Which UPS?

[Scott Allen]

On 12 June 2012 11:41, Lennart Sorensen <lsorense-1wCw9BSqJbv44Nm34jS7GywD8/FfD2ys at public.gmane.org> wrote:
> Efficiency wise, yes.  But it ought to be much cheaper to build a UPS on
> the DC side for a computer.

Somewhat cheaper, maybe. I wouldn't go so far as to say *much* cheaper.

You still need a battery, of course (or some other form of energy
storage), and a charging system for it.

Today's PCs require multiple voltages. These voltages need to be
fairly well regulated; typically better than the voltage discharge
curve of a battery. For cost effectiveness, it would be best that a
single battery be used, with a single output voltage. Therefore, you
still need circuitry similar to that in a PC's power supply to provide
the regulation and multiple voltages.

A good solution might be to have dual input capable PC power supplies.
They would accept both 120/240VAC and some standard DC voltage. The
power supplies would favour the AC input and automatically switch to
accepting DC when necessary, as with a standard UPS. Ideally, they
would have an additional standardised DC connector, or combination AC
and DC connector.

A UPS would then basically consist of just a battery and charging
system (and the necessary cabling). You could build this directly into
the PC or have a larger external system, allowing connection to
multiple PCs.

This would eliminate the cost of the AC inverter circuitry in existing
UPSs but possibly increase cost of the PC power supply.

Note that dual input supplies, like I described, already exist but
they're not common or standardised and generally not cheaper than
using an AC output UPS.
E.g.:
<http://www.nipron.com/dc_ups/>

> Of course many high end UPSs always run the PC on generated power since
> it is cleaner (supposedly) than what comes from the wall.  I wonder how
> much efficiency that costs.

As well as supposedly cleaner power, these UPSs also provide
instantaneous switchover (since there really isn't a switchover). If
you're concerned about either of these, efficiency is a secondary
consideration.

There are also UPSs, that are a little higher end than the basic
models, that provide filtering and regulation for cleaner AC power,
but don't do continuous conversion. You can also get standalone
systems for cleaner AC (e.g. "Monster" power bars).

-- 
Scott
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