chapter 3 aircraft storage battery. ways of "generating" electricity on the aircraft...
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Chapter 3 Aircraft Storage battery
ways of "generating" electricity on the aircraft
• Magnetically→Generator
• Chemically→Battery
Classification of Cells
• "primary" Cells
• non-rechargeable
• "storage" or "secondary" cells
• rechargeable
Primary batteries
• Primary batteries can only be used once,
• Also called disposable batteries, are
intended to be used once and discarded.
Secondary batteries
• Secondary batteries can be recharged
• Can reverses the chemical reactions
"storage" battery
• The "storage" battery does not "store"
electricity at all, but changes chemical
into electrical energy when "discharging,"
and changes electrical into chemical
energy when "charging," the two actions
being entirely reversible.
Symbols representing a single Cell
Capacity
The dischargeable ampere-hours (Ah)
available from a fully charged cell/battery at
any specified discharge rate/ temperature
condition.
Rated Capacity
The quantity of electrical energy, measured
in ampere-hours (Ah), that the battery can
deliver from a completely charged state to
1.0 volt per cell at 23 ±3 (73.4°F±5.4°℃ ℃
F).
• Cn = Ah
• C = 38 A-h
Greater capacity of the cell
• More electrolyte
• More electrode material
• discharge conditions
• magnitude of the current
• the duration of the current
• the allowable terminal voltage of the battery
• temperature
Aircraft Storage Battery
Open Circuit Voltage
The open circuit voltage of a NiCad under
loaded conditions is about 1.4 volts per cell,
compared to about 2.1 volts for an lead-acid
cell.
Constant Voltage Charging
• Connect the battery to a constant power
source.
• This doesn’t work for Ni-cads.
Series and Parallel:
Batteries are often connected in series but
should rarely be connected in parallel.
Connecting two 12-volt
40 amp-hour batteries in
parallel is equivalent to a
single 12-volt battery
capable of supplying
amp-hours.
12 volts
12 volts
12 vo lts
80 am p-hours
Tw o batteries in para lle l
Batteries in series
Connecting two 12-volt 40 amp-hour batteries in
series is equivalent to a single 12-volt battery
capable of supplying amp-hours.
12 volts 12 volts
24 vo lts
40 am p-hours
Tw o batteries in series
Overcharging
That is, attempting to charge a battery
beyond its electrical capacity — can also
lead to a battery explosion, leakage, or
irreversible damage to the battery. It may
also cause damage to the charger or device
in which the overcharged battery is later
used.
LEAD-ACID BATTERIES
Features of Lead-acid battery
• Less expensive
• Less maintenance
• Use where constant high current output is
not required
Substances in a LA battery in the chemical actions
• Sulphuric acid,
• water,
• pure lead,
• lead sulphate,
• lead peroxide
A single storage cell made up of:
• Electrolyte
• One positive plate
• One negative plate
Chemical action in a storage cell during charge
Fully charged battery is made up of
• Peroxide of lead (PbO2)
• The negative plate of pure lead (Pb)
• The electrolyte of dilute sulphuric acid
(H2SO4)
(a). PbO2 + 2H2SO4 = PbSO4 + H2O +O
At the Positive Plate:
Lead peroxide and sulphuric acid produce lead sulphate, water, and oxygen
Charging
At the Negative Plate:
Lead and sulphuric acid produce lead sulphate and Hydrogen
(b). Pb + H2SO4 = PbSO4 + H2
The oxygen of equation (a) and the hydrogen of equation (b) combine to form water, as may be shown by adding these two equations, giving one equation for the entire discharge action:
(a). PbO2 + 2H2SO4 = PbSO4 + H2O +O
(b). Pb + H2SO4 = PbSO4 + H2
(c). PbO2 + Pb + 2H2SO4 = 2PbSO4 + 2H2O
Discharge action:
The sulphuric acid of the electrolyte is used up
in forming lead sulphate on both positive and
negative plates, and is removed from the
electrolyte.
(c) PbO2 + Pb + 2H2SO4 = 2PbSO4 + 2H2O
Discharge action:
During discharge the acid goes into the plates.
