping, but not usually very loud (you can often tweak to reduce that).
                Static converters are particularly bad for making machines noisy, but even a well set up rotary doesn't give perfectly balanced phases.
                I was really surprised when I put a VFD (fed via the RPC as it's 415V 10hp) on my big lathe at how much quieter it is now than direct from the RPC, I can actually listen to the radio while it's running

                Tim

                Comment


                • #9
                  I recently picked up a premade "soft start" RPC box from American Rotary, to set myself up with some basic 3-phase.

                  Now, I've been a big fan of VFDs since I got my first one almost two years ago. But I got to the point where I had enough machines that needed basic 3Ph, that I needed to change my plan of attack a bit.

                  I'd planned to just fit everything with a VFD as I got them finished, but once I picked up the surface grinder, it alone had three motors to power- that meant I needed six VFDs to finish everything I was working on. Or over a thousand bucks worth.

                  On the other hand, the surface grinder (and it's vacuum and coolant pump) the Wells bandsaw and the pedestal grinder didn't necessarily need the cool VFD features like variable speed. They basically just needed straight 3-phase power.

                  So I bought the AR kit, which is a preassembled and prewired enclosure with the contactors, capacitors, buss bars and whatnot, which you use with your own motor. I'll be wiring it up, and then just plug the various machines in as they're needed.

                  If it weren't a matter of cost, I'd have probably just kept buying VFDs. But I figure in this case, even buying the RPC kit, I saved about $500. (I'll still need a VFD for the mill-drill.)

                  And once that mill's done, I'll have nine of my machines running on 3-phase, so cost was, indeed, an issue. but as above, if cost were no object, I'd be more than happy to just keep slapping VFDs on everything.

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

                  Comment


                  • #10
                    my comments

                    I have both. My 17" Delta is converted to 3ph and a VFD. The variable speeds from the VFD is great and often the loss of torque at the 50 - 200% range is usually not an issue and I do change the step pulley when I need to remove a lot of metal. And the motor is mounted on a hinged plate so one lever moves it making it a fast change.

                    My SB 10L is also on a VFD for the same reasons, I'm usually turning small parts and the instant speed change is fantastic while there was excess torque for small parts. The 14x40 gets the bigger parts. (I'm a small hobby type of shop)

                    OTOH, I have a RPC feeding a fanout plug box to which the bandsaw, surface grinder, TC&G, horizontal mill, and my bigger vertical mill are plugged into. None of these seem to scream the need for the VFD features (except maybe the vertical) so they stay on the RPC.

                    YMMV, and I bet it will. :-)

                    - Reed


                    Originally posted by jaybird
                    I need to wire up a Bridgeport mill I bought a bit ago. It has a 1½ hp 3ph motor. I also have a small shaper that has a small 3ph (<1hp) motor. I won’t run the two machines at the same time. My shop is a hobby shop. Seems I do a lot more putzing than any production work but I do have a good time.
                    I have been doing a little research for a phase converters, VFD and RPC.
                    My question is why mess around with an RPC when it seems a VFD is simpler and fewer parts to worry about? There looks like more hardware is involved with an RPC.

                    Am I being to simplistic or am I missing something.

                    Comment


                    • #11
                      Originally posted by jaybird
                      I need to wire up a Bridgeport mill I bought a bit ago. It has a 1½ hp 3ph motor. I also have a small shaper that has a small 3ph (<1hp) motor. I won’t run the two machines at the same time. My shop is a hobby shop. Seems I do a lot more putzing than any production work but I do have a good time.
                      I have been doing a little research for a phase converters, VFD and RPC.
                      My question is why mess around with an RPC when it seems a VFD is simpler and fewer parts to worry about? There looks like more hardware is involved with an RPC.

                      Am I being to simplistic or am I missing something.
                      Going back to this original question...

                      The nicest solution for the mill is going to be a VFD.
                      Using a VFD on the mill assumes the motor can be configured for a suitable voltage.

