[Tfug] FTGH: APC Back-UPS Pro 650

[Sean Warburton]

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
second battery went somewhere...so whatever configuration that is...could I
add more batteries (hooked up positive to negative, like the original two
were) to get increased run time (I think Rich as hinting at this...)?
        Sean


On 4/20/07, Bexley Hall <bexley401 at yahoo.com> wrote:
>
>
> --- Adrian <choprboy at dakotacom.net> wrote:
>
> > On Wednesday 18 April 2007 17:52, Sean Warburton
> > wrote:
> > [snip]
> > > lead acid batteries. There are two of them (in the
> > backup, they were
> > > togeather...in parallel (I think? where the
> > current lasts longer than one
> > > battery, as opposed to in series, which yields
> > more current/voltage,
> > > right?).
> >
> > Not quite... You actually want them in series, not
> > parallel, for 2 important
> > reasons (in most applications that is).
> >
> > First, P=VI, so power is voltage times current.
> > However, power is lost thru
> > resistance in the battery and connecting wires,
>
> But each battery only sees half of the load -- in
> theory (given ideal batteries and chemistries).
> And, the IR losses in the wiring are minimal.
> The bigger issue is the overall *efficiency*
> that the switcher can deliver -- see my previous
> post.
>
> I had a 3KW UPS that had a 120VDC battery pack.
> It was *lethal* to operate it with the covers off!
> But, ran quite efficiently since such a small
> portion of the input power was "wasted".
>
> > given by V=IR. Reducing
> > factors to find power lost: P(loss)=RI^2. So for a
> > given amount of power, if
> > you double the amount of current, you halve voltage,
> > but you quaduple the
> > power lost (as heat). If you double the voltage, you
> > halve the current
> > needed, and hence cut loses to 1/4.
> >
> > Second, batteries are rated in "Amp hours", the
> > theoretical value based on a
> > discharge rate over a period of 20 hours (SAE
> > standard). So an 8Ah battery
> > theoretically could supply 8amps for 1 hour... in
> > reality, it could supply
> > something closer to 0.4amps for 20 hours. At a high
> > discharge rate, its
> > capacity is drastically reduced.
> >
> > So by putting batteries in series you both decrease
> > loss to resistance/heating
> > in the batteries and get a greater capacity out of
> > the battery.
> >
> > Adrian
> >
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