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Learn about lead-acid batteries, voltage ratings, ampere-hour capacity, generators, alternators, circuit control devices, and voltage regulation in aircraft electrical systems.
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Batteries • A device composed of one or more cells in which chemical energy is converted into electrical energy. • The most commonly used storage battery for aircraft is the lead-acid battery.
Batteries • Lead-acid Batteries • Used for Starting engines and supplying power in the event of generator failure. • Stabilize and smooth out the generator output during extreme load changes. • 12 volt or 24 volt batteries are available.
Batteries • Battery Ratings • Voltage • Voltage of any battery is always a function of its state of charge and current load placed on the battery. • The number of cells in a battery determines the voltage it will produce.
Batteries • Battery Ratings • Ampere-hour Capacity • The area of the plates, the amount of active material in the plates, and the amount of electrolyte determine the ampere-hour capacity of the battery. • The capacity is a measure of the battery’s ability to produce a current flow for a specified time.
Batteries • Ampere-hour • One ampere-hour of capacity is the amount of electricity that is put into or taken from a battery when a current of one ampere flows for one hour. • Any combination of flow and time that moves the same amount of electricity is also one ampere-hour.
Batteries • Rated capacity • Indicates the battery’s ability to perform when it is new. What determines the battery’s actual capacity?
Batteries • Actual capacity depends on: • Battery temperature • Battery state of charge • Battery condition
DC Generator • Disadvantages • All of the AC load current is produced in the rotating armature of a generator. • The AC must be changed into DC by the commutator and brush assembly. • The brushes and commutator typically require regular maintenance.
DC Alternators • Generate AC in their windings. • Before the AC leaves the housing it is converted (rectified) into direct current. • The rectifier of an alternator is made up of six silicon diodes.
DC Alternators • Advantages • The load current is generated in the stator or stationary winding and does not have to flow through brushes.
DC Alternators • The coils in the stator are connected as three windings, joined together to form a Y. Three phases of alternating current are generated.
Voltage Regulator • Alternator output is controlled (regulated) with a solid-state voltage regulator. • Senses the alternator voltage output and controls the field current to keep this voltage within the desired range. • Circuit Breakers are current sensitive devices, not voltage sensitive, so they provide no protection against high voltages.
Circuit Control Devices • Control Devices • Switches • Toggle • Rocker • Wafer • Relay/Solenoids
Relay Solenoid
Circuit Control Devices • Protective Devices • Fuses • Circuit breakers • Thermal breakers • Magnetic breakers
Circuit Control Devices • Circuit Breakers • Will automatically open the circuit if the current becomes excessive. • May be reset by moving the operating control. • If a fault such as a short circuit exist the breaker will trip again, and should be left open. • Trip-free type.
Circuit Control Devices • Resistors • Inserted into circuits to drop voltage by converting some of the electrical energy into heat. • Fixed • Variable
Circuit Control Devices • Inductors • Induced current back flow as the current induced magnetic field collapses when DC current is shut off, causing switch contact arcing. • Create magnetic fields for relays.
Circuit Control Devices • Capacitor is a device which will store an electrical charge (electrons). • Quick use: strobe flash • Can also be used to limit the amount of electrons flowing in the circuit (an opening switch that is arcing).
Circuit Control Devices • Transformer • Permits voltage of AC current to be increased or decreased. • Rectifier • Converts AC into DC. • Inverter • Converts DC into AC.
