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DC + speed controller vs. 3ph motor + VFD

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  • Chris Tofu
    Can anyone discuss the benefits of either? Everyone is telling me that the latter is much cheaper, but I m not necessarily seeing it. My bias is toward a 1/2 -
    Message 1 of 9 , Apr 8, 2013
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      Can anyone discuss the benefits of either? Everyone is telling me that the latter is much cheaper, but I'm not necessarily seeing it. My bias is toward a 1/2 - 1hp DC motor for a small lathe (6-8" swing). I suppose if you could find some piece of crap 3 phase motor for next to nothing there's a cost differential.
      And if it isn't too much trouble, what's the benefits, beyond the obvious, of brushless DC motors?
    • Stan Stocker
      Hi Chris, Either a DC motor and controller or three phase motor with VFD would work well for a lathe of this size. If you get a deal, a VFD and motor combo MAY
      Message 2 of 9 , Apr 9, 2013
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        Hi Chris,

        Either a DC motor and controller or three phase motor with VFD would
        work well for a lathe of this size.

        If you get a deal, a VFD and motor combo MAY be less expensive in the 1
        HP size. I've used the Penn State Industries 1/2 HP DC motor and
        controller on my Taig and been very pleased. Others have used it on
        slightly larger lathes with good results. My 12 inch wood lathe has a
        similar motor and controller and is very smooth and seems sufficiently
        powerful for my needs.

        It's only in the last few years that the DC motor/controller option in
        this size has become a straightforward off the shelf solution. Before,
        it tended to be a case of buying separate motors and controllers, and
        wiring the things up according to iffy poor photocopies and word of
        mouth directions. Lots of fun in some cases, but not if you just want
        to get on with running a business rather than dinking around in the shop
        for giggles.

        Where VFD / 3 phase solutions shine is when you need 1+ or particularly
        2+ HP for the task. Used 3 phase big motors are fairly inexpensive,
        although scrap metal prices have taken many from the market. The less
        obvious benefit of 3 phase versus single phase motors of a given power
        are that 3 phase motors, driven correctly, give very smooth operation.

        Many larger used machines will come equipped with 3 phase motors, so
        using a VFD is less expensive than remotoring the machine. Particularly
        as the larger machines likely will not be well behaved with a 1 1/2 HP
        120 volt motor.

        Take care,
        Stan

        On 04/09/2013 01:17 AM, Chris Tofu wrote:
        >
        > Can anyone discuss the benefits of either? Everyone is telling me that the latter is much cheaper, but I'm not necessarily seeing it. My bias is toward a 1/2 - 1hp DC motor for a small lathe (6-8" swing). I suppose if you could find some piece of crap 3 phase motor for next to nothing there's a cost differential.
        > And if it isn't too much trouble, what's the benefits, beyond the obvious, of brushless DC motors?
        >
        >
      • Chris Tofu
        So Stan how did you obtain just the motot and controller and if so what was the cost? Is the motor brushless? Is it advisable to use a brushless DC motor for
        Message 3 of 9 , Apr 9, 2013
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          So Stan how did you obtain just the motot and controller and if so what was the cost? Is the motor brushless? Is it advisable to use a brushless DC motor for this type of endeavor? Thanks for responding by the way.

          ------------------------------
          On Tue, Apr 9, 2013 5:53 AM PDT Stan Stocker wrote:

