Welcraft 232 Coastal, Owner'S Manual

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Chapter 4:
ELECTRICAL SYSTEMS
4.1 General
Your boat is designed for 12-volt lead acid, wet cell
marine batteries. They will require similar
maintenance as those found in automobiles. You
should not mix the size or brand of the wet cell
batteries. Always consult your Wellcraft dealer
before changing the type of batteries in your boat.
All wires in the electrical systems are color coded to
make identifying circuits easier. Wiring schematics
and a wire code identification list have been included
with this manual to aid in following an individual
circuit of the boat.
4.2 12-Volt System
The 12-volt system is a typical marine system
equipped with two batteries. The batteries are
charged by the engine.
All 12-volt power is distributed to the 12-volt
accessories through individual circuit breakers
located in the head compartment near the battery
switch. Main fuses protect the primary DC circuits
from an overload.
Single Battery Switch
The following is a general usage of this battery
switch.
In the OFF position, the two batteries are
disconnected from all loads. The OFF position is
used when the boat is being stored or otherwise not
in use. It prevents any drain from the batteries. This
can be useful if a circuit has been accidentally left
on, say a cabin lighting circuit or similar drain. Such
a load can completely discharge a battery in a day
or two, leading to an unanticipated dead battery
situation when you return to your boat.
In the 1 position, all loads and charging currents are
connected to the No. 1 battery. Starting current for
the engine starter motor is supplied by the PORT
battery. When the engine is running, surplus current
developed by its charging circuit will flow into the
PORT battery. Current to lighting and other loads
will flow from the PORT battery. The STDB battery is
completely isolated and has no load current, nor
does it receive any charging current.
In the 2 position, all loads and charging currents are
connected to the No. 2 battery. Now it supplies
current required by starting and running, and it
receives all the charging current from the engine.
The PORT battery is totally isolated.
In the BOTH position, the two batteries are
connected in parallel. This has a number of
implications. Unless the batteries have exactly the
same state of charge, the combined voltage to the
two batteries in parallel will sag to a voltage
somewhat lower than the highest battery's terminal
voltage. Current from the higher voltage battery will
flow into the lower voltage battery and begin
charging it. As long as the state of charge in one
battery is higher than the other, the lower battery is
more of a load than a source of power. Eventually,
the batteries will reach equilibrium, and they will
both have the same terminal voltage. At that point
they will both tend to supply current to loads that
are attached to them, and they will both receive
charging current furnished by the engine.
It would seem like operating in the BOTH position
would be beneficial, but that is not always the case.
Even thought the batteries will eventually rise or fall
to the same terminal voltage when connected
together, they will not necessarily become exactly
the same. A battery (or any source of electrical
energy) can be though of as having an internal
resistance. The lower this internal resistance the
greater the current it can supply. The internal
resistance will also affect how the battery absorbs
charging current. Even though they are connected in
parallel, it is possible that they will supply unequal
currents to the loads, and it is also possible that
they will accept unequal currents from the engine
charging source.
If the batteries are significantly different in their
age, their type of construction, and their state of
charge, this unequal distribution of current can be
more significant. To describe the situation in the
simplest of terms, when two batteries are connected
in parallel, they will probably tend to behave more
like the weakest battery of the two than the
strongest.
Paralleling the batteries can come in handy in some
situations. For example, both batteries may be
discharged to a point where neither alone can
provide enough current to crank the starter motor,
but combined in parallel they can turn the engine
over.
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