• Aircraft Powerplant Electrical Systems• AMT 109C• Course Outline• Introduction – Outline• Properties of Matter• Review of DC theory

– Circuits – series/parallel– Ohm’s, Kerchoff’s and Henry’s Laws

• Power Sources– Power storage devices

• Batteries• Capacitors

– Power producing devices• Electro-mechanical• Electro-chemical• Alternate – solar, etc.

• AC theory– AC Power generation– Inductance, capacitance and resistance

• Schematics• Purpose, use and types• Schematic devices and diagrams• Logic theory

– facts vs assumptions• Wiring

– Connectors– Identification, routing and mounting

• Busses• Controllers

– Mechanical– Solid State

• Circuit rating and protection• Load devices

– Electro-mechanical - Motors– Lights/heaters– Others

• Circuit diagnosis– Plan of attack– Testing techniques and analysis– Verification

• Failures – causes and patterns• Circuit repair

– Component replacement – Soldering

• Properties of matter• Atom = the smallest particle that will retain the properties of an element.• The combined properties of an element are specific to that element although other elements may

have similar properties.• An element can be composed of single atoms, or they may be compose of multiple atoms of the

same nature.• When two or more atoms combine they form into a molecule. • A molecule of the same atoms is still an element, but if they have more than one type of atom

they become a compound.• Atoms “combine” for various reasons usually relating to a change in their mutual state of energy.

• The process of combining, or un-combining requires energy to initiate it, and will use or release energy to complete the transition.

• All atoms are made up of three types of particles, Neutrons, Protons and Electrons.• Neutron and protons make up the atom’s core, and the electrons orbit about the core in various

“shell” levels.• Electrons can be convinced to move from one atom to another.• Electrons exist in a orbital shell around a core that has a limit to the number of electrons for each

shell level.• The inner level allows for two electrons, then 8, then 8, 18, 32, 18 etc. with the outer shell always

being no more than 8.• Depending on the number of electrons in the outer shell some atoms allow electron movement

easily, some not so easily, and some resist such movement a lot.• These are conductors, semi-conductors and insulators, respectively.• Typically when atoms combine they will share electrons in their outer shells. • This may or may not effect the conductivity of the resultant compound.• Typically an atom that has one outer shell electron is a good conductor, and if the outer shell is

full (stable) it will be a good insulator.• By mixing certain elements we can make a semi-conductor that can vary its conductivity.• The sub-atomic particles exert various types of force upon each other.• The three predominate forces are electro static force, magnetic force, and gravitational force.• Neutrons react to the gravitational force but are neutral to the other two.• Electrostatic force and magnetic force are polarized, gravitational isn’t.• Electrostatic and gravitational forces exist at all times, magnetic force only exists when electrons

are moving.– Exception: some materials will easily retain their magnetic properties without electron

movement.• Electrostatic polarization is between electrons and protons.• Two likes repel, opposites attract.• The polarity is labeled positive for protons, negative electrons.• Magnetic polarity is established by the direction of force lines in a magnetic object.• This is labeled as the North and South ends, flowing from North to South externally. • Like poles repel, opposites attract.• But like directions of “flux” lines attract, and opposite directions repel.• Electrons moving in matter will cause magnetic lines of force (flux).• Magnetic lines of force moving through matter can cause electrons to move.• A few materials are very receptive to this interaction such as iron, and a few other metals.• A good electron conductor isn’t necessarily a good flux conductor.• A good electron insulator isn’t necessarily a good flux insulator.• All forces weaken exponentially with relative distance.• As these forces interact, and electrons are moved, heat is generated, and therefore this energy is

usually lost.• The temperature of any material will effect its qualities including its conductivity.• System design is always limited by these qualities, and must take into account the heating that

occurs from the interaction of these forces.• Atoms can exist in a state where they are missing an electron, or have one extra electron. These

are called ions.• Chemically induced ions can be used to inspire electron movement much like magnetism.• Electrons will not move unless they are being forced to move.• They are commonly moved by friction, magnetism, or chemical reaction.• These are electromotive sources. (They inspire electron movement)• Electrons traveling in a common direction, typically through a conductor, are called “current”, are

measured in units of Ampere, labeled “I”• An electromotive source will create a difference of electrostatic potential between its conductive

input/outputs.• One end will have many extra electrons, the other will be missing an equal amount.

