Aircra& Electrical Systems Chapter 9 Six Pack with HSI Horizontal Situa>on Indicator -­‐ HSI Horizontal Situa>on Indicator -­‐ HSI Aspen Avionics EFD1000 Aspen Avionics EFD1000 Aspen Avionics EFD1000 Aspen Avionics EFD1000 Aspen Avionics EFD1000 Aspen Avionics EFD1000 Aspen Avionics EFD1000 Aspen Avionics EFD1000 Aspen Avionics EFD1000 Aspen Avionics EFD1000 Instrument Pricing •  Bendix/King KCS55A HSI ! 
Starts at $22,188 •  Aspen Avionics EFD1000 ! 
Starts at $6,180 •  Includes backup baQery •  2011 Avia>on Consumer declares the HSI dead ! 
It costs more to repair an HSI than to replace it with a EFIS Electrical Systems •  Engine igni>on and controls ! 
• 
• 
• 
• 
• 
• 
• 
• 
BaQery powered propulsion systems Communica>ons Naviga>on & Autopilots Lights Flight controls Landing gear Environmental controls Entertainment system NASA is studying structural control Part 23 Requirements •  Must be able to furnish the required power at the proper voltage to each load circuit essen>al for safe opera>on •  Must be free from hazards in itself, in its method of opera>on, and in its effects on other parts of the aircra& •  No failure or malfunc>on of any electrical power source may impair the ability of the remaining source to supply load circuits essen>al to safe opera>on Part 23 Requirements •  Each system must be designed so that essen>al load circuits can be supplied in the event of reasonably probable faults or open circuits •  There must be at least one generator/alternator if the electrical system supplies power to load circuits essen>al for safe opera>on •  There must be a means of giving immediate warning to the flight crew of a failure of the generator/alternator Part 23 Requirements •  There must be a master switch installed in the electrical system that allows the electrical power source to be disconnected from the main bus ! 
The point of disconnec>on must be adjacent to the source controlled by the switch •  Copper ! 
Wire Selec>on BeQer conductor •  Aluminum Less expensive !  Lighter weight !  Corrosion issues !  Easy to nick when removing insula>on !  #6 gage or larger !  Should not be used in areas of severe vibra>on ! 
•  Specialty wires (e.g. coax or twisted pair) ! 
Follow the manufacturer’s recommended procedures Wire Selec>on •  Selec>ng insula>on type ! 
Copy what is on the aircra& •  Check for updates ! 
Follow the manufacturer’s recommended procedures •  The general rule of thumb for replacing aluminum electrical cable with copper is that copper of two wire gages smaller (larger number) may be used to replace aluminum e.g. 8 gage aluminum can be replaced with 10 gage copper !  Check load charts to be sure ! 
Wire Selec>on •  Wire size selec>on factors Allowable power loss !  Permissible voltage drop !  Current carrying capability !  Con>nuous or intermiQent load ! 
Wire Types Wire Current Carrying Capacity The American Wire Gauge (AWG)
system is used to indicate the size,
cross-sectional area, of electrical
wire
Allowable Voltage Drop Electrical Wire Size Chart Sample Problems •  Round up to the larger size •  28V, 20 A con>nuous for 30’, in a bundle ! 
#10 •  14V, 200 A for a starter (intermiQent) for 15’, single wire ! 
#1 •  28V, 50 A con>nuous for 60’, in a bundle ! 
#4 •  What is the maximum length of single #16 wire carrying 28V and 25 A intermiQent ! 
8’ Connectors •  Use only high quality connector Lasts longer !  Reduces troubleshoo>ng >me and cost !  Mil spec (AN or MS) are a good start ! 
•  Use crimp style connectors when possible ! 
Soldered connec>ons can “bird cage” •  Female side should be the power side •  Male side should be the ground or no power side •  Use the correct crimper and follow the manufactures recommended procedures Connectors •  Use moisture-­‐proof connectors when it may be exposed to moisture ! 
