Electrical Fundamentals and Battery Technology

Lead-Acid Battery Basics

• Temperature correction range for electrolyte specific gravity (SG) measurement: $70^{\circ}\mathrm{F} \le T \le 90^{\circ}\mathrm{F}$.
• SG measurement instrument: Hydrometer.
• Battery compartment corrosion protection: Paint with an asphaltic (tar-base) paint or with a polyurethane enamel.
• Spill neutralization for electrolyte: A solution of bicarbonate of soda (baking soda) and water.
• Proper electrolyte level in a serviced lead-acid battery: Only up to the level of the indicator in the cell.
• Why closed-circuit voltage is lower than open-circuit voltage: Voltage is dropped across the internal resistance of the battery.
• Open-circuit voltage of a lead-acid cell: $V_{OC} = 2.1\text{ V}.$
• Gases released during charging: Hydrogen and oxygen.
• Shop precautions when servicing lead-acid and nickel-cadmium batteries: Acid and nickel-cadmium batteries should be kept separate; tools used on one type should not be used on the other.

Lead-Acid Battery Capacity, Electrolyte, and Cells

• Capacity rating meaning: The number of hours a battery can supply a given current flow.
• Capacity units: Ampere-hours, $\text{Ah}.$
• Lead-acid electrolyte composition: A mixture of sulfuric acid and water.
• Specific gravity (SG) trend with discharge: SG decreases as the battery becomes discharged.
• SG of a fully charged lead-acid battery: Between $1.275 \le SG \le 1.300.$
• Number of cells in a 24-volt lead-acid battery: $12$ cells (a 24-volt battery typically has 12 cells; a 12-volt battery typically has 6 cells).

Nickel-Cadmium (NiCd) Battery Safety and Spillage

• How to prevent thermal runaway: Carefully monitor the temperature of the middle cells and control charging current to prevent excessive current into the battery.
• Fully charging NiCd by a specific process: Completely discharge the battery and then apply a constant-current charge to $140\%$ of its ampere-hour capacity.
• NiCd electrolyte spill neutralizer: A solution of boric acid and water.
• NiCd electrolyte and SG behavior: The electrolyte SG does not enter into the chemical changes during charging/discharging; SG does not change appreciably.
• NiCd electrolyte level: Lowest when the battery is fully discharged.
• NiCd cell imbalance consequence: Low internal resistance allows current to flow between unbalanced cells and generate heat.
• Thermal runaway definition (NiCd context): Large current flow causes middle cells to overheat; heat further lowers resistance, allowing more current, leading to battery destruction.

Inductors, Impedance, and Magnetic Effects

• Example of an inductor used in a magneto: The coil.
• In an AC circuit, current behavior with respect to voltage: The current lags the voltage.
• Polarity of an electromagnet: Determine north pole by the left-hand rule – hold the electromagnet in the left hand with fingers curling in the direction of electron flow (negative to positive); the thumb points to the north pole.
• Impedance definition: The total opposition to the flow of alternating current; the vector sum of resistance, capacitive reactance, and inductive reactance.
• Impedance units: Ohms ($\Omega$).

Capacitors and Capacitance

• What constitutes a capacitor: Two conductors separated by an insulator.
• Purpose of a capacitor: Stores electrical energy in electrostatic fields.
• In AC circuits, does a capacitor cause current to lead or lag voltage? The current leads the voltage.
• Basic unit of capacitance: Farad (F).
• Why electrolytic capacitors are not used in AC circuits: They are polarized and will conduct current for one polarity but block current for the opposite polarity.

DC Circuits: Components, Types, and Ohm's Law

• Three essential elements of any electric circuit: A source of electrical energy, a load to use the energy, and conductors to join the source and the load.
• Three types of DC circuit arrangements by components placement: Series, parallel, and series-parallel.
• Ohm's Law (the foundational relation for DC circuits):
  • Basic relation: $E = I R$ where $E$ is voltage, $I$ is current, and $R$ is resistance.
• Basic Ohm's Law equations:
  • If voltage and resistance are known: $I = \dfrac{E}{R}.$
  • If voltage and current are known: $R = \dfrac{E}{I}.$
• Effect of increasing voltage with fixed resistance: The current increases.
• Effect of doubling conductor length (fixed material, area, and cross-section, and same material properties): The current decreases (approximately halved for the same voltage), since resistance increases with length.
• Parallel resistors to a 12-volt battery: Voltage across each resistor in parallel is $12\text{ V}.$
• Series resistors current: If three resistors are in series and the total current is $I_{tot} = 3\text{ A}$, then the current through each resistor is $3\text{ A}$ (same current flows through all components in series).
• Series resistance of equal resistors: For three 12-Ω resistors in series: $R_{tot} = 12 + 12 + 12 = 36\,\Omega.$
• Parallel resistance of equal resistors: For three 12-Ω resistors in parallel: $\dfrac{1}{R<em>{tot}} = \dfrac{1}{12} + \dfrac{1}{12} + \dfrac{1}{12} = \dfrac{3}{12} = \dfrac{1}{4} \Rightarrow R</em>{tot} = 4\,\Omega.$
• Measuring resistance in a component: Do not energize the circuit when using an ohmmeter; power must be removed before measurement.
• Continuity in a circuit: The circuit is continuous (complete) for current to flow from one terminal of the power source to the other.
• Instrument for measuring continuity: Ohmmeter.
• Instrument for measuring resistance: Ohmmeter.
• Voltage measurement instrument: Voltmeter; voltage is measured with the voltmeter in parallel with the source.
• Current measurement instrument: Ammeter; current is measured with the ammeter in series with the component.
• When measuring current, power must be off? Yes – measurements of resistance/current should be done with no power in the circuit.

