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Another "which VFD" for MSC bridgeport clone

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  • Another "which VFD" for MSC bridgeport clone

    We have a 3-phase mill that is being moved to a shop where there is no 3-phase. FWIW this is a mill that sees very occasional, light and non critical use. Simplest solution seems to be a VFD, and the motor nameplate info is:

    Manufacturer: Wan Nan, China
    Type: YD90L-4/2TH
    1.3/1.8 KW 60Hz
    220V
    5.8/7.5 A
    Conn: [delta]/YY
    1720/3430 RPM

    Right now it's seems to be connected to a rotary switch giving slow (soft start) and fast (hard start). Wye and Delta I assume. The machine sometimes stalls in the first position. There are six leads from the motor to the rotary switch.

    Automation Direct shows their largest GS1 series (the GS1-22PO) as 2HP & 7.0A, whereas this motor seems slightly over that. Next up would be their GS2-23PO which is rated for 10A.

    Would one of these be appropriate for the use I've described, and are there better options?

  • #2
    The VFD isn't large enough for that motor. Please tell us more about the motor.

    With six motor leads, there are lots of ways to miswire it. One assumes that the motor documentation tells one how to connect the leads.

    Added: Are there any switches between VFD and motor?
    Last edited by Joe Gwinn; 12-22-2016, 10:37 AM.

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    • #3
      1.8KW = 2.4HP, or thereabouts. The real problem that I see if that the current wiring is for a 2 speed motor, and some VFDs are not happy with external switching of the load while the VFD is running.

      I think I'd look at the wiring, see how it's being switched and see if I couldn't get a VFD that could be informed of the switching and be happy with it.

      Alternatively you could get a 3HP VFD, leave the mill on the high speed with the belts on a medium setting and make all the speed changes with the VFD. That's what I've done with my Lagun, but it might not be possible unless your mill has a backgear.

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      • #4
        rkepler, we definitely would do away with the rotary switch. Sorry; I figured that was a given. Since the VFD can control speed I see no reason for the switch. It doesn't even do a good job now. When I turn to the first position the spindle slowly starts to turn but sometimes just wiggles a bit. Going from there to position 2 the speed suddenly jumps up to at least double, maybe more. Turning from there back to position 1 the speed change is so sudden the belts chirp. And then from there it slows gradually to a stop. "Unless the mill has a backgear.." what do you mean?

        Joe: there is no current VFD. I'm looking for options. It's just 3-phase from the wall to the rotary switch and then six leads from there to the motor. I'd be astonished if we could still find any documentation on the motor, but the leads are colored. I can get that info.

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        • #5
          Just wire a 3hp vfd (like an Hitachi WJ200-022sf) to the high speed connections (or don't touch the switch in use!) and set your max output current to 7.5 amp. Your motor is likely an inefficient pig with dubious nameplate rating so don't under-rate the vfd.

          At 60hz you will have 3450 rpm and 2.4hp

          At 30 hz you will have 1750rpm and roughly 1.2hp

          You can likely even wire a simple LV swith to flip between "high" and low" but it won't buy you much.

          ANTON : Please put you location or even county in your profile. Electrical questions are not well served without that information.

          This isn't a "soft start" system - it's dual speed. If it stalls on low speed something is wrong. It's probably a Dahlanger wound motor and something isn't switched correctly (bad wire, loose wires, bad switch etc for low speed).



          ANTON : Please put you location or even county in your profile. Electrical questions are not well served without that information.
          Last edited by lakeside53; 12-22-2016, 11:44 AM.

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          • #6
            +++1 on The hitachi VFD. That is an excellent choice.

            When choosing which winding to wire, consider what you cut with the mill. I would be inclined to wire the low speed end, to get more torque when milling or drilling steel. Running the VFD up to 90 Hz would get you up to 2500 rpm, which is more than sufficient on a manual mill with no coolant. Most manual mills come with a 1800 rpm motor installed.