Any liquid Terminal Strips A barrier-­‐type terminal strip. Terminal Strips •  Terminal strip – used to manage wire connec>ons •  O&en use for centralized power and/or ground ! 
Bus bars •  All terminal studs are anchored against rota>on •  AC43.13-­‐1B Par 11-­‐174(c) ! 
No more than four terminal lugs or three terminal lugs and a bus bar should be connected to any one stud. Total number of terminal lugs per stud includes a common bus bar joining adjacent studs. Four terminal lugs plus a common bus bar thus are not permiQed on one stud. Terminal Strips •  All stud nuts should be >ghtened ! 
Even nuts with no connec>ons •  Connec>ons should be firmly held together with two nuts or suitable locking provisions •  Spacers or washers should not be used between the tongues of terminal lugs •  Tightening terminal connec>ons should not deform the terminal lugs or the studs Terminal Strips •  Terminal lugs should be so posi>oned that bending of the terminal lug is not required to remove the fastening screw or nut •  Terminal lugs should be so posi>oned that movement of the terminal lugs will tend to >ghten the connec>on. Wire Terminal Lugs Figure 7-­‐69. Method of installing crimped-­‐on terminals. Wire Terminal Lugs •  The tensile strength of the wire-­‐to-­‐terminal joint should be at least equivalent to the tensile strength of the wire itself •  Wire should extend past the barrel and be visible a&er crimping •  The terminal must crimp both the bare wire and the insula>on •  Use ring type terminals to prevent wire disconnect Wire Terminal Lugs •  Aircra& grade color coding: Red -­‐ #22 through #18 wire !  Blue -­‐ #16 through #14 wire !  Yellow -­‐ #12 through #10 wire ! 
Wire Terminal Lugs Wire Terminal Lugs X
X
Wire Splices •  Splicing is permiQed on wiring as long as it does not affect the reliability and the electromechanical characteris>cs of the wiring •  No more than one splice in any wire segment between any two connec>ons or other disconnect points ! 
Except: •  AQaching to the spare pigtail lead of a poQed connector •  Splicing mul>ple wires to a single wire •  Adjus>ng wire size to fit connector contact crimp barrel size •  Making an approved repair Wire Splices •  When several wires in a bundle are to be spliced, the wires should be cut so that the splices are staggered along the bundle •  Use crimp type splice ! 
Don’t use solder splice •  Splices should not be used within 12 inches of a termina>on device ! 
Except: •  AQaching to the spare pigtail lead of a poQed connector •  Splicing mul>ple wires to a single wire •  Adjus>ng wire size to fit connector contact crimp barrel size Stagger Wire Splices Wire/Cable Labeling •  Wires and cables should be labeled or marked for future maintenance •  Many aircra& have individual wires manufactured with iden>fica>on markings to match their wiring diagrams •  Wires markings (AC43-­‐13-­‐1B par 11-­‐208): ! 
At each end and every 15” •  Under 3”, no label •  3” to 7”, label in center ! 
Indirect (aQached labels) •  At each end and then every 6’ (feet) •  Video Cable Lacing •  Used secure and organize bundles of wires and cable ! 
Can secure a bundle with in a bundle •  Don’t use zip >es Sharp edges !  Chafes insula>on !  Gets briQle when old ! 
•  Use flat lacing: MIL-­‐T-­‐43435B ! 
Waxed coa>ng makes it easier to lace •  See AC 43-­‐13-­‐1B par 11-­‐158 Wire Harnesses Video An aircra& can have miles of wire The wiring is organized into a wiring harness A wire harness is made up of individual wires and wire bundles •  New wire harnesses are created using a wiring board or jig •  Electrical upgrades may come with their own harness • 
• 
• 
• 
Wire Harnesses Wire Harnesses Wire Harnesses Wire Harnesses •  Wire connec>ons may be protected in a junc>on box Non-­‐vapor-­‐>ght boxes must have a drain hole !  Unused holes must be plugged up !  Fire proof junc>on boxes are constructed of stainless steel (CRES) !  Oil canning boxes can cause electrical shorts ! 
