I have had a lot of time and reason to think of a "12 volt home", as I own a
41 foot sailboat that I plan to head out on a world cruise in about 2 years.
The typical power source on a sailboat is its 12 volt batteries.  The
batteries with the most A/Hr rating available for such use are AGM (gel
batteries with glass mat inside).  These are closed cell batteries that can
operate in any position (good idea for when you turn the boat upside down).
I have installed two such batteries, each rated at 215 amp hrs. Batteries
are typically charged by the primary engine alternator (in my case the stock
alternator is rated at 45 amps, but I have a new 125 amp alternator for the
engine).  Alternate sources of energy include wind, solar and water (via an
alternator that is drug behind a boat while sailing).  I am including wind
and solar sources and also an auxiliary diesel engine with a 175 Amp
alternator.  The primary engine uses a little over a gallon of diesel an
hour, the auxiliary uses a little over a pint an hour.  My diesel tank holds
125 gallons.  I have an inverter on board that develops a true sine wave.
It is capable of sustaining 1800 watts, with surges to 3000 watts.

When I set out to power my boat, I decided that 12 volts was the answer and
the most practical and efficient way to go.  All lights are 12 volts, my
laptop has a 12 volt adapter, I can buy typical kitchen appliances that run
off 12 volts (microwave, blender, mixer).  My refrigeration is all 12 volt,
as is the instrumentation on the boat.  I think what one has to realize is
that by living off 12 volts there are certain restrictions and fluff that
one has to give up.  While I can run my small heat pump (7000 btu) off the
inverter, it takes 102 amps at 12 volts.  Not very practical.  We,
especially in the US, have grown accustomed to a very energy intense life -
and I am no exception - the electric bill for my house is $200/month, plus
about the same for natural gas.  Living otherwise will take a real
challenge.  I think that trying to power a home designed for 120 vac,
complete with appliances designed 120 vac by using 12 volts via in inverter
is possible, but not practical without an enormous numbers of batteries, and
they are expensive - my AGM batteries were ~$400 apiece.  In that you should
not run a battery below 1/2 charge, that means I could run my 7000 btu heat
pump for 2 hours.

NPR radio's Science Friday program covered this topic a couple of years ago,
and spoke with people that were living off 12 vdc via inverters to provide
120 vac, so it can be done.  While the rest of the US is not yet reached the
level of power crisis that California has, the world supply of fuel is
limited, and we all are going to be lacking if new methods of generating
power are not developed.

Just so this does not wander to far away from PIC's, there will be a couple
on board my sailboat - to monitor the amount of chain that is out on my
anchor.  As a single person sailor, I installed an electric winch to raise
and lower my anchor.  In order to be able to play out an appropriate amount
of chain for the water depth (4:1 ratio), I have modified my windlass to
have a pair of hall effect sensors and a pair of magnets so that every
rotation of the final gear gives me a pair of pulses indicating another 6"
of chain and the direction of the chain movement.  This will be displayed in
the cockpit where the windlass control is located.

David V. Fansler
DFansler@MindSpring.com
Now Showing www.dv-fansler.com

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