Page 22 - WestlawnMasthead19_Sept11.pub

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As well as this system works; there are decided advantages
and disadvantages to the equalizer approach. Because the
12-volt power is drawn directly from a battery rather than
through the equalizer, its use is preferable for particularly
high 12 loads, such as winches and thrusters. With limita-
tions, the equalizer simply ensures a proportionate state of
charge between the two batteries.
The potential draw-
back to the equalizer
is that it must be in-
stalled at the 24-volt
battery bank. The 12-
volt supply from the
bank/equalizer loca-
tion must then be run
to the main electrical
panel or from wher-
ever 12-volt loads will
be distributed. If the
distance between the
battery bank and the
panel is great, as is
likely to be the case on
larger vessels, then
the issue of especially
large cables rears its
ugly head once again,
albeit in a limited fash-
ion. Because 12-volt
loads may include
critical items such as
navigation lights, navi-
gation and communi-
cation electronics or
bilge pumps, the voltage drop and commensurate wire size
must be calculated at the 12-volt, 3% rate.
The other method of producing 12 volts from a 24-volt
source is the DC-to-DC converter. Converters do this by first
converting the 24 DC volts from the main battery bank to 24
volts AC. Then the AC voltage is stepped down or converted
to 12 volts AC and then converted
once again to 12 volts DC. The con-
version from DC to AC and then
back to DC is necessary because
DC voltage cannot be stepped
down or transformed while AC can.
A similar process is used in mod-
ern inverters.
In the case of a converter, all of
the 12 volt DC current that it sup-
plies is drawn through the con-
verter rather than from the battery
bank directly. Therefore, the con-
verter must be appropriately sized
to accommodate all of the 12-volt
loads, including start-up surges for motorized equipment.
This means the converter may have to be quite large, which
will drive up the overall price of the 24-volt system.
A converter, unlike an equalizer, supplies a fixed, usually
adjustable output voltage from a wide range of input volt-
ages. The converter is capable of providing a steady, con-
stant and electrically “clean” (converters offer the added
advantage of filtering out unwanted voltage spikes and in
terference) voltage that may be set anywhere between 1
and 15 volts. Most DC electrical equipment is designed t
operate efficiently
a voltage of some-
where between 12
and 13.8 volts. Usi
the converter, this
could be set and it
will not vary provid
the 24-volt battery
bank doesn’t fall b
low a preset thres
old voltage.
Why might this
source of stabile
power be so desir-
able? After all, it’s
available on the c
ventionally wired 1
or 24-volt system.
True, and it is for t
reason that haloge
florescent and inc
descent lights bur
out with such ann
ing regularity (in th
case of fluorescen
it’s typically the m
expensive ballast t
fails rather then the more easily replaced and less expen
bulb). All of these lighting sources are sensitive to the hig
voltages present during the bulk charging phases produc
by high output alternator/regulators and three-stage shor
powered chargers. The converter eliminates this potential
life-shortening high voltage by providing a fixed voltage p
set by the user or marine electrician.
The converter possesses sever
other advantages over the equ
izer. Several smaller converters
may be installed at various loc
tions throughout the vessel wh
12 loads are present, at the he
nav station, engine room etc.
Wherever there is 24-volt powe
available, a converter may be i
stalled to supply 12 volts. This
keeps wiring runs short and th
smaller.
Additionally, converters are ava
able with the option of providin
uninterrupted power (a UPS, of sorts), utilizing a small 12
volt battery. This is handy and provides added safety for
communication and navigation electronics installations.
converter will also act as a 12-volt battery charger, opera
A 12-Volt/24-Volt Circuit Panel
Typical Cabin Dome Light