Wire Harnesses •  Conduit may be used to route wire Protec>ve piping -­‐ rigid or flexible !  Protects wire from physical or mechanical damage ! 
•  Moving parts Supports wire !  Ends of conduit should be flared or have end coverings to protect wire !  Use bonded clamps, electrically conduc>ve, to secure conduit ! 
•  Conduit Wire Harnesses Should be placed so it is not used as a handhold or step !  Use installa>on powder (soapstone) to help with wire installa>on ! 
Wire Bundles •  Used to organize wiring •  Wires should be parallel in a bundle •  Should be placed so crew or cargo will not damage •  Should be routed away from where water will collect •  Should be routed over baQery •  Redundant systems should take separate routes •  Should be routed above fluid lines ! 
6” above hazards fluids Wire Bundles Wire Bundles •  Conduit should be routed as direct as possible •  FAA recommends minimizing the number of wires per bundle to reduce failure risk •  Use shielding for: ! 
Cri>cal connec>ons •  Cartridge actuated fire ex>nguishers, rescue hoist shear, and emergency jepson devices ! 
EMI (Electromagne>c Interference) sensi>ve circuits Wire Bundles •  Bend radius should be at least 10 >mes the outside bundle diameter ! 
Individual coax bend radius is 6 >mes the outside diameter •  Wiring at terminal lugs or connectors should have sufficient slack to allow two re-­‐
termina>ons without replacement of wires. Wire Mechanical Issues Wire Mechanical Issues •  Support wire so there is less than 1/2” deflec>on between support points •  Connectors should have strain relief ! 
Hold wire secure •  Use MS-­‐21919 clamps Cushioned clamps !  Insulated for wire bundles !  Bonded (connected to ground) used for conduit and fluid lines !  Close opening with safety wire to help with installa>on ! 
Zip Tie Standoff Wire Mechanical Issues •  MS-­‐21919 clamps Interval not to exceed 24” !  Snug fit without pinching wires ! 
• 
• 
• 
• 
Use grommets Use edge grommet Seal wire coming through firewall or landing well Wire sleeving helps protect and organize wires Clamps Clamps Adel Clamps
Adel Clamp Pliers Clamps Clamps Edge Grommet Wire Sleeving Circuit Protec>on Circuit Protec>on – Part 23 •  Protec>ve devices, such as fuses or circuit breakers, must be installed in all electrical circuits other than: Main circuits of starter motors used during star>ng only !  Circuits in which no hazard is presented by their omission ! 
•  A protec>ve device for a circuit essen>al to flight safety may not be used to protect any other circuit Circuit Protec>on – Part 23 •  Each reseQable circuit protec>ve device (“trip free” device in which the tripping mechanism cannot be overridden by the opera>ng control) must be designed so that: A manual opera>on is required to restore service a&er tripping !  If an overload or circuit fault exists, the device will open the circuit regardless of the posi>on of the opera>ng control ! 
Circuit Protec>on – Part 23 •  If the ability to reset a circuit breaker or replace a fuse is essen>al to safety in flight, that circuit breaker or fuse must be so located and iden>fied that it can be readily reset or replaced in flight •  For fuses iden>fied as replaceable in flight: There must be one spare of each ra>ng or 50 percent spare fuses of each ra>ng, whichever is greater !  The spare fuse(s) must be readily accessible to any required pilot ! 
Circuit Protec>on – AC 43 •  A circuit breaker must be rated so that it will open before: The current ra>ng of the wire aQached to it is exceeded !  The cumula>ve ra>ng of all loads connected to it are exceeded !  Whichever is lowest ! 
Circuit Protec>on – AC 43 Rated in Current
Circuit Protec>on – AC 43 •  A circuit breaker must always open before any component downstream can overheat and generate smoke or fire •  Wires must be sized to carry con>nuous current in excess of the circuit protec>ve device ra>ng ! 
