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Continued charging of a fully charged battery
will cause a rise in battery temperature and excessive gassing.
When connected to shore power, the batteries are kept charged
by an onboard charger. Small 12-volt boat refrigeration systems
will run many hours per day in warm climates while drawing current
from the batteries. The current is then replaced by the charger.
Many battery chargers cannot handle the continuous balancing
of current flow. The simplest way to determine it your charger
is over stressing batteries is by the loss of water or battery
temperature. Although all of these charger examples are not
marine equipment their charging patterns are similar to the
different chargers found in many boats. These example voltages
only apply to common lead acid batteries. Other type Batteries
may require lower voltage
Fixed Output
12-Volt Charger
Fixed output chargers have no automatic control
over voltage. Their transformers
are wound to produce from 14.2 to 15 volts. These chargers are
designed to be left on batteries for only the length of time
it takes to bring them up to full charge. This type charger
may have been the best way to do it 25 years ago but not today.
Automatic Shutoff
Charger
Automatic shut off is the answer to over charging
batteries only if there is no load connected
to the battery. The basic operating principle of this type charger
is to shut down when full charge is reached and reactivate when
charge drops to 90%, which would be several hours or days. When
a 12-volt refrigerator 5-amp load is added, the automatic charger
turns on to its fixed output of 15-volts that will overload
a fully charged battery for several hours each day.
Fully Automatic
Charger
Some fully automatic chargers are nothing more
than an auto shutoff with a trickle charger added. When these
chargers see a full charge, they switch to a pulse charge of
less than one tenth amp. Again, when a refrigerator load is
added to the battery, the charger switches to full output voltage
overcharging the battery.
Fully automatic
3 stage charger
The new step voltage regulators for alternators
and battery chargers have become the boat
battery's best friend by reducing the voltage several times
during charging. The final charge step is know as the float
phase and should maintain the battery and act as a power supply
for small current drawing equipment such as a refrigerator The
more expensive chargers provide various settings for operator
control to compensate for seasonal battery temperatures and
battery types.
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