          >Hi Chris,
          >
          >Either a DC motor and controller or three phase motor with VFD would
          >work well for a lathe of this size.
          >
          >If you get a deal, a VFD and motor combo MAY be less expensive in the 1
          >HP size. I've used the Penn State Industries 1/2 HP DC motor and
          >controller on my Taig and been very pleased. Others have used it on
          >slightly larger lathes with good results. My 12 inch wood lathe has a
          >similar motor and controller and is very smooth and seems sufficiently
          >powerful for my needs.
          >
          >It's only in the last few years that the DC motor/controller option in
          >this size has become a straightforward off the shelf solution. Before,
          >it tended to be a case of buying separate motors and controllers, and
          >wiring the things up according to iffy poor photocopies and word of
          >mouth directions. Lots of fun in some cases, but not if you just want
          >to get on with running a business rather than dinking around in the shop
          >for giggles.
          >
          >Where VFD / 3 phase solutions shine is when you need 1+ or particularly
          >2+ HP for the task. Used 3 phase big motors are fairly inexpensive,
          >although scrap metal prices have taken many from the market. The less
          >obvious benefit of 3 phase versus single phase motors of a given power
          >are that 3 phase motors, driven correctly, give very smooth operation.
          >
          >Many larger used machines will come equipped with 3 phase motors, so
          >using a VFD is less expensive than remotoring the machine. Particularly
          >as the larger machines likely will not be well behaved with a 1 1/2 HP
          >120 volt motor.
          >
          >Take care,
          >Stan
          >
          >On 04/09/2013 01:17 AM, Chris Tofu wrote:
          >>
          >> Can anyone discuss the benefits of either? Everyone is telling me that the latter is much cheaper, but I'm not necessarily seeing it. My bias is toward a 1/2 - 1hp DC motor for a small lathe (6-8" swing). I suppose if you could find some piece of crap 3 phase motor for next to nothing there's a cost differential.
          >> And if it isn't too much trouble, what's the benefits, beyond the obvious, of brushless DC motors?
          >>
          >>
          >
        • Adam Simmons
          Varying the voltage on a DC motor not only changes the speed, but the torque output. Changing the frequency on a 3 phase motor changes the speed, but torque
          Message 4 of 9 , Apr 9, 2013
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            Varying the voltage on a DC motor not only changes the speed, but the torque output.  Changing the frequency on a 3 phase motor changes the speed, but torque is retained.




            On Tue, Apr 9, 2013 at 11:05 AM, Chris Tofu <rampaginggreenhulk@...> wrote:
             


            So Stan how did you obtain just the motot and controller and if so what was the cost? Is the motor brushless? Is it advisable to use a brushless DC motor for this type of endeavor? Thanks for responding by the way.

            ------------------------------


            On Tue, Apr 9, 2013 5:53 AM PDT Stan Stocker wrote:

            >Hi Chris,
            >
            >Either a DC motor and controller or three phase motor with VFD would
            >work well for a lathe of this size.
            >
            >If you get a deal, a VFD and motor combo MAY be less expensive in the 1
            >HP size. I've used the Penn State Industries 1/2 HP DC motor and
            >controller on my Taig and been very pleased. Others have used it on
            >slightly larger lathes with good results. My 12 inch wood lathe has a
            >similar motor and controller and is very smooth and seems sufficiently
            >powerful for my needs.
            >
            >It's only in the last few years that the DC motor/controller option in
            >this size has become a straightforward off the shelf solution. Before,
            >it tended to be a case of buying separate motors and controllers, and
            >wiring the things up according to iffy poor photocopies and word of
            >mouth directions. Lots of fun in some cases, but not if you just want
            >to get on with running a business rather than dinking around in the shop
            >for giggles.
            >
            >Where VFD / 3 phase solutions shine is when you need 1+ or particularly
            >2+ HP for the task. Used 3 phase big motors are fairly inexpensive,
            >although scrap metal prices have taken many from the market. The less
            >obvious benefit of 3 phase versus single phase motors of a given power
            >are that 3 phase motors, driven correctly, give very smooth operation.
            >
            >Many larger used machines will come equipped with 3 phase motors, so
            >using a VFD is less expensive than remotoring the machine. Particularly
            >as the larger machines likely will not be well behaved with a 1 1/2 HP
            >120 volt motor.
            >
            >Take care,
            >Stan
            >
            >On 04/09/2013 01:17 AM, Chris Tofu wrote:
            >>
            >> Can anyone discuss the benefits of either? Everyone is telling me that the latter is much cheaper, but I'm not necessarily seeing it. My bias is toward a 1/2 - 1hp DC motor for a small lathe (6-8" swing). I suppose if you could find some piece of crap 3 phase motor for next to nothing there's a cost differential.
            >> And if it isn't too much trouble, what's the benefits, beyond the obvious, of brushless DC motors?
            >>
            >>
            >


          • David G. LeVine
            ... The obvious one is that there are no brushes to get messed up. A less obvious one is elimination of contaminants - totally enclosed and totally enclosed
            Message 5 of 9 , Apr 9, 2013
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              On 04/09/2013 01:17 AM, Chris Tofu wrote:
              Can anyone discuss the benefits of either? Everyone is telling me that the latter is much cheaper, but I'm not necessarily seeing it. My bias is toward a 1/2 - 1hp DC motor for a small lathe (6-8" swing). I suppose if you could find some piece of crap 3 phase motor for next to nothing there's a cost differential.
               And if it isn't too much trouble, what's the benefits, beyond the obvious, of brushless DC motors? 

              The obvious one is that there are no brushes to get messed up.

