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  • #16
    That Polyspede bears a scary resemblance to the Huanyang, aka "IED" VFDs.
    CNC machines only go through the motions

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    • #17
      You might want to get one and look closer - they are actually solid industrial units...

      Right now they they are out of stock at Drives Warehouse and they recommend a 3 phase 15hp Hitachi L700 as a substitute - and less money at $910. http://driveswarehouse.com/p-2565-l700-110lff.aspx
      Last edited by lakeside53; 04-19-2014, 10:34 AM.

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      • #18
        Go with the RPC especially at that price. No worry about VFD failures in the future. The RPC just works and that's all there is to it, don't know if your lathe has reverse, assuming it does with the three phase convertor it works as it should. My Emco also has a 2 speed motor, works as designed with the RPC, mine is homemade BTW.

        With that much spare capacity you will find used 3 phase equipment is much cheaper and more reliable than single phase.
        Last edited by wmgeorge; 04-19-2014, 12:31 PM.
        Retired - Journeyman Refrigeration Pipefitter - Master Electrician

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        • #19
          [QUOTE=atomarc;915673]
          Originally posted by Rich Carlstedt View Post
          Hands down, a VFD
          You can buy a 10 HP Hitachi unit for less than 600
          http://driveswarehouse.com/p-1384-sj200-075hfu.aspx/QUOTE]

          Whoa Mr....this drive is not a single phase input...need many more shekels for that item. Don't quote me, but I would say a 15 hp unit would be required and they ain't cheeeep!

          Stuart
          15 HP is over kill.
          I run my 3 HP mill on a 5 HP Mitsubishi VFD and have never had a fault .
          I used a 10 HP Hitachi VFD on 480 single phase to run a Nardini 7 HP Lathe at 480 V for a good friend

          Talked to an engineer that designs them. The difference between single phase and 3 phase is in the capacitor banks which have/provide a DC supply.
          Using a 3 phase unit on single phase reduces the capacity by 1/3 rd according to this gentleman . He also said that not all banks are equal
          and that trying single phase on each of the three banks may show one as superior to the others. I have found that to be true.

          Rich
          Green Bay, WI

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          • #20
            Well... you might be getting away with it (likely at the expense of capacitor life), but Hitachi has a recommend method for sizing a 3 phase vfd on single phase. It's also not just the capacitor banks, but the rectifier current at has to be considered. Capacitors on single phase vfd are substantially larger for the same HP than on 3 phase - not just "1/3" bigger.

            From Hitachi : take the 3 phase motor nameplate current, double it and match that to a suitable vfd... VFD's "know" about current, not HP. In most cases this will map to "double HP".

            Here's the Hitachi paper : http://www.hitachi-america.us/suppor...ngle-Phase.pdf

            And.. not all inverters can use this "rule of thumb". My high-end ABB 7.5hp driver are only good for 1.5hp on single phase (according to ABB).
            Last edited by lakeside53; 04-20-2014, 12:35 AM.

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            • #21
              As noted above, the folks that build the drive tell you exactly how to size the drive when powering it from single phase, and that's good enough for me. I opted to switch my 7.5 hp lathe to a 5 hp motor to be able to use a 10 hp Hitachi drive..less $$$$. I saw this as the most cost effective move for me. A 17" lathe with a 7.5hp motor will do a whole bunch of work...I didn't think I would ever need that much oink. The 5hp has worked perfectly...and it was free too!

              When weighing costs remember that the frequency drive gives you motor overload protection as well as a built in 'starter'..no need to purchase a contactor and overload assembly.

              Stuart
              Last edited by atomarc; 04-20-2014, 12:59 AM.

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              • #22
                Originally posted by Rich Carlstedt View Post
                Hands down, a VFD
                You can buy a 10 HP Hitachi unit for less than 600
                http://driveswarehouse.com/p-1384-sj200-075hfu.aspx

                A 20 Rotary wastes too much power
                Your consumption will be half with a VFD

                Rich
                I read what you wrote and looked up a 20 hp capacity VFD to replace my 20 hp Rotary phase converter. My Rotary unit uses a 2 pole 60 amp breaker to feed it. If I read the info correctly for the 20hp VFD the source amps is 132... Am I reading the wrong line?

                http://driveswarehouse.com/documenta...spede/PC1M.pdf
                Last edited by flutedchamber; 04-20-2014, 02:51 PM.

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                • #23
                  My Lathe a smart and Brown 10 24 vsl variable speed meant I could not use a vfd or a static convertor I had to buy a new expensive rotary convertor and since then it has worked great so please check this before buying..vfd's won't run every machine. Alistair
                  Please excuse my typing as I have a form of parkinsons disease

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                  • #24
                    Originally posted by flutedchamber View Post
                    I read what you wrote and looked up a 20 hp capacity VFD to replace my 20 hp Rotary phase converter. My Rotary unit uses a 2 pole 60 amp breaker to feed it. If I read the info correctly for the 20hp VFD the source amps is 132... Am I reading the wrong line?

                    http://driveswarehouse.com/documenta...spede/PC1M.pdf
                    A rectifier, such as the "front end" of a VFD has a relatively poor power factor.

