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  • VFD Question

    A quick question about VFD's. I have a Logan 821, which uses a 1/2hp single-phase motor. I have been keeping my eyes open for a VFD to upgrade the motor to a 3-phase unit, and have found a deal on one. My question is: Should I replace my 1/2hp single-phase motor with a 1/2hp three-phase motor, or with a larger three-phase motor? I'm just thinking that when the motor is running at lower rpms the torque will be reduced and may make the lathe underpowered. And could someone please confirm that I will need a inverter-duty motor to have variable rpms?

    -Tom

  • #2
    Hi,

    I recently replaced the 1/2hp motor on my 9 inch southbend with a 3/4hp three phase motor and have been very pleased. The lathe is now very quiet and the variable speed is way cool. There were only a couple dollars difference in price between 1/2 and 3/4hp motors so that was a no-brainer. There are some losses with VFD so that was my main reason for picking a slightly larger motor.

    For a drive I selected the Automationdirect GS2 drive (1hp, 220v model). I liked the ability to just add external resistors for breaking. Also their manual was easy to understand and the drive had good reviews from other users.

    The motor is the rolled frame version also from Automation. The main difference between invert type motors and non is the quality of insulation used on the windings. For homeshop use I rolled the dice and went cheap. I also purchased the adjustable mount but ended up not using it as things did not align easily with it on my Southbend.

    Robert
    Last edited by RTPBurnsville; 05-13-2010, 11:10 AM.

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    • #3
      You do not need an inverter rated motor.

      You will need a larger motor IF you need 1/2 hp at low rpm, AND you do not keep the existing pulley system in place. At 10hz, you'd have about 1/6th HP, so you'd need a 3hp motor...

      Realistically, if you keep the existing pulleys/back gear or whatever, a 3/4 to 1hp motor will work fine. Only "change down" if you need more torque.

      If you intend to run the motor at low rpm, you'll need an additional/replacement fan - a "muffin" 4 inch computer fan suffices.
      Last edited by lakeside53; 05-13-2010, 11:53 AM.

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      • #4
        I will usually fit an inductor between VFD and motor on systems that use the original non-vector motor.
        See this tech sheet from Baldor.
        http://net.grundfos.com/doc/webnet/b...-%20Baldor.pdf
        Max.

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        • #5
          The main reason I am asking about if a 1/2hp model will suffice is because I have the opportunity to buy a used 1/2hp Allen-Bradly drive for $60, while the next size up is a 2hp Toshiba for $175. I guess if I keep the drive system intact I can always gear down and keep the rpm's up at the motor.

          -Tom

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          • #6
            Output inductors? I don't bother, and have seen hundreds of commercial installations where VFD's are connected to "non-inverter" rated motors with no problems.

            They are of course technically correct, and the caution of keeping the carrier frequency low is good, but wonder how much of this was written to promote Baldor's inverter-rated motors?

            For a HSM.. a surplus 1hp motor is going to cost a lot less than the series inductors.
            Last edited by lakeside53; 05-13-2010, 11:53 AM.

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            • #7
              Drive

              You will have to use a larger drive unit when operating on single phase. Typically use a 3/4 hp drive on a 1/2 hp motor when on single phase unless the drive has a single phase rating. Check the drive specs carefully.

              JRW

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              • #8
                Originally posted by Tom S
                The main reason I am asking about if a 1/2hp model will suffice is because I have the opportunity to buy a used 1/2hp Allen-Bradly drive for $60, while the next size up is a 2hp Toshiba for $175. I guess if I keep the drive system intact I can always gear down and keep the rpm's up at the motor.

                -Tom

                You might be much happier with a brand new $114 Teco - 115 input , 3 phase 230 out, 1hp.

                Comment


                • #9
                  That might be the better option. Then there is no question if there is enough power in the drive, and if I find the motor can't cut it I can swap it for a 3/4hp.

                  -Tom

                  Comment


                  • #10
                    If you're used to 1/2 HP from that lathe then you'll be delighted with a 3/4 horse motor. The inverter is not there to replace your step pulley, just to add some flexability. If you need low speed and lots of torque (taking monster cuts on very large diameter material?) then you'd still have to gear down with the pulleys and tweak your speed in with the VFD. If you're looking for low speed with little torque (tapping, etc) then by all means leave the pulleys alone and just turn down the drive. My point is that the physics of mechanically gearing up/down don't go away just because you put a control on your motor.

                    Teco is said to be a fine, inexpensive drive... Automation Direct has some as well. I've installed several of the AD's and am very happy with them. Either way you do not need an inverter duty motor unless you're running your lathe hard for three shifts a day.

                    Pretty much all the manufacturers offer drives designed to run on single phase input - these do not have to be derated and can run any 3ph motor up to the rated capacity of the drive.

                    I have a little experience with AB drives and I wouldn't go with them if it were my first install. Not that they aren't fine drives, but they're marketed to the industrial crowd and their documentation is written accordingly.

                    (edited for stupidity)

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                    • #11
                      Originally posted by MaxHeadRoom
                      I will usually fit an inductor between VFD and motor
                      Max, do you just use the primary of an old transformer or what? Actually, I guess you'd need 3 matched transformers. It is usually really hard to find 3-phase inductors, and spendy. I would love to do this. Maybe 3 transformers from old computer UPS boxes? Shouldn't be too hard to find a matching pile of those ..

                      metalmagpie

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                      • #12
                        My Logan came with a (presumably retrofitted) 3/4HP single phase when I first got it. It was adequate for a while, but definitely underpowered if I tried to push it.

