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  • VFD Power question for electrical peoples...

    Hey guys,
    Note : I have no electrical experience at all, so sorry if this is a dumb question.

    So i'm getting Jack of my 2.4kw spindle (and 2.4kw VFD) (80mm chinese ER20) stalling out, and wanted to know if running a bigger VFD will help.
    The VFD that came with it trips out under what I would think is a reasonable load for the spindle. I do mostly aluminum, and what I think are reasonable cuts but it's just too damn risky now, I have some complex parts that come out well but boy do I go in small DOC to stop spindle stall.

    I see I can get a VFD thats 7.5kw for not much money, and was thinking of upgrading to it to simple have the extra amp draw handy if the tool loads up. Is this the way it works? Bigger VFD= More head room = more available torque? I find that in drilling operations I cringe as I hear the spindle load up... even drilling at 8000rpm it simply fails to do any reasonable peck depth with the torque it gets. I'm forced to drill at 12000 rpm!
    I'm also guessing I'm going to be schooled like I'm an idiot for asking, but will simply using a bigger VFD help?
    Thanks in advanced.
    Race.

    P.S: Maybe a 7.5kw VFD and a servo motor if I can find one that goes to 12000 rpm???

  • #2
    A bigger VFD won't necessarily have more power. You may have a setting wrong for the max current. Check the max current on the spindle motor and compare to the max current setting in the VFD parameters.

    If you have no power at lower speeds you might try a flux vector VFD, they have better power. Generic VFDs suck at low speed because they lower the voltage at the lower frequencies.

    A VFD will not drive a servo motor. It will fry one or both.

    Comment


    • #3
      Macona cheers bro. I have was thinking "There must be a high torque alternative in the 80/125 mm chinese spindle market."
      I found this, it's a direct bolt on for nearly the same price and I can switch spindles depending on what I'm doing. What do you think? I currently have a 2.4kw high speed (24000) rpm spindle, maybe this is the ticket?http://www.aliexpress.com/item/Large...333242502.html
      Has 6nm of torque, not sure if thats good or bad but it comes with a 3.7kw vfd anyway. I could go bigger spindle but would need a new spindle attachment too. I think this might be good bang for buck???
      Is 6nm what you class decent torque for milling aluminum? It has to be better then a high speed spindle?
      Last edited by raceneer; 05-06-2015, 02:22 PM.

      Comment


      • #4
        I am guessing that motor is something like a 4 or 6 pole motor. Which should give you better low end torque.

        But you are still dealing with a chinese VFD and you get what you pay for.

        Comment


        • #5
          True. I guess I want to get buy with something for now, eventually looking to save enough to get a 550L or similar small VMC, however I just need something that's going to give a loads more torque for milling more aluminum, don't get me wrong the 24000 rpm does ok... just, but i feel like I'm always doing a work around.

          Does anyone here own one of these high torque spindles?

          Comment


          • #6
            Motors have a linear voltage/frequency curve. If you run a regular 50 or 60Hz motor with high frequency, the voltage should increase in proportion. A 400V 50Hz motor needs 800V to run correctly (with the same torque) at 100Hz. My lathe motor is connected for 230V 50 Hz and I run it on a 400V VFD to 100HZ. Up to around 87Hz, the torque remains the same because the drive at this frequency supplies the motor with 400V which can't increase anymore until it reaches the maximum of 100Hz. The VFD is configured for the motor's name plate 230V 50Hz and calculates the correct voltage for the correct frequency.

            Normal motors can be rewound for lower voltage to take advantage of the VFD at high frequencies.
            Helder Ferreira
            Setubal, Portugal

            Comment


            • #7
              Seems like I remember reading that these spindles run at 400 Hz. Is your VFD set for that? Andy Olney

              Comment


              • #8
                Many questions:

                1) have you verified the settings are correct for your motor? If it trips out it must NOT be set right, at least for what you are trying to do.

                2) Are you then running 200Hz on a 3000 rpm 50Hz motor? If so, you are running way overspeed for the motor/VFD combo. In that condition you have probably "run out of volts", and your power/torque will stink.

                3) You have 240V power , what voltage is the spindle motor made for?

                4) If spindle motor is made for 240V, can you reset it up for 120V? Some can be, and that would give you more power/torque.

