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Re: [multimachine] DC + speed controller vs. 3ph motor + VFD

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  • 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 1 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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