Electrical Measurements: Voltage, Current, Power, and Power Factors

• Electrical power in a DC circuit: $P = VI = E I$.
• Basic units of power: The watt (W).
• Power units: Kilowatt (kW) = $10^3\,\text{W}$; Megawatt (MW) = $10^6\,\text{W}$.
• Relationship between mechanical and electrical power: 1 horsepower (hp) = 746 watts (W).
• True power in an AC circuit: The product of the circuit voltage and the current that is in phase with the voltage: $P_{true} = V I \cos\phi$ where $\phi$ is the phase angle between voltage and current.
• Apparent power in AC circuits: $S = V I$ with units of volt-amperes (VA).
• Reactive power in AC circuits: The power consumed by the inductive and capacitive reactances; also called wattless power; units: VAR (volt-amps reactive) or kilovolt-amps reactive (kVAR).
  • Formula form often used: $Q = V I \sin\phi$.
• Power factor (PF) in AC circuits: The ratio of true power to apparent power: $\text{PF} = \frac{P_{true}}{S} = \cos\phi$; equivalently, the ratio of resistance to impedance in a given circuit.

Inductance, Capacitance, and Impedance: Concepts and Formulas

• Inductance:
  • Definition: The ability to store electrical energy in electromagnetic fields.
  • Basic unit: Henry (H).
• Capacitance:
  • Definition: The ability to store electrical energy in electric fields (electrostatic).
  • Basic unit: Farad (F).
• Impedance:
  • Total opposition to AC flow; combination of resistance and reactances (XL and XC) in AC circuits.
  • In general, impedance magnitude: $|Z| = \sqrt{R^2 + (X<em>L - X</em>C)^2}.$
• Relationship of reactive components to power (recap):
  • Inductive reactance causes current to lag voltage; capacitive reactance causes current to lead voltage.

Miscellaneous Electrical System Details and Observations

• Sources of electrical energy (conceptual): Magnetism, chemical energy, light, heat, and pressure.
• Basic energy/power relationship (DC): The basic unit of power is the watt; in DC circuits, power is the product of voltage and current: $P = V I.$
• Common electrical terms consolidation:
  • Voltage: Electrical pressure; unit: volt (V).
  • Current: Flow of electrons; unit: ampere (A).
  • Resistance: Opposition to current; unit: ohm ((\Omega)).

Additional Notes on Title Blocks and Documentation (Garbled Content in Transcript)

• The transcript contains garbled lines about the information in the title block of aircraft drawings. Typical information found in title blocks includes drawing title, part number, drawing number, scale, revision level, date, and author. The exact garbled content cannot be reliably interpreted from the provided text, so use standard aerospace drawing conventions as a reference when studying title blocks.

Quick Reference Formulas and Facts (Summary)

• Lead-acid cell open-circuit voltage: $V_{OC} = 2.1\text{ V}.$
• Lead-acid electrolyte SG range for full charge: $1.275 \le SG \le 1.300.$
• Lead-acid SG measurement temperature correction range: $70^{\circ}\mathrm{F} \le T \le 90^{\circ}\mathrm{F}$.
• Electrolyte spill neutralization: $\text{NaHCO}<em>{3} + \text{H}</em>{2}\text{O}$ solution.
• Battery capacity unit: $\text{Ah}$ (ampere-hours).
• Battery energy sources concept: Lead-acid, NiCd, etc., with modeling in terms of voltage, current, temperature, and chemical changes.
• Inductor: Unit $H$; capacitor: Unit $F$; resistor: unit $\Omega$.
• Ohm's Law fundamentals: $E = I R$; $I = \dfrac{E}{R}$; $R = \dfrac{E}{I}$.
• DC power: $P = VI = E I.$ (units: W)
• AC power components:
  • True power: $P_{true} = V I \cos\phi$ (W)
  • Apparent power: $S = V I$ (VA)
  • Reactive power: $Q = V I \sin\phi$ (VAR)
  • Power factor: $\text{PF} = \dfrac{P_{true}}{S} = \cos\phi$.
• Trigonometric and phasor concepts summarized: Resistive, inductive, and capacitive effects determine phase relationships and reactive power in AC circuits.
• Safety and measurement reminders:
  • When measuring resistance or current, remove power from the circuit first.
  • Use an ammeter in series to measure current; use a voltmeter in parallel to measure voltage.
  • Use an ohmmeter to check continuity and resistance.