              A less obvious one is elimination of contaminants - totally enclosed and totally enclosed fan cooled motors are easy to find in 3 phase, but not so easy with brushed motors.  Put metal chips, magnets and electricity together and you are asking for trouble. 

              Generally, brushed motors have higher HP per pound and are less efficient, 3 phase motors have longer service life, and, if maintained, are easily rebuildable.

              Dave  8{)

              --


              "Among the many misdeeds of British rule in India, history will look upon the Act of depriving a whole nation of arms as the blackest."

              Mohandus Ghandi, An Autobiography, Page 446.
            • David G. LeVine
              ... Another issue I forgot is torque ripple, which can cause chatter. A 2 pole, single phase motor generates a lot of 120 Hz (or 100 Hz) torque ripple, a 3
              Message 6 of 9 , Apr 9, 2013
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                On 04/09/2013 08:53 AM, Stan Stocker wrote:
                Where VFD / 3 phase solutions shine is when you need 1+ or particularly 
                2+ HP for the task.  Used 3 phase big motors are fairly inexpensive, 
                although scrap metal prices have taken many from the market.  The less 
                obvious benefit of 3 phase versus single phase motors of a given power 
                are that 3 phase motors, driven correctly, give very smooth operation.
                
                Many larger used machines will come equipped with 3 phase motors, so 
                using a VFD is less expensive than remotoring the machine.  Particularly 
                as the larger machines likely will not be well behaved with a 1 1/2 HP 
                120 volt motor.
                
                Take care,
                Stan

                Another issue I forgot is torque ripple, which can cause chatter.  A 2 pole, single phase motor generates a lot of 120 Hz (or 100 Hz) torque ripple, a 3 phase motor generates MUCH less, and it is at a higher frequency.

                Dave  8{)

                --


                "Among the many misdeeds of British rule in India, history will look upon the Act of depriving a whole nation of arms as the blackest."

                Mohandus Ghandi, An Autobiography, Page 446.
              • Chris Tofu
                Therefore if a DC motor is totally enclosed, it must be brushless? When I first read your reply, and saw the word *contaminant*, my instinct lead me to think
                Message 7 of 9 , Apr 9, 2013
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                  Therefore if a DC motor is totally enclosed, it must be brushless?

                  When I first read your reply, and saw the word *contaminant*, my instinct lead me to think about lathe bearings. A few seconds later it logically occurred to me that the contamination could/would take place in the motor itself - correct?

                  ------------------------------
                  On Tue, Apr 9, 2013 12:02 PM PDT David G. LeVine wrote:

                  >On 04/09/2013 01:17 AM, Chris Tofu wrote:
                  >> Can anyone discuss the benefits of either? Everyone is telling me that the latter is much cheaper, but I'm not necessarily seeing it. My bias is toward a 1/2 - 1hp DC motor for a small lathe (6-8" swing). I suppose if you could find some piece of crap 3 phase motor for next to nothing there's a cost differential.
                  >> And if it isn't too much trouble, what's the benefits, beyond the obvious, of brushless DC motors?
                  >
                  >The obvious one is that there are no brushes to get messed up.
                  >
                  >A less obvious one is elimination of contaminants - totally enclosed and totally enclosed fan cooled motors are easy to find in 3 phase, but not so easy with brushed motors. Put metal chips, magnets and electricity together and you are asking for trouble.
                  >
                  >Generally, brushed motors have higher HP per pound and are less efficient, 3 phase motors have longer service life, and, if maintained, are easily rebuildable.
                  >
                  >Dave 8{)
                  >
                  >--
                  >
                  >/"Among the many misdeeds of British rule in India, history will look upon the Act of depriving a whole nation of arms as the blackest."/
                  >
                  >Mohandus Ghandi, An Autobiography, Page 446.
                • David G. LeVine
                  ... Not exactly, a brushed DC motor can be totally enclosed, BUT they are much rarer than TEFC/TENV 3 phase motors. Brushes create dust and ozone, both of
                  Message 8 of 9 , Apr 9, 2013
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                    On 04/09/2013 05:40 PM, Chris Tofu wrote:
                    Therefore if a DC motor is totally enclosed, it must be brushless?
                    
                    When I first read your reply, and saw the word *contaminant*, my instinct lead me to think about lathe bearings. A few seconds later it logically occurred to me that the contamination could/would take place in the motor itself - correct?

