Two Kinds of Electricity
Landfall operates on two separate electrical systems. When we
are tied up to a dock, we can plug into shore power, which is
a 110-AC volt system similar to that in your house or classroom.
When we are underway or at anchor, we use a 12-volt DC electrical
system, very similar to the system in an automobile. One of our
biggest needs for electricity is to power our electronics.
The 110-volt AC system allows us to plug our television or computer
into a wall socket just as you would on land. Most important to
us, using the 110-volt shore power system means we do not drain
our battery bank very much when we are plugged into the shore
power. There is also an automatic battery charger wired between
the 110-volt AC system and the 12-volt DC system to maintain the
charge in the battery bank.
When we are off of the dock, we depend solely on the 12-volt
DC battery bank for electricity. We have an electrical inverter
on board that allows us to operate our 110-volt appliances. The
inverter takes the 12-volts DC coming in from the battery bank
and changes it into the required 110 AC volts.
The biggest difference between an automobile's battery system
and Landfall's battery system is that the car's engine is almost
always running when the batteries are being used. This means that
the car's alternator is constantly recharging the batteries. Since
Landfall is a sailboat, we try to run the engine as little as
possible. When the engine isn't running, there is nothing charging
Every time we turn on a light or turn on the water faucet, we
drain power from the battery bank. Therefore, we constantly have
to monitor how much electricity we use and the charge status of
the battery bank. When it starts to get low, we have to replenish
Charging the Battery Bank
There are four ways that we can recharge the batteries. The easiest
way is to plug into the dock and use the automatic battery charger.
However, since we plan to spend most of our time away from docks
and marinas, this method does not meet our long-term needs.
The second method is to run the engine and let the alternator
charge the batteries the same way an automobile's alternator would.
Unfortunately, running the engine consumes fuel, and we need to
conserve fuel to ensure that we can run the engine when there
is no wind. Running the engine is also smelly and noisy, so we
prefer alternative methods.
The third way to charge the battery bank, and a simple, abundant,
clean and quiet way to recharge it, is to use the sun. Solar panels
collect sunlight and convert the rays into electricity. This electricity
can then be fed back into the battery bank. But while this method
is clean, quiet and free, it does not work at night or on overcast
days. Therefore, we must supplement this method with the fourth
way to recharge the battery bank, by using a wind generator.
A wind generator is a propeller connected to an alternator (again,
like in an automobile). When the wind turns the propeller, it
drives the alternator to generate electrical current, and the
current is fed into the battery bank.
By combining wind generation and solar generation, we can create
enough electricity to recharge the battery bank without wasting
our fuel or polluting our environment with engine exhaust and
What is a Battery Bank?
We use the term "battery bank" because rather than a single battery,
we have several batteries that are wired together to meet our
electrical needs. In fact, there are actually three separate battery
banks on Landfall.
The first battery bank is used solely for starting the engine.
This ensures that if we drain the other batteries too much without
recharging, we still have enough power to start the engine and
then recharge the other banks.
The second bank is used to run the windlass, which raises and
lowers the heavy anchor and rode. This is a separate bank because
it requires a lot of energy to lift the weight of the anchor and
the heavy chain rode from the bottom.
The largest battery bank is called the "house bank". The house
bank supplies the electricity to the cabin lights, appliances
and electronics that are constantly in use on the boat. The house
bank consists of six, 6-volt "golf cart" batteries. The golf cart
batteries are wired in pairs. By wiring two 6-volt batteries together,
you can create the equivalent of a single 12-volt battery. The
three pairs are wired in parallel. So, this system has the equivalent
of three 12-volt batteries.
Amp Hours, Series and Parallels
The amount of power in a battery is measured in "amp-hours".
A 12-volt battery that can store 10 amp-hours of electricity will
provide enough electricity to run a single 12-volt light that
draws one amp of power for 10 hours.
When batteries are wired in series, as each of our golf cart
battery pairs is, the voltage is equal to the total voltage
of both batteries added together, but the amperage available
is limited to the amperage of one of the batteries.
When batteries are wired in parallel, the voltage remains
the same but the total amperage of the bank is the amperage
of the batteries added together.
Therefore, if two 12-volt batteries rated at 50 amps each are
wired in parallel, you have created the equivalent of a single
12-volt battery with a total of 100 amps.
Needless to say, we have had to do a lot of math to determine
how much power each of our appliances draws and how much power
we have available in our battery banks.