Re: CNC power supply question

Hey,
Thanks for the great, informative replies. I'm learning alot, but
still have tons more to learn, especially on the electrical side.

I've been looking at some of the extra 'features' you can add to
homemade PS's. For example, Mariss's capacitor bleed circuit, and
I've seen precharge circuits that limit the initial current when the
PS is first powered on like Mr. Fortune uses on his 1kw/1.5kw
monsters. These added features seem like they could almost be
considered essential even for smaller/less powerful supplies. What
other safety/component protection circuits are common for a full
featured power supply?

Thanks again for all the help, you people are great.

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Jon Elson <elson@p...> wrote:
>
>
> snagglexr650 wrote:
>
> >Hello,
> >
> > I'm trying to get the 'big picture' on designing my own servo
> >based cnc control using a Gecko based system. I'm currently
trying
> >to tackle the power supply issue; Why some kinds are better than
> >others and how to determine PS size from the motor specs in
general.
> >
> > I've read here and elsewhere that the varying loads associated
> >with CNC motor control is a problem for commonly available
> >regulated/switched power supplies.
> >
> > What makes a 'homemade', unregulated(?), PS (Jerry's PS, or Doug
> >Fortunes 1kw/1.5kw monsters) better at handling varying loads than
> >the 'comercial/professional' grade regulated PS you see on Ebay or
> >other retailers?
> >
> >
> Regulated power supplies are almost always current limiting. So,
if a peak
> current is required when all 3 axes are accelerating, the regulated
power
> supply may go into current limit, dropping the voltage until the
current
> peak eases. This will cause all sorts of problems with the servo
drives.
> A bulk, unregulated power supply can handle momentary surges without
> any trouble. it can handle a very large surge for a very short
interval,
> or a moderately large surge, like 2X the continuous rating, for
maybe
> 1/2 to one second, repeated every minute.
>
> Also, regulated power supplies often have overvoltage "crowbar"
circuits
> to short the power supply if the voltage rises above some set limit.
> Many larger motors can return energy to the power supply when
decelerating.
> This can be true of both stepper and servo motors where the
inductance is
> large. If the power supply activates its crowbar, it could cause
damage
> to the machine, the drives, and possibly the power supply, too.
>
> On the other hand, a number of users have reported excellent results
> using commercial switching power supplies on stepper and servo
motion
> control systems.
>
> Jon