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,
>> >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?