Electrical Systems Flashcards
Describe the systems which typically require DC power in an aircraft. (10)
Lights (external and internal) •Radios •Transponders •Starter motor •AHRS / MFD / Turn Indicator •Fuel quantity indicators •Oil T and P gauge (possible) •Trim (possible) •Flaps (possible) •The alternator to initially power the electromagnet!
Explain the function(s) of the following in a typical electrical system:
(a) the battery;
(b) a ground power source;
(d) bus bars;
(e) over voltage protection.
(A) storage container for electricity, provides initial starting crank power and an emergency power source if alternator or generator fails
(B) supplies entire electrical requirement if battery power is insufficient to start the engine.
(D) metallic strip or bar for power distribution. The main conductor and distributor for electrical systems.
(E) prevents overvoltage or too much current going out which prevents damage.
Given appropriate data, determine the duration of battery operation following a generator failure.
•If an electrical system draws 30 Amps, and a battery is rated at 15 AH, what is the maximum time the battery will be able to power the system?
Battery capacity measured in Ampere Hours (Amp Hrs, AH)
30 minutes
What are the two types of batteries?
Lead acid or Nickel Cadmium
Describe the relative advantages and disadvantages of:
(a) a generator;
(b) an alternator.
Alternator -
Advantages
•Lighter than a generator (for the same amount of power produced)
Disadvantages
• Need power to get the electromagnet excited
Generator
Advantages
•Does not need power to get the electromagnet excited (as it does not have an electromagnet)
Disadvantages
• Heavier and larger than an alternator for the same amount of power produced
•Produce less current per RPM and so are less suited for low RPM situations
Explain the functions and interpretation of:
(a) left-zero ammeters;
(b) centre-zero ammeters.
Left zero:
Indicates the amount of current flow (load) from the alternator/generator
•The load will change as items are switched on and off
•Sometimes called Load Meter
•It does NOT measure what the battery is doing
Centre Zero:
Indicates current flow into or out of the battery
•Battery discharge ‘ – ’
•Battery charging ‘ + ’
Explain the functions and correct operation of a:
(a) single battery master switch;
(b) split battery/alternator switch.
(A) •Some aircraft, generally older ones, have only one switch. If so, that switch will control all electrical circuits in the aircraft
(B) Controls all aircraft electrical system
•ON – electrical services and charging of battery
•OFF – after engine shutdown
•Split switch – alternator and battery/master
Explain the operation of:
(a) fuses;
(b) circuit breakers;
(c) overload switches.
Fuses and circuit breakers
•Protect the equipment from electrical overload
•If an overload is experienced the fuse will blow or circuit breaker – trip
•Breaks the circuit so that no current flows
•Circuit breakers are more common now
Overload switches
•Turn themselves off if an overload occurs
•Only reset O/L switches and CB’s once!
Explain operational principles for the handling of the electrical DC system including avoiding overheating electrical services if operated during pre-flight
Operate only briefly those electrical services that require airflow past them for cooling
Explain operational principles for the handling of the electrical DC system including not starting or stopping the engine with unnecessary electrical equipment switched on
Don’t start with unnecessary electrical equipment switched on as large voltage fluctuations produced when starter is engaged may severely damage sensitive electronic circuits.
Switch on ancillary equipment after the engine is started and after you have checked alternator is charging battery.
Turn off electrics before shutting down equipment
Explain operational principles for the handling of the electrical DC system including avoiding prolonged use of starter motor
Starter motors put large drain on aircraft battery so avoid prolonged use of the starter motor.
Release starter button or starter key from START when engine is running.
Explain operational principles for the handling of the electrical DC system, including checking satisfactory operation of the alternator/generator after start and periodically during flight.
After start - check working by looking for a relatively high charge being shown on the ammeter due to it charging the battery. When fully charged ammeter will read either zero ( centre zero) or a slight positive charge (left zero)
During flight - monitor the ammeter and voltmeter. Large continuous deflection in one direction indicates malfunction.
Explain operational principles for the handling of the electrical DC system, including: ensuring the battery master is switched off before vacating aircraft after flight
Leaving on will discharge the battery overnight
Explain operational principles for the handling of the electrical DC system, including: use of a ground power unit
Only use if trained
Explain the identification of:
(a) an excessive charge rate;
(b) alternator/generator failure;
(c) a total electric failure.
(A) insufficient current, a centre-zero ammeter will indicate a constant negative reading and a left-zero ammeter will indicate a zero or abnormal to low charge rate. Too much current, both ammeters will indicate a high positive charge rate
(B) cycle alternator switch, if it doesn’t work switch it off and reduce the electrical load
(C) total electrical failure, and theres too much current, battery could overheat and create a hazard
