which will convert the Alternating Current (AC) from the alternator
into DC - normally set for a 24V system in most large vessels.
2 Rectifier/Charger: The rectifier will change AC to DC and will
produce a DC supply high enough to keep the batteries fully charged
whilst supplying the radio/satcom equipment. The voltage produced
by the rectifier, for a 24 V lead-acid system, will be in the order of 27-
29 Volts DC.
::3 Batteries: 12V lead acid batteries are the most common type used in
commercial shipping. Nickel Cadmium (NiCad, or alkaline) batteries
may also be used. Batteries are connected together to make a 24V
supply system. In the example shown in figure ILl, this is achieved
by connecting the negative (-) terminal of batteries A to the positive
(+) terminal of batteries B and taking your supply from across both
batteries together.
NiCad batteries have a different cell voltage to lead acid batteries.
A six cell NiCad battery will give terminal voltage of 7·2 Volts against
the 12 Volts for lead acid. The connection arrangement shown above
will have to be altered where NiCad batteries are fitted, to provide a
24 Volt supply. Capacity (i.e. the number of hours that the battery
bank can supply the equipment) is increased by connecting A 1 to A2
to A::3 and Bl to B2 to B3, as shown. SOLAS vessels must have enough
battery capacity to supply the radio/satcom equipment in an
emergency, for a stipulated period of time.
Some vessels will have two banks of batteries - the radio equipment
being run off one bank whilst the other bank is being recharged. The
idea with a two bank system is that you run the equipment off one
bank, until the capacity drops to about 50% - and then switch over to
the second bank whilst the first is being recharged. The second bank
is run down to around 50% and you switch back to bank one. More
modern vessels have a single bank of batteries, as depicted in figure
ILl, with the rectifier supplying the radio equipment on a day-to-day
basis - the battery bank being kept on a 'float charge' at the same
time. Should the main supply fail, the batteries are already in circuit
and available to power the radio/satcom equipment.
4 Distribution Panel: Individual items of equipment are supplied
through a distribution panel. This panel will usually incorporate 'circuit
breakers' and/or fuses, so that individual items of equipment can be
'isolated' from the supply, if required.
.5 Changeover Switch and Meter: The changeover switch allows you
to disconnect the batteries from the distribution panel, supplying the194 THE NAUTICAL INSTITUTE