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Xantrex UPS

Rich Braun wrote:
> Tom Metro wrote:
>> ...they're just trading off VA rating for run time length. You
>> should be able to get the same effect by purchasing a UPS with a
>> much higher VA rating than you need.
> VA rating and runtime length are orthogonal concepts. 

Of course, but...

> Yes, they put (somewhat) larger batteries into short-runtime high-VA
> units:  but nowhere near enough to provide substantially longer
> runtime for medium-level loads.

I'm operating under the assumption that manufacturers are going to try 
and maintain an approximately constant run time - say 10 or 15 minutes - 
at the rated VA.

But I realize in actuality they don't do this. I've seen the "slim" 1000 
VA units on the market in the past few years that clearly don't have the 
same capacity batteries as typical 1000 VA units. But they're also 
priced below typical 1000 VA units.

> directing attention to those ratings, they can offer a
> cheaper-to-build product but still attract buyers by touting a
> headline number.

Well if the typical consumer only cares about shutting down their system 
cleanly, and they're looking for the capacity to handle their 
high-powered gaming system with a 600 Watt power supply, loaded with 
peripherals, then maybe the marketers are on the right track.

It's more likely to be the geeky types like us that want to run servers 
that care about UPS run duration.

> If you look inside the Xantrex unit, you find so many batteries that you'll be
> convinced. 

OK, that's good to know. That's the kinda detail I wasn't seeing on the 
BestBuy site.

> someone posted a pretty thorough review at:

It's smaller than I expected.
It's also lighter, at 32 lbs. But I see the batteries for my 1400 VA UPS 
  clock in at about 30 lbs, which has a similar battery capacity.

You can probably use weight as a good proxy for battery 
least until a new battery technology becomes popular where lead isn't 
the dominant component.

> Well the factory rating of the internal battery is 40Ah; 
> Let's take an example:  the APC Back-Ups XS900 available for...$89.99
> the APC unit contains two 7.5Ah batteries, total 15Ah--less than half
> the capacity of the Xantrex.

OK, good comparison.

I have a 1000 VA Opti that uses three 12 AH batteries, so 36 AH, but 
those are 6 V batteries, so half that (18 VA) if you're comparing energy 
capacity to 12 V packs.

I recently acquired an APC Smart-UPS 1400 that takes a pair of 18 AH 
(12V) batteries (36 AH), with an upgrade option to 22 AH (44 AH). At $60 
and $88 respectively, I haven't decided yet whether to buy the batteries 
and put it into service.

> Google around to find 40Ah worth of 12-volt sealed lead-acid
> batteries, I'd be curious to see what the best price for this
> commodity is.

The prices above are for commodity lets say 3x 12 V @ 18 
AH and you'd get 54 AH at $30 x 3 = $90, or 2x the 22 AH for 44 AH at $88.

Even better is using a single batter with 40 HA capacity, like:

which is priced at $70. We're getting into car battery territory if space wasn't an issue, buying a commodity car battery might 
be a little cheaper, though it may not be optimal for deep-cycle use.

Here are other prices from an order in 2003 for UPS batteries for 
smaller UPSs and the 1000 VA Opti:

Two-Pack BP8-12T2 8 AH 12V SLA Battery
   Qty:  1 at $36.98 :.......................................   36.98

Two-Pack BP7.5-12T2 7.5 AH 12V SLA Battery
   Qty:  0.5 at $25.98 :.....................................   12.99

Two-Pack BP12-6T1 12 AH 6V SLA Battery
   Qty:  2.5 at $25.98 :.....................................   64.95

> Well over half the manufacturing cost of a UPS is the batteries.

About half of the UPSs I own were purchased for the cost of the 
batteries. :-) (The UPSs were free, but needed new batteries installed.)

I usually upgrade them to the highest amp-hour possible in the original 
battery form factor.

> One other note:  UPS batteries don't last forever. 

Of course. They're typically stated to last about 3 years. The vendor 
linked above claims 6 years for their batteries.

>> If long run time is really your goal, you'd be better off using less
>> expensive UPSs in conjunction with a gas generator.
> Need an automatic transfer switch, electrical permits, new house wiring,
> plumbing for another natural gas connection...

Sure, but I was suggesting something that would be far less formal, like 
an extension cord to a gasoline powered generator in a garage. The idea 
wasn't to provide a completely automated solution, but a low cost method 
of maintaining power during the rare outage that spans more than an 
hour, and less than a few days.

Consider that you might be overpaying for battery capacity if you only 
use run time in excess of 2 hours once every few years. With a 3 year 
lifespan on the batteries, you may only get one or two uses from it 
before you have to pay the replacement cost again.

If you amortize across 3 or 4 UPSs, buying cheaper UPSs and putting the 
difference into the cost of a generator, might put you ahead, albeit 
with a somewhat less convenient solution for outages in the 2 to 8 hour 


Tom Metro
Venture Logic, Newton, MA, USA
"Enterprise solutions through open source."
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