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Thread: How I put a VFD on a drill press for no more belt changes

  1. #1

    How I put a VFD on a drill press for no more belt changes

    With several recent threads about VFDs, I thought I’d share how I equipped a drill press with a 3-phase motor and VFD to avoid needing to change belts.

    First, the drill press: a pretty junky Taiwan-era Delta that I picked up for $75 on craigslist. It hadn’t been used very much, though, and had almost no measurable slop in the quill. It got stripped down, completely repainted, and put back together (this is the before picture, obviously )


    Next, the motor. I found an old 3-phase motor in the “junk box” at work (so it was “free”). It’s a 200V, 2HP, 1725 rpm motor. It also got stripped apart, repainted, and new bearings installed. It’s probably much too big for this application, but it was free, so I’ll work with it.



    Then, the VFD itself. Trying to be thrifty, I picked up a no-name “ebay special” shipped-from-China VFD for $100 (including shipping), rated for 2HP. Additionally, this VFD had a remote-mountable control panel, and a built-in speed adjustment pot, which I wanted.



    The VFD I bought also supported “space vector control”. To explain the value of this, we need a quick detour to motor drive theory: When a VFD varies the frequency of the output, it also varies the amplitude of the voltage. Most VFDs increase the voltage proportionally to the speed, and this is called “V/Hz” control. This is done to maintain constant magnetic flux within the motor, and since flux is what produces torque, it results in constant torque over all speeds. However, power is speed times torque. If torque is constant as speed is varied, it results in very low power at low speeds, and full power only at full speed. For something like a drill press, we likely desire plenty of power at low speeds (for large diameter cutters), so this is undesirable.

    One way to overcome this is to simply use a larger motor. In this case, I’m doing that, already. The larger motor will produce more torque at a given speed than a smaller motor, and that, alone, may be sufficient to get enough low-speed power. However, another method of increasing power delivery at lower speeds is to deviate from V/Hz control and use space vector control, instead. The one sentence explanation of space vector control is that it uses current sensors to actively monitor the 3-phase currents and adjust the pattern of switching of the transistors to produce more torque at low speeds.

    I hooked the motor to the VFD and programmed the various parameters. Of note, since the motor is only rated for 200V, I needed to program a 200V limit into the controller (since the supply voltage is 240V). I also needed to program several other motor nameplate parameters into the controller and let it run a “tuning” algorithm to “learn” the motor parasitic parameter values in order to use the SVC mode.

    Unfortunately, this motor was physically much larger than the 3/4HP motor originally installed, and the mounting plate didn’t align in any way with the holes on the new motor.



    I ended up fabricating a replacement out of some aluminum (note: this is probably the only part of the project I was disappointed with: the aluminum wasn’t stiff enough and the motor sags a bit).




    With the motor mounted, I removed the center (idler) pulley, mounted a new sheave to the motor shaft, and used a link belt to connect to the remaining sheave.



    I mounted the control panel of the VFD in the space previously occupied by the on/off switch – luckily, it fit almost perfectly, and a little black RTV filled the small gaps around it.



    A RJ-45 cable runs from the control panel to the VFD, which is located in a small metal box near the base of the drill press. This control cable and the power cord for the motor are held together in a piece of looming that keeps the cords neat.



    The VFD offers the ability to display various parameters while running. One very useful parameter is “load speed”. It also offers the ability to set a “load speed multiplier” to adjust for any pulley ratios, etc, that might be in the system. Mine is thus configured so that, when running, it displays the actual speed (in RPM) of the chuck. A turn of the knob on the control panel runs it from zero to 3,000 rpm. Pressing the “stop” button brings the chuck to a standstill in 1.0 seconds (also a programmable value).



    My total investment in this project is <$200 (which is obviously because I got the motor for free, but 1-2HP 3-phase motors can often be had very cheaply, anyways).

    I was worried about the reliability of the VFD, but I believe even the no-name VFD manufacturers are using control ICs from reputable chiphouses, and the transistors in these drives come in a “pack” of 7 (6 for the 3 phase, and 1 for braking resistor) that are also sourced from reputable vendors. The VFD manufacturer is merely adding a user interface and mechanical packaging.

    Anyhow, hope you enjoyed this. I’d be glad to answer any questions.

  2. #2
    Join Date
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    I've cursed the tangle of belts on my drill press for years. Thanks for posting this fix.

