[Tfug] FTGH: APC Back-UPS Pro 650

[Bexley Hall]

--- johngalt1 <johngalt1 at uswest.net> wrote:
> From: "Jeremy D Rogers" <>
> > On 4/20/07, Sean Warburton <> wrote:
> >> I'm sorry! I didn't know a series/parallel
> discussion would ensue...Here 
> >> was
> >> how I found it: the positive went somewhere into
> the unit, and the 
> >> negative
> >> went directly to the positive in the second
> battery. the negative from 
> >> the
> >
> > Umm.. so they were in series, not parallel. So if
> you added more in
> > series, you would increase the voltage. That
> doesn't sound like a good
> > idea.
> 
> Actually, it is a good idea. UPSes are rated by

No, it *isn't*!  Just like running a 110VAC hair
dryer on 220VAC won't magically dry your hair 
faster -- it will fry the hair dryer, instead!

> power rating (VA, or KVA) A 
> formula for power is P=IV, where I is current and V
> is voltage. Another 
> formula for power is P=I^2 R

You are assuming the design of the UPS can
automagically adapt to whatever DC supply is present.
Most electronic devices are designed with slim
operating margins.  Chances are, putting 36V (24+ one
12V battery) or 48V (24 + two batteries) on the DC
input of the inverter will probably result in a puff
of magic smoke escaping from the unit.

> As someone else in the thread pointed out, if
> increase teh voltage, you 
> lower the current ( I ). Then, I^2R (power) losses
> are reduced.  As a 
> result, power loss due to heat (resistance ( R ) in
> the wiring, connections 
> and circuitry) will be less for higher voltage in
> the battery bank.
> 
> Low end UPSes typically use 24V battery storage.

*Low* end UPS's use 12VDC.  Then, there are a slew
of "middle end" ( :> ) UPS's that run on 24V.
The next step seems to be 48V, then 96V.  I had one
that ran on 120VDC.  So, there isn't really any
"standard"...

> However, when you look at 
> the 2KVA-3KVA range, they use 48V battery packs to
> reduce lossses. In higher 
> capacity UPSes, they design the battery voltage to
> be even higher.
> 
> Another way to look at it is: If your UPS uses a
> higher battery voltage, the 
> transformer used to boost the voltage to 115VAC will
> be smaller and more 
> efficient. The transformer (or inverter really),
> will not have to boost the 
> voltage as much, and pay for that difference with a
> high current. 


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