Car battery
Car batteries are type of rechargeable battery,
which supplies electric
energy to an automobile. Usually this refers to an SLI battery
(starting, lighting, and ignition) to power the starter motor, the
lights, and the ignition system of a vehicle’s engine. These also may
describe traction battery used for the main power source of an electric
vehicle and auto parts.
Lead-acid batteries for automotive use are made with slightly different
construction techniques, depending on the application of the battery.
The typical battery in use today is of the "flooded cell" type,
indicating liquid electrolyte. AGM or absorbed glass mat type battery
has no free liquid electrolyte and are gaining acceptance by consumers
in SLI applications. This article deals with the flooded type of car
battery.
Automotive starter batteries (usually of lead-acid type) provide a
nominal 12-volt potential difference by connecting six galvanic cells in
series. Each cell provides 2.1 volts for a total of 12.6 volt at full
charge. The lead-acid batteries are made up of plates of lead and
separate plates of lead oxide, which are submerged into an electrolyte
solution of about 35% sulfuric acid and 65% water. This causes a
chemical reaction that releases electrons, allowing them to flow through
conductors to produce electricity. As the battery discharges, the acid
of the electrolyte reacts with the materials of the plates, changing
their surface to lead sulfate. When the battery is recharged, the
chemical reaction is reversed: the lead sulfate reforms into lead oxide
and lead. With the plates restored to their original condition, the
process may now be repeated.
The starting or shallow cycle type is designed to deliver large bursts
of energy, usually to start an engine. The SLI batteries usually have a
greater plate count in order to have a larger surface area that provides
high electric current for short period of time.
Motive type is designed to continuously provide power for long periods
of time (for example in a trolling motor for a small boat, auxiliary
power for a recreational vehicle, or traction power for a golf cart or
other battery electric vehicle). They can also be used to store energy
from a photo voltaic array or a small wind turbine. They usually have
thicker plates in order to have a greater capacity and survive a higher
number of charge/discharge cycles. The energy to weight ratio, or
specific energy, is in the range of 30 Wh/kg (108 kJ/kg).
Batteries intended for SLI systems are intended to deliver a heavy
current for a short time, and to have a relatively low degree of
discharge on each use. They have many thin plates,thin separators
between the plates, and may have a higher specific gravity electrolyte
to reduce internal resistance. Deep-cycle batteries have fewer, thicker
plates and are intended to have a greater depth of discharge on each
cycle, but will not provide as high a current on heavy loads.
Some battery manufacturers claim their batteries are dual purpose
(starting and deep cycling).
Use and maintenance
Fluid level
Car batteries using lead-antimony plates, which would require regular
watering top-up to replace water lost due to electrolysis on each
charging cycle. By changing the alloying element to calcium, more recent
designs have lower water loss unless overcharged. Modern car batteries
have reduced maintenance requirements, and may not provide caps for
addition of water to the cells. If the battery has detachable
caps then a top-up with distilled water may be required from time to
time. Prolonged overcharging or charging at excessively high voltage
causes some of the water in the electrolyte to be broken up into
hydrogen and oxygen gases, which escape from the cells. The sulfuric acid in the battery
normally does not require replacement since it is not consumed even on
overcharging. If the electrolyte liquid level drops too low, the plates
are exposed to air, lose capacity, and are damaged.
Charge and discharge
Generally in automotive service the vehicle's engine-driven alternator
powers the vehicle's electrical systems and restores charge used from
the battery during engine cranking. When installing a new battery or
recharging a battery that has been accidentally discharged completely,
one of several different methods can be used to charge it. The most
gentle of these is called trickle charging. Other methods include
slow-charging and quick-charging, the latter being the harshest.
Some manufacturers include a built-in hydrometer to show the state of
charge of the battery. This lucite "eye" has a float immersed in the
electrolyte. When the battery is charged, the specific gravity of the
electrolyte increases (since all the sulfate ions are in the
electrolyte, not combined with the plates). The built-in hydrometer only
checks the state of charge of one cell and will not show faults in the
other cells. In a non-sealed battery each of the cells can be checked
with a portable or hand-held hydrometer. Batteries will last longer if
not stored in a discharged state.