  3. #3
    Join Date
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    Prince Edward Island, Canada's Ocean Playground
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    Nice job Dan, I put a VFD and 3 phase motor on my General 340 press last year and I had a 2 hp motor initially as it was the size that fit the pulley and was in the rathole. At the suggestion of a friend I set the current limit of the VFD as if it were a 1 hp motor so all I get is 1 hp, because I really didn't want 2 hp on the 340, I have a bigger press for larger drilling tasks where I can clamp the work securely and give it more torque.

    I have since sourced a 1 hp motor for the 340 so the 2 hp motor is back on the shelf. Sure is handy having digital speed control on the press and I did the same with my wood lathe.
    Erik

    Canada's Atlantic Paradise - Prince Edward Island

  4. #4
    That's a good idea, Erik - I may need to put a current limit on mine, too. I've noticed that with larger-diameter bits (forstners, etc), I can EASILY get so much power at ~300rpm that the belt slips or the keyless chuck becomes impossible to release without some channel locks

  5. #5
    That really an inspiring project. I've wanted to do something similar for quite a while. Good job.

    Mike
    Go into the world and do well. But more importantly, go into the world and do good.

  6. #6
    Join Date
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    As a lover of VFDs, ( I have 7 in use now and two more almost ready to go), my only concern it the box that has the VFD in it. They do produce heat and need ventilation. I mount mine high and out of the way like in the photo below.
    CPeter
    IMG_2396 (Small).JPG

  7. #7
    Join Date
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    Well done Dan, nice project.
    NOW you tell me...

  8. #8
    It is some times a good idea to keep the old mechanical drive in tack. that way you don't need the full range from a drive . the motor and drive like a range of about 30hzs at the low end and thats plenty for woodworking drill presses , after that the power and toque drop off. it maintains a good motor speed for cooling to. Often you don't want high toque and so setting the VFD to a lower hrz in a higher speed pulley gears lets you do sensitive work like tapping threads without snapping the tap. Also higher gears and over running the motor to say 2 times speed or 120 hzs get the spindle up to 10,000 rpm for cutter router bits. you need the right chuck but i do this on mine . I wounder if you set the base frequency on your drive for that 200 volt motor? not all drive can do this. 200 volts is not a common 3 phase voltage and is out side your house hold range. Any plans for external switches.
    Last edited by jack forsberg; 01-09-2017 at 12:30 PM.
    jack
    English machines

  9. #9
    Good point, Jack. It wouldn't have hurt to leave the belts. In my case, the drill press gets little use, to begin with, and with such a big motor, I'm not worried too much about cooling. I also never ever ever want to touch one of those belts, again

    This is plugged into a 240V (RMS) single-phase supply, and since it's using SVC, I don't think I need to explicitly set a base frequency. It's programmed not to exceed 200V output (which I have confirmed works properly), and other than that, the SVC algorithm takes care of adjusting the voltage to whatever is necessary for the given frequency.

  10. #10
    Dan.

    I also have a 200 volt motor that needs a VFD.
    Where did you order yours from?

    Thx.

    Fred

  11. #11
    Quote Originally Posted by Dan Friedrichs View Post
    Good point, Jack. It wouldn't have hurt to leave the belts. In my case, the drill press gets little use, to begin with, and with such a big motor, I'm not worried too much about cooling. I also never ever ever want to touch one of those belts, again

    This is plugged into a 240V (RMS) single-phase supply, and since it's using SVC, I don't think I need to explicitly set a base frequency. It's programmed not to exceed 200V output (which I have confirmed works properly), and other than that, the SVC algorithm takes care of adjusting the voltage to whatever is necessary for the given frequency.

    Dan has nothing to do with RMS its got to do with the Volt /Hzs relationship. More than likely you have provision to set the base frequency in the motor overload section . on that drive for that motor if base frequency is not set than the only time that the voltage and Hzs are in sink is at 72hzs assuming your voltage is 240. the vector control will not operate properly if base is not set. you don't need to limit the motor to 200 volts what you need is to set base so that the relationship to volts is the same at 200 as it is at 240 volts . in your case you would set base to 72 hzs. that is because at 200 volts that motor likes 60 hzs so you have a ratio of 3.3333volt to 1 hz.

    proper math is in the PDF

    http://controltrends.org/wp-content/...ndamentals.pdf
    Last edited by jack forsberg; 01-09-2017 at 1:39 PM.
    jack
    English machines

  12. #12
    Jack, I don't know what you mean by "voltage and Hzs are in sink".

