Transcript Chapter 7 Batteries

Chapter 7
Batteries
Objectives (1 of 2)
• Define the role of a battery in a vehicle
electrical system.
• Outline the construction of standard,
maintenance-free, and gelled electrolyte
batteries.
• Describe the chemical action within the
battery during the charging and discharging
cycles.
• Outline how batteries are arranged in multiple
battery banks in truck chassis.
Objectives (2 of 2)
• Verify the performance of a lead-acid battery using
a voltmeter, hydrometer, refractometer, and carbon
pile tester.
• Analyze maintenance-free battery condition using
an integral hydrometer sight glass.
• Describe the procedure required to charge different
types of batteries.
• Jump-start vehicles with dead batteries using
another vehicle and generator methods.
• Outline how batteries should be safely stored out of
chassis.
Battery-operating Principles
• A battery is a galvanic device.
• The lead-acid battery is the electrical energy
storage device used on most vehicles.
• It performs a secondary role as a stabilizer
for the voltage in the vehicle electrical
system.
42-volt Systems
• A 42V system is one in which battery voltage
is 36 volts and charging pressure is 42 volts.
• Most manufacturers expect that at least
some of their chassis systems will use 42V
system voltage before 2010.
Battery Construction
• Six series connected cells in a polypropylene
casing
– Each cell has positive (anode) and negative
(cathode) plates.
– The plates are arranged so that positive and
negative plates are located alternately with
each other.
– Each cell in a battery is separated by
partitions.
Electrolyte (1 of 2)
• It is any substance that conducts electricity.
• It is the liquid solution that enables the
galvanic or chemical action of the battery.
• It is a solution (mixture) of sulfuric acid
(H2SO4) and pure water (H2O).
• The solution proportions should be 36
percent sulfuric acid and 64 percent distilled
water.
Electrolyte (2 of 2)
• This produces a specific gravity of 1.265 at
80° Fahrenheit.
• The acid-to-water proportions should never
be tampered with.
• During discharge, the ratio of sulfuric acid to
that of water is reduced.
– This reduces the specific gravity which can be
measured with a hydrometer or refractometer.
Specific Gravity and Temperature
• Temperature directly affects specific gravity.
• The hydrometer reading must always be
temperature adjusted.
• To adjust specific gravity to temperature:
– Add 0.004 for every 10 degrees above 80°
Fahrenheit.
– Subtract 0.004 for every 10 degrees below 80°
Fahrenheit.
• Electrolyte tested using a refractometer does not
require temperature correction.
84 Factor
• Specific gravity relates directly to cell voltage.
• The 84 factor enables cell voltage to be
calculated by adding 0.840 to the specific
gravity measured.
• If the specific gravity is 1.260, cell voltage
would be 1.260 + 0.840 = 2.100 volts.
• The 84 factor is a “ballpark” method that does
not apply to discharged batteries.
Discharge Cycle
• The lead peroxide (PbO2) on the positive plate
reacts with the sulfuric acid solution electrolyte
(H2SO4) releasing an oxygen molecule (O2) to the
electrolyte, forming water (H2O).
• The negative plate (Pb) reacts with the electrolyte
to form lead sulfate (PbSO4).
• This chemical action will continue until both the
positive and negative plates are coated with lead
sulfate (PbSO2) and the electrolyte has been
chemically reduced to water (H2O).
Charge Cycle
• The sulfate coatings that have formed on
both the positive and negative plates are
reacted to return them to the liquid
electrolyte.
• Water molecules in the electrolyte reduce to
hydrogen and oxygen.
• Hydrogen combines with the sulfate in the
electrolyte to form sulfuric acid, while the
oxygen is drawn to the positive plate to
reconstruct the lead peroxide coating.
Sulfation
• When a battery becomes discharged, both plates
are coated with lead sulfate (PbSO4).
• During the charge cycle, this sulfate coating is
converted back into electrolyte.
• When the sulfate coating hardens on the plates, it
can no longer be converted.
• Battery output then becomes limited and the
condition progresses to complete battery failure.
• A failed battery is said to be sulfated.
Maintenance-free Batteries
• Substances such as calcium, cadmium, and
strontium replace antimony in the plates.
– These substances reduce gassing.
• There is not a means for adding water which
has been depleted.
• A low-maintenance battery is one that uses
essentially the same construction as the
maintenance-free battery, but does provide
for periodic inspection and replenishing of the
electrolyte.
Gelled Electrolyte Batteries
• A special electrolyte is used that liquefies
when stirred or shaken, but when left at rest,
returns to the gelled state.
