chapter 3 aircraft storage battery. ways of "generating" electricity on the aircraft...

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