                A 1 HP 460V motor connected for 230V and set up to run 120Hz at 480V (slower as speed comes down) will develop 2HP at 120Hz, but the volts/Hz will be the same, and the motor will not overheat. You need to do something like that.

                The use of a vector drive, or higher power VFD unit probably will not do anything for you. What you need is to have a motor that can be set up for 120V, so your 240V will be applied at double speed (100 hz for you)

                Running at 12,000 rpm, means 200Hz, and at 200Hz on a 50Hz motor, your current will be 1/4 what it should be, and torque will stink. You are approaching the range of speeds where by law (some places, at least) you cannot make a VFD to run.... nuclear enrichment centrifuge speeds.
                CNC machines only go through the motions.

                Ideas expressed may be mine, or from anyone else in the universe.
                Not responsible for clerical errors. Or those made by lay people either.
                Number formats and units may be chosen at random depending on what day it is.
                I reserve the right to use a number system with any integer base without prior notice.
                Generalizations are understood to be "often" true, but not true in every case.

                Comment


                • #9
                  I think you guys are getting confused hey about the spindle. The is nothing wrong with the settings. The motor/ vfd is set right. The machine is designed to, when overloaded to cut power to the vfd and steppers as a protection for the machine. Doesn't always work though and you'll snap a tool or just continue on with no spindle running dragging your cutting tool over the workpiece. It is setup correctly from factory. The problem is the spindle and vfd are just weak as **** and cant remove decent alloy at any appreciable rate. Also it cant drill cause it just doesn't have the torque. It's a common problem with these spindles.
                  Last edited by raceneer; 05-06-2015, 10:36 PM.

                  Comment


                  • #10
                    Originally posted by raceneer View Post
                    I think you guys are getting confused hey about the spindle. The is nothing wrong with the settings. The motor/ vfd is set right. The machine is designed to, when overloaded to cut power to the vfd and steppers as a protection for the machine. Doesn't always work though and you'll snap a tool or just continue on with no spindle running dragging your cutting tool over the workpiece. It is setup correctly from factory. The problem is the spindle and vfd are just weak as **** and cant remove decent alloy at any appreciable rate. Also it cant drill cause it just doesn't have the torque. It's a common problem with these spindles.
                    So.... what are the answers about the spindle motor, etc?

                    We 'get it" that there is a problem. Now it's time to figure out if there is any sort of "fix" for it.

                    We really couldn't care less if it came from the factory like that. There is no reason to assume the "designers" of the system did anything right. Since "it's a common problem with these spindles", there is ample reason to assume they were NOT designed right, and that they have a fatal flaw.

                    That being the case, we have asked questions to determine, as much as possible, whether what SOUNDS like it is the problem, really IS the problem.

                    So, it's "designed to cut power when overloaded"? In other words, you are saying that it's acting as it was designed to.

                    OK, there are two choices.....

                    1) You are wildly overloading and abusing the machine and it is refusing to let you do it. You are kvetching about it not letting you abuse it even more.

                    2) It is a screwed up design and does not work right.

                    I don't know which it is. I don't even know what machine it is. Do you feel like you could let us know that?
                    CNC machines only go through the motions.

                    Ideas expressed may be mine, or from anyone else in the universe.
                    Not responsible for clerical errors. Or those made by lay people either.
                    Number formats and units may be chosen at random depending on what day it is.
                    I reserve the right to use a number system with any integer base without prior notice.
                    Generalizations are understood to be "often" true, but not true in every case.

                    Comment


                    • #11
                      Originally posted by J Tiers View Post
                      So.... what are the answers about the spindle motor, etc?

                      We 'get it" that there is a problem. Now it's time to figure out if there is any sort of "fix" for it.
                      We really couldn't care less if it came from the factory like that. There is no reason to assume the "designers" of the system did anything right. Since "it's a common problem with these spindles", there is ample reason to assume they were NOT designed right, and that they have a fatal flaw.
                      Fair point.

                      That being the case, we have asked questions to determine, as much as possible, whether what SOUNDS like it is the problem, really IS the problem.

                      So, it's "designed to cut power when overloaded"? In other words, you are saying that it's acting as it was designed to.

                      OK, there are two choices.....

                      1) You are wildly overloading and abusing the machine and it is refusing to let you do it. You are kvetching about it not letting you abuse it even more.
                      -This is probably true.

                      2) It is a screwed up design and does not work right.

