> -----Original Message-----
> From: Gene Heskett [mailto:ghesk...@shentel.net]
> Sent: May-19-20 1:50 PM
> To: emc-users@lists.sourceforge.net
> Subject: Re: [Emc-users] hypothetical, maybe not, switching psu question
>
> On Tuesday 19 May 2020 15:44:51 John Dammeyer wrote:
>
> > Hi Gene,
> > Since I'm running DC Servos I wanted the ability to clamp the back emf
> > from a decelerating motor. I built a small circuit that sensed both
> > high voltage and AC power. It puts a resistor across the DC rail to
> > pull it down and the resistor is connected with both a relay and a FET
> > in parallel.
> >
> > When power vanishes the relay is de-energized and the 105VDC power
> > supply is quickly drained through the NC connection on the relay. The
> > FET does the same but at high speeds to avoid that over voltage
> > condition.
> >
> > Since the little PIC processor senses AC voltage it can also run a
> > relay on a second small board that switches across an inrush resistor.
> > The advantage over a high power thermistor is no heat and you can
> > cycle power without worrying about the inrush thermistor still being
> > way too hot and therefore too low a resistance.
> >
> > Schematics attached.
> >
> Both would seem to be more complex than a few lines of hal code I can
> easily write.
Hey Gene,
That might be unless your PC dies or locks up. But even more important, in my
case I'm running dual boot and there is no HAL file for MACH3.
Besides. I don't think safety critical stuff should depend on the PC.
John
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