Re: [CAD_CAM_EDM_DRO] power supply

The outputs of a transformer are given at full rated load. The output
voltage will rise as the load is reduced. In the full specs there will be a
figure for how well the transformer regulates it's output. ISTR that
toroidal transformers are much better in this respect. Also remember that
mains voltage is a nominal value and can vary quite widely.

I wouldn't worry about it unless the off load voltage exceeds the rated
voltage of the controller. I definately wouldn't put a zener across the
output. If the mains voltage rises for any reason (and sod's law says it
probably will at some point) you could easily fry the zener. At work we have
a 2KW high frequency spindle on a cnc router that occasionally trips out due
to overvoltage. Unfortunately the controller doesn't realise this and keeps
going - we have a good selection of boomerang shaped cutters!

Les

PS Discharging the caps with a screwdriver is more fun (bang!) but it can
damage the caps.

> 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.
>