OT: Continuous mode UPSes

[Ben Scott]

On Sun, Apr 19, 2009 at 9:34 PM, Bruce Dawson <jbd at codemeta.com> wrote:
> ... supply at least 500 watts for 15 minutes ...

  110 volt single-phase AC, I assume.

  I don't suppose you know what the power factor is?

  From what I've read, not all loads are created equal.  Some draw a
larger "apparent power" than "real power", or something like that.
(It's all black magic to me, but I'm willing to take the word of the
EE types.  Attempting to 'splain it all to this here country bumpkin
ain't worth yer time.)  The ratio between apparent and real power is
the "power factor".  UPSes supply real power.  Equipment is typically
rated in/measured for apparent power.

  The power factor on PC power supplies is often as bad as 0.6, so
this is a big difference.  More recently, PFC (Power Factor
Correction) supplies have improved that to around 0.8 or 0.9.

  It's a UPS industry convention to spec real power in volt-amps, and
apparent power (at some assumed power factor) in watts.  This is why
the VA ratings are higher than the watt ratings.  The watt ratings
reflect the apparent power, which is more than the real power the
equipment actually needs.

  Note that this has nothing to do with the fact that nameplates
usually specify more watts than the equipment will ever actually draw,
as a safety margin.

  Are we sufficiently confused yet?  :)

> Note: This needs to be *continuous mode*; line-interactive and
> standby will *not* work

  The industry terms are "double conversion" or "online".

> The usual contenders such as APC, TrippLite, ...

  APC doesn't do double conversion.

  Best Power/MGE/PowerWare/Eaton/whoever-they-are-this-year does.
Looks like the PW9130L700R-XL2U would meet your requirements.  14
minutes @ 700VA/490W.  Longer with expansion batteries.

http://powerquality.eaton.com/9130-rackmount-ups-specs-700VA-120V.aspx

  Tripp-Lite does.  "Smart Online" is the brand name, I believe.  I
don't think they have as many model variants as Eaton does.

  YMMV, etc.

> Line and battery monitoring would be nice but is not mandatory.

  In the double-conversion product space, they pretty much all do
this.  Whether you can get it to work with Linux or not, I'm not sure.
 Most of the big brands have introduced at least some Linux support by
now.  However, some of the offerings I've seen still needed a Windows
server to run the show; Linux just gets a "shutdown agent".

  Many models support the option of a network-attached SNMP monitoring
card.  If you can afford it, this is the way to go.  You don't have to
have a computer-with-serial-port physically close to the UPS.  You can
have multiple hosts monitoring the same UPS without shenanigans.  SNMP
is platform agnostic and well-supported by just about everybody.

> If it
> can use my batteries (deep-discharge marine type), that would be preferable.

  According to random vendor web pages I've come across in the past,
"marine" batteries aren't quite the same thing as the batteries used
in UPSes.  The nature of the usage is certainly different, so that
might even be true.  That might explain why you kept killing your
batteries.  Or maybe your power electronics were an inappropriate
design, or your batteries were cheap junk, or cosmic rays overloaded
the oscillation overthruster in the charger circuit.  I dunno.  :)

-- Ben