UPS Recommendations

Levi Pearson levipearson at gmail.com
Thu Aug 12 16:00:57 MDT 2010


On Thu, Aug 12, 2010 at 11:25 AM, Aaron Toponce <aaron.toponce at gmail.com> wrote:
> On Thu, Aug 12, 2010 at 10:38:18AM -0600, Michael Torrie wrote:
>>
>> Regular UPS units use normal, sealed leadacid batteries.  Anyway, going
>> solar is a neat idea.  Let us know how it works out and how the
>> economics fly.  Are you planning, then, an off-grid system?
>
> I thought they were "gel cells", but looking at Wikipedia, I guess
> they're essentially the same, except the cell chemical is different, and
> the lack of needing to add water. I don't know about the power draw
> differences between the two, though.

There's a wide variety of lead acid batteries.  There are two basic
categories, starting and deep cycle.  There's also a sort of hybrid
between them.  Starting batteries are optimized for delivering high
current for short periods of time, while deep cycle are optimized for
delivering lower amounts of current for longer periods of time.
Starting batteries are not very good for reserve power applications,
since they can't be discharged very far before they start to be
damaged.  If you put a bunch of car starting batteries in your system,
you'll be replacing them before too long, especially if they were used
to begin with.

There are also different types of electrolyte.  Auto batteries are
typically an open wet cell battery, which has serviceable electrolyte
and vents hydrogen gas when it changes.  There are also deep cycle
batteries of this variety, and they're relatively inexpensive, but you
have to be careful with maintenance and storage to ensure the gas
doesn't corrode the terminals and that there's enough air circulation
to vent the hydrogen so it doesn't build up to dangerous levels.
There are also sealed varieties, such as gel cells and AGM.  These
don't typically vent, they don't have serviceable electrolyte, and
they don't spill so they can be installed in different orientations.
Gel cells can be ruined by charging them with too high of a voltage,
but AGM don't typically have that problem.  AGM are the most common
type of sealed battery now, I believe.  I've got one as a starter
battery in the trunk of my Miata, and I've got a small deep-cycle one
as the house battery in my Vanagon Camper.

>
> It'll be hybrid. Eventually, I would like to go 100% off-grid, but that
> might be a bit. Looking at 220W panels for roughly $500 makes it very
> attractable for my wife and I.
>
>
> Not only solar, but I've looked at a gas generator as well. Gas is
> cheap, and the generators are inexpensive, so that could work in an
> emergency for a day or two worth of power (as long as I can keep feeding
> it gas).

There's more to the system than just the panels, of course.  You'll
need to factor in the correct batteries for your needs (different
kinds of batteries have different points at which further discharge
starts to cause damage, so you have to factor this into capacity
calculations), a charge controller to make sure that the batteries are
charged and discharged properly, a properly-sized full sine wave
inverter to run your AC appliances, and whatever other gadgets that
are necessary to integrate your system with the grid and gas
generator.  Presumably you don't want to go shuffling plugs at your
breaker panel whenever you want to switch power sources, and hooking
things up the wrong way can backfeed power where it shouldn't go and
cause serious problems.  You could blow up your own equipment or
electrocute a utility worker if you hooked things up wrong.  The above
equipment is generally not cheap.  :)

As far as solar goes, you might also want to consider solar water
heating, which could also reduce your gas bill.  It doesn't involve
expensive photovoltaic cells, so it could be cheaper to implement.

    --Levi


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