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Thread: VFD Newbie questions

  1. #1
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    VFD Newbie questions

    Have a 3-phase, 208 v, 3 HP motor.

    It is currently setup with typical motor starter/fused disconnect with forward/reverse contacts and thermal OL's.
    A direction selector switch (non-latching) is located on the side of the unit.

    The customer wants to set it up with a VFD to control the speed, minimize the sudden jerk of starting and stopping.

    I don't have first-hand experience. I understand how VFD's work, but have questions about getting it setup to do what the customer wants.

    I plan to leave the existing motor starter box where it's located and mount the VFD in an adjacent box with a nipple between the 2 enclosures.

    -I'm assuming that I'll by-pass the existing contactors and re-route the conductors (load side of fuses at disconnect). Does a typical VFD perform OL functions, or do I have to continue to use the existing OL's?

    -they want controls mounted to the side of the enclosure that will allow the operator to choose the direction (forward/reverse) of motor and the speed.
    My understanding is that the speed is controlled by some sort of potentiometer, typically does each manufacturer provide a potentiometer for their VFD or are there "universal" potentiometers that I should look at choosing?

    -how does the operator select the motor direction? I.e., what sort of button setup should I be looking for?

    -I'm sure the customer will want a display of some sort that shows which direction is selected before using the potentiometer to operate the button.

    These are all fairly basic functions, I know how to do this with your typical motor starter setup. I just don't have experience with VFD's.

    Thanks for any basic info/answers!

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    Go online and download an installation manual for a VFD. Read it. Then go for the operators manual. Pick a basic VFD like an AB PowerFlex 4, or AD GS2 or 3.

    Leave the more complicated and higher end ones alone. You don’t need the confusion at this stage. Nobody doese.

    eta: https://literature.rockwellautomatio...m001_-en-e.pdf
    Tom
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    FWIW

    We always had a contactor on the output side of the VFD. For safety reasons, we had to have a physical disconnection means But we had a shutdown sequence that ensured that the VFD was shut off before the contactor was opened.
    Reversing?
    Normally available via the keypad but you can very likely use an external relay into a VSD input if you needed to do it from a remote rather than local position.

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    Quote Originally Posted by ptonsparky View Post
    Go online and download an installation manual for a VFD. Read it. Then go for the operators manual. Pick a basic VFD like an AB PowerFlex 4, or AD GS2 or 3.

    Leave the more complicated and higher end ones alone. You don’t need the confusion at this stage. Nobody doese.

    eta: https://literature.rockwellautomatio...m001_-en-e.pdf
    The customer has a referral to a Mitsubishi VFD that is used for this application in other locations similar to this one. I have already downloaded the manual and am reading through it.

    My local supply house carries AB. I have a call in to them to get info on a comparable AB version.

    Any thoughts about AB vs Mitsubishi? The only reason I was looking at AB is tech support from the supply house regarding peripheral items, like the enclosure and potentiometer, etc. but maybe I'm overthinking things...

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    Quote Originally Posted by sw_ross View Post
    The customer has a referral to a Mitsubishi VFD that is used for this application in other locations similar to this one. I have already downloaded the manual and am reading through it.

    My local supply house carries AB. I have a call in to them to get info on a comparable AB version.

    Any thoughts about AB vs Mitsubishi? The only reason I was looking at AB is tech support from the supply house regarding peripheral items, like the enclosure and potentiometer, etc. but maybe I'm overthinking things...
    I try to use what is available locally if I feel I need an immediate replacement or help (AB). I don't remember working on a Mitsubishi, so I can't compare. Do you have a supplier of Mitsubishi in State?
    Tom
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    If you get a unit with interface keypad/display you generally can stop, start, change direction, monitor output, etc all from that interface unit as well as change operating parameters with it. Usually set up for keypad control as default, but you can change settings to allow remote devices to control it. External potentiometer for external speed control - usually requires either a 5k or 10k 3 wire pot. Other speed control options may be 4-20 mA or 0-10 V input by some other analog device and works great if automatic speed control is necessary for an application. Then there is usually other digital communications abilities for control by PLC's or other digital items., just need to know how to set parameters and use these features, but simple start, stop, FWD,REV and three wire speed pot are pretty common on simpler installations, and so is just using keypad on the unit in some instances.

    Many of those units even are capable of remote location of the keypad if you don't want the drive located right at the operator station but still want to use the keypad for contol.
    I live for today, I'm just a day behind.

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    Quote Originally Posted by ptonsparky View Post
    I try to use what is available locally if I feel I need an immediate replacement or help (AB). I don't remember working on a Mitsubishi, so I can't compare. Do you have a supplier of Mitsubishi in State?
    My customers referral is to the website VFDs.com
    I'm not sure if the link was sent to them (referral) or if they googled the VFD that was referred to them.

    Maybe I'll contact the tech support and see how helpful they are regarding the installation...

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    They are not that hard to install and it sounds like you have a very basic operation.

    You may want to meg your motor and conductors to it, before applying a VFD. It will find problems you didn't know you had and of course, you will be blamed.
    Cooling of the motor via its fan will be reduced as the rpm is reduced, so continued operation at low speeds can be a problem. A minimum speed can be set.
    Newer motors are more likely to have better insulation rated for use with VFDs and in that context, try to limit your distance to the motor as indicated in the manual.
    Line reactors are a good idea, as are load reactors for older motors and/or the distance to it is excessive.

    In short again, read the manual.
    You will be fine.
    Tom
    TBLO

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    Quote Originally Posted by ptonsparky View Post
    They are not that hard to install and it sounds like you have a very basic operation.

    You may want to meg your motor and conductors to it, before applying a VFD. It will find problems you didn't know you had and of course, you will be blamed.
    Cooling of the motor via its fan will be reduced as the rpm is reduced, so continued operation at low speeds can be a problem. A minimum speed can be set.

    When driving a variable torque load such as a fan or pump, this may not be a problem. constant torque loads cooling of the motor can be a problem at lower speeds. Externally powered cooling fans sometimes is necessary.

    Newer motors are more likely to have better insulation rated for use with VFDs and in that context, try to limit your distance to the motor as indicated in the manual.
    Line reactors are a good idea, as are load reactors for older motors and/or the distance to it is excessive.

    That insulation rating of motor is usually more critical on older motors (that are not using same magnet wire as newer motors usually have) if operating at 480 volts as the base 60 Hz volts. If running a dual voltage motor on 208-240 volts you simply won't stress the insulation on same windings with the voltage spikes seen at the low voltage as you will at the high voltage. 480 volt drive output can see voltage peaks that are over 800 volts and that tends to be a problem for the winding insulation, is worsened by long circuit runs from the drive to the motor.

    In short again, read the manual.
    You will be fine.
    I'm not trying to educate you tom, I think you know most of what I said, just adding some content to what you said for possible benefit of OP.
    I live for today, I'm just a day behind.

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    Quote Originally Posted by kwired View Post
    I'm not trying to educate you tom, I think you know most of what I said, just adding some content to what you said for possible benefit of OP.
    I had already forgot he said 208v. Educate me. Someone has to. Over and Over and over. CRS!!
    Tom
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