                      I don't know which it is. I don't even know what machine it is. Do you feel like you could let us know that?
                      -Easy dog, no need to get funny, I'm not trying to be disrespectful. Let me try to answer some more questions for you...

                      4) If spindle motor is made for 240V, can you reset it up for 120V? Some can be, and that would give you more power/torque.
                      Not sure I'll look into this today. My neighbour is an electician/telecommunications fella and is good with stuff i'll go see him and see if I can find a VFD manual for this machine... So how much extra power/torque we talking about?

                      A 1 HP 460V motor connected for 230V and set up to run 120Hz at 480V (slower as speed comes down) will develop 2HP at 120Hz, but the volts/Hz will be the same, and the motor will not overheat. You need to do something like that.
                      -Very interesting, the spindle and vfd are setup to run at 240, maybe I could run it at 120??? Or would I need to buy a 120V input VFD? Like I said I don't really understand any of this stuff but I''m learning and doing my best to not sound like an idiot.

                      Machine Is a Jcut 6090B with a few extra mods/upgrades from factory. Very capable torque on steppers and feeds/speeds are good, spindle lets it down massively.
                      Last edited by raceneer; 05-07-2015, 12:24 AM.

                      Comment


                      • #12
                        OK.... its a rough crowd here.... mebbe I was a little too sarcastic....

                        This seems to be one version of the machine:

                        Model NO.: JCUT-6090B Engraving Machine Type: CNC Engraving Machine Control: CNC Current: AC Usage: Metal, Stone, Plastic, Wood, etc Trademark: JCUT


                        So, it's generally listed as either a router for plastics and wood, OR an engraving machine as in the link.

                        My suspicion is that door #1 is the answer, it's just not MADE for more than routing or engraving. Engraving is not very high power, in general. Routing can go various ways.

                        Since the listing shows it as 220V OR 120V, that likely puts a limit on power, it can't be more than about 12A to 15A draw when operating at 120V, including ALL things that draw power, not just the spindle. That means it isn't going to be very powerful to begin with, no matter which voltage it is used on.

                        Since it is a "system", it probably is made to be used with motor and built-in VFD together. For the intended purpose, it should work OK. I don't know what voltage the motor works on in reality, and they probably are not telling.... The "unit" apparently can use either 120 or 240V as input power, but that doesn't set the bus voltage, it might use a PFC, or a voltage doubler on 120V, either of which will give a 325V DC bus and work just as if it had 240V. Without knowing more than they may tell about it, no useful suggestions about modifications are possible.

                        With a regular motor, and a VFD, one can play tricks. The double speed double HP thing works specifically with certain conditions.

                        The motor has to be able to take the higher voltage (480 V for example).
                        The motor needs to be WIRED for the lower voltage (240V in this discussion).
                        The VFD needs to be set to run at 120Hz for the high voltage (480V), and to run at 60Hz at the low voltage (240VAC). That means the "motor rated" values would be set to 60Hz and 240V, but the maximum would be 120Hz and 480V. Setting up like that (details may vary by VFD) sets the curve of frequency vs voltage, the so-called "V/Hz curve".

                        You get double power because the input current is the normal current, but the voltage is double, which means double power in on a V x Amps basis (the power factor is about the same in both cases and drops out of the equations).

                        Since we have little useful info here, we can't assume anything, not even that we know the motor voltage. It could be specially made.

                        Normally, no 3 phase motor uses 120V 3 phase, so a 120/240 3 phase motor is very rare. 240/480 is a common pair, however, which is why I made the example like that.
                        CNC machines only go through the motions.

                        Ideas expressed may be mine, or from anyone else in the universe.
                        Not responsible for clerical errors. Or those made by lay people either.
                        Number formats and units may be chosen at random depending on what day it is.
                        I reserve the right to use a number system with any integer base without prior notice.
                        Generalizations are understood to be "often" true, but not true in every case.

                        Comment


                        • #13
                          Originally posted by J Tiers View Post
                          OK.... its a rough crowd here.... mebbe I was a little too sarcastic....

                          This seems to be one version of the machine:

                          Model NO.: JCUT-6090B Engraving Machine Type: CNC Engraving Machine Control: CNC Current: AC Usage: Metal, Stone, Plastic, Wood, etc Trademark: JCUT


                          So, it's generally listed as either a router for plastics and wood, OR an engraving machine as in the link.

