Re: [CAD_CAM_EDM_DRO] DC versus 3 Phase

The considerations between DC and three phase become significant for
industry when there is some serious on-line time and power involved. When
you run several 200 hp motors at 24 hours a day, the costs build up
quickly. This leads the engineer to size the motor quite close to the
power needs and also to look closely at the torque/speed curves. Some
winding styles will show efficiency limitions at the high or low range of
speed. DC can offer field weakening which will change the motor curve
considerably. In the application the engineer needs to identify the most
typical speed of operation and find the motor which is happy at that speed.
The acceleration is also important. AC tends to have lighter weight
rotors and can speed up faster.

Typical considerations between AC and DC are not important to machine
tools. Machine tools cannot be sized closely. You need to have
considerable reserve power and will most often be using less than 10% of
what the motor can offer. Motor maintenance is not much of an issue, since
machine tools rarely run 24 hours a day. I would recommend you buy what is
cheap. These days, AC is cheaper than DC.


At 02:12 PM 2/19/01 +0000, you 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 thought there was a thread on the subject a while back but I can't
>find it. If there is, perhaps someone can point me.
>
>Thanks in advance
>Jerry
>
>