(c) PbO2 + Pb + 2H2SO4 = 2PbSO4 + 2H2O
Charging
At the Positive Plate: Lead sulphate and water produce that sulphuric acid, hydrogen and lead peroxide
(d). PbSO4 + 2 H2O = PbO2 + H2SO4 + H2
At the Negative Plate: Lead sulphate and water produced sulphuric acid, oxygen, and lead
(e). PbSO4 + H2O = Pb+ H2SO4 + O
The hydrogen (H2) produced at the positive plate, and the oxygen (0) produced at the negative plate unite to form water
(e). PbSO4 + H2O = Pb+ H2SO4 + O
(d). PbSO4 + 2 H2O = PbO2 + H2SO4 + H2
(f). 2PbSO4 + 2 H2O = PbO2 + Pb + 2H2SO4
Charge action:
During charge, acid is driven out of the plates.
(f). 2PbSO4 + 2 H2O = PbO2 + Pb + 2H2SO4
If we continue to send a current through the cell
after it is fully charged, the water will continue
to be split up into hydrogen and oxygen. The
hydrogen and oxygen rise to the surface of the
electrolyte and escape from the cell. This is
known as "gassing," and is an indication that the
cell is fully charged.
WHAT TAKES PLACE DURING CHARGE
• voltage remains almost constant between the points M and N
• At N the voltage begins to rise, the concentrated acid formed
by the chemical actions in the plates is diffusing into the main
electrolyte.
• At the point marked 0, the voltage begins to rise very rapidly.
This is due to the fact that the amount of lead sulphate in the
plates is decreasing very rapidly.
• Bubbles of gas are now rising through the electrolyte.
• At P, the last portions of lead sulphate are removed, acid is no
longer being formed, and hydrogen and oxygen gas are
formed rapidly.
• the voltage becomes constant at R at a voltage of 2.5 to 2.7.
WHAT TAKES PLACE DURING DISCHARGE
At the end of a charge, and before opening the charging circuit,
the voltage of each cell is about 2.5 to 2.7 volts. As soon as the
charging circuit is opened, the cell voltage drops rapidly to about
2.1 volts, within three or four minutes.
The final value of the voltage after the charging circuit is open
ed is about 2.15-2.18 volts.
When a current is being drawn from the battery, the sudden
drop is due to the internal resistance of the cell, the formation
of more sulphate, and the abstracting of the acid from the elect
rolyte which fills the pores of the plate.
It is diluted rapidly at first, but a balanced condition is reached
between the density of the acid in the plates and in the main
body of the electrolyte
Theoretically, the discharge may be continued until the voltage
drops to zero, but practically, the discharge should be
stopped when the voltage of each cell has dropped to 1.7 (on
low discharge rates).
Care of the Battery on the Aircraft
Care
• A. Keep the Interior of the Battery Box
Clean and Dry.
• B. Put Nothing But the Battery in the
Battery Box.
• C. Keep the battery clean and dry.
• D. The battery must be held down firmly.
Care• E. The cables connected to the battery must have sufficient
slack so that they will not pull on the battery terminals, as
this will result in leaks, and possibly a broken cover.
• F. Inspect the Battery twice every month in Winter, and once
a week in Summer, to make sure that the Electrolyte covers
the plates.
• I. The specific gravity of the electrolyte should be measured
every two weeks and a permanent record of the readings
made for future reference.
Inspect height of electrolyte
Remove the vent caps and look down
through the vent tube. If a light is
necessary to determine the level of the
electrolyte, use an electric lamp. Never
bring an open flame, such as a match or
candle near the vent tubes of a battery.
Explosive gases are formed when a
battery "gasses," and the flame may
ignite them, with painful injury to the face
and eyes of the observer as a result.
Such an explosion may also ruin the
battery.
During the normal course of operation of the
battery, water from the electrolyte will
evaporate. The acid never evaporates. The
surface of the electrolyte should be not less
than one-half inch above the tops of the plate.
Insert one end of a short piece of a glass
tube, having an opening not less than one-
eighth inch diameter, through the filling
hole, and allow it to rest on the upper edge
of the plates. Then place your finger over
the upper end, and withdraw the tube. A
column of liquid will remain in the lower
end of the tube, as shown in the figure,
and the height of this column is the same
as the height of the electrolyte above the
top of the plates in the cell.
• Never add well water, spring water, water from a
stream, or ordinary faucet water.
• These contain impurities which will damage the
battery, if used. It is essential that distilled water be used for this purpose, and it must be handled carefully so as to keep impurities of any kind out of the
water. Never use a metal can for handling water or
electrolyte for a battery, but always use a glass or
porcelain vessel. The water should be stored in
glass bottles, and poured into a porcelain or glass
pitcher when it is to be used.
