4-1) Batteries & Battery Maintenance

Question 1

What were the first electrical storage devices?

Answer 1

Large capacitors called laden jars

Question 2

How does a battery store energy and how is a battery constructed?

Answer 2

A battery stores energy in the form of electrical potential energy that is held in solution. A battery is constructed of a set of metal plates that can attract and repel electrons. The electrons are held in solution in a dielectric that surrounds the metal plates.

Question 3

What is a voltaic pile and who came up with it and when?

Answer 3

Alessandro Volta invented the first battery as a voltaic pile in 1800. He made his battery with a stack of alternating layers of zinc, blotting paper soaked in salt water and silver. The top and bottom layers of the pile must be different metals. If you attach a wire to the top and bottom of the pile, you can measure a voltage and a current from the pile.

Question 4

What feature divides batteries into two basic categories?

Answer 4

Their ability to recharge or not.

Question 5

What is a primary battery?

Answer 5

A primary battery cannot be recharged, due to the deterioration of the material in its construction from normal discharge. Most small batteries purchased from a store for small electronics are classified as primary cells.

Question 6

What is a secondary battery?

Answer 6

A secondary battery cell is designed to be recharged. Charging is accomplished by applying a voltage higher than that of the cell to the cell terminals. The higher voltage to the cells is reverse flow and charges the battery that causes a change in ions inside the battery. The electrons flow out of solution and back to the metal plates of the battery.

Question 7

What is a wet cell battery?

Answer 7

Liquids are used for electrolytes as opposed to modern dry cells.

Question 8

What is a Daniell cell and what could it be used for?

Answer 8

The Daniell cell is a wet cell battery invented in the 1800s consisting of copper and zinc plates and copper and zinc sulfates. It could be used for stationary applications.

Question 9

What are 3 other names for the Daniell cell battery?

Answer 9

1. Crowfoot cell–because of the typical shape of the zinc electrode
2. Gravity cell–because gravity keeps the two sulfates separated
3. Wet cell–because it uses liquids for the electrolytes as opposed to the modern dry cell

Question 10

What is a voltaic cell?

Answer 10

Plates of dissimilar metals are placed in a chemical solution called an electrolyte, opposite electric charges are established between the two plates. When a rod of carbon and a plate of zinc are placed in a solution of ammonium chloride, the result is an elementary voltaic cell. The carbon and zinc elements are called electrodes. The carbon is the positively charged anode, the zinc is the negatively charged cathode. The combination of the two surrounded by the electrolyte for a battery cell.

Question 11

What happens when two electrodes are connected by an external conductor?

Answer 11

Free electrons from the zinc plate (negative terminal) will flow to the carbon rod (positive terminal), and hydrogen ions move to the carbon rod, where each ion pics up one electron and because a neutral hydrogen atom.

Question 12

What is the process of polarization in a wet cell battery?

Answer 12

Hydrogen gas bubbles form on the carbon rod and insulate it from the electrolyte solution. This process is called polarization and will cause the current flow to stop until the hydrogen is removed.

Question 13

How do dry cell batteries mitigate polarization?

Answer 13

Dry cell batteries employ a compound called manganese dioxide (MnO₂) to prevent accumulation of hydrogen at the positive electrode in the cell. In a dry cell battery, the electrolyte is in the form of a paste.

Question 14

How is a primary dry cell constructed?

Answer 14

Dry cell batteries employ a compound called manganese dioxide (MnO₂) to prevent accumulation of hydrogen at the positive electrode in the cell. In a dry cell battery, the electrolyte is in the form of a paste. The surrounding case is made from zinc, which acts as a negative electrode. The space between the carbon rod and the zinc can be filled with manganese dioxide saturated with electrolyte to reduce the internal resistance of the cell. The top of the cell is sealed with a wax compound to prevent leaking and dry electrolyte.

Question 15

What is the typical voltage developed by a carbon zinc dry cell?

Answer 15

1.5 volts, but voltage of any cell depends on the materials used as the electrodes.

Question 16

What is the typical voltage developed by a lead-acid secondary cell, such as those employed in storage batteries?

Answer 16

2.1 volts.

Question 17

What determines if an alkaline cell is a rechargeable secondary or non-rechargeable primary?

Answer 17

The electrode materials

Question 18

What is the typical voltage produced by most common alkaline battery cells?

Answer 18

1.5 volts

Question 19

Where are mercury cells most often used?

Answer 19

Mercury cells are used for small button batteries found in miniature equipment such as watches and calculators.

Question 20

How are nickel-cadmium cells constructed?

