Airframe Electrical Systems
A CSD holds a AC frequency of
400-hertz
The total continuous electrical load permitted in a given system is limited to?
80 percent of the total rated generator output.
Solenoid
A coil of wire that produces a magnetic field when carrying an electric current. ex: electrically connects or removes the field rheostat from the circuit as the voltage varies.
Voltage Regulator
A device that maintains a constant voltage level for either AC or DC electrical energy.
Two different types of battery chargers?
Constant-Current and Constant Voltage
Rectifiers
Convert AC to DC
Reverse-current cutout
Disconnects the battery from the generator when the GENERATOR output is LOWER than the BATTERY output.
To determine the frequency of an AC generator by an alternator is by
F = P/2 * N/60 = PN/120
Amount of volts per cell, reflects upon the battery's state of charge.(True or False)
False
DC Generator Construction
Field Frame, Armature, Commutators, and Brushes
Compound-Wound
Field and armature connected to each other by both series and parallel circuits
DC generator is unable to keep an aircraft battery charged, and if the ammeter does not show the proper rate of charge...
First check the aircraft electrical system associated with the battery and generator. Physically check every connection in the generator and battery circuit. check the condition of all ground connections for the battery, battery contacts, and the generator control units. Very last if none of above is the problem Check the generator and the voltage regulator when the engine is cranked.
Three different types of Compound-Wound
Flat-Compound, Under-Compound, and over-compound
Faster the rotor, the higher the
Frequency
More poles on a rotor, the higher the
Freuqency
Only way to determine the actual condition of a ni-cad battery?
Fully charge it, and then discharge it at a specified rate to measure its ampere-hour capacity
Less Voltage is induced into the armature then....
Generator output decreases
Revolving-field alternator
Has a stationary armature winding(stator) and a rotating-field winding(rotor). Armature is connected directly to the load without sliding contacts int he load circuit.
A good diode produces a
High resistance reading when reverse biased
How do you check for specific gravity?
Hydrometer
How are batteries gasses neutralized when installed in an aircraft?
Inside the battery box through sump jars containing absorbent pads moistened with a solution of sodium bicarbonate and water.
IDG
Integrated Drive Generator high output generator that uses brushes and slip rings to carry DC exciter current to the rotating field.
What occurs when an ni-cad battery won't hold a charge?
Internal short circuits Check for leakage between the cells and steel case
If the reverse-current cutout would not disconnect the battery then..
It would discharge through the generator armature when the generator voltage falls below that of the battery. The battery attempts to drive the generator as a motor.
Constant-Speed Drive Unit
Maintain a uniform frequency between multiple generators connected to a common electrical bus
Solid State Voltage Regulator
Maintains a constant output voltage from the generator under varying load conditions
Generator Control Unit
Monitors and regulates the main generator's output by controlling the amount of current that flows into the exciter field.
When an CSD or IDG are disconnected in flight can you reconnect them in flight?
No
Armatures are also tested for shorts by....
Placing in growler holding a thin steel strip slightly above the armature. Slowly rotate the armature on the growler. If any shorts in the armature windings, the blade will vibrate vigorously.
Test an armature for an open circuit with a growler?
Probes attached to the test lamp test each armature coil by placing the probes on adjacent segments lamp should light with each set of commutator bars. Failure of the test lamp to illuminate indicates an open circuit in that coil.
Flashing the Field
Restoring residual magnetism to a generators field pole by applying battery voltage in the same direction as normal voltage in the field windings of a generator.
What is an Alternator made up of?
Rotor, Stator, rectifiers, brush assembly
Three types of DC Generators
Series-Wound, Shunt-Wound and Compound Wound
Pig tail
Short piece of electrical cable with connector plugging device at both ends.
Types of AC alternators
Single-Phase, Two-Phase, and Three-Phase
Single-phase alternator
Stator made up of several windings connected in series. Windings connected so AC Voltages induced into each winding are in phase.
Growler
Test unit for DC generators and motors and a variety of tests on the armature and field coils is performed using this equipment.
Armature Reaction
The bending and twisting (distortion) of the main magnetic field caused by the magnetic field of the current in the armature.
Brushes
The contact points connected to a current source and the commutator of a motor
Armature
The rotating part of an electrical generator.
Three-Phase Alternator
Three coils at 120 degrees to one another which produce EMF 120 degrees out of phase. Produces three phases of AC current so is more
Left-Hand Rule
Thumb = conductor, first finger = flux forward and second finger = Induced EMF
What is a growler connected to?
To 110 volts AC.
Brush Assembly(Alternator)
Two brush springs, and brush holders. Brushes in an alternator supply current to the field coils
Interpoles
counteract some of the effects of field distortion when the speed and load of the generator are changing constantly. Placed in-between the main poles.
Three-Unit Regulator components
current limiter, reverse current cutout, and a voltage regulator
In an alternator when output voltage rises above the desired value, the field current is _______
decreased
Commutators
devices used to convert direct current (DC) to alternating current (AC)
When lead acid batteries are charging, they give off ___________ gas
hydrogen and oxygen.
In an alternator when the output voltage ______ below the desired value, the field current is______
increased
Coil ends of the armature are brought out to
individual segments of the commutator.
Nic-cad batteries have a low
internal resistance, so voltage remains constant until it is almost totally discharged
Current Limiter
limits the generator's output current
Stator
load current induced into stationary stator coils by rotor. Stator has three separate coils that are 120 degrees apart. Coils making up the stator are wound in slots around the inside periphery of the stator frame.