Figure 3-10. Correct height of Electrolyte in Exide Cell
A convenient method of adding the water to
the battery is to draw some up in a
hydrometer syringe and add the necessary
amount to the cell by inserting the rubber
tube which is at the lower end into the vent
hole and then squeezing the bulb until the
required amount has been put into the cell.
In the summer time it makes no difference when water
is added. In the winter time, if the air temperature is
below freezing (32°F), keep the battery charging for
about one hour after the battery begins to "gas."
Otherwise, the water, being lighter than the
electrolyte, will remain at the top and freeze. Be sure
to wipe off water from the battery top after filling. If
battery has been wet for sometime, wipe it with a rag
dampened with ammonia or baking soda solution to
neutralize the acid.
Never add acid to a battery while the battery is on
the aircraft. By "acid" is meant a mixture of
sulphuric acid and water. The concentrated acid, is
of course, never used. The level of the electrolyte
falls because of the evaporation of the water
which is mixed with the acid in the electrolyte.
The acid does not evaporate. It is therefore evident
that acid should not be added to a cell to replace
the water which has evaporated.
It is true that acid is lost, but this is not due to evaporation, but to
the loss of some of the electrolyte from the cell, the lost
electrolyte, of course, carrying some acid with it. Electrolyte is
lost
when a cell gasses; electrolyte may be spilled; a cracked jar will
allow electrolyte to leak out; if too much water is added, the
expansion of the electrolyte when the battery is charging may
cause it to run over and be lost, or the jolting of the aircraft may
cause some of it to be spilled; if a battery is allowed to become
badly sulphated, some of the sulphate is never reduced, or drops
to the bottom of the cell, and the acid lost in the formation of the
sulphate is not regained.
Care must be taken not to add too much water
to a cell, Figure 3-11. This will subsequently
cause the electrolyte to overflow and run
over the top of the battery, due to the
expansion of the electrolyte as the charging
current raises its temperature. The electrolyte
which overflows is, of course, lost, taking
with it acid which will later be replaced by
water as evaporation takes place. The
electrolyte will then be too weak. The
electrolyte which overflows will rot the
battery case, and also tend to cause
corrosion at the terminals.
If one cell requires a more frequent addition of
water than the others, it is probable that the jar
of that cell is cracked. Such a cell will also
show a low specific gravity, since electrolyte
leaks out and is replaced by water. A battery
which has a leaky jar will also have a case
which is rotted at the bottom and sides. A
battery with a leaky jar must, of course, be
removed from the aircraft for repairs.
The specific gravity of the electrolyte
should be measured every two weeks
and a permanent record of the readings
made for future reference.
The specific gravity of the electrolyte is the
ratio of its weight to the weight of an equal
volume of water. Acid is heavier than water, and hence the heavier the electrolyte, the
more acid it, contains, and the more nearly it is fully charged. In automobile batteries, a
specific gravity of 1.300-1.280 indicates a
fully charged battery. Generally, a gravity of
1.280 is taken to indicate a fully, charged cell, and in this book this will be done.
readings and status
• 1.300-1.280--Fully charged.
• 1.280-1.200--More than half charged.
• 1.200-1.150--Less than half charged.
• 1.150 and less--Completely discharged.
Figure 3-12 Hydrometer and hydrometer-syringe
• For determining the specific gravity,
a hydrometer is used. This consists
of a small sealed glass tube with an
air bulb and a quantity of shot at
one end, and a graduated scale on
the upper end. This scale is marked
from 1.100 to 1.300
Some hydrometers are not marked with figures
that indicate the specific gravity, but are
marked with the words "Charged," "Half
Charged," "Discharged," or "Full," "Half Full,"
"Empty," in place of the figures.
Specific gravity readings should never be taken
soon after distilled water has been added to the
battery. The water and electrolyte do not mix
immediately, and such readings will give
misleading results. The battery should be
charged several hours before the readings are
taken. It is a good plan to take a specific gravity
reading before adding any water, since accurate
results can also be obtained in this way.
• Having taken a reading, the bulb is squeezed so as
to return the electrolyte to the cell.
• Care should be taken not to spill the electrolyte from
the hydrometer syringe when testing the gravity.
Such moisture on top of the cells tends to cause a
short circuit between the terminals and to discharge
the battery.
• In making tests with the hydrometer, the electrolyte
should always be returned to the same cell from
which it was drawn.
• The specific gravity of all cells of a battery should
rise and fall together, as the cells are usually
connected in series so that the same current
passes through each cell both on charge and
discharge.