                      The simplest and cheapest solution for the shaper is a static converter.
                      My pillar drill uses a dedicated static converter and runs very nicely. It again requires that the motor can be configured for a suitable voltage. In my case, the motor was 415v start wired and with no provision to reconfigure in for 240v Delta. I dismantled the motor, found and broke the Star point, added new tails and connected it for 240v Delta.

                      The phase converter was then base on information from http://home.att.net/~waterfront-wood...econverter.htm

                      Given that I'm on UK 240v, I didn't like the starting system. Instead, I used a tiny 12v secondary transformer connected to a 12v relay via a wire wound potentiometer. By adjusting the pot, I could set the point at which the starting capacitor dropped out.

                      I think you could extend such a system to a multi machine/motor setup without the expense of a slave motor. Each motor would be equipped with its matching run capacitors, whilst the start circuit would be central.
                      Paul Compton
                      www.morini-mania.co.uk
                      http://www.youtube.com/user/EVguru

                      Comment


                      • #12
                        gellfex, all you need for a basic RPC is the motor, a switch to turn it off and on with and a rope to spin it up. You DON'T need balance caps or start caps or run caps or a magnetic switch. Remember, KISS.

                        I used my RPC with a rope start for a few years until I got tired of the rope trick and put a pony motor on it. I still don't have balance caps on it and it has been used by me and the first owner for about 24 years now with no problems at all. I may have $30 in my RPC if that much.

                        I have posted wiring diagrams and photos of my setup.
                        Last edited by Carld; 11-19-2009, 10:13 AM.
                        It's only ink and paper

                        Comment


                        • #13
                          Originally posted by Carld
                          gellfex, all you need for a basic RPC is the motor, a switch to turn it off and on with and a rope to spin it up. You DON'T need balance caps or start caps or run caps or a magnetic switch. Remember, KISS.

                          I used my RPC with a rope start for a few years until I got tired of the rope trick and put a pony motor on it. I still don't have balance caps on it and it has been used by me and the first owner for about 24 years now with no problems at all. I may have $30 in my RPC if that much.

                          I have posted wiring diagrams and photos of my setup.
                          I guess that works for you, but even with balance caps, if I work my 2hp buffer hard it can throw the thermal overloads in the contactor, showing it isn't balanced well enough for high loads. The 2 hp RPC worked fine for years never overloading when using the 1/2hp lathe or 2hp mill since they never get loaded as close to their rated hp.

                          Comment


                          • #14
                            The RPC's are only good for about 70% of the rated hp of the machines motor. Anything close to that or more can overheat the machine motor and is not good. I have seldom used my lathe, 3 hp or the mill a 2 hp at or near %70 and my RPC is a large 5 hp motor.

                            Only once did I use the lathe hard and I had a clamp on Amprobe Jr. to measure the current so I didn't go to high.

                            I have considered putting balance caps on some time. I want to make an auto start panel so all I have to do is hit a start button and it's up and running. I have the parts, just haven't got 'er done yet.
                            It's only ink and paper

                            Comment


                            • #15
                              Originally posted by Carld
                              The RPC's are only good for about 70% of the rated hp of the machines motor. Anything close to that or more can overheat the machine motor and is not good. I have seldom used my lathe, 3 hp or the mill a 2 hp at or near %70 and my RPC is a large 5 hp motor.

                              Only once did I use the lathe hard and I had a clamp on Amprobe Jr. to measure the current so I didn't go to high.

                              I have considered putting balance caps on some time. I want to make an auto start panel so all I have to do is hit a start button and it's up and running. I have the parts, just haven't got 'er done yet.
                              Another reason the contactor with the thermal breakers is a good idea! I built mine according to a common online recipe using a momentary switch to start it up, hold it down for a couple of seconds till it's going, and another momentary to break current to the contactor. I used the 2hp because it's what I had lying around from dumpster diving a HVAC unit.

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