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windlass, davit, inverter/chargers, bilge pumps, domestic
water pumps and sanitation system pumps. Cabin lighting
and navigation lights are also candidates for 24-volt power,
provided fixtures and bulbs are readily available. If elec-
tronic gear is multi-voltage, such as the aforementioned 11-
30 volt radar, then it too could and should be operated from
the 24-volt bus. Beyond that, however, the remainder of the
gear, other electronics, certain lights, phone and computer
chargers etc. will operate at 12 volts. Therefore, nearly all
24-volt-equipped vessels will utilize a composite electrical
panel that supplies both 12 and 24-volt service.
How It’s Done
There are two approaches to obtaining both 12 and 24-volt
service aboard. The first involves two completely separate
systems, two battery banks, two (or more) alternators, and
two shore-powered chargers, one each for 12 and another
for 24 volts service. No interconnection of the system exists.
The second involves a single, large, 24-volt bank from which
12 volts is
If a 24-volt battery bank is made up of two 12-volt batteries
that are wired in series, why not just tap 12 volts off the mid-
dle of this bank? Using this method for obtaining 12-volt
service from a 24-volt battery bank
must never be done.
deriving 12 volts out of a 24-volt bank will result
in an imbalance that will seriously shorten the life of the
battery bank. Because this bank may be made up of a num-
ber of large, and expensive, batteries wired in series/parallel
combination, the “center tap” electrician may find him or
her self replacing batteries after just a short time.
A 24-volt battery bank must always be drawn from as if it
were one large battery, equally. This will ensure the longest
life and even cycling for each battery in the bank and for the
bank as a whole. There are two methods of accomplishing
this, one utilizes a device known as an equalizer and the
other uses a device referred to as a converter. The result is
the same, 12 volts, properly and equally drawn from a 24-
volt bank.
Although the product is the same, 12 volts from a 24-volt
bank, there are differences between how equalizers and
converters achieve the same end. Depending upon the lo
and electrical configuration of the vessel, one may be mo
preferable than the other.
Equalizers are designed to supply precisely half the input
voltage. If the 24-volt battery bank has been depleted an
registering 23 volts, the equalizers output will be 11.5. If,
the other hand, the 24-volt bank is under bulk charge, fro
the alternator or shore powered charger and is registerin
29 volts, the output will be 14.5 volts.
The equalizer delivers this half voltage by supplying powe
from half the 24-volt bank. Wait a minute, that’s a strict
no, right? It is, however, the equalizer manages to do this
without harming the bank. The 12-volt loads are connect
to one half of the 24-volt bank, to one 12-volt battery in a
two battery, 24-volt bank. The equalizer senses the voltag
of the battery supplying 12 volt loads and when this volta
falls below one half of the 24-volt bank’s overall voltage,
equalizer uses the other 12-volt battery in the bank to
“recharge” the battery that’s being depleted. Thus, both b
teries provide an equal amount of overall power.
Belts Powering Alternators
Battery Equalizer