Learn About Batteries
Batteries are available from several
different manufacturers utilizing several different
technologies. But when considering life expectancy, price per
kilowatt hour of storage, maintenance and availability, the
all time champion for renewable energy applications is the
true deep cycle lead acid battery.
We use the term true deep cycle
because a common mistake that many people make that are new to
renewable energy is to run out to their nearest automotive
store and buy marine deep cycle batteries. Marine deep
cycle batteries are just slightly better than a car battery
when it come to use in a true deep cycle application, and car
batteries are absolutely the worst type of battery for deep
cycle applications.
When designing a marine deep cycle
battery, manufacturers must keep in mind that the battery may
be used for starting a boat's engine. In order to start an
engine, the battery must contain a lot of plates which give
the battery it's high cranking capacity. In order to squeeze
enough plates into a standard battery case, the plates must be
made thin.
The problem is that the thinner the
plates, the less amp hour capacity the battery possesses and
the shorter the life span of the battery when it is used in
a deep cycle application. In fact when used in a typical
renewable energy application, you would be lucky to get more
than a year or two of life out of this type of battery.
A much better choice is the golf cart
battery. It's plates are much thicker and has been designed to
be deep cycled below 50% depth of discharge day in and day
out, year after year. In fact a properly maintained golf cart
battery should last 3 two 5 years in a typical renewable
energy application. A typical golf cart batteries is available
in a 6 volt 220 amp hour ratings which means you will need to
purchase two batteries and wire them in series to get 12 volts
@ 220 amp hours. Click here to learn
more about wiring batteries.
Golf cart batteries are considered a liquid
cell type of battery and do require the addition of
distilled water as its electrolyte is used up. Typically wet
celled batteries should be checked once a month to make sure
that their electrolyte is at the appropriate level. Failure to
monitor the battery's electrolyte level will shorten the
battery's life.
SMART TIP Use
only distilled water when replenishing a battery's electrolyte
level. And always, always use extra clean utensils for filling
the battery's cells with water. Be sure to clean the battery's
caps and surrounding area so as not to accidentally drop dirt
or other contaminants in the battery's cells.
Wet cell batteries are basically
miniature chemical factories and as such should be kept clean
and free of contaminants. It is especially important to wipe
the tops of these batteries so that they are free of dust
before attempting to open the battery's caps to add water. Any
dust that manages to fall into the battery's cells or carried
into the cell by dirty utensils such as funnels or hydrometers
will contaminate the chemical process and can shorten the life
or destroy the battery in short order.
It is also important to keep the
battery terminals free of corrosion, as this will impede the
flow of current from the battery and interfere with proper
battery charging which again will shorten the battery's life.
Golf cart batteries are considered the
minimum type of battery that is used in renewable energy
application. There are larger batteries available in 6, 4 and
even 2 volt configurations which have even larger plates and
thus longer life expectancies. Of course the cost for such
batteries are higher but their extended lives tend to offset
their purchase price. larger batteries of this type tend to
have life expectancies of from 6 to 20 years.
Liquid celled batteries do have
some drawbacks. For one, they do tend to produce hydrogen gas
and a corrosive acid mist when under charge or heavy
discharge, which means that they are better off installed in a
well ventilated, non populated area that is free from sources
of ignition, or in a sealed box which has a ventilation pipe
that leads to outside air.
If you would rather not check your
battery's electrolyte level on a monthly basis or your
application's remote locate would make it impossible to do so,
or you're concerned about the hydrogen issue, then you are
better off choosing a VRLA or sealed battery.
VRLA batteries (Valve Regulated
Lead Acid) or sealed batteries are not truly sealed. They
contain valves which are designed to relief pressure in an
emergency, if the battery is overcharged. The problem is that
once the valves have blown, the battery is typically ruined.
VRLA batteries are available in
voltages and amp hour ratings that are typical of their wet
cell cousins. They tend to have a longer shelf life and
typically last longer than wet cell batteries in standby mode
and never need to have water added to them. They can be
mounted in virtually any position and they do not vent
hydrogen gas or corrosive acid mist.
You might be asking " Why would I
want to buy a wet cell battery when sealed batteries have all
these advantages ? " In one word, price, Sealed batteries
tend to cost 2 to 3 times more than wet cell batteries and
typically are more finicky about charging. A wet cell battery
can typically be overcharged without suffering much damage.
Overcharge a Sealed battery which causes their seals to blow
and basically what your left with is a very expensive lead
weight !
But if your application demands a
sealed battery and your careful about charging, and your
budget can tolerate it. Then a sealed battery is the only way
to go. Sealed batteries come in AGM or (Absorbed
Glass Mat) and Gel Cell varieties. A Gel Cell battery has had
silica gel added to its acid which forms a gel which looks
like hard Jell-O. One advantage of creating a gelled
electrolyte is that it makes it virtually impossible to spill
acid even if the battery's case is damaged. Gel Celled
batteries are more sensitive to overcharge than liquid cell
batteries or AGM technologies.
AGM batteries use a fiberglass mat to
absorbed and immobilize the acid. This fiberglass mat also
acts as a separator which prevents the plates in the battery
from shorting out. AGM batteries tend to tolerate overcharging
a bit more than Gel Celled batteries can.
Battery Charging
Most modern renewable energy class
battery chargers or charge controllers charge batteries in
three stages. Bulk, Absorption, and Float.
Bulk Charge
The initial stage of this 3 stage
charging sequence is the bulk stage. The current which is
applied to the batteries is at the maximum rate that they can
accept. Voltage will slowly rise to its peak charge level
which can reach as high as 15 volts for a liquid cell battery
and 14.3 to 14.4 volts for a sealed battery.
Absorption Charge
The second stage of this charge
sequence is the absorption stage. In this stage voltage
will remain constant and the current that is applied to the
battery will gradually taper off as the battery's internal
resistance increases. It is during this stage that the charger
or charge controller will output its maximum voltage which is
typically 14.3 to 15.5 volts. The batteries will be held at
this level for up to several hours.
Float Charge
The third and final stage of this
charge sequence is the float stage. After the batteries have
reached a fully charged state the current and voltage level of
the charger or charge controller is reduced to a lower level
to reduce gassing and prolong battery life. Often referred to
a trickle charge, voltages at this stage are typically between
13.2 to 13.6 volts, again depending on the type of battery
technologies that you are using. Batteries are kept at this
level until they are once again discharged at which point the
process repeats itself.
Click here
to view battery wiring diagrams
