Re: Power supply options / use PWM DC motor controller?

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "knives01us" <knives01@a...>
wrote:

>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "Scott Riddle"
> <sariddle@l...> wrote:
> >
> > I already have this DC motor supply though.
> > My main question is, will it work or not?
> >
> > If I can use this power supply for more than one thing it helps

on

> > the clutter and my pocket book.
> >
> > Thanks for the replies.
> > Scott
> ::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
>
> I'm probably stepping out on a limb because electronics aren't my
> strong point, but I don't think a PWM DC motor controller will make

a

> good DC power supply for step motor drivers.
>
> I think the motor controller varies motor speed by changing time on-
> off ratios, and doesn't actually vary voltage output. I expect some
> of the real electronics wizards to chime in on this one way or the
> other.

You hit on one of the three reasons the DC motor controller is not a
fit for supplying the DC voltage needed by a modern chopper type
motor controller.

1. It's not smooth DC. DC motors don't care. Motor controllers DO!
2. The circuitry is made to supply a DC motor (fairly constant speed
and torque) and most likely uses some form of feedback (Usually back
EMF) to try and keep the speed constant. You don't have the bulk of
a transformer to take on the varying load so your DC controller has
to do it. Used with a chooper motor controller, It won't see the
correct back emf and your voltage will do unpredictable things.
3. This point has been over hyped but in systems where the secondary
voltage is 48V or less transformer isolation offers a level of
safety. Grounding your exposed equipment to safety ground is your
best protection.

The transformer and large cap in a linear supply offer a "flywheel"
for energy storage so a real non-linear load like steppers or even
servos's running from chopper type motor controllers has a source of
stored voltage to draw from.


If simple DC PWM (or SCR) were a viable solution you can bet that
there would be a low cost solution offered from the hobby cnc
vendors. There is nothing to prevent you from finding a transfomer
of higher voltage and that wil carry the current and using a Triac
based speed controller, set the secondary DC voltage by adjusting the
input AC voltage.