radio/satcom equipment from the rectifier only whilst batteries are
being maintained and/or prepared for testing. There will be a meter
for measuring Volts and Amps, which will help the operator to judge
the performance of the power supply/batteries (see regular checks
and maintenance, following).6 Main DC Supply Fuse: There will normally be an in-line DC supply
fuse for the complete system.Regular checks and maintenance
Batteries supplying the ship radio station should be checked daily for:
State of charge.- To confirm that the electrolyte level is correct.
In a single-bank system, you should be checking that the batteries
are fully charged. For a two-bank system, you are watching for the state
of charge to approach that 50% mark - at which point you will switch to
the other bank and recharge the bank that was in use. The normal way
of checking state of charge is by use of a voltmeter. When using the
voltmeter, you should disconnect the rectifier/charger from the batteries
and allow the batteries to settle down for 30 minutes. Radio equipment
should not be drawing current from the batteries when the readings are
being taken. In figure ILl the radio equipment would be supplied direct
from the rectifier.
A hydrometer could be used - but that would require taking
samples of electrolyte from every cell, in every battery - quite a time-
consuming job. Hydrometer readings do not provide an indication of
state of charge for NiCad batteries - only for lead acid batteries.
Approximate readings for Voltage (12 and 24V systems) and Specific
Gravity (SG) for different states of charge, for lead-acid batteries, with
no equipment drawing current, are shown below:
12 Volt 24 Volt
battery system SG
Full charge > 13 Volts > 26 Volts 1250-1280Half charge 12 Volts 24 Volts 1180
Discharged < 11 Volts < 22 Volts^1100
The electrolyte level in liquid lead-acid batteries should be about
lcm above the plates (NiCads about 5mm). You normally need to open
each cell to check this level and, as the electrolyte is a mix of water and
MARINE COMMUNICATIONS 195