• The difference is measured in units of Voltage, labeled “E” or “V”.• This potential can exist without actual current flow.• If matter is place across the “poles” of the source electrons may flow through the matter.• The amount of electron flow will depend upon the difference of potential between the poles, and

the conductivity of the matter.• All matter has some resistance to electron flow. • This always increases with the length of flow path.• This resistance always converts electron kinetic energy into heat.• Resistance is measured in Ohms, labeled “R”.• The relationship between voltage, amperage and resistance is known as Ohm’s law.• E=I*R• R=E/I• I=E/R

E I | R

• Conductors, insulators and semi-conductors that are so arranged with any electromotive source in a manner that causes the electrons to move only in those directions so designed are called a circuit.

• Electrons move at the speed of light, but because of the chain effect within the “tube” of a conductor as one electron enters into the tube, one electron instantaneously leaves the other end.

• Review of D.C. Theory• All circuits must have an electromotive source, one or more conductors, and a load.• An optional device is a controller.• An electromotive source can move electrons in one direction through the circuit, or in both

directions.• In direct current circuits the electrons move in only one direction.• In alternating current circuits the electrons move back and forth at a high rate of reversal.• The three basic types of circuits are:

– Series– Parallel– Series/parallel, or combined

• In a series circuit the electrons must travel in only one path from the source through the circuit and back to the source.

• In a parallel circuit there is more then one path.• In a combined circuit there will be places where both occur.• Kirchhoff’s laws – The sum of the voltage drop’s across all the loads in a circuit must equal the

source voltage.• The current going into any point of a circuit must be equal to the current coming out.• In a series circuit the voltage drops partially across each load.• The sum of the resistances times the current must equal the source voltage.• In a parallel circuit the voltage drops will be equal across all loads at the same parallel level.• The sum of the currents must equal the total circuit current.• Within a circuit, current, voltage and resistance can be measured.• Voltage, or voltage drop will be measured across a load, a conductor, a controller, or a source

with the circuit on and off.• Current will be measured at the desired point along a circuit with the circuit on.• Resistance will be measured across a load, a conductor or a controller with the circuit off, and the

component disconnected and/or the circuit open.• Magnetism - caused by electrons moving.• Electron orbit about core tends to cancel due to random movement from thermal action.• Electron rotation can cancel if pairs spin opposite, or add up if many un-paired spin the same.• Henry’s Laws cover rules magnetism.• Flux(ø) = The entire field of magnetic lines that emit from a pole.• Maxwell(Mx) = one magnetic field line.

• Weber(Wb) = 108 Maxwells• 2 systems of magnetic units• Centimeter-gram-second = cgs• Meter-kilogram-second = mks = Systeme Iinternationale• Mx = cgs, Wb = mks or SI• Gauss(G) = flux density(B) = Mx per cm2

• Tesla(T) = flux density(B) = Wb per M2 • Magnetomotive Force(mmf)(Gb) = Current X No. of turns in a coil.• Field Intensity(H)(Oe) = mmf per meter = I*N/Meters• Permeability(µ) = a material’s ability to produce lines of flux = B/H or G/Oe

– Ferromagnetic material easily allows unpaired electrons spinning in same direction.• Reluctance = inverse of µ = resistance to production of flux.• Hysteresis = Changes in flux lag behind force causing change.• Hysteresis Loss = the energy loss due to hysteresis, energy is lost as heat.• Magnetizing = to subject a magnetic material to a magnetizing force (flux) using current coil or

permanent magnet.• Degaussing = using alternating current to demagnetize the material.• Electrostatic flux increases with voltage increase.• Magnetic flux increases with current increase.• Power Sources - Storage devices• Two primary types;

– Batteries– Capacitors

• Power Sources - Batteries• A battery is a device where two different metals (usually) are placed a specific distance apart and

are chemically connected with an “electrolyte”.• The number of electrons this unit will store depends on;

– The chemical nature the metals used to make the “plates”.– The type, temperature & concentration of the electrolyte.– Surface area of the metal exposed.

