2. WHY BOTHER?
Last Updated on July 11, 2004
INDEX:
2.1. How Is a Battery Made?
2.2. How Does a Battery Work?
2.3. How Do Batteries Die?
2.4. Why Are Vehicles Negatively Grounded?
Because only the rich can afford
cheap batteries.....
A lead-acid battery (also know as an "accumulator")
is a secondary (rechargeable) electrochemical device
that stores chemical energy and releases it as electrical
energy upon demand. When a battery is connected to
an external device, such as a motor, chemical energy
is converted to electrical energy and direct current
flows through the circuit. The terms of the quantity
of lead-acid batteries that are produced, starting
batteries represent approximately 88% of the total.
The total breaks down to 65% Car, 23% Other Starting
Batteries (motorcycle, etc.), 8% Deep Cycle Motive
(wheelchairs, golf carts, fork lift trucks, etc.),
and 4% Deep Cycle stationary (backup, UPS, standby,
etc.).
BATTERY PRODUCTION
In the order of importance, the four
major purposes of a car or "SLI" (Starting,
Lighting and Ignition) battery, as it is known in the
battery industry, are:
- To start the engine.
- To filter or stabilize the pulsating
DC power from the vehicle's charging system.
- To provide extra power for the lighting,
two-way radios, audio system and other accessories
when their combined load exceeds the capability
of the vehicle's charging system. This commonly occurs
while the vehicle's engine is idling.
- To supply a source of power to the vehicle's
electrical system when the charging system is not
operating.
A good quality car battery will cost
between $50 and $100 and, if properly maintained, it
should last five years or more. With a 5% compounded
annual growth rate, worldwide retail sales of car lead-acid
batteries represent roughly 63% of the estimated $30
billion annually spent on batteries. In North America, BCI reports
that of the 106.6 million car batteries that were sold
in 2001, of which approximately 80% were for replacement
and 20% were for original equipment. For 2003, Eurobat
estimates that in Western Europe 58.5 million car batteries
will be sold and 71% will be replacement (after market)
and 29% will be OEM (Original Equipment Manufacturer).
At the Robert W. Baird Industrial Technology Conference,
Johnson Controls reported of the 350 million starting
batteries that will be made in the world in 2004, Johnson
Controls is the largest manufacturer with 24% of the
total followed by Exide with 14%, GS Yuasa (pending
merger of Yuasa and Japan Storage Battery) with 10%,
Delphi with 7%, Matsushita with 4%, East Penn with
3%, FIAMM with 3%, and all others with 35%.
The purpose of a deep cycle battery
is to provide power for wheelchairs, trolling motors,
golf carts, boats, fork lift trucks, uninterruptible
power supplies (UPS), and other accessories for marine
and recreational vehicle (RV), commercial and stationary
applications. A good quality wet deep cycle (or "leisure")
battery will cost between $50 and $300 and, if properly
maintained and used, will give you at least 200 deep
discharge-charge cycles. For differences between a
car and deep Cycle battery, please see Section 7.1.8. Purportedly, Exide and EnerSys
are the two largest deep cycle battery manufacturers
in the world.
2.1. How is a Battery
Made?
A 12-volt lead-acid battery is
made up of six cells, each cell producing approximately
2.1 volts that are connected in series from POSITIVE (+) terminal of the first cell to the NEGATIVE
(-) terminal of the second cell and so on. Each
cell is made up of an element containing positive plates
that are all connected together and negative plates,
which are also all connected together. They are individually
separated with thin sheets of electrically insulating,
porous material "envelopes" or "separators" (in the
diagram below) that are used as spacers between the
positive (usually light orange)
and negative (usually slate
gray) plates to keep them from electrically
shorting to each other. The plates (in the diagram
below), within a cell, alternate with a positive plate,
a negative plate and so on.
CAR BATTERY CONSTRUCTION
[Source: Eurobat]
DEEP CYCLE BATTERY CONSTRUCTION
[Source: US Department of Energy]
The most common plate in use today
is made up of a metal grid that serves as the supporting
framework for the active porous material that is "pasted" on
it. After the "curing" of the plates, they are made
up into cells, and the cells are inserted into a high-density
tough polypropylene or hard rubber case. The positive
plates in cells are connected in parallel to the external POSITIVE
(+) terminal and the negative plates in
each cell are connected to the NEGATIVE (-) external
terminal. Instead of pasted Lead Oxide, some batteries
are constructed with more expensive solid lead cylindrical
(spiral wound); Manchester or "Manchex" (buttons inserted
into the grid); tubular; or prismatic (flat) solid
lead (Planté) positive plates. The case is covered
and then filled with a dilute sulfuric acid electrolyte.
The battery is initially charged or "formed" to
convert the active yellow Lead
Oxide (PbO or Litharge) in the positive plates
(cathode) into Lead Peroxide (PbO2),
which is usually dark brown or black.
The active material in the negative pasted plates (anode)
becomes sponge Lead(Pb), but with a very porous
structure which is slate gray.
If sponge Lead is rubbed with a hard object, it will
be silvery in color.
The electrolyte is replaced and the battery is given
a finishing charge. A "Wet charged" battery is a wet
lead-acid battery shipped with electrolyte in
the battery and a "dry charged" battery is shipped without electrolyte.
When dry charged batteries are sold, electrolyte (battery
acid) is added, allowed to soak into the plates, is
charged (or "formed"), and put into service. This avoids
having to maintain the batteries until they are sold.
