Re: [CAD_CAM_EDM_DRO] DC versus 3 Phase

ozzietwo2001@... wrote:

> I'm getting really tired of changing belt pulleys and want to change
> to a variable speed system on my shoptask machine.
>
> Can someone out there help me with the pros and cons of DC and 3
> phase systems. I would probably buy the controller and motor on E-
> bay, 220 v is no problem, single phase supply, want about 1 HP.

I don't think there is a great difference. It more depends on
what you can find, especially in motors, space available, pulley
size and speed range. If a 3-phase 1725 or 3450 RPM nominal
motor is a good fit (physically, as well as speed range), then the
3-phase option will be fine. DC may have a slight advantage if you
need a very great speed range, and the machine has a limited pulley
selection. A machine like the Atlas lathe, which has 16 speeds available
by belt selection would not need a wide motor speed range.
A machine which had just one belt groove in the motor and spindle
pulleys would be most likely to need such a great range.

One other thing is that DC motor drives might be more likely to
accept a tach input from the motor, for closed-loop speed control.

I am running a 1 Hp Bridgeport (3-phase) mill from a Magnetek
VFD, using 220 V single-phase input. The VFD specifies 3-phase
input only, but this unit seems to handle it fine. Probably running near
full load for long periods might overheat the rectifier, but I have had
no problems with it.

Jon