• Typically more surface area means more electrons.• But the voltage will be determined by the chemical nature of the metals and electrolyte and their

internal resistance.• Resistance is due to the time it takes for reactions to occur as well as the temperature and

contamination of the plates.• In a lead acid battery porous lead (- anode) and lead peroxide (+ cathode) are the two metals.• H2SO4 is mixed with H2O for the electrolyte.• This mix has a higher density than water.• The Pb can become PbSO4 if it loses the hydrogen by sending two electrons through the circuit.• The PbO2 can become PbSO4 if it gains the two electrons and hydrogen.• The electrolyte loses the H2SO4 and gains 2 H2Os.• As the battery discharges the plates become lead sulfate and the electrolyte becomes water.• It will get weaker, and if it goes too low it will be impossible for it to completely reconvert back,

when recharged.• As they become colder this works less.• As they get discharged the electrolyte freezes at higher temperatures.• Since H2SO4 is denser than water the state of charge can be measured by checking the density of

the electrolyte.• This is done with a hydrometer.• At fully charged battery should be about 37% H2SO4 and the rest is pure water.• This will equate to a specific gravity of 1.275-1.300• The maximum voltage of each cell will be 2.113 with 6 cells for a maximum of 12.68 volts static

charge.• If the charging voltage exceeds 14.2 volts the electrolyte will start producing oxygen and

hydrogen gasses.

• The source of the gasses is the water, not the acid.• Replenish fluid with pure water.• If over charged it a high rate the cells will heat enough to flake off the H2SO4

• This will drop to the bottom of the cell no longer participating in the reaction.• It will eventually build up enough to short across the plates.• A hydrometer is a glass tube with a glass float in it.• The float is a long thin piece with a scale and a thermometer.• It is calibrated for the relative density scale to be accurate at 70°f

• If the temperature varies from this then the scale reading is adjusted.• As the density increases the float will sit and read higher.• More acid or colder temperature will increase temperature.• Standard lead acid batteries should be charged slowly, with 1-2 amps never exceeding 14.2V• This rarely happens.• Several rating factors to consider.• Amp-Hour = number of amps of current flow for a given amount of time.

– 27AH = 1 amp of current for 27 hours.• Cold Cranking Amps = the maximum amps it can put out under full drain. Amps per 30 sec >>

7.2V @ 0°f – Typically they can only put out so much at one time due to internal resistance.– This gets worse as it is discharging.– This gets worse as the battery gets older (sulfated)– A load tester is used to see max output performance.

• Load tester is used with battery at full charge.• Full charge = 12.68V after surface charge depleted.• Electrolyte density 1.275 or higher.• Battery should be able to stay in green (voltage) for ten seconds.• Batteries most often fail their plates due to shorting and sulfating.• Plates or posts can break internally.• Posts can corrode severely.• Dirty battery can conduct current through grease and dirt.• It is normal for a sitting battery to slowly loose its charge over extended time.• It is not uncommon for batteries to come dry, with box of electrolyte.• Don’t save electrolyte to top off other batteries.• Dispose of properly, diluting greatly with water.• Wet Cell batteries can come with serviceable cells or sealed cells.• Both of these types will gas if charged too high/fast.• Cells are vented, sometimes with slight PRD and fluid trap.• Fluid trap will have a drain, drain should go someplace non-critical, and stay clean.• Some brands will have a cheap hydrometer installed. (A/C Delco green eye is good)• Sealed types should stay sealed.• Typical life is 5 years regardless of use.• Extensive discharging will shorten life due to excessive sulfation.• Too basic types of structure, deep cycle, and rapid cycle.• Rapid cycle good for starting• Deep cycle good for long low current use such as motor home or marine.• Gel Cell Batteries• Geletinized (w/silica) electrolyte keeps battery from leaking.• Good for deep cycle use.• Non-vented