                          My suspicion is that door #1 is the answer, it's just not MADE for more than routing or engraving. Engraving is not very high power, in general. Routing can go various ways.

                          Since the listing shows it as 220V OR 120V, that likely puts a limit on power, it can't be more than about 12A to 15A draw when operating at 120V, including ALL things that draw power, not just the spindle. That means it isn't going to be very powerful to begin with, no matter which voltage it is used on.

                          Since it is a "system", it probably is made to be used with motor and built-in VFD together. For the intended purpose, it should work OK. I don't know what voltage the motor works on in reality, and they probably are not telling.... The "unit" apparently can use either 120 or 240V as input power, but that doesn't set the bus voltage, it might use a PFC, or a voltage doubler on 120V, either of which will give a 325V DC bus and work just as if it had 240V. Without knowing more than they may tell about it, no useful suggestions about modifications are possible.

                          With a regular motor, and a VFD, one can play tricks. The double speed double HP thing works specifically with certain conditions.

                          The motor has to be able to take the higher voltage (480 V for example).
                          The motor needs to be WIRED for the lower voltage (240V in this discussion).
                          The VFD needs to be set to run at 120Hz for the high voltage (480V), and to run at 60Hz at the low voltage (240VAC). That means the "motor rated" values would be set to 60Hz and 240V, but the maximum would be 120Hz and 480V. Setting up like that (details may vary by VFD) sets the curve of frequency vs voltage, the so-called "V/Hz curve".

                          You get double power because the input current is the normal current, but the voltage is double, which means double power in on a V x Amps basis (the power factor is about the same in both cases and drops out of the equations).

                          Since we have little useful info here, we can't assume anything, not even that we know the motor voltage. It could be specially made.

                          Normally, no 3 phase motor uses 120V 3 phase, so a 120/240 3 phase motor is very rare. 240/480 is a common pair, however, which is why I made the example like that.
                          Give me a few minutes here I'm just grabbing a bunch of info. Part of me wonders if I should just run a new 7.5kw VFD and get that VFD/8000rpm high torque spindle combo but I'd really like a bit more oomph.
                          But, if I can do something drastic here, that would be idea, mainly cause it would cost me 1000 bucks or more!

                          Comment


                          • #14
                            My 1.5kw spindle mills and drills aluminum just fine. Are you using a feed and speed calculator like GWizard or FSWizard to determine your settings or just winging it?

                            Comment


                            • #15
                              Just attaching a VFD with more power capability will NOT necessarily make any difference. The limit has to be something OTHER than voltage. And it might be possible to re-set the current limit on what you have. OR the thing you have may be defective, bad current limit, and you have a warranty claim to file (a warranty in china? HA!).

                              The only way that the motor can be "made more powerful" is to allow it to draw more current. Assuming (a big assumption) that more current will not burn it up, a different VFD would need to supply more current. That's possible. But one thing that high Hz does is to severely limit the possible current draw. The high frequency just can't get through the motor inductance, which tends to block high frequencies.

                              BUT, since the VFD has to operate at a large overspeed, as much as 8x (400Hz), the problem is far more likely to be running out of voltage, since a 230V motor needs to be supplied with a much higher voltage to maintain torque at anything reasonable. That would limit torque, and force the spindle to slow down radically in an attempt to draw more current.

                              To counteract that, the maker may actually have made a motor rated at a normal voltage of considerably less than 240V, and be doing something similar to what a couple of us suggested above, running the overspeed at a higher effective voltage. A motor rated at 30VAC / 50Hz, would (with correct insulation), be perfectly happy at 240V and 400Hz, as an example.

                              Jumping in without knowing any of this, you stand a decent chance of slagging the whole thing and being left with an expensive problem and useless machine. Since I see it is not a low cost item, that may not be a good plan.

                              The unit may have a warranty problem. The unit may just not BE for what you wish to do..... which sounds pretty likely given the on-line info. They CALL it a router for plastics, or an engraver, depending on who you believe.
                              Last edited by J Tiers; 05-07-2015, 09:44 AM.
                              CNC machines only go through the motions.

                              Ideas expressed may be mine, or from anyone else in the universe.
                              Not responsible for clerical errors. Or those made by lay people either.
                              Number formats and units may be chosen at random depending on what day it is.
                              I reserve the right to use a number system with any integer base without prior notice.
                              Generalizations are understood to be "often" true, but not true in every case.

                              Comment

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