    I think what you mean is that most VFDs maintain a constant V/f ratio, in order to maintain a constant value of magnetic flux (because the amount of flux is determined by the quantity of volt-seconds applied to the motor). Increasing the voltage without increasing the frequency proportionally will result in more magnetic flux, which may magnetically saturate the motor. Thus, to avoid magnetic saturation (essentially "short circuiting" the motor), many VFDs maintain a fixed V/f ratio. You're suggesting that I need to program the VFD to use a V/f ratio of 200V/60Hz. Normally the "base frequency" is the actual rated frequency of the motor (60Hz), but in this case, since I'm running a 200V motor off 240V, I need to "trick" the VFD into producing the correct V/f ratio (200/60) by telling it that the motor is rated for 72Hz (because 240/72 = 200/60).

    I agree that you are correct if this were a V/f drive. However, when using sensorless vector control, the V/f ratio is NOT constant. The frequency is set by the operator (ie - I turn the knob to set the desired speed, and the drive sets the electrical frequency to produce that), and the voltage amplitude is determined by an algorithm. There is no need to maintain a fixed V/f ratio, since the drive measures the actual current, separates the current into the magnetizing and torque-producing components, and adjusts the timing and amplitude of the voltage to maximize torque.

    So I believe the only parameter I need to set is the maximum voltage (200V). The only reason to maintain fixed V/f is to avoid magnetic saturation, and since this drive contains current sensors which monitor the 3-phase output, it knows if it exceeds the magnetic saturation threshold without having to merely rely on a "hard" V/f limit. This is why SVC allows greater low-speed torque.

  13. #13
    Quote Originally Posted by fRED mCnEILL View Post
    Dan.

    I also have a 200 volt motor that needs a VFD.
    Where did you order yours from?
    Fred, here's the one I bought:

    http://www.ebay.com/itm/361155386082...%3AMEBIDX%3AIT

    It might be too small for your 3HP motor, though. Based solely on the appearance, I'd guess the Amazon one you linked in the other thread is probably by the same manufacturer.

  14. #14
    Quote Originally Posted by Dan Friedrichs View Post
    Jack, I don't know what you mean by "voltage and Hzs are in sink".

    I think what you mean is that most VFDs maintain a constant V/f ratio, in order to maintain a constant value of magnetic flux (because the amount of flux is determined by the quantity of volt-seconds applied to the motor). Increasing the voltage without increasing the frequency proportionally will result in more magnetic flux, which may magnetically saturate the motor. Thus, to avoid magnetic saturation (essentially "short circuiting" the motor), many VFDs maintain a fixed V/f ratio. You're suggesting that I need to program the VFD to use a V/f ratio of 200V/60Hz. Normally the "base frequency" is the actual rated frequency of the motor (60Hz), but in this case, since I'm running a 200V motor off 240V, I need to "trick" the VFD into producing the correct V/f ratio (200/60) by telling it that the motor is rated for 72Hz (because 240/72 = 200/60).

    I agree that you are correct if this were a V/f drive. However, when using sensorless vector control, the V/f ratio is NOT constant. The frequency is set by the operator (ie - I turn the knob to set the desired speed, and the drive sets the electrical frequency to produce that), and the voltage amplitude is determined by an algorithm. There is no need to maintain a fixed V/f ratio, since the drive measures the actual current, separates the current into the magnetizing and torque-producing components, and adjusts the timing and amplitude of the voltage to maximize torque.

    So I believe the only parameter I need to set is the maximum voltage (200V). The only reason to maintain fixed V/f is to avoid magnetic saturation, and since this drive contains current sensors which monitor the 3-phase output, it knows if it exceeds the magnetic saturation threshold without having to merely rely on a "hard" V/f limit. This is why SVC allows greater low-speed torque.
    I don't see any function to set voltage . In fact the drive states that its is only for 220 to 240 volts .

    i take it this is your manual.

    http://www.hclub.ee/download/varia/K...0119(V1.1).pdf

    just trying to help out and would like you to get the most from your drive.

    found this on page 79



    i am just a woodworker with about 15 drives in the shop so maybe those with more knowledge can comment? does Mr Norton get out much anymore? been year! but he does know his singa faze and tree faze,
    Last edited by jack forsberg; 01-09-2017 at 5:24 PM.
    jack
    English machines

  15. #15
    Yes, that's the manual. It's confusing because the drive supports both V/f control AND vector control.



    In vector control, the max voltage (and other parameters) are set in this table:



    Note that you only have to input parameters 0-4. Parameters 5-9 are automatically calculated when it performs the dynamic auto-tuning.

    I looked through the manual, and couldn't immediately find a way to set the frequency differently if V/f mode was desired, though.

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