Circuit breakers are designed as circuit protec>on for the wire, not for protec>on of black boxes or components •  Circuit protec>on should be as close to the power bus/source as possible Circuit Protec>on – AC 43 •  Use of a circuit breaker as a switch is not recommended ! 
Use of a circuit breaker as a switch will decrease the life of the circuit breaker •  Automa>c reset circuit breakers, that automa>cally reset themselves periodically, are not recommended •  Circuit breakers should be periodically cycled with no load to enhance contact performance by cleaning contaminants from the contact surfaces Circuit Protec>on Circuit Protec>on •  Protec>on based on current not voltage •  Circuit breaker: Automa>cally opens a circuit any >me excessive current flows through it !  Pilot can reset !  Mechanic can disable with zip >e ! 
•  Fuse: ! 
One use device •  Internal wire or metal strip melts away ! 
Slow and fast blow types •  Slow blow are used for devices that have a large startup current spike like an electric motor Circuit Protec>on •  Current Limiter: ! 
Very large slow blow fuse •  Use for very large current applica>ons Switches •  Switches should be derated from their nominal current ra>ng for the following types of circuits: Circuits containing incandescent lamps !  Induc>ve circuits have magne>c energy stored in solenoid or relay coils !  Direct-­‐current motors ! 
Switches Switches •  Dera>ng a switch will obtain reasonable switch efficiency and service life •  Any abnormal side to side movement of the switch should be an alert to imminent failure •  “On-­‐off” two-­‐posi>on switches should be mounted so that the “on” posi>on is reached by an upward or forward movement of the toggle •  Inadvertent opera>on of switches can be prevented by moun>ng suitable guards over the switches Grounding •  Inadequate bonding or grounding can lead to unreliable opera>on of systems, e.g., EMI, electrosta>c discharge damage to sensi>ve electronics, personnel shock hazard, or damage from lightning strike •  Ground types: AC returns !  DC returns !  All others ! 
Grounding •  For distributed power systems, the power return point for an alterna>ve power source should be separated •  Power return or fault current ground connec>ons within flammable vapor areas must be avoided ! 
Use a separate return lead Bonding Bonding Bonding •  The process of electrically connec>ng all isolated components to the aircra& structure •  Provides a path for return current from the components •  Provides a low-­‐impedance path to ground to minimize radio interference from sta>c electrical charges •  Provides a path to ground to dissipate sta>c charge from fire hazards like fuel systems •  Provides lightening strike protec>on Bonding •  All conduc>ng objects on the exterior of the airframe must be electrically connected to the airframe through mechanical joints, conduc>ve hinges, or bond straps capable of conduc>ng sta>c charges and lightning strikes •  All isolated conduc>ng parts inside and outside the aircra&, having an area greater than 3 in2 and a linear dimension over 3 inches must be bonded to the aircra& structure Bonding •  The metallic conduit should be bonded to the aircra& structure at each termina>ng and break point •  Bonding connec>ons should be secure and free from corrosion ! 
Stainless steel components use copper jumpers •  Bonding jumpers should be made as short as prac>cable •  Resistance of each connec>on does not exceed 0.003 ohm ! 
Measured with a milliohmmeter (AN/USM-­‐21A) Bonding •  Bond aQachment hardware selec>on considera>ons: Mechanical strength !  Ease of installa>on !  Amount of current to be carried ! 
•  BaQery Electrical System Stores electrical energy !  Provides DC electrical energy !  Starts engine(s) !  Filters power !  Provides needed power during short high load situa>ons !  Must be recharged ! 
•  A baQery stores only about 10 to 30 minutes worth of energy •  Recharging comes from engine driven alternator/
generator or auxiliary power unit (APU) BaQery and Master Switch Solenoid
A reverse-­‐biased diode installed across the coil of the baQery contactor allows the induced current that is produced when the master switch contacts open to be dissipated in the coil rather than arcing across the switch contacts. •  Examples: ! 
