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Bridgeport motor issues - VFD vs VSD

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  • Bridgeport motor issues - VFD vs VSD

    I am in the process of purchasing a Bridgeport by Adcock and Shipley with the 2J head. I live in Australia and my shop only has 240V single phase power. The mill I am considering has a 415V three phase pancake motor and obviously I need to find a solution for powering this mill. I initially thought it would be simple. Just get a variable frequency drive to convert the 240V single phase to 415V three phase. But, you guessed it, it's not that simple. I have previously used VFD's on two mills and a drill press. The two good ones were Invertek Optidrives and the drill press has a Huanyang el cheapo drive but it works OK.
    My research so far indicates that:
    (a) 240V single phase to 415V three phase VFD's are mighty thin on the ground and hideously expensive.
    (b) rotary phase converters are expensive, noisy and lack some refinements that VFD's offer.
    (c) swapping out the native pancake motor for a single phase motor or a 240V three phase motor is not that simple on the Bridgeport 2J model due to the long overhang required on the motor shaft
    (d) fitting a more commonly available 240V single phase to 240V three phase VFD will derate the motor torque considerably.
    However; I have found a vendor who will supply a "1.5 kW (2HP) Single Phase 240 V to 3 Phase 0-415V Variable Speed Drive, VSD, VFD" for just over AU$1000.
    https://www.ebay.com.au/itm/1-5-kW-2...97.m4902.l9144
    My question is: has anyone used one of these/purchased one of these/ rejected one of these on sound advice/considered one of these or experienced problems with one of these?
    I don't mind paying the (high-ish) cost if it does the job. But I don't want to use a VFD if it hobbles the torque of the motor.
    Advice is welcome.
    Regards,
    Mark Presling

  • #2
    All the vendor seems to be doing is adding a transformer to a 415V VFD, supplying it with single phase, and using the VFD to convert to 3 phase. The VFD is listed as a 415V input unit, so it is not doing any voltage conversion itself.

    In addition the VFD appears to be one of the Huanyang variations, not in any way comparable to the Invertek. Invertek is one of my favorite brands, I am very familiar with their older models, and used to be associated through my employer with the Invertek US importer, doing modifications etc.

    The use of single phase input in no way "hobbles the torque of the motor". What actually happens is that the VFD has to be de-rated in most cases, to allow it to handle the larger peak currents involved with single phase.

    You can do what that vendor does, better. A step-up transformer, into a VFD which is rated double what the motor rating is, would be the usual approach, and it works.

    A few details.... the VFD has to be able to accept single phase, that is, it cannot have a "phase loss detector" unless that can be disabled. It s best of the VFD is rated for single phase input (many of the optidrives are , at the 240V level) and that the appropriate de-rating is known, so that you have certain knowledge of what you need.

    The VFD must have a regular bus capacitor, some newer ones have a small capacitor because they are designed ONLY for 3 phase input. The transformer should be rated for "somewhat more than" the motor power, perhaps 1.5x, in order to assure that it will supply the current peaks needed to keep the VFD bus capacitors charged.

    So, with a 1.5 KW motor, you would want, in general, a 3 kW VFD, and at least a 2 kVA transformer, preferably 3 kVA.

    At the 240V level, many of the optidrives could operate with no de-rating on single phase. That is not at all common at the 415V level.
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    • #3
      What about a transformer after the 240V VFD to boost up to 415V? It is my understanding that as long as you go straight to the motor and aren't trying to power anything additional (controls etc.) with the VFD that a transformer can be used on the VFD output if necessary.

      Comment


      • #4
        A transformer between the VFD and motor may not be a great solution:
        1. You need a 3 phase transformer. If you put the transformer between the main power and VFD, you only need single phase transformer (cheaper, smaller). Unless you have one in your scrap bin already that matches you specs.
        2. Most transformers are optimized for a given frequency (50/60Hz). The VFD will put out a range (say 0-80Hz). Transformer will run hot when operating at less than rated frequency.

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        • #5
          Originally posted by Preso View Post
          I am in the process of purchasing a Bridgeport by Adcock and Shipley with the 2J head. I live in Australia and my shop only has 240V single phase power. The mill I am considering has a 415V three phase pancake motor
          Are you sure or have you checked to see if it is 415v/230v most pancake motor fitted to these mills were, I know the XLO had them on their pancake motors.
          Then use 230v 1ph VFD.
          The wiring change diag. is usually in the terminal cover.
          Max.
          Last edited by MaxHeadRoom; 04-11-2020, 01:01 PM.

          Comment


          • #6
            Originally posted by ChrisK View Post
            A transformer between the VFD and motor may not be a great solution:
            1. You need a 3 phase transformer. If you put the transformer between the main power and VFD, you only need single phase transformer (cheaper, smaller). Unless you have one in your scrap bin already that matches you specs.
            2. Most transformers are optimized for a given frequency (50/60Hz). The VFD will put out a range (say 0-80Hz). Transformer will run hot when operating at less than rated frequency.
            That is true. For some reason I was reading it as he already had a 240V input VFD in his possession. Upon rereading I see that I was mistaken. In that case, if the mill's motor isn't reconfigurable for 240V, I'd put the transformer in front of the VFD as well.