PASTED PLATE
[Source: BCI]
FLAT AND TUBULAR PLATE
PLANTE PLATÉ
[Source: US Department of Energy]
SPIRAL WOUND PLATE
[Source: US Department of Energy]
Two important considerations
in battery construction are porosity and diffusion.
Porosity is the pits and tunnels in the plate that
allows the sulphuric acid to get to the interior
of the plate. Diffusion is the spreading, intermingling
and mixing of one fluid with another. When you are
using your battery, the fresh acid needs to be in
contact with the plate material and the water generated
needs to be carried away from the plate. The larger
the pores or warmer the electrolyte, the better the
diffusion.
[Source: Varta]
There is an excellent detailed
description of how battery is made, equipment used
and quality assurance on the Best Manufacturing Practices
Web site at http://www.bmpcoe.org/library/books/navso%20p-3676/index.html.
[back to Index]
2.2. How Does a Battery
Work?
DISCHARGING PROCESS
PbO2 + Pb + 2H2SO4 ? 2PbSO4 +
H2O
CHARGING PROCESS (Reverse of Discharging Process)
2PbSO4 + H2O ? PbO2 +
Pb + 2H2SO4
A battery is created by alternating
two different metals such as Lead Dioxide (PbO2),
the positive plates, and Sponge lead (Pb), the
negative plates. Then the plates are immersed in diluted
Sulfuric Acid (H2SO4), the
electrolyte. The types of metals and the electrolyte
used will determine the output of a cell. A typical
fully charged lead-acid battery produces approximately
2.11 volts per cell. The chemical action between the
metals and the electrolyte (battery acid) creates the
electrical energy. Energy flows from the battery as
soon as there is an electrical load, for example, a
starter motor, that completes a circuit between the
positive and negative terminals. Electrical current
flows as charged portions of acid (ions) between the
battery plates and as electrons through the external
circuit. The action of the lead-acid storage battery
is determined by chemicals used, State-of-Charge, temperature,
porosity, diffusion, and load. A cycle is defined as
one discharge and one recharge of the battery.
A more detailed description of
how a battery works can be found on the BCI web site
at http://www.batterycouncil.org/works.html.
[back to Index]
2.3. How do Batteries
Die?
When the active material in the
plates can no longer sustain a discharge current, the
car battery "dies". Normally a battery "ages" as the
active positive plate material sheds (or flakes off)
due to the normal expansion and contraction that occurs
during the discharge and charge cycles. This causes
a loss of plate capacity and a brown sediment, called sludge or "mud," that builds
up in the bottom of the case and can short the plates
of a cell out. In hot climates, additional causes of failure are positive
grid growth, positive grid metal corrosion, negative
grid shrinkage, buckling of plates, or loss of water.
Deep discharges, heat, vibration, fast charging, and
overcharging all accelerate the "aging" process. At
approximately 50%, the number one cause of premature
car battery failure is loss of water caused from high
under hood heat or overcharging and for Deep Cycle
batteries it is sulfation, at an estimated 85%. Sulfation
is caused when a battery's State-of-Charge drops below
100% for long periods or under charging. Hard lead
sulfate crystals fills the pours and coats the plates.
Please see Section 16 for more information on sulfation.
Recharging a sulfated battery is like trying to wash
your hands with gloves on.
In a hot climate,
the harshest environment for a battery, a Johnson Controls
survey of junk batteries revealed that the average life
of a car battery was 37 months. In a separate North
American study by BCI, the average life was 48 months.
In a study by Interstate Batteries, the life expectancy
in extreme heat was 30
months. If your car battery is more than three years
old and you live in a hot climate,
then your battery is probably living on borrowed time.
Abnormally slow cranking, especially on a cold day,
is another good indication that your battery is going
bad. It should be externally recharged, surface charge
removed, and load tested. Dead batteries almost always
occur at the most inopportune times. You can easily
spend the cost of a new battery or more for an emergency
jump start, tow or for a taxi ride.
Most of the "defective" batteries
returned to manufacturers during free replacement warranty
periods are good. This strongly suggests that some
sellers of new batteries do not know how to or fail
to take the time to properly recharge and test batteries.
This situation is improving with the widespread use
of easy to use conductance type battery testers like
those made by Midtronics used to predict the capacity
of the batteries.
[back to Index]
2.4. Why Are Vehicles
Negatively Grounded?
The best explanation to this question
comes from a 1978 Rolls-Royce Enthusiasts' Club service
manual.
"...it has been found that
cars wired positive earth [ground] tend to suffer
from chassis and body corrosion more readily than
those wired negative earth. The reason is perfectly
simple, since metallic corrosion is an electrolytic
process where the anode or positive electrode corrodes
sacrificially to the cathode. The phenomenon is made
use of in the "Cathodic Protection" of steel-hulled
ships and underground pipelines where a less 'noble'
or more electro-negative metal such as magnesium
or aluminum is allowed to corrode sacrificially to
the steel thus inhibiting its corrosion."...
For more information on cathodic
protection, please read Roger Alexander's article, An
idiots guide to cathodic protection at http://www.airsledge.co.uk/idiots.htm
By 1956, all the North American manufactured cars and trucks, except
the Metropolitan, were using negative (or earth) grounding. For more
specific information on grounding systems used in North American vehicles,
please go to Antique Automobile Radio's http://www.antiqueautomobileradio.com/chart
or http://www.antiqueautomobileradio.com/battery.htm.
.
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