Re: [CAD_CAM_EDM_DRO] Re: AC Motor Speed Control

Dave,

The G-series of VFD's from automationdirect have "auto torque boost" for low RPM operation. Just one of the many many variables that can be adjusted to accomodate almost any application. Even dynamic braking. The biggest problem with low RPM operation is cooling, the motor's cooling fan just doesnt rotate fast enoough to have much effect. An external constant speed cooling fan on the motor would help.

Anyways, I just set a VFD up on a 8x36 Jet with Mach3 and Bob Campbell's spindle speed board, 2 hp 3 phase dayton motor. It will spoil one to use it. Just put an S value in the G-code and the spindle takes care of itself. Very quiet too. That particular mill is a bear to change belt ratios on. The customer loves it.

With the torque boost set at default, the spindle at 200 rpm could almost be stopped by hand. We cranked the torque up and it was unstoppable/unphasable, big difference. Best practice would be if some low speed high torque operation was neccesary and over a long period, is just drop the belt to a lower ratio.

Ron

turbulatordude <dave_mucha@...> wrote:
--- In CAD_CAM_EDM_DRO@yahoogroups.com, R Rogers
wrote:

>
> GS2 VFD from automationdirect.com and a 3 phase spindle motor.

Softwares like Mach3 can control it with an analogue signal.

>
> Ron

That begs the question of motor size.

If hp is dependant on speed, and torque is constant, should one use
a larger motor so it has more power at lower speeds ?

I can see some huge benifits from variable speed, but at the same
time, it would appear that one might not get all the way from 1% to
100% speed and have enough power for all machining in-between.

And, yes, a simple high/low belt change would make that less of a
problem.

The reason I ask is that I put a treadmill motor and power
controller on my 9" lathe and notice it has some weak spots at lower
speeds.

Dave







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