            Comment


            • #7
              "240V single phase to 415V three phase VFD's are mighty thin on the ground and hideously expensive."

              Mark, try AliExpress. They're common enough there, and reasonably cheap.

              Comment


              • #8
                Thanks for the advice. Unfortunately, the mill is still with the vendor and I haven't been able to have a good look at the motor. The advertisement says that it definitely needs 415V three phase and there will be accessories like the X axis power feed and a work light etc that will need their own power requirements. I tried and failed to find a 240V to 415V transformer on Ebay except for the one sold by the same vendor as the boosted VSD. I guess it is just the same one they use in their own VSD's. I could just make up my own system with an Invertek VFD and a 2KVA boost transformer but it is going to be considerably more expensive than the package solution that I can get for just over $1000. I still have the option of having the motor rewound. I was hoping that someone who had purchased one of the units I am considering would be able to comment on their experience.
                Regards,
                Mark

                Comment


                • #9
                  All you need is a 240V to 240V isolation transformer, which is very common. Connect the windings in series as an autotransformer to get 480 VAC for the VFD. You could actually use a 1 kVA transformer to get 2 kVA in this configuration. Of course a larger transformer would be better.
                  http://pauleschoen.com/pix/PM08_P76_P54.png
                  Paul , P S Technology, Inc. and MrTibbs
                  USA Maryland 21030

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                  • #10
                    I have in the past replaced 2J motors with NEMA 182JM & 184JM frame pump motors 3&5 HP respectively-

                    https://www.lewismotorrepair.com/pdf...Dimensions.pdf

                    These motors have long enough shafts, that they can be taken apart and re-machined to match the 2J head motors. This is assuming the A&D version of the 2J head is built similar.

                    The other option if one of those isn't available in your locale, is to buy whatever size face mount motor you have available that has a large enough bearing, disassemble and modify/make a new shaft to fit.

                    I just need one more tool,just one!

                    Comment


                    • #11
                      Originally posted by Preso View Post
                      Unfortunately, the mill is still with the vendor and I haven't been able to have a good look at the motor. The advertisement says that it definitely needs 415V three phase
                      Mark
                      Are you sure the vendor is knowledgeable enough to be sure that it is not re-configurable?
                      Or in a position to be sure.
                      Max.

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                      • #12
                        If you are going to use a VFD you can do without the adjustable pulley on the motor which is why the shaft is so long. So using a pump motor with a long shaft you ought to be able to make the adjustable pulley fixed and adapt it to the motor with some bushings. You'll still have the back gear for low speed high torque. Use a 3hp pump motor because that currently is the largest motor size easily run on single phase 240 power.

                        By the way the reason the VFD has to be derated in most cases is because converting 3 phase to DC is very easy as the ripple is very low. Using single phase input not only is the current higher but the ripple current is huge and stresses the filter capacitors. Some drives, like Hitachi have replaceable filter cap modules. I have often wondered how difficult it would be to add external caps to a VFD to help it out.

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                        • #13
                          Thanks again for all the replies. I have just pulled the trigger on the purchase and I should have the machine in a week or so which will allow me to evaluate how I proceed. I like the idea of replacing the entire motor and still using a VFD. I had another look at the photos of the head and the motor is quite tall which is quite unlike the "pancake" motor that is supposed to be harder to adapt to 240V. I have made some tentative enquiries about having the motor frame rewound to 240V - 3 phase. I will get back here when I have the machine in front of me and report on what I find.

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                          • #14
                            Hi Mark,

                            VFD and VSD are the same thing in my opinion.

                            I agree with posters who say you need to see the motor before deciding anything. If it can be re-configured for 240 volt, problem solved. I have a mid-1970's Adcock Shipley UK-built Bridgeport and it has a "U.S. Electrical Motors" 1.5 hp motor able, to run on 210 or 420 volts. I haven't checked the rest of the electrics, but hopefully they are configurable too.

                            Otherwise I would be looking at fitting a 240/415 volt three phase motor, they are not just better, but cheaper than a single phase motor.

                            Re-reading the above, I think you have a good handle on it, I am probably re-stating the obvious

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                            • #15
                              I have used a couple solutions quite successfully and inexpensively by utilizing used parts. One is a step up single phase transformer to a 415V VFD, another is a 240V RPC feeding a three phase step up transformer, or sub a 240V VFD for the RPC. The cheapest and easiest is probably the single phase step up followed by a VFD but you could rig up an RPC in it's place.

                              Between myself and my friends shops we have done all of the above, parts price and availability are usually the determining factors.

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