                        I swapped that for a 1-1/2HP single, which really appeared to make little difference- it was still a bit underpowered for some things. In my turret lathe video, you can hear it slow down during the knurling step, and really, I couldn't even push the drills all that hard or it'd bog too.

                        I finally swapped that for a 2HP 3-phase, and also stepped up from 1725 to 3450. I powered this with an AD GS2 and a new control box that laid out all the usual stuff- start/stop, speed dial and a reverse switch.

                        Now, instead of using the top speed on the Logan- which originally gave me about 600 rpm, max- I now use the lowest non-backgear speed, which, with the faster motor, gives me about the same 600 rpm, but a pile more torque.

                        I can no longer stall the thing even if I try. I took a .200 deep cut at .009" in aluminum and it hardly noticed.

                        Unless every last penny was a major issue, I'd suggest at least going up to a full 1HP motor and 1HP controller. As noted, you'll keep more HP at the lower speeds so you'll have to do less belt-swapping.

                        And no one, in the history of the world, has ever said "Darn, my lathe just has too much power!"

                        Doc.
                        Doc's Machine. (Probably not what you expect.)

                        Comment


                        • #13
                          Variable Frequency Drive (VFD) Answers For Common Questions

                          INVERTOR GRADE MOTORS ARE NOT NEEDED FOR LESS THAN 24/7 DUTY.

                          LONG TERM OPERATION AT REDUCED/INCREASED MOTOR SPEEDS, MIGHT REQUIRE AN ADD ON COOLING FAN FOR MOTOR.

                          DERATING OF SINGLE PHASE INPUT RATED VFD's NOT NEEDED.

                          SOME 3 PHASE INPUT VFD's WILL NOT OPERATE (DERATED) WITH SINGLE PHASE INPUT ONLY. SOME WILL.

                          MANY VFD's AVAILABLE UP TO 2 HP, WITH SINGLE PHASE ONLY INPUT.

                          THE STANDARD MACHINE BELTING AND GEARS, HANDLE ALL TORQUE MULTIPLICATION REQUIREMENTS.

                          MANY SMALL (< ~1.5HP) VFD's, ARE MADE FOR 110 INPUT VOLTAGE, AND PROVIDE 220 V 3 PHASE OUT.

                          MOTOR BEARING LIFE WILL NOT BE AFFECTED ON 220 VOLT VFD's.

                          INDUCTORS ARE JUST NOT NEEDED IN A HOME SHOP.

                          VFD'S OUTPUT SHOULD BE WIRED DIRECTLY TO MOTOR INPUT, NO DISCONNECT OR SWITCHES. VFD IS CONTROLLED BY LOW VOLTAGE WIRING.

                          VFD's PROVIDE MOTOR PROTECTION STANDARD.

                          VFD's ALLOW MOTOR SPEED TO BE RUN UP 100% ABOVE NORMAL MOTOR SPEED. BEARINGS, VIBRATION, AND OILING, MUST BE CONSIDERED.

                          VFD"S ALLOW MOTOR SPEED TO BE RUN DOWN TO ~ 25% OF NORMAL MOTOR SPEED AND STILL PROVIDE PLENTY OF TORQUE.

                          BRAKING RESISTORS MIGHT NOT BE A GOOD IDEA WITH THREAD MOUNTED CHUCKS.

                          VFD's ALLOW FOR INSTANT OR RAMP DELAYED REVERSE. VERY HANDY FOR TAPPING. NOT SO HANDY WITH A THREAD MOUNT CHUCK.

                          VFD"s DO CAUSE MOTORS TO EMIT A HIGH PITCHED WHINE.

                          ADJUSTING VFD CARRIER FREQUENCY UP WILL HELP. DO NOT ADJUST HIGHER THAN NEEDED TO REDUCE WHINE.

                          VFD's ARE THE BEST THING INVENTED SINCE SLICED BREAD.

                          LESS (NOT NONE, HOWEVER) BELT/GEAR CHANGES.

                          VFD's ARE NOT IDEAL FOR MULTIPLE MOTOR APPLICATIONS. THEY ARE CHEAP ENOUGH TO PLACE MULTIPLE VFD's ON MULTI MOTORED MACHINES THOUGH.

                          EDIT: 2 HP ON A 9 INCH SOUTHBEND/ATLAS WILL BREAK THINGS.
                          Last edited by Bguns; 05-13-2010, 04:30 PM.

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                          • #14
                            Thanks for all the info. Lots to base my purchase on.

                            Doc, are you sure that your lathe was not modified before you purchased it? My Logan's top speed is in the 1200 range if I remember correctly, and it is bone stock as far as drive components.

                            I think I will look into the 1hp. I would love to be able to run without the backgear, and the 1hp may have enough torque to allow me to do that. I don't mind switching speeds on the step pully.

                            -Tom

                            Comment


                            • #15
                              ^-- Shouting Makes Me More Correct Then Other People And Makes Everything I Type Easyer To Read If The Reader Is Nearly Blind.
                              Wow, He had to actualy go back and edit that to all caps too, because the forum automaticly decapatlises all caps posts.
                              Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

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