Sulfating occurs when a battery is not fully charged, and the longer it
remains in a discharged state the harder it is to overcome the sulfation.
These may be overcome with slow, low-current (trickle) charging.
Sulfation is due to formation of large, non-conductive lead sulfate
crystals on the plates; lead sulfate formation is part of each cycle,
but in the discharged condition the crystals become large and block
passage of current through the electrolyte.
In emergencies a battery can be jump started, by the battery of another
vehicle or by a hand portable battery booster. Generally, this is not
recommended on newer, computer-controlled vehicles as damage could
easily occur.
Jumper cable connected to battery post. White powdery corrosion products
visible on top of battery. This Group 24F battery claims 525 cold
cranking amperes and 125 minutes reserve capacity.
Recycling the old battery
In only United States, about 97% of lead from used batteries is
reclaimed for recycling. Many cities offer battery recycling services
for lead-acid batteries.
In several U.S. states and Canadian provinces, purchasers of new
lead-acid batteries are charged a small deposit fee, refunded when the
replaced battery is returned. This encourages recycling of old batteries
instead of abandonment or disposal with household waste. Some businesses
will accept old batteries on a "walk-in" basis (not in exchange for a
new battery). Most battery shops and recycling centers will pay for
scrap batteries. This can be a lucrative business, enticing especially
to risk-takers because of the wild fluctuations in the value of scrap
lead that can occur literally overnight. When lead prices go up, scrap
batteries can become targets for thieves.
Battery Storage
Battery should be monitored and periodically charged if in storage,
to retain their capacity. Batteries intended to be stored should be
fully charged, cleaned of corrosion deposits, and left in a cool dry
environment. High temperatures increase the self discharge rate and
plate corrosion. Lead-acid batteries must always be kept in a fully
charged condition. the terminal voltage can be measured as an indication
of state of charge. Batteries may be charged periodically by a constant
voltage method, or attached to a "float" charger.
Changing a battery
In new generation automobiles, the grounding is provided by
connecting the body of the car to the negative electrode of the battery,
a system called 'negative ground'. In the past some cars had 'positive
ground'. Such vehicles were found to suffer worse body corrosion and,
sometimes, blocked radiators due to deposition of metal sludge.
When changing a battery, battery manufacturers recommend disconnecting
the ground connection first to prevent accidental short-circuits between
the battery terminal and the vehicle frame. A study by the National
Highway Traffic Safety Association estimated that in 1994 more than 2000
people were injured in the United States while working with automobile
batteries.
The majority of automotive lead-acid batteries are filled with the
appropriate electrolyte solution at the manufacturing plant, and shipped
to the retailers ready to sell. Decades ago, this was not the case. The
retailer filled the battery, usually at the time of purchase, and
charged the battery. This was a time-consuming and potentially dangerous
process. Fortunately, this is less of a problem these days, and the need
to fill a battery with acid usually only arises when purchasing a
motorcycle or ATV battery.
Freshness
Because of "sulfation" lead-acid batteries stored with electrolyte
slowly deteriorate. Car batteries should be installed within one year of
manufacture. In the United States, the manufacturing date is printed on
a sticker. The date can be written in plain text or using an
alphanumerical code. When first installing a newly purchased battery a
"top up" charge at a low rate with an external battery charger
(available at auto parts stores) may maximize battery life and minimize
the load on the vehicle charging system. The top-up charge can be
considered complete when the terminal voltage is just above 15.1 V DC.
15 V DC is the voltage level where any sulphation that may be present is
driven from the plates back into the electrolyte solution. A new battery
can have some sulphation even though it has never been in service. If
the top up charge cannot be done it is not harmful to place the battery
in immediate service.
Corrosion
Corrosion at the battery terminals can prevent a car from starting. To
prevent corrosion, during regular battery service the terminals may be
cleaned with a wire brush and a solution of baking soda and water and
corrosive products washed away with water. When the battery terminals
are re-assembled, they are often coated coated with petroleum jelly
(grease is not desired) or a commercially available anti-corrosion
product to reduce the rate of corrosion accumulation.
