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  • VFD questions

    Good morning everyone!

    I know that the VFD thing has been just about run into the ground but I need some help from the gurus around here and the search function wasn't turning up quite what I was looking for.

    I'm working on running a new power line in my shop for my lathe. At current I will be running it on the original 110v 1/3hp motor. In the future I intend to use a 1.5hp 3ph motor driven by a VFD. To that end, I want to run the wire for both the 110 circuit and the 220 circuit for the VFD now to make future me happier. To help me decide what type of wire to run I decided that I needed to select my VFD now. Which brings me to my questions.

    Will the VFD at this link be sufficient to run a 3ph motor with the nameplate data in the photo?

    Click image for larger version

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    The drive is supposed to be rated for 7A on the output. I've read that the drive needs to be sized with a bit of extra head space in the current capacity but I've not seen a rule of thumb about how much over.
    Now for a question about the input side from my panel. I know that the breaker needs to be sized to protect the input, how do I know how much it will draw? I've not seen this in the data for any drive I've looked at. Can I reasonably assume that the input current will not exceed the output current? If that is the case, is a 220V 15A breaker too large? Would I need to add some sort of fuse or specialty breaker between the panel and the VFD?

    VFD users, do any of you have VFDs equipped with dynamic braking? Is that something that is nice to have but not essential? I will be using this on a belt driven Logan model 200, would the braking just cause the flat belt to slip?

    One final question for now. Should I be looking for a constant torque drive, a variable torque drive, or one that supports both?

    I think that's all I have for now.

    Thanks in advance!

    Jerrod
    Attached Files

  • #2
    That drive is rated 2 HP for both three phase and single phase input. So it should be fine.

    For drives that are not specifically rated for single phase input, the usual rule of thumb is 2x, so a 3 HP drive for 1.5 HP motor.
    http://pauleschoen.com/pix/PM08_P76_P54.png
    Paul , P S Technology, Inc. and MrTibbs
    USA Maryland 21030

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    • #3
      It should work, and It looks like max amps is 7.
      At the end of the project, there is a profound difference between spare parts and left over parts.

      Location: SF East Bay.

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      • #4
        If you intend to use 220v single phase input vfd there is no need to do anything different with wiring. 110v uses hot, neutral plus ground. 220v volt uses hot,hot plus ground. You would just take the white wire off the neutral bus and put it on one pole of a 2 pole breaker when you switch to 220v black wire on the other pole. Add some colored electrical tape on each end of the white wire to identify it as a hot wire and you're done.

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        • #5
          You need the phase vector control type, not the V/F version. it looks like the one mentioned has both options.
          As this is a typical 2 pole 3450rpm motor, you do not require the specialized shielded cable from VFD to motor used for the 400Hz motors.
          In that case the wiring from VFD to motor can be either 3 THN/TEW etc conductor twisted with separate earth conductor or a 4 conductor cable.
          If the motor is stationary, I use flexible metalic conduit for preference.
          Max.

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          • #6
            I prefer a vfd with a potentiometer knob to change rpm of the output. It's faster and simpler than
            hitting the up or down arrow to change speed.
            Larry S
            Larry Swearingen
            Fort Wayne, IN
            New Hoosier

            Comment


            • #7
              Originally posted by MaxHeadRoom View Post
              You need the phase vector control type, not the V/F version. ........
              Max.
              Why do you say that he "needs" that?

              Are you suggesting that the V/F would not operate the lathe?
              CNC machines only go through the motions

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              • #8
                As a guy with 13 or so of these in my shop, I have a little experience and I will say that I think that the GS3 series might be overkill. I have all GS2 series Automation Direct. I do have one with dynamic braking on my Clausing 5914, but it has very heavy chucks and the coast to stop time was longer than I wanted to deal with. All of mine have remote control for the speed and fwd/off/rev. The cost to build the remote is less than $20! If that were my lathe I would not use that motor. I like 1725 or even 1140 RPM motors. The HP output on the motor driven by a VFD is this. From zero to rated (nameplate) speed, the hp is proportional to the speed. 50% speed = 50% hp. Above the rated speed, the hp is constant at the rated HP. Most modern motors can be run at least up to 150% or more. The motor on my mill/drill is a 1725 motor. It is rated for a max speed of 5400 and I run it up to 4000. This motor was from Automation Direct and approved by them for this installation.

                This is one of my drill presses.
                Peter

                Click image for larger version

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                Grantham, New Hampshire

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                • #9
                  Max,

                  Thanks for the tip about wire from the VFD to the motor. I hadn't thought that far out yet. 😁

                  What's the difference between the phase vector type and the V/F type?

                  Jerrod

                  Comment


                  • #10
                    Peter,

                    Thanks for the feedback, I appreciate your input. My chucks aren't overly large so brakes might not be a big deal. I think I'll probably skip that for now but spec a drive that could have that added later. Bummer about the 3450 rpms, I didn't think about that being an issue. Sometimes free stuff is too good to be true.

                    If I kept this motor but just limited the speed to 1725 most of the time, I'd get about 3/4hp out of it, correct? That might not be bad, going from a 1/3hp motor. I know this lathe doesn't need anything nutty like a 10hp unit! 😉

                    Jerrod

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                    • #11
                      Jerrod, the circuit breaker in your panel is sized to protect the wire and to provide short circuit protection. Primary motor protection is usually provided by a fusible disconnect ,at least in an industrial setting, but your VFD has protection built in that will usually protect the motor in case of a fault. There is sometimes a limit as to the amp trip span on some drives. Could the speed of the motor be adjusted down some by different size pullies? Jim

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                      • #12
                        Jim,

                        Yes, I think I could use a motor pulley that would reduce the speed input to the lathe. I'm not sure how small I could go though. Doubling the motor speed would need the pulley attached to the motor to be quite small. At least the way I'm thinking of the issue it would.

                        I think the VFD could be used to limit the top speed electronically, or at least I think they can!

                        Maybe I need to take a look at selling this motor on and getting a new one of a lower speed.

                        Jerrod

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                        • #13
                          I understand the purpose of the breaker in this system. My concern is centered on how to size the circuit to the VFD. I've not seen anything that states a max amp draw from the input. It seems to make sense to me that the output current can't exceed the input current. Thus, with a 7A output rating, the input should be a 15A breaker and 14ga wire. Am I right in thinking this way? Or should I just go for a 20 circuit like everything else in the house?

                          Just thinking it out right now! =)

                          Jerrod

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                          • #14
                            I would suggest using a 20 amp breaker and #12 AWG wire. The single phase current will be roughly twice (actually 1.7) times that of the 3 phase outputs to the motor. There will be an initial current surge when the VFD is connected to the mains and the bus capacitors are charging.
                            http://pauleschoen.com/pix/PM08_P76_P54.png
                            Paul , P S Technology, Inc. and MrTibbs
                            USA Maryland 21030

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                            • #15
                              Paul,

                              Ah! Good points! Thanks so much for your help.

                              I learn something new here everyday!

                              Jerrod

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