• If one cell of a battery shows a specific gravity
which is decidedly lower than that of the other cells
in series with it, and if this difference gradually
increases, the cell showing the lower gravity has
internal trouble.
If the entire battery shows a specific gravity below
1.200, it is not receiving enough charge to replace
the energy used in starting the engine and
supplying current to the lights, or else there is
trouble in the battery. Use starter and lights
sparingly until the specific gravity comes up to
1.280-1.300. If the specific gravity is less than
1.150 remove the battery from the aircraft and
charge it on the charging bench, as explained
later.
In the winter, it is especially important not to allow the
battery to become discharged, as there is danger of the
electrolyte freezing. A fully charged battery will not
freeze except at an extremely low temperature. The
water expands as it freezes, loosening the active
materials, and cracking the grids. As soon as a
charging current thaws the battery, the active material
is loosened, and drops to the bottom of the jars, with
the result that the whole battery may disintegrate. Jars
may also be cracked by the expansion of the -water
when a battery freezes.
Specific
GravityFreezing Pt.
1.000 32°F
1.050 26°F
1.100 18°F
1.150 5°F
1.200 -16°F
1.250 -58°F
1.280 -92°F
1.300 -96°F
Battery Troubleshooting
Trouble Cause Remedy
Discharged battery.
worn out. Replace battery.
Low electrical system voltage. Check voltage regulator voltage.
Standing too long.
Remove and recharge battery if
left in unused airplane three
weeks or more.
Equipment left on accidentally. Remove and recharge.
Impurities in electrolyte. Replace.
Short circuit (ground) in wiring. Check wiring.
Broken cell partitions. Replace.
Battery life is short.
Overcharge due to level of
electrolyte being below top of
plates.
Maintain electrolyte.
Sulfation due to disuse. Replace.
Impurities in electrolyte. Replace battery.
Low charging rate. Check voltage regulator voltage.
Cracked cell jars. Hold-down bracket loose. Replace battery and tighten.
Frozen battery. Replace.
Compound on top of
battery. melts. Charging rate too high.
Reduce charging rate. Check
voltage regulator voltage.
Electrolyte runs out of
vent plugs.
Too much water added to battery
and charging rate too high.
Drain and keep at proper level and
check voltage regulator voltage.
Excessive corrosion
inside container.
Spillage from overfilling. Use care in adding water.
Vent lines leaking or clogged. Repair or clean.
Charging rate too high. Adjust voltage regulator voltage.
Battery freezes.
Discharged battery Replace.
Water added and battery not
charged immediately.
Always recharge battery for 1/2
hour following addition of water in
freezing weather.
Leaking battery jar. Frozen. Replace.
polarity reversed. Connected backwards on airplane
or charger.
should be slowly discharged
completely and then charged
correctly and tested.
consumes excessive
water.
Charging rate too high (if in all
cells). Correct charging rate.
Cracked jar (one cell only). Replace battery.
VRLA battery
VRLA battery
• Valve-regulated lead-acid batteries (VRLA
battery) is a rechargeable battery which
does not require adding water.
• The batteries offer excellent high rate
performance characteristics and
increased life expectancy.
• Positive plates
• porous lead dioxide as the active material.
• Negative plates
• spongy lead as the active material.
• Electrolyte
• Diluted sulfuric acid is used as the medium for
conducting ions in the electrochemical reaction
in the battery.
• Separators• The advanced micro porous Absorbed Glass Mat (AGM)
separators retain electrolyte and prevent shorting between
positive and negative plates.
• Valve (One way valve)• The valve is comprised of a one-way valve. When gas is
generated in the battery under extreme overcharge
conditions due to erroneous charging, charger malfunctions
or other abnormalities, the vent valve opens to release
excessive pressure and maintain the gas pressure
Features
• Leak-resistant structure
• Long service life
• Easy maintenance
• No sulfuric acid mist or gases
• Exceptional deep discharge recovery
NICKEL-CADMIUM BATTERIES
Nickel-cadmium battery
• The nickel-cadmium battery uses nickel
hydroxide as the active material for the
positive plate, and cadmium hydroxide for
the negative plate.
• The electrolyte is an aqueous solution of
potassium hydroxide
Nickel-cadmium cells
• Unlike the lead acid battery, there is little
change in the electrolyte density during
charge and discharge.
• Nickel-cadmium cells have a nominal
voltage of 1.2 V
• The electrolyte level is checked and water
added only when a nickel-cadmium battery
is fully charged.