Answer 20

They have been developed to a high degree of efficiency and dependability. The electrodes are welded together (sintered).

Anode is nickel or nickel carbonyl and the cathode is cadmium.

Question 21

What is the advantage of a Ni-Cad battery?

Answer 21

The cells can remain in a discharged condition indefinitely at normal temperatures without degradation.

Question 22

What would happen if a lead acid battery is left in a discharged condition for extended periods?

Answer 22

Sulfation of the plates occurs, and the cells lose much of their capacity.

Question 23

How does peak power of a Ni-Cad battery compare with a lead-acid battery?

Answer 23

A Ni-Cad battery has tremendous peak power and delivers far more power than a lead-acid battery of the same size and weight.

Question 24

How does peak power of a Ni-Cad battery compare with a lead-acid battery?

Answer 24

A Ni-Cad battery has tremendous peak power and delivers far more power than a lead-acid battery of the same size and weight.

Question 25

What is the typical internal resistance of most vented Ni-Cad batteries? How does its internal resistance effect battery performance?

Answer 25

Internal resistance is very low (less than 1mOhm per cell), which allows the cells to maintain a high discharge current and still maintain acceptable voltage levels. The output of a Ni-Cad battery is relatively constant, even in harsh operating conditions such as very cold weather.

Question 26

What is the typical internal resistance of most vented Ni-Cad batteries? How does its internal resistance effect battery performance?

Answer 26

Internal resistance is very low (less than 1mOhm per cell), which allows the cells to maintain a high discharge current and still maintain acceptable voltage levels. The output of a Ni-Cad battery is relatively constant, even in harsh operating conditions such as very cold weather.

Question 27

What is thermal runaway?

Answer 27

Thermal runaway is a condition where the battery chemicals overheat to such a degree that the battery can be destroyed or even explode.

Question 28

How is thermal runaway prevented?

Answer 28

To prevent or stop thermal runaway, the charging system must be isolated from the battery. Because of the overheating issue, all aircraft Ni-Cad battery installations include a temperature sensor.

Question 29

What is open circuit voltage (OCV) in a battery?

Answer 29

Voltage measured when there is no load applied to the battery is called open circuit voltage.

Question 30

What is closed circuit voltage (CCV) in a battery?

Answer 30

Voltage measured while a load is applied to the battery is called closed circuit voltage. The CCV of a battery is usually a function of the load applied and the state of charge of the battery.

Question 31

How does state of charge effect a battery’s OCV?

Answer 31

The OCV of a battery is typically effected very little by its state of charge until the battery reaches near complete discharge.

Question 32

What is the measurement of voltage of a battery when it is not connected to the system?

Answer 32

Open Circuit Voltage (OCV)

Question 33

What is the measurement of voltage of a battery when it is connected to the system?

Answer 33

Closed Circuit Voltage (CCV)

Question 34

What is a battery’s internal resistance (IR)? What is another name for internal resistance?

Answer 34

The resistance that is present inside a battery while connected to a load. Also referred to as a battery’s impedance.

Question 35

How do you calculate a battery’s internal resistance?

Answer 35

A battery’s IR is equal to the difference between the OCV and CCV divided by the applied load.

IR = OCV - CCV / I Load

Example:

IR = 14VDC - 12VDC / 100A

IR = 2VDC / 100A

IR = 0.02 ohms

Question 36

What are the two types of lead acid batteries currently being used in aviation?

Answer 36

Vented cell and sealed (recombinant gas) battery.

Question 37

What is the difference between vented cell and sealed batteries?

Answer 37

Sealed-cell lead-avid batteries are more powerful and require less maintenance than old vented style batteries. There is no need to add water. For this reason, sealed, no maintenance lead acid batteries are being used to replace the more expensive nickel cadmium batteries in some turbine powered aircraft.

Lead-acid batteries are also cheaper to construct and have lower maintenance costs.

Question 38

What is a drawback of a lead-acid battery compared to a Ni-Cad battery?

Answer 38

Lead-acid batteries do not hold peak voltage through the charging cycle like Ni-Cad batteries can. This makes lead-acid batteries more difficult to certify in large air carrier aircraft that need to comply with a 30 minutes of emergency power requirement.

Question 39

What is the OCV and CCV of a typical lead-acid battery cell?

Answer 39

2.1V and 2.0V respectively

Question 40

What about the individual cells determines the output of a battery?

Answer 40

A battery is an arrangement of single cells. How these cells are arranged determine the output of the battery.

Question 41

What is the effect on battery output by arranging its individual cells in parallel?

