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Questions and Answers
What occurs during the discharging of a lead-acid battery?
What occurs during the discharging of a lead-acid battery?
What is the approximate specific gravity of a fully charged lead-acid battery electrolyte?
What is the approximate specific gravity of a fully charged lead-acid battery electrolyte?
What happens to the crystals of sulphate on the battery plates during charging?
What happens to the crystals of sulphate on the battery plates during charging?
What is a potential consequence of leaving a lead-acid battery discharged for an extended period?
What is a potential consequence of leaving a lead-acid battery discharged for an extended period?
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What needs to be done to batteries in service to maintain their proper function?
What needs to be done to batteries in service to maintain their proper function?
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What is one effect of internal resistance in a lead-acid battery cell?
What is one effect of internal resistance in a lead-acid battery cell?
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What happens during the final charging phase of a lead-acid battery?
What happens during the final charging phase of a lead-acid battery?
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What voltage level can severely damage a lead-acid battery when discharged?
What voltage level can severely damage a lead-acid battery when discharged?
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What is the primary function of a solar cell?
What is the primary function of a solar cell?
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What is the role of photons when they hit a solar cell?
What is the role of photons when they hit a solar cell?
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What percentage of sunlight could a solar cell ideally absorb?
What percentage of sunlight could a solar cell ideally absorb?
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Why is an antireflective coating applied to solar cells?
Why is an antireflective coating applied to solar cells?
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How are solar modules generally constructed?
How are solar modules generally constructed?
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What does it mean when it is said that solar cells produce electricity from vaporized silicon?
What does it mean when it is said that solar cells produce electricity from vaporized silicon?
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What commonly happens to electrons in the semiconductor of a solar cell when photons are absorbed?
What commonly happens to electrons in the semiconductor of a solar cell when photons are absorbed?
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In the context of solar cells, what does the term 'mobile electron-hole pairs' refer to?
In the context of solar cells, what does the term 'mobile electron-hole pairs' refer to?
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What is the primary process occurring in a cell during electrochemical action?
What is the primary process occurring in a cell during electrochemical action?
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What factors affect the internal resistance of a cell?
What factors affect the internal resistance of a cell?
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Which type of cell cannot be recharged satisfactorily?
Which type of cell cannot be recharged satisfactorily?
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What happens to the negative electrode in a primary cell during chemical action?
What happens to the negative electrode in a primary cell during chemical action?
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Which statement is true regarding the size of electrodes in a cell?
Which statement is true regarding the size of electrodes in a cell?
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Why is it generally cheaper to replace a dry cell than to recharge it?
Why is it generally cheaper to replace a dry cell than to recharge it?
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What determines the current delivered by a cell?
What determines the current delivered by a cell?
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Which of the following statements about secondary cells is correct?
Which of the following statements about secondary cells is correct?
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What is the purpose of the vent plugs in a lead-acid battery?
What is the purpose of the vent plugs in a lead-acid battery?
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Which of the following accurately describes secondary cells?
Which of the following accurately describes secondary cells?
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What materials are commonly used for separators in lead-acid batteries?
What materials are commonly used for separators in lead-acid batteries?
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Which electrolyte is used in alkaline cells?
Which electrolyte is used in alkaline cells?
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How do alkaline cells compare to carbon-zinc cells in terms of performance?
How do alkaline cells compare to carbon-zinc cells in terms of performance?
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What is the typical structure of cells in a lead-acid battery?
What is the typical structure of cells in a lead-acid battery?
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Which of the following is NOT a type of secondary cell?
Which of the following is NOT a type of secondary cell?
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What charging method is used for secondary cells?
What charging method is used for secondary cells?
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What is the primary purpose of using thermocouples in aircraft?
What is the primary purpose of using thermocouples in aircraft?
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Which thermocouple type is typically used in gas turbine engines?
Which thermocouple type is typically used in gas turbine engines?
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How is the EMF generated in a thermocouple?
How is the EMF generated in a thermocouple?
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What is the maximum temperature that a Copper-Constantan thermocouple can measure?
What is the maximum temperature that a Copper-Constantan thermocouple can measure?
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What factor greatly affects the performance of a thermocouple?
What factor greatly affects the performance of a thermocouple?
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At what frequency range does visible light occur?
At what frequency range does visible light occur?
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What is the speed of light in a vacuum?
What is the speed of light in a vacuum?
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Which light type has wavelengths above 750,000 gigahertz?
Which light type has wavelengths above 750,000 gigahertz?
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Study Notes
Thermocouple
- Thermocouple is composed of two dissimilar metal wires connected at two junctions to form a loop.
- When there is a temperature difference between the two junctions a small Electromotive Force (EMF) is generated.
- The EMF is proportional to the temperature difference, typically 4 to 5 millivolts per 100ºC.
- Common combinations used for thermocouples in aircraft include:
- Chromel-Alumel (up to 1200ºC) - common in gas turbine engines.
- Iron-Constantan (up to 850ºC) - common in piston engines.
- Copper-Constantan (up to 400ºC) - common in piston engines.
Thermocouple Construction
- Two dissimilar metal wires are joined at one end.
- Constructed of various combinations of materials.
- "Thermoelectric difference" between the two materials is an important factor.
- A significant difference between the two materials results in better performance.