            However, as Lakeside pointed out, the symptom of "stalling" using the low speed (4 pole winding) means something might be wrong with that set of windings. I would be disinclined to smoke-test a VFD by hooking it up to a motor that has been unreliable. I have my doubts that the "wannan motor" is the great of an electric motor even when it was new. But a good 3 phase 2 HP baldor or marathon motor... a little shopping on eBay will find you a good deal on a quality motor.
            Last edited by tmarks11; 12-22-2016, 12:13 PM.

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            • #7
              While you likely CAN (just) use a smaller VFD than the motor rating, there is the question of "Why?".

              Yes, yes, low power non-critical use..... until later, when it's wanted for something else.

              A standard 3HP motor is listed in the NEC as 9.6A at 230V. Slightly less at 240V, then. Your motor is actually rated lower, so.... A 3 HP VFD (2.2 kW) is what one would use for a 3HP motor, or anything between 3 HP and the next lower common VFD rating, which is usually 2 HP (and 7A).

              Then here is the question of use as a converter. If the VFD is rated 3 HP with single phase input, then fine. If it is not, then there is probably some derating needed, so you might move up to a 5 HP VFD, which is about double the actual motor power, which is roughly 2 HP. That is "usually" the correct de-rate, although some units may have a de-rate as low as 1/8.

              At 2 or 3 HP (1.5 to 2.2 kW) it is reasonably common to find single phase input VFDs.

              Your choice is between those sizes if you use a unit rated for single phase input.

              Either will probably work acceptably. The 1/5 kW is edgy on current, and may shut down if you DO try to get full power. But with a suitable accel parameter setting, it should work if you do not push the machine hard.

              That chinese motor may have problems. They are known for it. Even the chinese admit they do not reliably make good electric motors, and suffer failures well before they should. Or it may just have a wiring issue. Yes, check it carefully before wiring it to the VFD, even though VFDs are supposed to have protections built-in.
              Last edited by J Tiers; 12-22-2016, 12:20 PM.
              CNC machines only go through the motions

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              • #8
                Originally posted by AntonLargiader View Post
                rkepler, we definitely would do away with the rotary switch. Sorry; I figured that was a given. Since the VFD can control speed I see no reason for the switch.
                There are VFDs that will support 2 motors using an input to the VFD to indicate which set of parameters to use (my mill's Hitachi SJ200 is one such). It might have been possible to use the switch as input to the VFD (and likely a pair of contactors) so that you'd be able to retain the low and high speed motor functions.

                It doesn't even do a good job now. When I turn to the first position the spindle slowly starts to turn but sometimes just wiggles a bit. Going from there to position 2 the speed suddenly jumps up to at least double, maybe more. Turning from there back to position 1 the speed change is so sudden the belts chirp. And then from there it slows gradually to a stop.
                That would indicate a problem in the low speed windings or wiring. Kind of argues for just setting up on the high speed and staying there.

                "Unless the mill has a backgear.." what do you mean?
                A lot of turret mills have a mechanical backgear in the head - mine is something like a 6:1 reduction, so 1800 on the belt is 300 (backwards) on the spindle with the backgear engaged. Handy for heavy work.

                I've often thought of mounting a microswitch on the backgear handle and have it change the VFD drive settings - I have the VFD display show the RPM of the spindle (applying a fixed multiplier to the frequency and never moving the belt on the spindle) and if I had the switch I could show the proper RPM and make the remote fwd/rev switches work right

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                • #9
                  I seriously doubt you Will miss the extra 0.5 amp of current but a larger vfd might last a bit longer but personally I wouldn't pay much more for a 3hp unit for that reason. Average cutting currents are going too be much less than 7 amps.

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                  • #10
                    Originally posted by tmarks11 View Post
                    +++1 on The hitachi VFD. That is an excellent choice.

                    When choosing which winding to wire, consider what you cut with the mill. I would be inclined to wire the low speed end, to get more torque when milling or drilling steel. Running the VFD up to 90 Hz would get you up to 2500 rpm, which is more than sufficient on a manual mill with no coolant. Most manual mills come with a 1800 rpm motor installed.

                    .

                    But remember.. at 90hz you torque is 50% less than at 60hz... Belts are there to be changed for torque multiplication.
                    And... carbide cutting dry will need all the speed you can give it.

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