The proper offshore system consists of a design to meet YOUR needs.
Quality
equipment that is properly installed, inspected and maintained regularly
and
managed properly will give you years of service.
Designing a system starts with figuring your daily consumption expressed
in
amp-hours (Ah). Ah is the number of amps used over time (10 amps
per hour =
10 Ah ). To figure daily consumption add up your 24 hour usage
of lights,
radios, blender etc. to arrive at amp-hours consumed per day.
Once we know
daily consumption, multiply by 2 to figure capacity required for a
one day
supply (100Ah x 2 = 200Ah).
Following the 50% rule is a must for longer battery life. The
50% rule is to
not discharge the batteries more than 50% of total capacity and the
battery
will deliver the maximum amp hours over it's life. One day supply
is not
enough time between recharging cycles for most voyaging yachts, therefore
multiply your daily capacity by the number of days desired to go before
recharging (200Ah X 3 days = 600Ah supply). This means we can
use 300Ah
before reaching 50% discharge or 3 days at 100Ahs. 600Ah can
be arrived at by
using three 8D batteries (210Ah each @ 12vdc) or four 4D (170Ah
each @
12vdc), seven Group 27 (85Ah each @ 12vdc) or six GC-2 (180Ah @ 6vdc)
batteries. Weight is between 450 and 550 pounds for the different
arrangements.
Marine storage batteries come in two basic types, wet cell and gel cell.
Each
have advantages and disadvantages. A third type, absorbed glass
mat batteries
are sold in the marine market however will not address glass mat batteries
as
they are not as well suited for deep cycle use as wet and gel types.
Wet cell batteries are common and inexpensive. The primary drawbacks
to wet
cells is they have to be maintained (with distilled water only), ventilated
properly and contained in full boxes or enclosures. The sulfuric
acid fumes
created while charging will corrode near by materials and if overcharged,
wet
cell batteries can render the boat uninhabitable. They also will
not accept a
charge as quickly as gel batteries, requiring a longer charging cycle
and less
efficiency for the charging system. The advantage is a wider
selection of
sizes and lower initial cost. The average life of a properly
maintained wet
cell battery is 5 years.
Gel cell batteries do not need distilled water, ventilation or boxes.
They
have no liquid to spill or replace and they don't give off gases to
contaminate your environment. The batteries come in most sizes
and can be
mounted on there side or end. They are truly maintenance free.
The
disadvantage is initial cost, but they last 8 - 10 years when properly
charged
and used. For the long term, gel batteries are very desirable
and are a good
match for a modern high power charging system.
Once you have determined what your battery capacity will be to fit your
needs
and your boat, design a charging system to recharge the batteries easily.
The
main engine fit with a suitable high output alternator is the most
powerful
tool to quickly recharge a depleted battery bank. Check your
engine for
horsepower rating, alternator V belt width and alternator "foot" mounting
arrangement. For example: 35hp, 1/2" belt and 2" single mounting
foot.
At full output high output alternators use from 7hp for a 100 amp type
to 9hp
for a 200 amp model. If your engine has 18hp then half the power
will go to
driving a 200 amp unit! This wouldn't be a wise decision as you
may want all
your power going to your propeller while motoring. It is
possible to use a
regulator with a current limit adjustment that would limit the horsepower
required of the engine. This would allow you to use a larger
output
alternator while at ancor for full output and use current limiting
while
underway to lessen the horsepower draw on the motor.
Great care must be taken to properly mount the alternator to the engine.
If
the alternator is out of alignment or loose it will self destruct.
Be sure to
use a grade 8 bolt for the pivot bolt not stainless steel. Stainless
is too
brittle to use around the engine. Most alternators will only
need one belt if
it is a 1/2" width. If your engine has only a 3/8" pully on the
alternator
and engine you may need double belts. The belt(s) should be a
Heavy Duty type
with cogs on the inside for longer life. Gates belts are the
best for this
type of use.
Next, a quality multi - step regulator is needed to get a fast and full
charge
from the alternator to the batteries. A three step type regulator
should be
considered for maximum charging efficiency and care for the batteries.
Choose one that will adjust to your type of batteries (gel or
wet) and if
needed, current limiting. The faster you get to full charge the
less running
time will be needed.
The difference between wet or gel battery charging is considerable and
precision is required to achieve full charge. Wet cell batteries
will accept
in charging amps between 25% - 40% of the total Ah rating. For
example a 200
Ah battery will accept between 50 and 80 amps in the bulk charge (step
one).
A gel cell battery will accept 50% of the Ah rating (i.e.100
amps) in the
bulk charge. Once the batteries reach the absorption stage (step
two), the
voltage will be constant and the amps will decrease to 25% of Ah capacity
down
to 5% of capacity. The absorption voltage for wet cells
is 14.4 vdc, for gel
cells it is 14.2 vdc. The regulator must be able to adjust to
the required
voltage depending on which battery type you have installed. The
third and
last stage is "float" and both types of batteries should be set at
13.65 vdc
to keep the batteries fully charged.
All the systems on the boat MUST be inspected and maintained properly
on a
regular basis. This will help prevent failures and problems that
plague many
sailors. All equipment and systems should be installed with care
to prevent
water damage, corrosion and physical damage. If you don't know
already, boats
are a very harsh environment for anything electrical. All wire
connections
should be soldered and heat shrunk to insure water tight integrity.
Keep
things DRY and CLEAN!!
Lastly, you need to manage your use vs. supply to abide by the 50% discharge
rule and keep your systems with the proper voltage. This can
be done with a
simple amp / volt meter, but they lack accuracy and require close accounting
of amps being used. The volt reading of a battery doesn't
give you an
indication of the state of charge while it is in use. Monitor
systems that
keep track of amps, volts and Ahs consumed take the guess work out
of managing
your supply and give you the information all in one place. There
are many
types of monitors in different price ranges with a wide range of information
and accuracy. With a good monitor, management is easy.
Consult with a marine
professional to help with choosing the right system for you.
Accurate
monitoring is key to the longevity of your well designed and properly
charged
battery system.
In conclusion, if you take the time to design a system for your needs,
install
it properly, use quality equipment, maintain & inspect the system
and properly
manage your supply you will be among the many sailors who have more
time for
FUN on their voyages.
HAPPY SAILING!!
If you should have a question , give Ron Romaine a call at:
Farallon Electronics
2346 B Marinship Way
Sausalito, CA 94965
(415) 331-1924