Possible OT: power monitoring

Mon Jun 16 19:53:37 EDT 2008

The TrippLite is "Tripp Lite OMNI LCD UPS 8 Outlet / 900VA / 475 Watt /
Tower UPS", and I agree about the CyberPower, it kept connecting and
disconnecting the USB according to the (less important) XP machine that it
protects, so I had to remove the USB cable from it to keep the messages from
popping up on the taskbar.  So far I have not tried to use the USB
interconnect on the TrippLites, since one protects my SUSE machine and the
other protects a television and some game machines and a cable box.  All of
these came from Tiger Direct, incidentally, and I think some of my
comparison problems come from inconsistent information being provided about
the units.

Regarding the low line power, it doesn't cause any problems on the UPS but
just seems to be a harbinger of a blackout that will involve several blocks
around here.  Usually this is during or soon after a storm, but the low
voltage condition starts well before any storm in all cases I have noticed.
May just be a coincidence, but I still get concerned when I don't see a
range of 119v-122v like normal.

Thanks very much to all, I got a lot of good information on this and it
sounds like there is a consensus to my hunch about daisy chaining being
bad.

2008/6/16 Ben Scott <dragonhawk at gmail.com>:

> On Mon, Jun 16, 2008 at 4:19 PM, Curtis Sandoval
> <curtis.sandoval at gmail.com> wrote:
> > TrippLite 900s and a CyberPower 675 ...
> [...]
> > Is there a way, using these or other UPS units, to constantly monitor
> > input line voltage and length of outages?
>
>   Better UPSes can report detailed information like that (sometimes
> called "smart" or "intelligent").  Entry-level models ("dumb") often
> have either no monitoring at all, or just something that tells the PC
> line power has dropped, and maybe, if you're lucky, low-battery.  The
> dumb models generally use the moral equivalent of a contact-closure.
> In the old days, they'd most often re-purpose the flow control lines
> of RS-232 serial ports for this.  These days, they do the same thing,
> but hook the USB up to a USB-to-RS232 serial adapter, since almost
> nothing has RS-232 ports anymore.  The smart models will have an
> actual data communication protocol, usually run over serial or USB.
> It often allows for UPS control as well as monitoring.  The protocol
> is usually simplistic and cryptic, but I remember you could hook a
> VT-220 up to a Ferr-UPS and get a command prompt.  :)
>
>  Based on the info on the manufacturer website, the CyberPower UP625
> falls into the "dumb" category.  You won't be getting power quality
> stats from it.
>
>  Please clarify "TrippLite 900".  Checking their website, I find
> several different products with "900" in their model name.
>
> > ... a few hours of low input voltage (112v-114v) ...
>
>  As far as the power company is concerned, 112 VAC is usually not
> considered "low".  Anything within 110 to 120 VAC is usually
> acceptable.  Not that that helps you much if your equipment *does*
> care...
>
> > Power quality monitoring would be nice, but my searches seemed to
> > indicate that quality monitoring is much more expensive ...
>
>  Yup.  "Smart" vs "dumb" is one of the key differentiators between
> UPSes in different price bands.
>
> > I could find nothing specifically saying that a UPS or quality monitor
> would report
> > real-time to a computer (specifically SUSE 10.2 or Ubuntu 8.04).
>
>   Like anything else, support and features vary with manufacturer and
> model.  Not everything works well with Linux, either.  For some
> models, third-party software is the best bet; for others, the OEM
> provides good software.
>
>  I've had experience with various models from APC, TrippLite, and
> Eaton.  Quality and features vary.  Nothing was astoundingly bad,
> nothing blew me away with price/performance.  APC is prolly the
> best-known brand, and sometimes that's reflected in higher prices.
> (Note that "best known" is neither necessary nor sufficient for "best
> quality".)
>
>  I know the APC Smart-UPS line can report information like input
> voltage, output voltage, load (as a fraction of capacity), battery
> voltage, runtime remaining, and unit temperature.  Their "PowerChute"
> software has had various Linux releases of varying functionality and
> stability.  (This information does not constitute an endorsement of
> APC's products.  (The preceding statement does not constitute a
> condemnation of APC's products.))
>
>  TrippLite, Eaton (AKA PowerWare AKA Best Power), and Minute-Man also
> have "smart" UPS products, and claim various levels of Linux support.
>
>  Popular third-party UPS software for Linux includes "apcupsd" and
> "NUT" ("Network UPS Tools").  Google the project names to learn more.
> In particular, both projects list hardware known to work with their
> stuff.
>
>  YMMV.  Caveat emptor.  UPS manufacturers love to change things
> without telling anyone, often selling a very different product under a
> same or similar name.  Their software is sometimes astoundingly badly
> written.  They sometimes regard their communication protocols as
> proprietary trade secrets.  Etc.
>
> > I have been looking at getting some new or larger UPS units, and I've
> > noticed there is a nonlinear relationship between price and capacity ...
>
>  Look carefully at the specs.  You may be comparing apples to
> oranges.  Some parameters which affect price include:
>
> - Load capacity (determines connected equipment)
> - Battery capacity (determines maximum runtime)
> - Expandability (external battery packs)
> - Warranty and equipment coverage
> - Monitoring capabilities
> - Output waveform (square wave approximation vs "true" sine wave)
> - Transfer time
> - Operating principle (stand-by vs line interactive vs double
> conversion vs ferro-resonant vs ...)
> - Voltage regulation and surge suppression features (these are not
> inherent in all UPS designs)
>
>  There are non-technical factors, too.  If you're asking for a bigger
> UPS, manufactures assume you want something better than the
> bargain-basement crap you usually find at BestBuy, Circuit City, et.
> al.  So the bar for minimum quality is implicitly raised.  At the same
> time, if you're asking for a bigger UPS, manufactures assume you can
> afford to pay more, and thus charge more simply because they can.
>
> > makes me wonder why a person would not buy two or more smaller units and
> > daisy-chain them to get higher capacity and redundancy.
>
>   Daisy-chaining UPSes is sub-optimal at best.  The manfuactuers warn
> you never to do it, but maybe they're just trying to sell more UPSes.
> But there are technical reasons, too.  For one, the square-wave
> approximation output by many cheaper UPSes will generally cause any
> UPS downstream from it to trip over to battery, too.  So as soon as
> wall power is lost, everything trips to battery, and all but the last
> UPS is just generating heat.  More sophisticated UPSes can output
> better power, but they also have higher draws for
> supporting/conditioning, so you're adding inefficiencies.  And I've
> heard horror stories of UPSes self-damaging in such configurations.
> (Envision a UPS tripping on and off battery constantly...)
>
>  I'm not saying daisy-chaining UPSes is the ultimate evil, but it
> still seems like something to avoid.
>
> -- Ben
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