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Car battery UPS

Richard Sexton	writes:

> A UPS is just, essentially, a car battery, a chargng circuit
>  and an invertor that converts 12V DC to 120V AC.

Bob Dixon  writes:

I would not want a lead-acid battery in my house,
giving off all those fumes

The batteries in military fighter jets are muti-cell NiCads

Actually, there are slightly more complex issues.  For background; I
don't consider myself an expert but as a prior live-aboard sailor,
current sailboat owner, and certified gadget freak, I have a fairly good
practical knowledge of 12 systems.  A few years ago after a wife and two
daughters entered the picture, I added an inverter system. 
I also trained as a Naval Aviator (now retired) and have some experience
with tactical jet aircraft.  Significant NiCad storage is not very
common in these aircraft for several reasons.  One of which is thermal
runaway.  It relates to a condition that can occurr when a NiCad fails
internally sometimes for no reason at all.  Ususlly there is little
warning and the whole thing just melts.  For small batteries this is a
major inconvenience but with a large starting battery it can be
disasterous.  My last expreience was with a trainer, the T-2, almost 20
years ago.  I do not know of any other aircraft that uses NiCad starting
and I suspect the Navy has moved on to some other system by now.
The conventional lead-acid battery comes in several flavors.  Standard
car starting batteries are unacceptable for any sustained load
application.  The deep cycle variety has more robust construction and
will tolerate repeated charge/discharge cycles.  While both types use a
very caustic acid solution, in use, the only gas given off is hydrogen.
Hydrogen can present an explosive hazard but that would be an extreme
case in most installations.
The gel-cell battery uses much of the same technology but the
electrolyte is immobolized to prevent spills and minimize gas discharge.
Capacities are very slightly less but the effective life is longer.  The
8-D gel batteries on my boat are heavily used, are on their fifth year
and are still performing well.
The key to any of these systems is proper maintenance and charging.
Voltgage levels required to charge/equalize lead acid batteries will
destroy gel-cell batteries in short order.  
Quality inverters with sufficient capacity (several hundred watts
continuous) are not cheap but come as complete packages that includes
power management, automatic operation, and battery charging.  I chose a
Heart Interface, but there are several other manufacturers.  Check
boating or RV supply stores.
The bottom line is: 1) UPS systems must be properly sized for the
anticipated load.  2) They are not necessarily complex but do require
some knowledge.  3) You get what you pay for.

Lyndle Schenck