Electrical Load Radios and Instruments •  Radios take much more power when transmipng Lights !  Pitot tube heat !  Deicing hea>ng elements !  Flap and trim motors !  Entertainment systems !  Charging baQery ! 
Electrical Load •  Electrical power load is constantly changing and greater than the baQery can provide ! 
Requires an engine driven power source that can regulate/vary the amount of power provided •  Power sources Engine driven generators or alternators !  Auxiliary Power Unit (APU) !  Ground Power Unit (GPU) ! 
APU B-­‐17 APU Ground Power Unit (GPU) •  Source of electric energy external to the aircra& BaQery cart !  Engine driven generator ! 
•  Uses: Start aircra& !  Run power systems while aircra& is on the ground ! 
GPU Circuit A typical aircra& ground-­‐power circuit. Single Engine Power System A typical light-­‐aircra& DC alternator system. Twin Engine Power System Used to balance
parallel power by
keeping voltage
the same
Light twin-­‐engine aircra& electrical power system using individual electronic voltage regulators and overvoltage protectors. The alternator paralleling circuit is built into the voltage regulators. AC Generator DC Generators DC Generators •  DC generators have slip rings that are split to create DC voltage ! 
The split slip ring is called the commutator •  Generators are rated (sized) by the amount of current they provide at a given voltage e.g. 60 A at 12 volts !  Ra>ng is stamped on the generator case ! 
•  More coils reduce the voltage ripple and provide a “cleaner” power source DC Generators DC Generator Commutator DC Generator Commutator DC Generators Field Frame Field Pole Shoes
•  Field frame DC Generators Holds field windings/coil !  The magne>c material holding the coil is called the field pole shoes ! 
•  Made of laminated iron ! 
Reduces the eddy current effects •  Has a residual magne>c field ! 
! 
If the field coils are not energized, the residual magne>c field creates a “residual voltage” when the generator is turned Enables a generator to work without a baQery •  Residual magne>c field can be restored by flashing the field coil •  Field coils DC Generators Used to generate the magne>c field that generates the electricity !  The higher the current through the field coils the stronger the magne>c field ! 
•  The higher the output of the generator •  Varying the field coil current varies the output of the generator ! 
Should be a low resistance •  High resistance indicates a break in the coil DC Generator Armature Fan for cooling
DC Generators Types •  Defined by how the field coils are arranged •  Series Wound with armature coils ! 
Never used in aircra& •  Parallel (Shunt) Wound with armature coils •  Compound Wound Has both series and parallel wound field coils !  Best type !  Interpoles are used to counteract field distor>on ! 
•  Overcomes the effect of armature reac>on •  Reduces arcing at the brushes DC Generators Mechanical Regulators Simple light-­‐aircra& generator system. DC Generators Mechanical Regulators •  Also called vibrator-­‐type voltage regulator •  Controls the output voltage by controlling how much current goes to the field coil Changes the resistance in series with the field coil to control the current !  Higher resistance -­‐> lower field current -­‐> lower power/voltage output !  Lower resistance -­‐> higher field current -­‐> higher power/voltage output ! 
•  Uses three relays to control voltage, current limits and reverse current DC Generators Mechanical Regulators An A-­‐circuit, three-­‐unit generator control such as is used on light aircra&. DC Generators Mechanical Regulators DC Generators Mechanical Regulators DC Generators Mechanical Regulators •  Relays: ! 
Voltage Regulator •  Opens (high resistance) and closes (lower resistances) •  Constantly pulsing ! 
Generates a lot of EMI noise •  The longer closed the more current flows through the field coils ! 
! 
! 
Higher power output Higher current and/or voltage Current Limiter •  Increases the resistance to the field coil to limit current DC Generators Mechanical Regulators •  Relays: ! 
Reverse Current •  Disconnects baQery from the generator if the baQery voltage is higher than the generator ! 