                    But, why are you looking at a 20HP to run a 7.5 HP motor? the 7.5 HP unit draws 54 amps.

                    The heading on the table, page 8.2, shows that it is for single phase input, as does the PC-1 nameplate shown on page 1.1.

                    So you should be able to use it directly at nameplate rating od 7.5 HP on single phase input..... unless you are allowing a 'chinese discount" on the ratings... While the company shows as being in texas, I doubt they are built there.

                    There is some crummy "chinglish" information in the manual, also... the enclosure is supposed to be for pollution degree 2, but it should be for conductive dust, which is pollution degree 3, for industrial and farming applications. There are vent holes..... and factory environment includes grinding dust etc. Conventionally pollution degree 2 is for laboratories, one step short of "clean rooms".

                    Put it in an enclosure, observing the size and location requirements.


                    RPCs don't waste that much power.... more than a VFD, yes, VFDs can be 95% efficient. But the RPC is handling only 1/3 of the total power, and until you get to truly huge motors, is not a big consumer of power in an absolute sense. If the RPC loss is a big factor, then your utilization is poor, and you could probably put a much smaller motor on the load machine, allowing you to use a much smaller RPC to begin with.

                    However, the RPC does not just shut down when overloaded, it runs more than one motor, etc. The VFD has basically speed changing as its advantage, unless it is a very expensive model, including power factor correction on the input side.
                    Last edited by J Tiers; 04-20-2014, 06:42 PM.
                    CNC machines only go through the motions

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                    • #25
                      Rotary recommended 2 times my motor horsepower because my lathe uses a WEG motor, which I was told was electrically "thirsty" at startup, especially since it does not have a clutch to disengage the spindle. My lathe uses a 2 speed, 7.5/8.5 horsepower motor. The 20 horsepower Rotary phase converter was the closest match.

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                      • #26
                        Originally posted by flutedchamber View Post
                        Rotary recommended 2 times my motor horsepower because my lathe uses a WEG motor, which I was told was electrically "thirsty" at startup, especially since it does not have a clutch to disengage the spindle. My lathe uses a 2 speed, 7.5/8.5 horsepower motor. The 20 horsepower Rotary phase converter was the closest match.
                        Having built over 60 phase convertors of all sorts, I agree with your comment. 2 speed WEG motors are tough to operate at times, especially with no clutch ! I have had VFDs work on these motors, but fault signals occur periodically ...., so yes, go with a 20 HP

                        Rich
                        Green Bay, WI

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                        • #27
                          Originally posted by Rich Carlstedt View Post
                          Having built over 60 phase convertors of all sorts, I agree with your comment. 2 speed WEG motors are tough to operate at times, especially with no clutch ! I have had VFDs work on these motors, but fault signals occur periodically ...., so yes, go with a 20 HP

                          Rich
                          Rich, did I read that chart correctly...are the input amps 132 for the 20 HP unit? It seems very high, unless they mean the starting surge amps. I could find no info as to what they recommended as the correct size 2 pole breaker for the 20 HP VFD. Do you know what it would be?

                          Thank you for the input.

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                          • #28
                            Good advice above. I'm dealing with the same decision right now, with a single-phase shop and several nice 3-phase lathes recently acquired. I have several good Mitsubishi VFDs and a nice loaner RPC, so I have been researching and experimenting.
                            One thing about VFDs is they don't like downstream switchgear. You can't just plug the VFD into power, and then clip the plug off your machine and attach to the VFD, unless power goes straight to the motor with no switches in between. You have to use the low-voltage inputs from the VFD to control your on/off/reverse etc. On many machines that's fairly simple, but if there are contactors and such it may be complicated.
                            OTOH, and RPC is basically plug and play, using all the OE controls on your machine and it's accessories. And additional machines can feed on that RPC. Additional idling motors actually make it work better.
                            I'm a big fan of VFDs, but I must say walking over and plugging into that RPC is pretty nice. I think I will have to build an RPC soon.

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                            • #29
                              I have a 7 1/2 HP RPC and am sorry that I have it. What a power hog. The RPC draws 40amps @240vac running my 3 HP K&T which draws 7 amps a leg 3 phase. Like my buddy AL says, it's a rotary shop heater.

                              If I hadn't gotten this thing for free, I would of opted for a VFD. I still might spring for one as we have the highest electricity cost in North America. Thank you greenies.

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                              • #30
                                Unless you have some weird billing system in the great white north, you pay for power, not current. i.e., you're not paying for the 40 amps. Your power factor is probably 0.10- to 0.12 when powered up and no load and it's using maybe 700-900 watts at most to spin. You can likely get your current down to 5 amps with power factor capacitors, but it won't change your power bill.

                                BTW, if if your rpc drawing is drawing 40amps, it's probably a 20+ hp motor. Most 15hp motors I tested as rpc candidates run between 20 and 25 amps at no load, uncorrected for power factor.
                                Last edited by lakeside53; 04-21-2014, 11:05 AM.

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