Batteries

Question 1

What is the purpose of an aircraft battery?

Answer 1

In small aircraft - provides power to start the engine
In large aircraft - provides power to start auxiliary power unit (APU)

Also provides a source of emergency power in the event of failure of the electrical generating devices.

Question 2

What do batteries always and only produce?

Answer 2

DC

Question 3

An aircraft batter is rechargeable, what are the two types?

Answer 3

Lead acid 
Nickel cadmium (NiCd)

Electrolyte determines the type for both

Question 4

What type of batteries do light aircrafts have?

What type do large aircrafts have?

Answer 4

Light aircraft - lead acid batteries with a nominal voltage of 12 or 24 volts.

Large aircraft - NiCd batteries with a nominal voltage of 12 or 24 volts to suit the aircraft electrical system.

Question 5

What are the advantages of a NiCd battery?

Answer 5

Lighter than equivalent lead acid battery
Takes less time to charge
Maintains correct voltage for a much longer period during its discharge cycle

In comparison to latter, as a lead acid battery discharges, its voltage decreases meaning that any loads that it is supplying won’t receive the correct voltage.

Question 6

What does on load mean?

Answer 6

Batteries produce slightly lower voltage than their nominal value when they are powering consumers.

Question 7

What is negative and positive terminal?

Answer 7

Negative terminal - terminal with extra electrons
Positive terminal - one with fewer electrons

Battery symbol:

Long thin horizontal lines = positive terminal
Shorter thicker line = negative terminal

Question 8

What is a cathode?

What is an anode?

Answer 8

Cathode - Positive side of battery

Anode - negative side of battery

Question 9

Difference between primary and secondary cell?

Answer 9

Primary cell cannot be reused as one time use and not rechargeable.
Secondary cell is rechargeable.

Question 10

What are the individual cell voltage for a lead acid cell and a NiCd cell?

Answer 10

Lead acid cell = 2.2 volts

NiCd cell = 1.3 volts

Question 11

Difference between lead acid battery cells and NiCd batter cells

Answer 11

Lead acid:
Nominal voltage - 12v
6 cells (2.2v each) connected in series
Terminal voltage - 13.2v off load (not being used)

NiCd:
Nominal voltage - 12v
10 cells (1.3V each)
Terminal voltage - 13v

Question 12

How do you assess the state of charge of lead acid battery?

Answer 12

Voltage of battery must be measured whilst it is OFF LOAD (not being used) and then compared with the voltage when it is on load.

If large difference between the two then battery is not fully charged.

Question 13

Which type of battery and you complete charge checks on and why?

Answer 13

Lead acid batteries as it has a slow discharge time.

Question 14

What is specific gravity?

Answer 14

Weight of liquid

1.0 = matter

Question 15

What is the specific gravity of lead acid batteries when charged and discharged?

Answer 15

Charged - 1.27 SG

Discharged - 1.17 SG

Question 16

What must you use to check condition of a battery?

Answer 16

The aircraft’s voltmeter.

Voltage must be checked when loads are being applied.

Question 17

What is a connected with and why?

Answer 17

Connected in parallel with an electrical generator.

This provides higher voltage than the battery to keep the battery fully charged at all times.

Question 18

How much does the alternator maintain in a light aircraft compared to a large aircraft?

Answer 18

Light aircraft - 14v, 2 volts above battery’s nominal voltage of 12v
Larger aircraft - 28v, 4 volts above battery’s nominal voltage of 24v

Question 19

Why do NiCd batteries require a dedicated battery charger circuit?

Answer 19

NiCd battery prone to thermal runaway.

As internal temperature of a NiCd battery increases its internal resistance decreases, causing charging current to increase which further increases battery temperature.

Thus, a dedicated battery charger circuit controls the current into the battery and monitors battery temperature.

Question 20

What is thermal runaway?

Answer 20

Heat wastage

Can lead to dangerous overheating and battery failure.

Question 21

What is a NiCd battery constructed from?

Answer 21

Nickel hydroxide +
Cadmium hydroxide -
Potassium hydroxide (electrolyte paste)

Question 22

Describe the discharge of NiCd batteries

Answer 22

Rapid discharge

Question 23

What is the charged and discharged specific gravity of NiCad batteries?

Answer 23

Charged: 1.26 SG
Discharged: 1.26 SG

Question 24

What is battery capacity?

Answer 24

The battery’s ability to produce current during a specified time period.
Capacity measured in:
Amp hours (Ah) -the number of amps it can supply over a period of time.

Question 25

What two types of magnets generate magnetic fields?

Answer 25

Permanent magnets | Electromagnets

Question 26

What is a permanent magnet made of?

Answer 26

A material that can permanently maintain its magnetism. | Hard iron is the material to use make permanent magnets.

Question 27

What is hard iron?

Answer 27

The material used to make permanent magnets. Hard to magnetise but once magnetised it retains its magnetism.

Question 28

How do electromagnets generate magnetic fields?

Answer 28

When placed within an electric field. | This type of magnet made of soft iron.

Question 29

what is soft iron?

Answer 29

Used to describe ferromagnetic material used as the core of the magnet. Easy to magnetise with an electric field but loses its magnetism as Sonos as electric field removed.

Question 30

Where does a magnetic field exist?

Answer 30

Between the North and South poles. | Field not only surrounds the magnet but also exists inside the core of the magnet.

Question 31

What sort of lines does a magnetic field have?

Answer 31

Equal lines of force (flux) which are lines surrounding the magnet and running through it.

Question 32

How do the lines of force (flux) run?

Answer 32

Lines of force (flux) directional. Externally - lines of force come out of the North Pole and enter at the South Pole. Internally - they run from the South to the North Pole

Question 33

How can a magnet the demagnetised?

Answer 33

Heat it up | Hit it with a hammer

Question 34

How are magnetism and electricity linked?

Answer 34

A magnetic field can produce electric current. | An electric current can produce a magnetic field.

Question 35

How can you strengthen a magnetic field?

Answer 35

If caused by a current flow, it can be: Increased by increasing the current flow Or turning the wire into a coil The greater the number of turned of wire the stronger the magnetic field will be. The strength of the magnetic field can be increased by turning the wire around a ferromagnetic core. Iron bar also increase strength

Question 36

What two symbols indicate current flow of conductors?

Answer 36

``` X = indicates current is flowing into conductor . = indicates current flowing out of conductor ```

Question 37

What is soft iron used for?

Answer 37

Used in electrical components to enhance electromagnetism

Question 38

Examples of electromagnetic devices with soft core

Answer 38

Relay - a switch that is electromagnetically powered. Has a hinged arm and one set of contacts. Light duty device. Solenoid - similar to relay except ferromagnetic core allowed to move. Has two sets of contact. Heavy duty device.

Question 39

What is electromagnetic induction?

Answer 39

Process of generating an electromagnetic force (EMF) or voltage using a magnetic field.

Question 40

How is EMF induced?

Answer 40

As the coil of wire cuts through the lines of magnetic flux. When the movement ceases there is no induced voltage.

Question 41

what is inductance?

Answer 41

The ability of a coil to induce a voltage. Inductance increases with an increase of the number of turns of wire and increases if the wire is turned around a ferromagnetic core.

Question 42

What 3 factors does the magnitude of the induced voltage depend on?

Answer 42

The speed of movement of the coil (rate of change of flux) - the faster the speed the greater the voltage. The number of turns of wire in the coil - the greater the number of turns the greater the voltage. The strength of the magnetic field - stronger (denser) magnetic field has a greater number of lines of flux thus, greater voltage.