Prevents draining of baQery •  If it fails, current flows through the generator armature opposite the normal direc>on and through the shunt field in the normal direc>on DC Generator Brushes DC Generator Brushes DC Generators Maintenance •  Check belt and moun>ng •  Check connec>ons •  Clean all oil and dust ! 
Track down source of oil •  Check brushes ! 
At least 1/2 their original length •  Usually has a wear mark ! 
Pig tail is secure •  Conducts current and prevents arcing to brush holders DC Generators Maintenance •  Check brushes ! 
Check spring strength •  Weak spring will cause brushes to bounce and create arcing ! 
Shape end of new brushes •  Check gap between commutator bars Gap should be at least as deep as the width of the mica (insulator) !  Clean gap ! 
DC Generators Maintenance •  Growler Test Checks for shorted coils in generators or motors !  Tester creates a magne>c field in each coil ! 
•  If the coil is shorted, the output voltage will be low ! 
! 
Can be measure with a volt meter or light Video •  Test insula>on with a Megohmmeter (Megger) Measures very high resistance ranges with high voltage !  Video ! 
DC Generators Dual •  Dual generator systems have an equalizing circuit that insures the two generators are pupng out the same voltage ! 
Raises the low generator and lowers the high generator DC Generators Dual Twin-­‐engine aircra& generator system using vibrator-­‐type voltage regulators and a paralleling relay. DC Generators -­‐ FAA Ques>on •  If any one generator in a 24-­‐volt dc system shows low voltage, the most likely cause is A.  an out-­‐of-­‐adjustment voltage regulator. B.  shorted or grounded wiring. C.  a defec>ve reverse current cutout relay. •  A DC Alternator Stator or Armature Winding
Field Winding
Field Winding
DC Alternator Stator or Armature Winding
DC Alternator The internal circuit of a typical light-­‐aircra& DC alternator. •  Components: ! 
DC Alternator Stator (Armature) windings (coil) •  The power comes from the stator winding •  Loca>on on the case and doesn’t rotate ! 
Field windings (coil) •  Rotates •  Smooth, gapless slip rings •  No permanent magnet ! 
Diodes •  Converts AC to DC ! 
Regulator •  Controls current to field windings •  Advantages: DC Alternator Lighter – no permanent magnets !  Slip ring used for field coils ! 
•  Lower current requirements •  Smooth •  Brushes last longer •  No EMI ! 
AC to DC conversion done by diodes •  Less EMI •  No reverse current relay •  Advantages: ! 
DC Alternator Solid state regulator •  Less EMI •  Wider adjustment range ! 
Power at lower RPMs •  Last longer than mechanical regulators •  Disadvantages: ! 
Needs baQery power to provide startup current for field coil DC Alternator •  Stator ! 
Usually three phase •  Six poles ! 
! 
Two per phase The frequency of the wave form is determined by the RPM of the alternator/engine Typical Charging System Power Bus Bar Alt Fld
Alt Fld
Breaker
Main
Switch
Black
Main Solenoid Shunt Resister Orange
+
Alt
Switch
-
LO/OV
Light
Alt Out
Breaker
Amp Meter Red
Over Voltage Sensor Alt Out
BaQery B
I
S
Voltage Regulator/ ACU A
F
F
ALT
DC Alternator •  Solid state regulator ! 
Components: •  Regulator •  Overvoltage protec>on •  Packaged separately, combined or built into alternator ! 
Regulator •  Regulates field winding current •  Circuit is very similar to solid state voltage regulator ! 
! 
! 
Zener diode used to reference alternator output voltage Transistors control field winding current Overvoltage protec>on •  Prevents alternator from producing too much voltage • 
• 
• 
• 
Alternator Troubleshoo>ng Steps Setup Connec>ons Electrical Components Finish Up Setup •  Avionic must be turned off ! 
• 
• 
• 
• 
• 
Protects them from damage Master switch – On – when checking voltage Master switch – Off – when checking resistance Select mul>-­‐meter range before measuring Secure item before running engine Check circuit breakers ! 
