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Some wiring questions for VFD and minipress

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  • Some wiring questions for VFD and minipress

    Hello everyone. I am about to embark on rewiring my Blum Minipress machine (which is 3-phase 220V) to work on single phase 220V power using a VFD. I've read a lot of posts on several forums about this and have a basic understanding but would really appreciate some advice from the experts. The VFD I am using is the Teco FM50 unit. Input voltage will be single phase 220V and output will be 3-phase 220V.

    The minipress is essentially a pneumatically actuated drill press used for drilling and installing hinges or for line boring applications. It has a 1.1 Hp 3-phase motor. The control box (would like to attach the schematic but don't know how) has a switch and on/off light as well as the controls for the pneumatic system which seem to be totally independent. I can connect the system to compressed air and run the plunge mechanism without any electrical power. I assume that when the machine is running normally that pressing the pneumatic switch also activates the electrical system and starts the drill for the cycle. That is nice...

    I understand that I can simply bypass all this switch stuff and connect the 3-phase motor directly to the VFD, turning the motor off and on directly with the VFD (and having variable speed). To do this seems as simple as connecting the L1 and L2 from the wall (and ground) to the VFD and then connecting the T1, T2 and T3 (and ground) directly to the motor. I've read in several places that this is the only way to connect a VFD to a motor.

    On the other hand, I would very much like to retain the functionality of the original machine and allow the switching circuitry to work as normal. Is this possible with this VFD? What would happen if I simply replaced the "T1, T2, T3" from the original wall plug with the "T1, T2, T3" from the VFD and connected the VFD to the wall using L1, L2 as normal? Obviously, I am a beginner at this but to the idiot's eye view, isn't 3-phase power coming out of the VFD and can't that "simulate" the normal 3-phase power that goes into those switches, etc? Is the problem that the VFD is sensing something that makes this a nonstarter? Is the problem just getting variable speed (which is NOT a needed feature in this device).

    Second question, If I set this thing up and don't intend to use variable speed, how do I assure that the motor is spinning at the appropriate speed and getting the appropriate power from the VFD?

    Third question, after buying the VFD, I noticed that the thing just has terminals on the outside of the unit and no containment box to keep the wires away from other things. This seems a bit dangerous - did I perhaps not select the appropriate vfd? I can't enclose it as it clearly has fans and needs to have airflow.

    Sorry if these are just newbie questions but I would really appreciate some input. Thanks in advance.

    Richard

    Last edited by Richard Link; 09-17-2010, 11:32 PM.

  • #2
    VFDs do not like the motors they are powering to be switched off while the VFD is powered up. For a machine like yours, I'd say an RPC (rotary phase converter) would be what you want, not a VFD.


    Andy

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    • #3
      Originally posted by murph64
      VFDs do not like the motors they are powering to be switched off while the VFD is powered up. For a machine like yours, I'd say an RPC (rotary phase converter) would be what you want, not a VFD.


      Andy
      Ahh...yes. I guess that makes sense. It does seem, though, that I can simply bypass all the switching circuitry and simply turn the drill on and off using the VFD. For a variety of reasons, I'm hoping to avoid the rotary phase converter option and jury rig this one. If I bypass the switch circuitry, I would simply have to push two buttons to activate the machine instead of one.

      On the other hand, I have read some threads that suggest that an external switch can be wired into the VFD circuit. Is there any reason to hope that either (a) the switch system inside the minipress could be used this way or (b) a new switch mechanism could be wired up so that the pneumatic on switch drives both the pneumatics and the vfd?

      Richard

      Comment


      • #4
        Originally posted by Richard Link
        ...I would very much like to retain the functionality of the original machine and allow the switching circuitry to work as normal. Is this possible with this VFD? What would happen if I simply replaced the "T1, T2, T3" from the original wall plug with the "T1, T2, T3" from the VFD and connected the VFD to the wall using L1, L2 as normal? Obviously, I am a beginner at this but to the idiot's eye view, isn't 3-phase power coming out of the VFD and can't that "simulate" the normal 3-phase power that goes into those switches, etc? Is the problem that the VFD is sensing something that makes this a nonstarter?...

        I've done exactly that, on a number of machines, for a number of years. It works perfectly well for me.

        In fact, I've gone one step further, and simply mounted a 3ph outlet to the VFD, allowing me to plug in any machine I want.

        In fact, I've mounted TWO 3ph outlets, so I don't have to go unplug stuff all the time. And I have a longass cord with a speed-control potentiometer dial with a magnet on the back that sticks onto any machine I happen to be using at the time.

        All of these are methods frowned upon by VFD experts.