– Valve Regulated Lead Acid = VRLA• Sensitive to charging rates• Can discharge at a higher rate then flooded cells,• Operate at pressure• Cost = higher• Non-serviceable other than charging

• AGM = Absorbent Gas Mat batteries.• Name describes it, compact compressed package of plates.• Separated by electrolyte soaked mats.• Will take a very high rate of charge.• Non-vented

– Valve Regulated Lead Acid = VRLA• Can discharge at a high rate, similar to flooded rapid cycle• Operate at pressure, tends to cause gassing to reform into water.• Cost = highest of lead acids• Non-serviceable other than charging• Disposal, hazardous material, non-FAA issue, but other Fed, State and local laws apply.• Are most often recyclable• Primary danger sources are pressure failure and flash explosion• Secondary concerns:

– is being zapped, but low chance.– Shorting, causing hot conductor, fire.

• VRLAs are more efficient– Wet cells 15-20%– Gels 10-15%– AGMs 4%– Charging energy into heat

• Wet Cells self discharge about 1% per day.• Gels and AGMs self discharge about 2% per month.• Nickel-cadmium - Nicad batteries• Use Nickel hydroxide for one plate and cadmium for the other, both in a porous state.• Polymide or polymer separator.• Uses a base usually 30% potassium hydroxide as the electrolyte, which doesn’t “convert” in the

process.• The chemical flow in the electrolyte is to move a oxygen (hydroxyl) ion from plate to plate.• Therefore electrolyte state does not equal charge state.• Like lead acid is a secondary cell (rechargeable)• Anode and cathode form an oxidizing-reducing reaction if electrons allows to conduct from one

plate to the other.• Very low internal resistance• Can charge and discharge very fast• If completely discharged, one or more cells may reverse.• Is very sensitive to overcharging.• Once plates are full the charging starts oxidizing the electrolyte since the plates can no longer

exchange oxygen ions.• This generates a lot of heat.• High rate charging must include temperature measuring.• High temp is bad for all batteries.• Limit on current rate of charging is due to time required for oxygen to exchange across plates.• Excessive rate will cause oxygen release rather than charging.• Will also change the nature of the nickel hydroxide plate, ruining it.• Ni-cad Memory = voltage depression.• Is due to changes in plate’s crystallized structure.• Very slow charging or repeated cycling of charge/discharge causes material nucleation to form

larger crystals which resist chemical interaction.• Properly discharging (no more than 95%) and then recharging can reform crystals properly.• But every cycling does reduce battery lifespan so don’t cycle just because.• Trickle charging to keep full is ok if less than 5mA.• Otherwise low current trickle charging can cause memory effect, and will overcharge, oxidizing

the electrolyte.• Medium current trickle charging based upon capacity is most common method.

• High rate charging methods = Constant V or Constant C• Constant voltage or voltage monitoring.• Relies on not exceeding cell temperature as current reduces when close to full.• Voltage state is kept fairly constant. But there is a slight drop when reaching full charge.• Sensing circuit measures this drop and shuts down charging.• System should monitor temperature.• Allows for higher rate charging, quicker.• Down side of using voltage drop sensing is a defective cell could fool sensing system which may

then fry other cells.• Constant current• Is cheapest method = wall chargers• Typically called trickle charging = slow rate, long time.• Charges at a rate that does not exceed gassing.• User is expected to not over-charge• Pulse and burp charging• One second on, 5 ms off• Burp actually does high discharge during 5 ms period.• Allows diffusion of oxygen in electrolyte.• Promotes better micro-nucleation of plate crystals.• Allows for short voltage measurement period between pulses• NiCads using this technology tend to last up to twice as long.• DON'T deliberately discharge the batteries to avoid memory • DO let the cells discharge to 1.0V/cell on occasion through normal use. • DON'T leave the cells on trickle charge for long times, unless voltage depression can be

tolerated. • DO protect the cells from high temperature both in charging and storage. • DON'T overcharge the cells. Use a good charging technique. • Full discharging should be done with individual cells only to prevent cell reversal. (called

