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Need 480V 3Phase from 240V 1Phase.

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  • Need 480V 3Phase from 240V 1Phase.

    I need 3phase 480 for my mill. 240V single phase is all I have available.
    The motor is an old school 2 speed (2 sets of windings) no dual voltage. 1.2 KVA is the theoretical power use of the motor at 1.5 HP high speed. See related post http://bbs.homeshopmachinist.net/thr...-3-phase-motor


    On today’s exchange rate, a UK type VDF 240 single phase to 415V 3 Phase (2HP) runs about US $800 with shipping. Not sure how much de-rating running on 415 may have.

    Not counting the UK vdf option, I’m going to need step up transformer action.

    Taking into account starting loads, how much transformer power (KVA – watts x 1000) rating do I need for the following?

    Opt 1. 240 to 480 1P transformer to the mill with a static converter circuit installed?

    Opt 2. Larger transformer 1P 240 to 480 to start and run a 3HP rpc (plus mill load)?

    Opt 3. Build a 240 RPC and run the output to a 3P (or 3 separate) transformer(s) for the 480.

    Both 1 and 2 could allow using a transformer as an autotransformer (ie 4KVA auto out of a 2KVA trans).

    Option 3 has the merits of using 3 smaller transformers and having the 240 RPC available for other machinery in the shop.

    Any other ideas?
    Any one know of a 1P 480 in 3P out VFD?

  • #2
    You could put together a rotary converter to create the 240V 3 phase .

    Feed that into a boost transformer to get the higher voltage 3 phase. 3 phase transformers can be expensive, but you can wire up a pair of single phase 230 to 460 transformers in an open delta configuration to boost the voltage. Google on open-delta to get the hookup wiring.

    It may seem hokey to make a transformer that way, it's not. It's a widely used method. I first found out about it from a transformer company's catalog showing the method.

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    • #3
      What about a 240/480 1ph transformer and a 480v VFD for the spindle.
      In all probability the spindle is the only thing 3ph.
      You don't see many 480v VFD's and I believe this is because most manuf figure that if you have 480, it will be 3ph?
      If the input is at it is with the majority of VFD's, a 3 ph rectifier, then it should run on 1ph OK, maybe derate it a HP or 2.
      Max.

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      • #4
        There three issues with single phase to 3 phase conversion. The first is higher current on the two input phases being used, which calls for derating. The second is higher ripple voltage on the filter caps in the input. The third is the need to disable phase failure detection to use single phase. Automation Direct VFDs in particular cannot be derated and used on single phase because you can't defeat the phase failure protection. If doing this with a transformer and inverter I would first step the voltage up to 480 single phase then use a 480 volt VFD that is derated by half. Putting a transformer between the VFD and the motor is not a good idea for lots of reasons.

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        • #5
          I run a 3 phase rotary to get 240 3 phase for my CNC mill, then use a 240 to 480 three phase transformer to boost the 240 to 480 for my Feeler lathe.

          Been using that combo for about 8 years now with no issues. 480 is nice, the wires are so thin!

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          • #6
            Originally posted by hitnmiss View Post
            I run a 3 phase rotary to get 240 3 phase for my CNC mill, then use a 240 to 480 three phase transformer to boost the 240 to 480 for my Feeler lathe.

            Been using that combo for about 8 years now with no issues. 480 is nice, the wires are so thin!
            I am in Canada and use 575 volt, at home I have used the 240 ,3ph motor than a 3ph transformer(very bad) I got very high voltage and current on one phase. A 240 to 575 1ph transformer and 575 idler motor give more consistent volts and current.
            John

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            • #7
              Use option 3.

              I have a single to 3 phase "phase perfect" (could have used a rotary) then a 15kva 240-480 3 phase transformer. Used Transformers are dirt cheap - freight can kill. For your small needs, a 3kva transformer will be just fine. Tune your rpc well as any error is 2X on the output.

              Be sure to fuse the transformer per code...

              I have a 6KVA 240-480 (rated for reverse connection) here, cheap, but at 100lb or so it would cost a bundle to ship it to Michigan.

              If you use a single phase transformer and a 480V vfd, take care with the derating I have a pair of high end 7.5hp ABB vfd's here (anyone want them cheap?) that are only 1.5hp on single phase - as per the manf. Don't "guess" or use "rules of thumb". The manf will tell you the correct answer.
              Last edited by lakeside53; 06-03-2015, 05:31 PM.

