Re: [Apcupsd-users] Slightly OT - APC UPS sizing

[Timothy J M. <tm...@ob...>]

"Jeff Boyce" <jb...@me...> wrote on 09/28/2011 05:30:24 PM:

> If my goal is to have approximately the same run time that my current 
server 
> and UPS have, then would a SmartUPS 1500VA be appropriate?  Would a 
SmartUPS 
> 1000VA be too small?  Would a SmartUPS 2200VA be overkill?

By the way, remember that *everyone* seems to only pay attention to the VA 
rating in spite of it being as meaningless for most users as their car's 
top speed.  UPS manufacturers know this, and over the last few years have 
really engineered their product line to address this.  Nearly every 
manufacturer makes multiple *series* of small, thin, light, high-VA UPS's: 
 something like the BackUPS ES 1000 or the Tripp Lite OmniLCD 900 or the 
Eaton 9110 1000VA.  And they all have a single, small battery that might 
give you 10 minutes of runtime for a client PC, and less than 5 for a 
decent server--and probably 3 minutes or less at max capacity, even on a 
brand-new battery!  Forget them unless you're only trying to protect 
against 30 second outages.

Keep in mind that these things are powered by car batteries.  Car 
batteries are HEAVY!  If the UPS you're looking at is thin and light, it 
has *very* little capacity.  If it's not as heavy and bulky as a car 
battery, you're not going to have more than a few minutes of runtime. Cell 
phone batteries are small, light and powerful.  UPS batteries are *NOT*.

And lest I be accused of slandering UPS makers by saying that they don't 
tell you any details about the battery capacity:  they do.  For example, 
they might tell you what the runtime at a particular load level is.  If 
you're *really* lucky, they give you a runtime graph.  (Eaton does:  
http://powerquality.eaton.com/103004258-5591.aspx?CX=3 ;  I don't remember 
seeing one from APC...).  But it's a lot harder to compare a bunch of 
graphs.  It would be *so* easy for them to simply tell you the Ah capacity 
of their UPS.  But they don't.  :(

Ah is not the end-all be-all stat, either.  There are some efficiency 
issues to be aware of as well.  If one UPS is 18Ah and one is 20Ah, you 
may not know exactly which one will have the longer capacity *at your 
load* without further digging.  But when you see that one is 9Ah and one 
is *36Ah*, it makes the comparison real easy.

Timothy J. Massey

 
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