UPS question

Ian Smith smithi at
Sat Aug 14 15:16:40 UTC 2010

In freebsd-questions Digest, Vol 323, Issue 9, Message: 3
On Wed, 11 Aug 2010 15:18:01 -0500 Ryan Coleman <ryan.coleman at> wrote:
 > On Aug 11, 2010, at 3:06 PM, David Brodbeck wrote:
 > > On Wed, August 11, 2010 12:25 pm, Ryan Coleman wrote:
 > >> He thinks that at 500W needed it would give me about 12 minutes on a
 > >> 1400VA. My consideration is, then, give the server 2 minutes on battery.
 > >> If full power has not been returned, shut down the server but leave the
 > >> modem (w/ wireless) and switch running with power for up to 6 hours.
 > > 
 > > A bit of advice: If this is an unattended system, give some thought to how
 > > you will boot the server back up if the outage is longer than two minutes
 > > but shorter than six hours.  Most UPS installations have *some* kind of
 > > race condition issue if power comes back after the servers have begun a
 > > shutdown, but in your case it's an unusually long window.
 > Meaning that my 2-minute window is unusually long? If the UPS can 
 > support the system for 12 minutes, I say give it 20% of the life of 
 > the support because our power outages here are usually spikes that 
 > kill my current web server (but amazingly *not* my file server). In 
 > fact, one of those power fluxes occurred last night. I love storms 
 > for the light shows, but hate them for the toll they take on my 
 > servers.

Indeed.  Ryan, I'm coming in late but I've read the whole thread, after
many people have added useful insights.

However I must question your initial power estimate for this server; in 
your first post you said (cutting a bit):

 > I am looking at a 1400VA / 980W UPS to run a single server with a 
 > usually not on monitor, a DSL modem and a simple switch. The server 
 > should generate about 330W in power consumption, the monitor another
 > 50-100, the modem about 10 and the switch about another 10 watts.
 > So:
 > UPS: 1400VA
 > Server: 400W (liberal estimate)
 > Modem: 10W
 > Switch: 10W
 > Monitor: 75W
 > Total: 495W

First, forget the monitor.  You said it's usually off anyway, as you'd 
expect on a server.  Plug it into the mains directly as needed, not on 
the UPS.  Or at least use DPMS to suspend it after a minute or so idle.

Secondly, get a power meter and actually measure your server running.  
Unless it's a real monster, it will likely draw less than 200W in normal 
use, possibly much less if using powerd to moderate CPU speed by load.

So I suspect you may get something like 5 times the full-load rated time 
out of your 1400VA UPS, maybe 20-25 minutes or so.  5 minutes should be 
a comfortable runtime, to shut it down with 70-80% capacity remaining.

Thirdly, I'll second using another UPS (eg 300VA units are cheap) for 
powering other than your server.  That way you can use features of your 
software (eg NUT) to properly signal the UPS to shutdown (irrevocably) 
just after your server shuts down, to get proper resumption when power 
returns.  Should you get multiple successive on-battery then on-mains 
events, good UPSs will delay restarting until there's enough capacity to 
run another cycle, which time may be tunable for your requirements.

 > Additionally I spent $34 on a video card today that reduces my power 
 > consumption by 150Watts, resulting in a $13 per month savings in my 
 > powerbill - in MN we have a fixed-rate utility fee structure per 
 > season (winter power costs less than summer, I believe, for whatever 
 > reason) and a $10 mail-in rebate on the card means I will be turning 
 > a net profit in 2 months! -- Ryan

Sorry, I don't get why you'd run a video card using in excess of 150W on 
any server?  Or is that for your hot gaming box? :)

cheers, Ian

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