        But, it works very well for me. Your mileage may vary.

        .

        Comment


        • #5
          Originally posted by Richard Link

          The control box (would like to attach the schematic but don't know how) has a switch and on/off light as well as the controls for the pneumatic system which seem to be totally independent. I can connect the system to compressed air and run the plunge mechanism without any electrical power. I assume that when the machine is running normally that pressing the pneumatic switch also activates the electrical system and starts the drill for the cycle. That is nice...

          I understand that I can simply bypass all this switch stuff and connect the 3-phase motor directly to the VFD, turning the motor off and on directly with the VFD (and having variable speed). To do this seems as simple as connecting the L1 and L2 from the wall (and ground) to the VFD and then connecting the T1, T2 and T3 (and ground) directly to the motor. I've read in several places that this is the only way to connect a VFD to a motor.

          On the other hand, I would very much like to retain the functionality of the original machine and allow the switching circuitry to work as normal. Second question, If I set this thing up and don't intend to use variable speed, how do I assure that the motor is spinning at the appropriate speed and getting the appropriate power from the VFD?

          Third question, after buying the VFD, I noticed that the thing just has terminals on the outside of the unit and no containment box to keep the wires away from other things. This seems a bit dangerous - did I perhaps not select the appropriate vfd? I can't enclose it as it clearly has fans and needs to have airflow.

          Sorry if these are just newbie questions but I would really appreciate some input. Thanks in advance.

          Richard
          You could retain the 3 phase contactor and just run the 1 ph 240 through two of the poles, it should however, only be used for emergency stop situation when using a VFD and only be wired on the input side, not output.
          VFD's come with switch inputs which are usually simple contact closure which can also be wired into your present machine for stop start, or fwd/rev or limits switches etc.
          They also have configurable (function programmable ) outputs which also could be integrated if you wish.
          If you want to just run the VFD at the original rpm only, then set the speed output to 60hz (or 50hz as the case may be).
          Normally the terminals are protected somewhat, otherwise you should provide some kind of cover for safety reasons or put inside an enclosure.
          Max.
          Last edited by MaxHeadRoom; 09-18-2010, 12:24 AM.

          Comment


          • #6
            While I havent done what you describe, it should be OK - as you say, the 3 phase doesnt care where its going, to an outlet or a motor --- but, it has to switched on/off at the VFD unit!

            This is my Hitachi unit, the wires at the top control the on/off and other functions like remote pot, etc. It will be low voltage, as I recall mine is 24-26v, and therefore can be switched with any common switch, like a toggle----or the existing switch on the machine/tool. My mill has a toggle and my lathe uses the original switch that came on it.

            Last edited by Bill Pace; 09-18-2010, 12:36 AM.
            If everything seems to be going well, you have obviously overlooked something........

            Comment


            • #7
              Richard,

              The above advise is correct. If I were to add the VFD as you describe, I would simply install the VFD in place of the K1 contacts (leave K1 installed just move the contact wiring to the VFD). Then I would wire one contact on K1 to be the start switch for the VFD. Hook up your 240 volt single phase to the original L1 and L2 terminals and leave L3 disconnected. Set the VFD frequency to 50 or 60 Hz depending on motor ratings for full speed. By doing it this way you leave most of the control wiring in place, the original on/off switch still kills the power to the machine, the original start switch works as expected and if needed it is easy to put back to original. The power light even still works. If you want the variable speed function you just set the speed on the VFD to what you want. All is good .

              As for the safety of the wiring... The VFD can be mounted in an enclosure. The proper sizing information will be in the manual. VFD's do not need free air flow, they DO need enough surface area in the enclosure to dissipate the heat and enough space around the VFD so the air can circulate properly. All this info is in the manual.

              Robin
              Robin

              Happily working on my second million Gave up on the first

              Comment


              • #8
                Well, as one who designs things like VFDs, the problem is not so much with turning OFF the motor.... the VFD basically does that thousands of times per second......safely. It can handle the inductive "kick" just fine.

                The problem is that dropping the motor STARTING load on the VFD will simply trip the overload...... Of course, if you use a 10 HP VFD with a 1.5 HP motor, then you can probably use a switch and never worry.... But there is no point to the switch if you can't BOTH start and stop the motor, so....

                The VFD starts the motor slowly specifically to avoid a high starting surge, which it is not designed to handle, and is protected against. So the overcurrent will trip, and you'll have to re-start it with the VFD's soft-start anyhow.

                Mostly the overcurrent is reliable, but why test the parachute every day when you don't have to and it does no good anyhow?
                1601

                Keep eye on ball.
                Hashim Khan

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