• In the charge cycle of the battery, the oxygen
that is released at the positive plate
recombines within the cell with the hydrogen
released at the negative plate.
• The recombination of hydrogen and oxygen
produces water that is then reabsorbed to the
electrolyte.
Battery Ratings
• Cold-cranking rating
– The current load a battery is capable of delivering for
30 seconds at a temperature of 0° F
• Ampere-hour rating
– The amount of current that a fully charged battery can
feed through a circuit before the cell voltage drops to
1.75V (For a typical 12V battery, this would be equal
to a battery voltage of 10.5V.)
• Reserve capacity rating
– The amount of time a vehicle can be driven with its
headlights on in the event of a total charging system
failure
Battery Banks
• Multiple batteries are
connected in banks.
• Batteries may be
connected in series or
parallel.
Battery Maintenance
• Neglect and abuse will
shorten battery service life.
• The battery should be
inspected at each chassis
lubrication.
• Battery maintenance
includes inspecting the
battery and its mounting for
corrosion, loose mounting
hardware, case cracks, and
deformation.
Winterizing Batteries
• When winterizing batteries, disconnect battery
cables and load test each battery individually.
• Because it is important to keep batteries warm to
optimize performance in cold weather, many trucks
are equipped with battery heaters.
• If you suspect a battery is frozen, do not attempt to
heat it rapidly.
– Trickle charge and observe for charge response.
Battery Testing
• A complete battery test includes these steps:
– 1. Visual inspection
– 2. State of charge test
– 3. Battery capacity (load) test
State of Charge Test (1 of 3)
• Measure and record
specific gravity,
corrected to 80°F.
• If specific gravity
readings are 1.225 or
higher and are within
50 points (0.050
specific gravity)
between the highest
and lowest cells,
proceed to the load
test.
State of Charge Test (2 of 3)
• If specific gravity readings
are low (below 1.225) or
vary more than 50 points
between highest and lowest
cells, recharge the battery
and retest.
• If, after charging, specific
gravity readings are greater
than 50 points between
highest and lowest cells,
replace the battery.
State of Charge Test (3 of 3)
• Integral hydrometers
– On many sealed maintenance-free batteries, a
temperature-compensated hydrometer is built
into the battery cover.
• Green dot = 65% or greater charged
• Dark = 65% of less charge
• Clear = low electrolyte level
Open Circuit Voltage Test (1 of 3)
• 1. Remove surface charge; crank the engine
for 15 seconds.
– Do not allow the engine to start.
– To prevent the engine starting, apply the
engine stop control or disconnect the fuel
solenoid valve lead wire as required.
• See Table 7-1 on page 195 of textbook.
Open Circuit Voltage Test (2 of 3)
• 2. After cranking the
engine, allow the
battery to rest for 15
minutes.
• 3. Connect the
voltmeter across the
battery terminals to
determine the battery
state of charge.
Open Circuit Voltage Test (3 of 3)
• 4. If the stabilized voltage is below 12.4 volts,
the battery should be recharged.
• Also, inspect the vehicle’s electrical system
to determine the cause of the low state of
charge. After charging the battery, proceed to
the load test.
Load Test
Electrochemical Impedance
Spectroscopy (EIS)
• EIS evaluates the electrochemical
characteristics of a battery by applying
alternating current (AC) at varying
frequencies and measuring the current
response of the battery cell.
Conductance Testing (1 of 2)
• In the trucking industry, modified EIS testing
has become known as conductance testing
or AC conductance testing.
– These test instruments have been proven to
significantly reduce the incidence of incorrectly
diagnosed battery problems.
• The advantages of AC conductance testing
are that it is noninvasive and quick, and test
instruments are inexpensive.
Conductance Testing (2 of 2)
Charging the Battery
• There are two methods of recharging a
battery:
– The slow-charge method
– The fast-charge method
• Either method can be used to recharge most
batteries.
• However, there are some batteries that must
be charged slowly.
Caution
• Hydrogen gas may be discharged during
charging and care should always be taken
when connecting or disconnecting battery
terminals not to create a spark that could
result in a battery explosion.
• Always disconnect the ground cable first and
reconnect it last.
Charging the Battery
• Fast-charging
Jump-starting
Shop Talk
• Frequent need for refilling battery cells is a
typical indication that the batteries are being
overcharged.
• Test the charging system and adjust the
voltage regulator as needed.
Tech Tip
• To obtain an accurate reading on a
refractometer, it is necessary to view the
reading in good light.
– Attempting to read a refractometer in poor
light will make it difficult to read the refractive
scale.