If tripped, find out why • 
• 
• 
• 
• 
Connec>ons Check all mechanical connec>ons are >ght Check grounding straps Cleanup all corrosion Check for damaged insula>on Recommend customer replace old aluminum baQery cable BeQer cold starts !  Save money through longer component life ! 
•  Check alternator belt •  Insure alternator bearings work smoothly Typical Charging System Power Bus Bar Alt Fld
Alt Fld
Breaker
Main
Switch
Black
Main Solenoid Shunt Resister Orange
+
Alt
Switch
-
LO/OV
Light
Alt Out
Breaker
Amp Meter Red
Over Voltage Sensor Alt Out
BaQery B
I
S
Voltage Regulator/ ACU A
F
F
ALT
Electrical Components •  Voltage Tes>ng Setup (Voltage On) Master switch (Bat & Alt) -­‐ On !  Alternator field switch – On !  Alternator field and Main alternator breaker – On !  To generate a load, turn landing lights on ! 
•  Check Amp Meter with load on If needle deflects, it is OK !  If no deflec>on plus voltage on connec>ons and shunt resistor, replace meter ! 
Voltage Regulator •  With Voltage On, check voltage regulator pins ! 
All pins should be close to Power Bus Bar voltage •  If Pin S is low, check Over Voltage Sensor (OVS) connec>ons ! 
If OVS connec>ons are good, OVS is bad •  If Pin F is low Disconnect Pin F to alternator lead !  If Pin F is s>ll low, replace Voltage Regulator ! 
•  Regulator is shorted, also check if alternator field shorted ! 
If Pin F is high, check alternator Voltage Regulator •  If Pin A is low ! 
Usually a connec>on problem •  If Pin I is high and LV/OV light is out ! 
Check bulb and wiring Alternator •  Disconnect alternator leads and check alternator – voltage off •  Check resistance between F (field lead) and ground connec>on Range – 3 to 6 ohms !  If low, field coil is shorted -­‐ replace alternator !  If high ! 
•  Service brushes and clean commutator •  Resistance s>ll high, field coil is broken -­‐ replace alternator Alternator •  Check for open Stator by measuring resistance between B (baQery lead) and ground If high, stator is open and alternator needs to be replaced !  May have to use “diode” mul>-­‐meter sepng ! 
•  Check for shorted diode bridge Place a mul>-­‐meter in series with alternator B lead to measure leakage current !  Power on !  If leakage current is over 0.5 mA, bridge is bad – replace alternator ! 
Alternator •  Check for open diode bridge Power on, engine at 1500 RPM and lights on !  Check AC voltage on B lead ! 
•  If over 0.5 V, bridge is bad – replace alternator Alternator •  Check alternator output Install mul>-­‐meter to measure current in to F lead !  Power on, engine at 1500 RPM and lights on !  If current is 3.5 A or higher and alternator output is s>ll low, replace alternator ! 
•  If s>ll unable to determine problem, run external regulator test outlined in Alternator Test Regulator handout Finish Up •  Do a final complete system test with engine running and lights on •  Charge/test baQery ! 
Remember Diamond DA42 crash •  Reinstall and >ghten all components •  Clean aircra& ! 
Return aircra& in as-­‐good or beQer shape than you received it •  Complete logbook entry and work order Large Aircra& Electrical Power •  Some turbine engine combine a starter motor and generator in a single unit The windings serve double duty !  Power is applied in the starter mode !  Power is produced in the generator mode ! 
•  AC (Alterna>ng Current) power is used on large aircra& ! 
Usually run at high voltage •  Low current means less power loss in wiring ! 
Easy to convert to different voltages with a transformer Large Aircra& Electrical Power •  AC (Alterna>ng Current) power is used on large aircra& Commonly run at 400 Hz !  Voltage must be regulated !  Frequency must be >ghtly controlled !  Mul>ple generator systems: ! 