A shorted diode typically causes a __________ ___________ when checked in the forward and reverse biased directions, while an open diode produces _____ ______ readings in both directions.
low resistance reading, high resistance readings
Always disconnect the ______ _____ first, when installing it, connect the ________ ______ last.
negative lead, negative lead
AC frequency produced by an AC generator is determined by
number of poles and the speed of the rotor.
Alternator Control Unit
protects the electrical system from over voltage conditions.
After the generator has run for a short period, the new brushes should be..
reinspected to ensure that no pieces of sand are embedded in the brush.
Difference in an alternator is that the magnetic poles ____ and induce voltage into a _____, or ______ winding.
rotate, fixed, stationary
Rheostat
set to increase the resistance in the field circuit. less current flows through the field coils and the strength of the magnetic field decreases.
AC current produced is rectified by a six __________ diodes instead of a ______ (Alternator).
solid-state, commutator
One way to reduce cell imbalance?
terminate a constant-voltage charge prior to the battery obtaining a full charge. Then, complete the charge at a constant current rate equivalent to approximately ten percent of the battery's ampere-hour capacity.
Capacity
the maximum amount that something can contain.
Five-hour discharge rating
the number of ampere-hours of capacity. Ex: a battery that supplies 5 amps for 5 hours has a capacity of 25 ampere-hours
What serves as the electrolyte of the Ni-Cad
thirty-percent-by-weight solution of potassium hydroxide and distilled water serves as the electrolyte.
Two-Phase Alternator
two or more single-phase windings spaced symmetrically around the stator, AC voltage induced in one is 90 degrees out of phase w/ the voltage induced in the other. Windings are electrically separate from each other.
Starter Generator Consist of?
two sets of windings and one armature winding. After done starting the engine, switches back to generator mode.
Transistorized Voltage Regulator
utilizes both vibrating points and transistors for voltage control. Instead of the field current flowing through the contacts, the transistor base current flows through them.
Armature coils in a drum type armature the coils are usually held in the slots by
wooden or fiber wedges.
How to verify if a lead-acid battery if the cell condition can be determined while under load
1) verify electrolyte is at the proper level 2) apply heavy load to the battery for about 3 seconds by cranking the engine w/ the magneto switch(s) off, or the mixture in the idle-cutoff position 3) Now, turn on the landing lights and taxi lights to draw about ten amps. While the load current is flowing, measure the voltage of each cell.
Specific Gravity of the liquid of Ni-Cad batteries?
1.24 and 1.30
Specific gravity of lead-acid cell
1.275 and 1.300 at 80 degrees
All individual cell produces an open circuit voltage between ____ and _____ volts of ni-cad
1.55 and 1.80 volts
A fully charged cell in good condition should have a voltage of _______ and all cells should be within _____ of each other. (Lead-acid)
1.95 volts, 0.05 volts
In an ni-cad battery if there is more than about _____ milliamps of leakage, battery should be _______ and throughly cleaned.
100, disassembled
Lead acid battery remains relatively constant at about
2.1 volts per cell
Fully charged, new battery, what is the ratio between Acid to Water
30:70
Thermal runaway
A rapid, uncontrolled increase in temperature causing additional increases in temperature, usually resulting in a hazardous situation
Rotor
A rotating electromagnet inside the stator.
Carbon-pile voltage regulator
A type of voltage regulator used with large aircraft generators. Field current is controlled by varying the resistance of a stack of thin carbon disks. This resistance is varied by controlling the pressure on the stack with an electromagnet whose force is proportional to the generator output voltage.
Which way do you add acid to the battery? Water then acid or acid then water?
Acid then water
Revolving Armature Type Alternator
An alternator that uses a rotating armature with slip rings to generate AC.
When is a lead-acid battery said to be discharged?
Below 1.150
How to correct Armature Reaction
Brushes are set so that the plane of the coils being shorted is perpendicular to the distorted magnetic field. Moving brushes forward in direction of rotation. (brushes to the neutral plane, or plane of commutation).
Field Frame
Completes the magnetic circuit between the poles, and acts as a mechanical support for the other parts
Third test for armature shorts is by..
Using a 110 volt test lamp to check for grounds One lead is touched to the armature shaft Second lead is touched to each commutator segment If a ground exists between any of the windings and the core of the armature, the test lamp illuminates
How to test for a generator's field coil for shorts
Using a test lamp One probe is placed at the field windings Other probe at the generator frame If light illuminates, a short exists
AC alternators are rated in
Volt-amps, kilo-volt amperes, or KVA
While charging lead-acid battery is charging where do you store it?
Well ventilated location, isolated from sparks and open flames
When are brushes normally replaced?
When-half worn
Shunt-Wound
Where the field winding in parallel with armature winding
How do you clean a lead-acid battery?
With a soft bristle brush and a solution of sodium bicarbonate and water.
Three sets of coils in a stater are typically brought together to form a?
Y connection
What are the two types of connections from each windings in a three-phase alternator called?
Y-connected or delta connected(end-to-end)
Load placed on a battery
active material begins to convert into lead sulfate. Increases battery's internal resistance, and causes the closed-circuit terminal voltage to drop
A battery's capacity decreases when it is discharged
at a higher rate
Pole Shoes
bolted to the inside of the frame and are usually laminated to reduce eddy current losses and concentrate the lines of force produced by the field coils.
Ni-cad low resistance allows high ______ rates without damage
charging
The proper maintenance of an alternator requires the unit the be kept ____ and all electrical connects _____ and in good repair.
clean, tight