• Positive plate
• nickel hydroxide
• Negative plate
• Cadmium
• A solution of potassium hydroxide and
lithium hydroxide
ALWAYS:
Wear eye protection when handling
batteries.
If you get a splash of electrolyte in your
eyes, immediately flush them generously
with clean water and seek medical attention
as soon as possible.
NEVER
Never ever store or leave electrolyte in
ordinary bottles, jars, cups, etc… as
someone could drink it by mistake.
Recommendations
• For skin protection, wear rubber gloves,
long sleeves, and safety glasses (or a face
shield).
• For protection of clothing, wear rubber or
plastic aprons or other appropriate
protection.
Recommendations
• Make sure all transport caps are properly
installed while moving or transporting
modules or batteries.
• Always keep water readily available for
rinsing and washing.
• Keep the batteries upright to prevent
spillage.
Recommendations
• In the eventuality of spillage, electrolyte
must not be disposed of in public drainage
systems. Use assigned absorbent material
for electrolyte removal.
• The electrolyte will corrode some metals
(e.g. aluminum), nickel and steel excepted,
and may cause minor damage to concrete.
Servicing Nickel-Cadmium Batteries
The electrolytes used by nickel-cadmium and
lead-acid batteries are chemically opposite,
and either type of battery can be contaminated
by fumes from the other. For this reason, it is
extremely important that separate facilities be
used for servicing nickel-cadmium batteries
and lead-acid batteries.
• The alkaline electrolyte used in nickel-
cadmium batteries is corrosive. It can burn
your skin or cause severe injury if it gets
into your eyes. Be careful when handling
this liquid. If any electrolyte is spilled,
neutralize it with vinegar or boric acid, and
flush the area with clean water.
• Every nickel-cadmium battery should have a
service record that follows the battery to the
service facility each time it is removed for
service or testing. It is very important to
perform service in accordance with the
manufacturer’s instructions, and to record all
work on the battery service record.
It is normal for most nickel-cadmium batteries
to develop an accumulation of potassium
carbonate on top of the cells. This white
powder forms when electrolyte spewed from
the battery combines with carbon dioxide. The
amount of this deposit is increased by
charging a battery too fast, or by the
electrolyte level being too high.
Scrub all of the deposits off the top of the
cells with a nylon or other type of
nonmetallic bristle brush. Dry the battery
thoroughly with a soft flow of compressed
air.
Check the condition of all the cell connector
hardware and verify there is no trace of
corrosion. Dirty contacts or improperly
torque nuts can cause over-heating and
burned hardware. Heat or burn marks on
nuts and contacts indicates the hardware
was torque improperly.
nickel-cadmium troubleshooting chart.
OBSERVATION PROBABLE CAUSE CORRECTIVE ACION
High-trickle charge – when
charging at constant voltage
of 28.5 volts (+0.1) volts,
current does not drop below 1
amp after 30-minute charge.
Defective cells. While still charging, check
individual cells. Those
below .5 volts are defective
and should be replaced. Those
between .5 and 1.5 volts may
be defective or may be
imbalanced, those above 1.5
volts are alright.
High-trickle charge after
replacing defective cells, or
battery tails to meet amp-hour
capacity charge.
Cell imbalance. Discharge battery and short
out individual cells for 8
hours. Charge battery using
constant-current method.
Check capacity and if OK,
recharge using constant-
current method.
fails to deliver rated capacity. Cell imbalance or faulty cells. Repeat capacity check,
discharge and constant-current
charge a maximum of three
times. If capacity does not
develop, replace faulty cells.
No potential available. Complete battery failure. Check terminals and all
electrical connections. Check
or dry cell. Check for high-
trickle charge.
Excessive white crystal
deposits on cells. (there will
always be some potassium
carbonate present due to
normal gassing.)
Excessive spewage. subject to high charge current,
high temperature, or high
liquid level. Clean battery
constant-current charge and
check liquid level. Check
charger operation.
Distortion of cell case. Overcharge or high heat. Replace cell
Foreign materials in cell – black
or gray particles.
Impure water, high heat, high
concentration of KOH, or
improper water level.
Adjust specific gravity and
electrolyte level. Check battery
for cell imbalance or replace
defective cell.
Excessive corrosion of
hardware.
Defective or damaged plating. Replace parts.
Heat or blue marks on
hardware.
Loose connections causing
overheating of inter-cell
connector or hardware.
Clean hardware and properly
torque connectors.
Excessive water consumption.
Cell dry.
Cell imbalance. Proceed above for cell
imbalance.
END OF CHAPTER 3