Types of Thermocouples
- T type: Copper-Constantan (up to 400ºC), typical on piston engines.
- J type: Iron-Constantan (up to 850ºC), typical on piston engines.
- K type: Chromel-Alumel (up to 1200ºC), typical on turbine engines.
Light
- Light is electromagnetic radiation that travels similarly to radio waves.
- Light is measured in wavelengths.
- Travels at 186,000 miles/second or 300,000,000 meters/second in a vacuum.
- Frequency range of light is 300 to 300,000,000 gigahertz (giga = 1,000,000,000).
- Below 400,000 gigahertz - infrared light.
- 400,000 to 750,000 gigahertz - visible to the human eye.
- Above 750,000 gigahertz - ultraviolet light.
- Light waves at the upper end of the frequency range have more energy than at the lower end.
Photo Cell
- Also known as a solar cell or photovoltaic cell.
- Converts sunlight directly into a usable amount of direct current (DC) electricity.
- Assemblies of cells are used to make solar panels.
- Photons in sunlight hit the solar panel and are absorbed by semiconducting materials.
- Electrons are knocked loose from their atoms, allowing them to flow through the material to produce electricity.
- Photons absorbed in the semiconductor create mobile electron-hole pairs.
- An antireflective coating is applied to the top of the cell to reduce reflection losses to less than 5 percent.
- Solar modules are made by connecting several cells (usually 36) to achieve useful levels of voltage and current.
- Cells could absorb around 25 percent, but more likely is 15 percent or less.
Electrochemical Action
- A cell is a device where chemical energy is converted to electrical energy.
- This process is called electrochemical action.
- When a load is connected, electrons flow from negative through the load to positive.
- Voltage across electrodes depends upon electrode materials and the electrolyte.
- Current delivered depends upon the resistance of the entire circuit, including the cell itself.
Internal Resistance
- Internal resistance of a cell depends on the size of the electrodes, the distance between the electrodes in the electrolyte, and the resistance of the electrolyte.
- The larger the electrodes and the closer they are in the electrolyte (without touching), the lower the internal resistance of the cell and the more current the cell is capable of supplying to the load.
Primary Cell
- A primary cell cannot be recharged satisfactorily.
- Part of the electrode deteriorates as the cell produces current and cannot be restored.
- In a galvanic-type cell, the zinc electrode and liquid electrolyte are usually replaced.
Alkaline Cells
- Similar to Carbon-Zinc cells.
- Electrolyte is an alkali solution (Potassium Hydroxide).
- Provide sustained high current delivery.
- More efficient than Carbon-Zinc cells.
- Much longer shelf life.
- Perform better during drain and in cold weather.
- Do not produce any gaseous products.
- May be rechargeable.
- Types: Mercury Oxide, Silver Oxide, Zinc air.
Secondary Cell
- Electrodes and electrolyte are altered when the cell delivers current.
- May be restored to original condition by charging.
- Charging is done by passing electric current through the cell in the opposite direction to that of the discharge.
- Sometimes known as wet cells.
- Automobile battery is a common example of a secondary cell.
Lead-Acid Battery Construction
- Battery container houses separate cells (6 cells for 12 volts, 12 cells for 24 volts).
- Most containers are made of hard rubber, plastic, or another insulating material.
- They should be resistant to electrolyte and mechanical shock, and withstand extreme temperatures.
- Vent plugs allow gases to escape.
- Separators are used to hold plates apart while allowing free movement of electrolyte.
- Separator materials include wood, perforated glass, rubber, or plastic.
- Space at the bottom of the cell collects sediment as the cell is used.
- There is always one more negative plate than positive plates. All cells have an uneven number of plates, i.e., a 9-plate cell has 5 negative and 4 positive plates.
Lead-Acid Battery Discharging
- During discharging sulfuric acid combines with active material in both plates.
- This forms "Lead Sulphate" on the plates and water (H2O) in the electrolyte.
- There is an increase in battery internal resistance and decrease in electrolyte specific gravity (SG - 1.150 when completely discharged).
- If left discharged for a substantial period, sulphation occurs, and the cells lose capacity.
Lead-Acid Battery Charging
- During charging, the chemical action is reversed.
- Sulphate on the positive and negative plates disassociates from lead.
- Sulphate returns to the electrolyte to form Sulphuric Acid (H2SO4).
- The positive plate changes back to lead peroxide and the negative back to spongy lead.
- The specific gravity of the electrolyte rises to the charged value (1.270 approx.).
Final Charging Phase
- Little or no sulphate is left on the plates.
- Charging current decomposes water into its Hydrogen and Oxygen components.
- Gases are released via vent plugs (Hydrogen gas is explosive).
- Batteries in service need to be periodically topped up with water (distilled water).
Lead-Acid Battery Operation Review
- Discharging a lead-acid battery below 10.5 volts will severely damage it.
Internal Resistance
- Every cell has internal resistance which opposes the current flow through the cell and limits battery output.
- Internal resistance is inversely proportional to the area of the electrodes exposed to electrochemical action.
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Description
This quiz covers the fundamentals of thermocouples, including their construction, operation, and common types used in aircraft. You will learn about the specific combinations of metals and their performance at various temperature ranges. Test your knowledge on the practical applications of thermocouples in different engine types.
