Re: [CAD_CAM_EDM_DRO] CNC power supply question

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