[CentOS] Power-outage

Robert Heller heller at deepsoft.com
Fri Jul 1 16:17:30 UTC 2011

At Fri, 1 Jul 2011 11:46:40 -0400 CentOS mailing list <centos at centos.org> wrote:

> centos-bounces at centos.org wrote:
> > On 7/1/2011 10:59 AM, Robert Heller wrote:
> >> 
> >> APC UPSes are supported by apcupsd.  Other brands, not so much.  Some
> >> (read: cheaper models) have their own special protocol and don't
> >> include Linux support.  These solutions are intended for the cheaper
> >> or otherwise 'unsupported' UPSes.  It *sounds* like the OP does not
> >> need something smart and is probably looking for something cheap.
> >> 
> > 
> > And the APC Smart-UPS 750 units are not all that expensive
> > either.  Even the 1500VA units are a lot less expensive then they were
> 5-10
> > years ago.   $250-$300 to protect $2000-$6000 worth of hardware is
> worth
> > it in my book.
> To what extent does a UPS *protect* the hardware?
> Maintaining up-time during brief brown-outs is one thing I expect of a
> UPS,
> Orderly shutdown is another thing I expect of a UPS.
> *protection* of the PC from irregularity in the AC Mains by a UPS,
> however, I question.
> Rather, it seems, any power irregularity that would kill a PC by
> propagating through the PSU will also propagate through the UPS.

A *good* UPS has a surge protector, then a good filtering power supply,
which functions as a battery charger.  Then there is an inverter
(powered by the battery) that generates 'fresh' AC.  'Normal' surges
are soaked up by the input 'battery charger' supply.  A UPS that
decouples the line power from its output by using the inverter all of
the (not just during a power failure) effectively isolates the output
from the the input -- all irregularities in the AC Mains are absorbed
by the battery charger supply.  The battery is very tolerant and does
not need the battery charger circuit to provide a *precise* continious
voltage -- eg dropouts that take the battery charger circuit 'off line'
for miliseconds are not going to affect the battery. Nor will modest
surges (regulation in the battery charger circuit should take care of
larger surges and MOVs on the AC Mains should take care of really large
surges). The inverter will be powered by the battery charger or
battery, depending on which is functioning at any given instant, and
the input to the inverter will be a flat, smooth DC voltage in either

> NO UPS MADE TODAY (according to my reading of the stats on
> advertisements) eats lightning strikes and asks for more.

It is likely that the UPS would die, leaving the computer, etc. untouched.

> So per your experiences and greater technical savvy: What PSU/PC kill
> power irregularities will be stopped by which UPS?

Certainly random 'low-level' surges (typical 'dirty' power as provided
by the power company).  The UPS would also be the front-line 'cannon
fodder' for more massive surges (eg lightning strikes). 

In reality, a *properly* wired building (one that is up to code), will
have effective lightning protection as part of the basic wiring.  A data
center wiring will be even better.

> Insert spiffy .sig here:
> Life is complex: it has both real and imaginary parts.
> Life is not measured by the number of breaths we take, but by the
> moments that take our breath away. 
> //me
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Robert Heller             -- 978-544-6933 / heller at deepsoft.com
Deepwoods Software        -- http://www.deepsoft.com/
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