[Nut-upsuser] ordered shutdown

[Julian Stacey]

> If you want to conserve power on your UPS, you should simply send a  
> client a command to shutdown. While it is shutting down, it makes no  
> point to cut the power and after that, the remaining power it draws is  
> so small, that cutting power is moot.

Programmable outlets could have use in direction Off as well as On, as
A lot of old computers do not obey "halt -p", only halting, but not
turning off. Modern ATX tend to obey "Off" more though.
   (BTW: Even my modern-ish laptop often fails to halt -p with
   power off, (some ACPI problem I guess - shrug - : it hangs, with fan
   going on & off a lot, presumably in high power mode.)

> You *will* need programmable outlets if you need to restart/reboot  
> part of loads attached to a UPS. 
...


> Having said that, you should *always* take into account that the  
> battery capacity may be less than expected (calculated) due to aging  
> batteries, so you can never fully rely on the reported battery.charge  
> and battery.runtime. If you search the archives, you'll find plenty of  
> examples where people found this out the hard way. This is one reason  
> why one should periodically run battery tests to find hidden battery  
> problems that only surface under load.

As batteries age, they might (or not) retain most of their Amp Hour
capacity, but as their internal resistance increases, can't deliver
same peak current load as a newer lower internal resistance battery.

An on line battery test does not tell much, just a binary Worked/
Failed, (unless it tells more by comms port to NUT?) I would guess
few (if any ?) UPS might have current measuring, for prediction ?
None of the 5 or 6 UPS I have serviced have individual voltage
sensors to individual batteries, so UPS & Nut can only measure the
whole stack, & as some UPS use eg 4 x 12V 17AH @ 60 Euros, replacing
all 4 when only some need it, is expensive.

Off line, with disconnected batteries, a few car headlight bulbs
in parallel can be used to calculate individual & aggregate battery
internal resistances, knowing that one can predict a UPS's reduced
max load which could be much less than UPS manufacturers nominal
max load with good new batteries.
   ( A few nice UPS allow one to slide out batteries & disconnect for
    replacement &/or test, while UPS remains running, albeit with no backup. )

Cheers,
Julian
-- 
Julian Stacey: BSDUnixLinux C Prog Admin SysEng Consult Munich www.berklix.com
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