There are 2 types of UPS. One, the load actually runs off the battery (the
UPS just keeps the battery charged and inverts the DC power to AC) and the
other the load actually runs on line voltage and switches to battery when
line voltage disappears (this is probably the type you are speaking of but I
have not tested that).
Also, should not need any heavier cables (except to account for the longer
length that may occur between truck battery and UPS) as long as using the
UPS within the design specifications. I think it is generally about 12 Ga.
wire between the battery and UPS (at least in the PC world, servers might be
a little bigger since the batteries are often in series).

--
Brent Atkerson
Anrod Screen Cylinder Co.
www.anrodscreen.com


"Ignoramus1487" wrote in message
...
On Tue, 22 Nov 2005 16:05:54 -0500, Brent Atkerson
wrote:
This one interests me. Wonder how many small UPSs you could run from a
truck battery (assuming using heavy enough cables between each UPS and
each
battery [when needed for the 24 volt input]). I am sure you would have
to
leave the vehicle running if running the UPSs for any length of time or
heavy load... Probably pretty basic questions but I am kind of
interested
because I have a couple laying around and never thought of using them as
an
inverter (powered by a vehicle). That would make a neat addition to a
garden tractor or something too...



Beware that some UPSes refuse to start without A/C voltage
present. Kind of stupid, but it's reality. That could hinder their use
for emergency.

12V is a very low voltage and you need big cables. Your battery can
produce a lot of amps intermittently, so with it, you could run loads
that are not too high on average.

For example, on 70 amps, you could run about 700 watts of power (after
considering all losses). That's enough to power up the furnace and a
few fluorescent lights or the TV. Maybe even a refrigerator.

Since your truck recharges the battery as it runs, the battery acts as
a buffer/smoother of your alternator's output and can help produce
power without frying the alternator.

i