Warning
• Never jump-start or attempt to recharge a
fully discharged maintenance-free battery.
– Jump-starting and charging can create an
explosion hazard.
– These batteries have limited means to vent
gas build-up and therefore should be replaced
if fully discharged.
Caution
• Do not overcharge batteries, particularly
maintenance-free type batteries.
– Overcharging causes excessive boil-off of
water from the electrolyte.
– Overcharging also causes the battery to
produce explosive combinations of hydrogen
and oxygen.
Shop Talk
• Batteries with charger indicators cannot be
charged if the indicator is clear or light in
color; replace these batteries.
Caution
• If smoke or dense vapor comes from the
battery, shut off the charger and reject the
battery.
• If violent gassing or spewing of electrolyte
occurs, reduce or temporarily halt the
charging.
Shop Talk
• Ensure that the vehicle with the dead
batteries and the boost vehicle do not directly
contact.
– If the two vehicles are in contact, a ground
connection could be established, which could
cause sparking when jumper cables are being
connected.
Shop Talk
• The ground connection must be sound. It
used to be recommended that you not
connect directly to the ground post of the
discharged battery. Due to the sensitivity of
electronic control modules connected to the
chassis data bus, OEMs today suggest that
ground clamps always be connected directly
to battery ground.
Warning
• Make sure that the clamps from one cable do
not contact the clamps on the other cable.
• Wear safety glasses, and do not lean over
the batteries when making connections.
Summary (1 of 7)
• A battery converts chemical energy into electrical
energy.
• A battery is a galvanic device.
• The storage device for electrical energy on current
trucks is the lead-acid battery.
• A lead-acid battery acts as a sort of electron pump
in a truck electrical circuit.
• A typical battery contains anode (positive) and
cathode (negative) plates arranged in cells that are
grouped in series within the battery housing.
• The electrolyte used in lead-acid batteries is a
solution of distilled water and sulfuric acid.
Summary (2 of 7)
• The electrolyte in a lead-acid battery is both
conductive and reactive.
• During the discharge cycle of the battery, lead
peroxide on the anode (positive plate) combines
with electrolyte, releasing its O2 into the electrolyte
to form H2O or water. Meanwhile, lead on the
cathode (negative plate) reacts with electrolyte to
form lead sulfate (PbSO4). The result of discharging
a battery is lead sulfate formation on both the
anode and cathode plates.
Summary (3 of 7)
• During the charge cycle, the sulfate coating on the
anode and cathode plates is drawn off and
recombined into the electrolyte.
– Charging reestablishes the correct proportions of
sulfuric acid and water in the electrolyte.
• A fully charged battery has an electrolyte solution
that consists of 36 percent sulfuric acid and 64
percent pure water.
• A fully charged battery should produce a specific
gravity reading of 1.260 at 80°F.
Summary (4 of 7)
• During the charge cycle, both oxygen and hydrogen
are released from electrolyte in a process known as
gassing.
– In maintenance-free and low-maintenance batteries,
the results of charge gassing are contained in a
condensation chamber.
• Gel cell batteries are designed to sustain deep
cycling and are used in truck electrical systems
requiring an isolated battery to power auxiliary
accessories during shutdown.
• Gel cell batteries should be recharged by direct
connection to the battery charger.
Summary (5 of 7)
• Only approved chargers may be used to charge gel
cell batteries.
– These regulate the charging voltage to between
13.8V and 14.1V. Most battery chargers use a
charging voltage of about 16V, which can destroy a
gel cell battery.
• On trucks equipped with gel cell batteries, the
voltage regulator must be set at 14.1V or less.
Voltages higher than 14.2V can destroy gel cell
batteries.
• Batteries are performance rated by cold-cranking
amps, reserve capacity, and ampere-hour rating.
Summary (6 of 7)
• Most truck batteries are specified to a chassis
electrical system by their cold-cranking amp (CCA)
rating.
• Temperature has to be considered when evaluating
the output capacity of any battery.
– Available cranking power significantly drops as
temperature falls.
• When removing a battery from a vehicle, always
disconnect the ground cable first.
• Battery electrolyte should be tested with either a
refractometer or a hydrometer.
Summary (7 of 7)
• When jump-starting vehicles, be sure to study the
battery configuration on both vehicles before
attempting to make electrical connections. Also
switch off all the chassis electrical loads before
connecting jumper cables.
• Generator charging is popular and effective, but
ensure that the correct procedure is followed before
using this method of charging.
• Capacitance testing using instruments such as the
Midtronics 700 is commonly used to assess battery
serviceability.
• Battery performance is best tested using a digital
AVR.