OT: UPS for FreeBSD

Perry Hutchison perryh at pluto.rain.com
Mon Dec 1 03:14:07 UTC 2014

Erich Dollansky <erichsfreebsdlist at alogt.com> wrote:
> On Sat, 29 Nov 2014 00:49:07 -0800
> perryh at pluto.rain.com (Perry Hutchison) wrote:
> > To integrate a UPS with the PSU, one would instead build something
> > along the lines of:
> > 
> >           multitapped
> > 120VAC ==> step-down ==> 6VAC ==> full-wave ==> ~15VDC ==> battery1
> >           transformer             rectifier
> >                   |
> >                   +---> 3VAC ==> full-wave ==> ~7.5VDC ==> battery2
> >                                  rectifier
> > 
> > battery1 ==> regulator ==> 12VDC
> > 
> > battery2 ==> regulator ==> 5VDC
> How much energy is then wasted?

In the transformer and rectifier, very little:  both are highly
efficient.  The battery will incur charge/discharge losses, but
we would have to contend with those in any UPS, regardless of
how the batteries are charged or how their energy is delivered
to the load.

That leaves the regulators.  I'm minimizing those losses by
providing a separate battery and regulator for each required
output voltage, so as to minimize the IV loss in the regulator.

If you prefer the (IMO questionable) relative simplicity of using
a single (multi-output) regulator, you can certainly use an 18-
or 24-volt battery and run the regulator(s) off of that to deliver
12VDC and 5VDC (or whatever voltages are needed).  The point is
that it is certainly simpler, and likely more efficient, to deliver
the DC battery power to the DC load by DC -> DC regulation than by
inverting to 120 or 240VAC only to have the PC's PSU convert the AC
right back to DC for the load -- which how external UPS operate.

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