UPS question

Ryan Coleman ryan.coleman at
Wed Aug 11 19:26:01 UTC 2010

Thanks, Chuck.

I talked with a former colleague that has a lot of experience in specing out UPS requirements (between battery-ready and generator-ready backups at the office they have up to 5 minutes of battery backup before the gas generator is needed with a 128-hour recharge time just to support their servers and wiring racks in the office).

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.

Now I need to build a server (looking at RAID5 8x2TB) for less than $1600 w/o a CPU if I can... a local custom builder quoted me $4000 today for a full system inc. CPU, RAM and DVD.


On Aug 11, 2010, at 11:44 AM, Chuck Swiger wrote:

> Hi, Ryan--
> On Aug 11, 2010, at 8:51 AM, Ryan Coleman wrote:
>> Total: 495W
>> According to a calculator if I enter all that information:
>> It says that it will use 693VA.
> That sounds reasonable.  The better PSUs have "80 Plus" certification for efficiency, and that's better than the typical wall warts used for modems and switches and the like commonly manage.  (The efficiency they're assuming is a bit over 70%; using 80% would be around 600VA.)
>> Enter that into
>> It requires Amps... 495W  / 120 voltage = 4.125 amps... doesn't seem right but...
>> 192 hours... that's not right, right?
> Assume for discussion their number was right.  In order to get 495W of output load, the UPS needs to provide 693 volt-amps of juice to your equipment.  After the inverter and 10:1 stepup transformer used to convert 12VDC or whatever the UPS batteries are charged to up to 120VAC, the current needed would be 5.77 amps.  However, the 12VDC battery source itself would be getting a draw of 57 amps (ideally; again, the inverter+transformer themselves might only rate about 90% efficiency for very good quality UPS, so would be drawing more like 60 or 65 amps).
> A standard APC/Tripplite/whatever 700VA UPS tend so have a lead-acid battery reasonably similar to a car battery, and typically will have around 100 amp-hours of charge; they'd probably give you 90 minutes of backup time.  But you can look up the detailed specs of specific models and work from their amp-hour (or watt-hour) ratings-- actually, I think I'm guestimating more from what a 1200VA unit might provide, and a 700VA model is probably going to provide more like 40-60 minutes of power...
> Regards,
> -- 
> -Chuck
> _______________________________________________
> freebsd-questions at mailing list
> To unsubscribe, send any mail to "freebsd-questions-unsubscribe at"

More information about the freebsd-questions mailing list