Battery defects
Common battery faults include:
* Shorted cell due to failure of the separator between the positive and
negative plates
* Broken internal connections due to corrosion
* Shorted cell or cells due to build up of shed plate material building
up below the plates of the cell
* Broken plates due to vibration and corrosion
* Low electrolyte
* Cracked or broken case
* Broken terminals
* Sulfation after prolonged disuse in a low or zero charged state
The primary wear-out mechanism was the shedding of active material from
the battery plates, which accumulates at the bottom of the cells and
which may eventually short-circuit the plates.
Early automotive
batteries could sometimes be repaired by dismantling and replacing
damaged separators, plates, intercell connectors, and other repairs.
Modern battery cases do not facilitate such repairs; an internal fault
generally requires replacement of the entire unit.
Exploding batteries
Any lead-acid battery system when overcharged will produce hydrogen gas.
If the rate of overcharge is small, the vents of each cell allow the
dissipation of the gas. However, on severe overcharge or if ventilation
is inadequate or the battery is faulty, a flammable concentration of
hydrogen may remain in the cell or in the battery enclosure. Any spark
can cause a hydrogen and oxygen explosion, which will damage the battery
and its surroundings and which will disperse acid into the surroundings.
Sometimes the ends of a battery will be severely swollen, and when
accompanied by the case being too hot to touch, this usually indicates a
malfunction in the charging system of the car. When severely
overcharged, a lead-acid battery gases at a high level and the venting
system built into the battery cannot handle the high level of gas, so
the pressure builds inside the battery, resulting in the swollen ends.
An unregulated alternator can put out a high level of charge, and can
quickly ruin a battery.
Terms and ratings
* Ampere-hours (A•h) is the product of the time that a battery can
deliver a certain amount of current (in hours) times that current (in
amperes), for a particular discharge period. These are one indication of
the total amount of charge a battery is able to store and deliver at its
rated voltage. These rating are rarely stated for automotive batteries.
* Cranking amperes (CA), also sometimes referred to as marine cranking
amperes (MCA), is the amount of current a battery can provide at 32 °F
(0 °C). The rating is defined as the number of amperes a lead-acid
battery at that temperature can deliver for 30 seconds and maintain at
least 1.2 volts per cell (7.2 volts for a 12 volt battery).
* Cold cranking amperes (CCA) is the amount of current a battery can
provide at 0 °F (−18 °C). The rating is defined as the current a
lead-acid battery at that temperature can deliver for 30 seconds and
maintain at least 1.2 volts per cell (7.2 volts for a 12-volt battery).
It is a more demanding test than those at higher temperatures.
* Hot cranking amperes (HCA) is the amount of current a battery can
provide at 80 °F (26.7 °C). The rating is defined as the current a
lead-acid battery at that temperature can deliver for 30 seconds and
maintain at least 1.2 volts per cell (7.2 volts for a 12-volt battery).
* Reserve capacity minutes (RCM), also referred to as reserve capacity
(RC), is a battery's ability to sustain a minimum stated electrical
load; it is defined as the time (in minutes) that a lead-acid battery at
80 °F (27 °C) will continuously deliver 25 amperes before its voltage
drops below 10.5 volts.
* Peukert's Law expresses the fact that the capacity available from a
battery varies according to how rapidly it is discharged. A battery
discharged at high rate will give fewer ampere hours than one discharged
more slowly.
* Battery Council International group size (BCI) specifies a battery's
physical dimensions, such as length, width, and height. These groups
determined are by the Battery Council International organization.
The following is common for a six-cell automotive lead-acid battery at
room temperature:
* Quiescent (open-circuit) voltage at full charge: 12.6 V
* Unloading-end: 11.8 V
* Charge with 13.2–14.4 V
* Gassing voltage: 14.4 V
* Continuous-preservation charge with max. 13.2 V
* After full charge the terminal voltage will drop quickly to 13V and
then slowly to 12.6V
* Wait at least 12 hours after charging to measure open circuit voltage,
the resting time allows surface charge to dissipate and enables a more
accurate reading.
