Re: [CAD_CAM_EDM_DRO] Re: Thoughts on PC Based Control Retrofit....Power Supply, advice?

stratton@... wrote:

> > admin@... wrote:
> >
> > > --- In CAD_CAM_EDM_DRO@y..., "Marty Escarcega" <escarcega@h...> wrote:
> > > > Ok, I have found some 44VCT 11A transformers for my series I
> > > > retrofit. Coupled with a 35A 1000V Bridge Rectifier and a
> > > > 14000MFD 75V Capacitor for each motor, do you folks think this
> > > > should be a good power supply? By my calculations, I should have
> > > > about 62VDC.
> >
> > This should work fine. You might put a very small resistor either in series
> > with one of the transformer secondary leads, or one of the bridge rectifier
> > leads, to reduce the current surge. Something of a few tenths of an Ohm
> > would probably be right. Otherwise, it should be fine. You may need a
> > little more capacitance there, you will have to evaluate the voltage ripple
> > when the stepper driver is drawing the maximum current.
>
> I wouldn't think a tiny little resistor would do anything. They do
> make devices specifically for limiting 'inrush current' when a power
> supply of this type is turned on. One form has a high resistance when
> cold, with the resistance dropping once it warms up. I suppose you
> could still get in trouble though if the unit gets switched off just
> long enough for the bleeder resistors to discharge the caps, but not
> long enough for the inrush limiter to cool down - so avoid excessive
> power cycling.

Yes, I'm quite familiar with the NTC inrush surge limiters. Unfortunately, they
don't work for a momentary power interruption, and they do nothing for the
current pulse on each half cycle of the power line, which was what I was really
thinking of. You might find, with a well-built transformer and a good capacitor,
that the current peaks every half cycle could exceed 50 Amps! This will shorten
the life of the rectifier.

Jon