Re: power supply

Peter,

A zener is not a bad idea. A lot of step motor drives return energy
extracted from mechanical kinetic energy stored in a moving mass
during deceleration. If the speed is high, the mass is large and the
rate of deceleration is high, then the drive can actually become a
source of current rather than a load on the power supply.

This returned current can charge the power supply capacitor to a
voltage that can be destructive to it and the drive in extreme
circumstances.

Pick a zener voltage just below the drive's maximum rated voltage yet
well above your power supply voltage. This can become problematic if
the supply voltage is near the drive's maximum voltage. In that case,
see the "returned energy dump .pdf" circuit posted in the "files"
section on this group.

The capacitor voltage is not a problem. If there is a load on the
supply, it will discharge it, if not, capacitor leakage currents
will. Either way, there is no harm unless the voltage is potentially
lethal (greater than 150VDC).

Mariss

--- In CAD_CAM_EDM_DRO@y..., cadcamcenter@y... wrote:
> How dependable are transformer specs?
>
> A Single phase 0-115-230V primary 24VAC secondary connected to a
> bridge rectifier and 15,000uF capacitor should produce 33 VDC. The
> actual output was 46VDC. The culprit? On checking the transformer
> secondary, the output was 33VAC instead of the specified 24VAC. Is
> this common experience?
>
> Based on what had been so emphatically put across recently, one
> should have no hesitation on using this power supply despite it
being
> out of specs - voltage being so unimportant for steppers, right?
>
> Just to be on the safe side - what size zener diode should one
place
> across the output?
>
> Peter
>
> BTW one should take care to discharge the capacitor, say, across an
> incandescent lamp at end of test.