                    Not exactly, a brushed DC motor can be totally enclosed, BUT they are much rarer than TEFC/TENV 3 phase motors.  Brushes create dust and ozone, both of which are not good to keep contained in the motor.  Sealed brush type DC motors exist, but they are not trivial to design.

                    Yup, open ball bearings (or just sealed on one side) and some sleeve bearings CAN pick up chips, but there is also the possibility of a chip catching the commutator or brush holder, or getting across the power leads internally.  All are really bad things.  Now, think about ferrous chips and motor magnets...

                    Dave  8{)

                    --


                    "Among the many misdeeds of British rule in India, history will look upon the Act of depriving a whole nation of arms as the blackest."

                    Mohandus Ghandi, An Autobiography, Page 446.
                  • Chris Tofu
                    Whereas as you state, ac 3 phase motors will retain torque if a vfd is used, dc motors are known for maintaining torque far better then single phase ac motors
                    Message 9 of 9 , Apr 9, 2013
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                      Whereas as you state, ac 3 phase motors will retain torque if a vfd is used, dc motors are known for maintaining torque far better then single phase ac motors when the voltage drops.

                      The thing is small 3 phase ac motors don't seem to be common as decent DC motors. Maybe I need to keep looking...

                      ------------------------------
                      On Tue, Apr 9, 2013 11:11 AM PDT Adam Simmons wrote:

                      >Varying the voltage on a DC motor not only changes the speed, but the
                      >torque output. Changing the frequency on a 3 phase motor changes the
                      >speed, but torque is retained.
                      >
                      >
                      >
                      >
                      >On Tue, Apr 9, 2013 at 11:05 AM, Chris Tofu <rampaginggreenhulk@...>wrote:
                      >
                      >> **
                      >>
                      >>
                      >>
                      >> So Stan how did you obtain just the motot and controller and if so what
                      >> was the cost? Is the motor brushless? Is it advisable to use a brushless DC
                      >> motor for this type of endeavor? Thanks for responding by the way.
                      >>
                      >> ------------------------------
                      >>
                      >> On Tue, Apr 9, 2013 5:53 AM PDT Stan Stocker wrote:
                      >>
                      >> >Hi Chris,
                      >> >
                      >> >Either a DC motor and controller or three phase motor with VFD would
                      >> >work well for a lathe of this size.
                      >> >
                      >> >If you get a deal, a VFD and motor combo MAY be less expensive in the 1
                      >> >HP size. I've used the Penn State Industries 1/2 HP DC motor and
                      >> >controller on my Taig and been very pleased. Others have used it on
                      >> >slightly larger lathes with good results. My 12 inch wood lathe has a
                      >> >similar motor and controller and is very smooth and seems sufficiently
                      >> >powerful for my needs.
                      >> >
                      >> >It's only in the last few years that the DC motor/controller option in
                      >> >this size has become a straightforward off the shelf solution. Before,
                      >> >it tended to be a case of buying separate motors and controllers, and
                      >> >wiring the things up according to iffy poor photocopies and word of
                      >> >mouth directions. Lots of fun in some cases, but not if you just want
                      >> >to get on with running a business rather than dinking around in the shop
                      >> >for giggles.
                      >> >
                      >> >Where VFD / 3 phase solutions shine is when you need 1+ or particularly
                      >> >2+ HP for the task. Used 3 phase big motors are fairly inexpensive,
                      >> >although scrap metal prices have taken many from the market. The less
                      >> >obvious benefit of 3 phase versus single phase motors of a given power
                      >> >are that 3 phase motors, driven correctly, give very smooth operation.
                      >> >
                      >> >Many larger used machines will come equipped with 3 phase motors, so
                      >> >using a VFD is less expensive than remotoring the machine. Particularly
                      >> >as the larger machines likely will not be well behaved with a 1 1/2 HP
                      >> >120 volt motor.
                      >> >
                      >> >Take care,
                      >> >Stan
                      >> >
                      >> >On 04/09/2013 01:17 AM, Chris Tofu wrote:
                      >> >
                      >> > Can anyone discuss the benefits of either? Everyone is telling me that
                      >> the latter is much cheaper, but I'm not necessarily seeing it. My bias is
                      >> toward a 1/2 - 1hp DC motor for a small lathe (6-8" swing). I suppose if
                      >> you could find some piece of crap 3 phase motor for next to nothing there's
                      >> a cost differential.
                      >> > And if it isn't too much trouble, what's the benefits, beyond the
                      >> obvious, of brushless DC motors?
                      >> >
                      >> >
                      >> >
                      >>
                      >>
                      >>
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