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              • #8
                I have a new? 240/460 good size transformer. Not trying to sell on here but I bought it when I had the 20 hp lathe & never used it. PM if interested.

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                • #9
                  I would research the possibility of using a VFD with a single phase boost xformer.A 5hp VFD can be had new for less than $200-


                  http://dealerselectric.com/T238.asp

                  Other option is have you thought about swapping motors for something 3~220vac?
                  I just need one more tool,just one!

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                  • #10
                    I use a 240:480V autotransformer to feed a 460V idler to get 3 phase for my Hardinge UM with a 3/4HP 550V motor.

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                    • #11
                      You can't run a vfd into a transformer.

                      I personally would use the 240v in 415 out vfd. If it was designed to do this it does not need to be derated.

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                      • #12
                        Option 4. Can it really be that difficult to find a 240V single phase, 1.5 hp motor? Worst case you'd have to do something imaginative to mount it.
                        "A machinist's (WHAP!) best friend (WHAP! WHAP!) is his hammer. (WHAP!)" - Fred Tanner, foreman, Lunenburg Foundry and Engineering machine shop, circa 1979

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                        • #13
                          Originally posted by macona View Post
                          You can't run a vfd into a transformer.

                          I personally would use the 240v in 415 out vfd. If it was designed to do this it does not need to be derated.
                          But the motor might - you are nearly 15% low on volts at full power.

                          Comment


                          • #14
                            When I was experimenting with a specially wound 3 phase 7.5 VAC 12 pole motor (originally 120 VAC single phase), I used two "wind your own" 120V to 0.4 volts/turn transformers (with 20 turns on secondaries) to a 2 HP GE/Fuji 220 VAC VFD on single phase. Worked fine up to about 240 Hz. Of course, I was dealing with only a few hundred watts.

                            If the VFD accepts an external DC bus link connection, you might be able to bypass the phase loss detection and run it on DC. Of course, you will need 400-800 VDC for a 440V VFD. It might be possible to use a PFC front end from a high power PFC switching supply to get about (but perhaps not quite) 400 VDC. It will more likely be about 360. But then you might be able to add a 48 VDC supply in series to get the minimum. The PFC is needed so that you can get a well-filtered DC at sufficient power without drawing too much current from the 240 VAC line.

                            If you don't care about power factor, you can make a "bad boy" voltage doubler from diodes and capacitors, and get the required bus voltage. Here is a 120 VAC to 320 VDC (250 VDC under load) doubler that puts out 1 kW. If you made the same thing with higher rated components and applied 240 VAC, you will get 640 VDC (500 VDC under load) at 4 kW. But PF is probably like 40% so you might draw 20 amps at 240V (4.8 kVA) to get 2 kW (3 HP) for the VFD and the motor.



                            You could also use eight of these 48V supplies set to their maximum of 52 VDC 3.3A in series for 416 VDC and 1200W. They are $37 each and are 4" x 8" x 1.5" and weigh just 1.6 LB. I don't know if they are PFC, however. You may find some much cheaper surplus, and you can add more in series or get higher power units if needed.
                            http://www.parts-express.com/48-vdc-...pply--320-3142

                            Here are many more:
                            http://www.mpja.com/48-Volt-Power-Supply/products/544/

                            And a 3A 48V supply from China for $15:
                            http://www.ebay.com/itm/AC-110-220V-...-/201278521527

                            Here is a 300W PFC front end circuit that provides 390 VDC, but it should be scalable to 2000W and 450 VDC output:
                            http://www.powerfactor.us/circuit.html

                            Last edited by PStechPaul; 06-04-2015, 03:59 AM. Reason: PFC circuit, 12 pole was 6 pole
                            http://pauleschoen.com/pix/PM08_P76_P54.png
                            Paul , P S Technology, Inc. and MrTibbs
                            USA Maryland 21030

                            Comment


                            • #15
                              Originally posted by macona View Post
                              You can't run a vfd into a transformer.

                              I personally would use the 240v in 415 out vfd. If it was designed to do this it does not need to be derated.
                              Well actually you can do that. I have and it works fine. It may not be so great at extremes, but it does work.

                              The voltage doubling VFD is, however, a better idea.
                              1601 2137 5683 1002 1437

                              Keep eye on ball.
                              Hashim Khan

                              If you look closely at a digital signal, you find out it is really analog......

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