Answer 41

Should you place the cells in parallel, the maximum voltage you could achieve is the same as the voltage across 1 cell. Total current will be the cumulative of all individual cells.

Question 42

What is the effect on battery output by arranging its individual cells in series?

Answer 42

By connecting the cells in series, voltage will be cumulative of the individual cell voltage, but output current will only be as strong as whatever is contained in a single cell. Six 2VDC batteries placed in series will generate 12VDC.

Question 43

What is the typical voltage on a commercial or business jet system?

Answer 43

24V

Question 44

How much battery storage is usually required on commercial jets for emergency supply?

Answer 44

30 minutes of emergency power in the case of complete engine driven electrical system failure.

Question 45

What care must a technician take when installing cells during maintenance?

Answer 45

The position of the cells and jumpers are critical. When a technician short-circuits a battery from incorrect maintenance, this will either burn out the wiring or discharge (damage) the batteries beyond repair.

Question 46

What are the positive plates, negative plates and electrolyte in a lead-acid battery made of?

Answer 46

The lead-acid battery consists of positive plates filled with lead peroxide (PbO₂); negative plates filled with pure spongy lead (Pb); and an electrolyte consisting of 30% sulfuric acid and 70% water by volume (H₂SO₄).

Question 47

How happens chemically when a lead-acid battery discharges and then is recharged?

Answer 47

During the discharge process, the electrolyte releases H₂ (+) ions and SO₄ ions (-) leaving mostly water (H₂0). The SO₄ ions combine with the lead plates to form lead sulfate (PbSO₄).

During the charging process, SO₄ ions are driven back into solution in the electrolyte and combined with H₂ ions in the water, thus forming sulfuric acid (H₂SO₄).

The plates then return to the original composition of lead peroxide and spongy lead. When this process is complete, the battery is said to be fully charged.

Question 48

What happens when a lead-acid battery is fully charged? What must one do?

Answer 48

There is a liberal release of hydrogen and oxygen gases. These gases must be vented so the battery internal pressure does not damage the case.

Question 49

What happens in electrolyte spills out of the battery?

Answer 49

Electrolyte will spill out of the battery if it’s left on its side. This electrolyte is extremely corrosive and does major structural damage if not cleaned up completely.

Question 50

Why must a technician wear safety glasses when doing lead-acid battery maintenance?

Answer 50

Even the slightest amount of acid will do permanent damage to eye. If you are exposed, flush with clear water and seek medical help. Do not put baking soda in your eyes because this can damage eyes as much as the acid.

Question 51

When maintaining a lead-acid battery, in what order should you install and remove the negative battery lead?

Answer 51

Remove the negative battery lead first and install it last.

Making the assumption that current flows from a negative electrical potential to a positive one, removing the lead first will break contact with the battery.

Question 52

What caution must be taken with tools and aircraft structure when handling a battery?

Answer 52

Caution must be taken not to short the battery terminals. Always treat the battery as a hazardous component.

Question 53

What caution must be taken with the batteries if they are fully discharged?

Answer 53

Never jumpstart an aircraft from another power source if the aircraft batteries are discharged fully. Trying to start the aircraft with a dead or nearly discharged battery is dangerous because of the massive amount of amperes that would flow into the battery.

Question 54

What is the safest way to charge a dead battery?

Answer 54

Charge the battery at a slow rate on a bench. Charging a dead battery at high amperes can cause the electrolyte to boil and begin outgassing, which can cause an explosion.

Question 55

How do you determine the state of charge for lead-acid aircraft batteries?

Answer 55

Use a hydrometer test.

Question 56

What is specific gravity?

Answer 56

Specific gravity of a substance is defined as the ratio of the weight of a given volume of that substance to the weight of an equal volume of pure water at +4°C.

Question 57

What is the temperature range for generally accurate hydrometer readings?

Answer 57

70°F - 90F

Outside this range, temperatures must be corrected from a conversion chart.

Question 58

What must you do with discharged batteries before you test them?

Answer 58

They must be recharged. If the CCV falls below 9.6V, the indication “bad” appears on the test unit. If this CCV is maintained above 9.6V during the entire load test, the unit will indicate “good.”

Question 59

What are the two general types of battery charging equipment?

Answer 59

Constant current chargers and constant voltage chargers

Question 60

How does a constant current charger work?

Answer 60

A constant current battery charger supplies a consistent current to the battery for the entire charge cycle.

Charging equipment monitors current flow and varies the applied voltage to charge the battery. The constant current charger will increase its voltage supplied to the battery during the charge to maintain the current flow set by the operator.