•  Matched voltage •  Matched frequency •  Synchronized AC wave forms ! 
! 
In phase Peaks and valleys must match perfectly Large Aircra& Electrical Power •  AC (Alterna>ng Current) power is used on large aircra& ! 
Constant Speed Drives (CSD) are used to control generator speed and phase Constant Speed Drive (CSD) Constant Speed Drive (CSD) Constant Speed Drive (CSD) Large Aircra& Electrical Power •  AC (Alterna>ng Current) power is used on large aircra& ! 
Constant Speed Drives (CSD) are used to control generator speed and phase •  Uses a mechanical transmission to control the frequency (speed) and phase •  Transmission consists of a hydraulic pump driving a hydraulic motor ! 
The amount of fluid going to the motor is varied to control the speed and phase •  Usually oil cooled •  Can be electrically taken off line with a cockpit switch •  In-­‐flight failures can only be fixed on the ground ! 
Example: Overhea>ng Large Aircra& Electrical Power •  AC (Alterna>ng Current) power is used on large aircra& ! 
Integrated Drive Generator (IDG) is a brushless generator •  Used in high power applica>ons •  Has a built-­‐in generator that provides the field current when the generator turns ! 
A generator inside a generator •  If metal found in oil, replace unit ! 
AC voltage can be converted to low voltage DC with a transformer and diode bridge (rec>fiers) Integrated Drive Generator (IDG) DC to AC Converter •  Called invertors •  Generates AC by switching the DC Method 1: Switch DC on and off !  Method 2: Switch direc>on of DC ! 
•  Switching is accomplished by: Electric motor !  Solid state switching circuit driven by an oscillator ! 
DC Electric Motors DC Electric Motors •  Very similar to generator except electric power is used to create rota>on •  Major components Armature assembly !  Field assembly !  Brush assembly !  End frame ! 
Series DC Motor Shunt (Parallel) DC Motor Compound DC Motor DC Electric Motors •  Types (based on the field windings): ! 
Series •  Field windings are a few turns of heavy wire connected in series with the armature winding •  Good star>ng torque ! 
! 
High startup current More current at low RPMs •  Bad speed control ! 
Shunt (Parallel) •  Good speed control ! 
Compound (Series and Parallel) DC Electric Motors •  Direc>on Change: Change the current direc>on in the field windings !  Change the current direc>on in the armature windings !  Changing both field and armature windings will not change direc>on !  Some motors have two field windings in opposite direc>ons to enable direc>on switching ! 
•  Speed can be varied by changing field winding current •  Brushless motors replace the commutator with switching transistor DC Electric Motors •  Armature Brake: Fric>on type brake applied to the armature !  A spring is used to apply the brake force and an electric magnet is used to withdraw the brake ! 
•  Stops the motor quickly when the electric power is removed ! 
Example: Landing light retrac>on motor External Lights •  Types: ! 
Posi>on (Naviga>on) •  Green – right wing >p •  Red – le& wing >p •  White -­‐ ver>cal stabilizer ! 
An>-­‐collision •  Types: ! 
! 
Rota>ng beam lights White strobe Landing !  Taxi lights !  TSO light required in IFR experimental aircra& ! 
•  Must have separate control switches Miscellaneous •  AC 43.13-­‐1B 11-­‐35(d) -­‐ In installa>ons where the ammeter is in the generator or alternator lead and the regulator system does not limit the maximum current that the generator or alternator can deliver, the ammeter can be redlined at 100 percent of the generator or alternator ra>ng •  Most accurate type of frequency-­‐measuring instrument is an integrated circuit chip having a clock circuit ! 
What about crystal controlled? Miscellaneous •  When using voltage to check a circuits resistance, the input voltage must be held constant FAA Ques>on •  How can it be determined if a transformer winding has some of its turns shorted together? a.  Measure the input voltage with an ohmmeter. b.  The output voltage will be high. c.  The transformer will get hot in normal opera>on. •  C 
Download PDF