Equalizing)• Electrolyte is very corrosive, use proper safety gear. • Never mix tools, facilities and equipment with lead acid tools. Might prove big bang theory.• Terminal corrosion is potassium carbonate.• Clean with water and fiber brush, (metal brush can cause arcing)• Excessive terminal corrosion may be a sign of overcharging. (gassing and venting fluid)• Electrolyte level may change with state of charge. • Service with distilled water at full charge only unless plates are exposed.• Plate reforming during charging can cause material to form dendrites in a manner that shorts

through separator.• Is grounds for removal from service.• A reversed cell if recharged in a pack will get hot and may thermally run away when charged.• Thermal runaway is when cell gets hot, maybe during charging, then shorts internally and gets

really hot discharging and melts or goes BOOM.• Nickel metal hydride• Similar to ni-cad• 30% more capacity, less memory effect, less toxic• But lower number of charging cycles, discharge current lower, charging temp higher and more

sensitive• Will often include temp probe in case.• Lithium Ion • 300-500 cycles, highest capacity per pound.• Deep discharge bad for them as well as NiMH.• Worst case, like above, is high charge high temp. • Long storage, store at 40% charge.• Cell voltage 3.6V• Lithium metal is lightest of metals, but unstable when charging/discharging.

• Hence the need for lithium ions place upon a substrate.• DOT standards apply to transport of lithium due to unstable nature.• Power Sources – Capacitors• Capacitors• Very similar to batteries in construction.• Usually has two plates, these may be rolled or folded in a case.• They do not really produce power but they store it.• They traditionally don’t use “chemical” reaction to function.• external power source charges plates• Plates are separated by thin dielectric material that keeps plate separated but promotes

electrostatic flux.• Tension from flux will cause electrons on one plate to push away electrons on opposite plate.• Can act like a “shock” absorber as in case of the condenser used with ignition points.• Can be used as short term battery for things like timer electronics.• Can be used to filter out AC, DC or various frequencies. (More later on this) • some species use electrolyte, some are polarized.• All will have two leads like a battery.• Capacitance measured in Farads = 1 Columb at 1 volt.• This is very big as capacitors go, common to see micro-, nano-, and pico- farads.• But very small as batteries go.• Dielectric strength determines voltage limit.• Barrier breaks down and unit shorts if delta V gets too high. • Advantage over battery is they move electrons much faster.• Power Sources - Power producing devices• Electro-mechanical• Electro-chemical• Alternate – solar, etc.• Power Sources - Electro-mechanical• Primary unit is the electromagnetic generator• Mechanical force rotates driveshaft which uses magnetic flux to drive electrons through circuit.• Magnetic flux can come from a permanent magnet (magneto) or from an electric magnet

(generator)• mechanical force can come from many sources.• Common ones are:

– reciprocating engines– steam engine, geothermal, coal, nuclear, etc.– turbine engine– kinetic, hydro-dam, hydro-wave-pump, etc.– wind

• In general unit produces alternating current, then current is converted to DC if needed.• One strategy uses AC phased in the armature with magnetic poles using a commutator switch to

create DC.• Armature = the output section, can be stationary or rotary.• Field = Electro-Magnetic Field = controls output, can be stationary or rotary.• Although unit can be designed to maximize efficiency at any RPM it will usually only be efficient at

that RPM.• OK though because most users prefer stable output frequency, which is established by RPM.• Two common frequencies are 60Hertz (full cycles per second) or 400hz• USA AC electrical systems use 60hz, but aircraft AC systems use 400hz.• This saves on weight in several areas.• Higher frequency means fewer coils of copper and less core iron in generator.• But higher Hz means greater line loss so longer runs used on planet bound power systems

benefit from lower 60Hz.• Aircraft DC systems use 12 or 24 volts most commonly.

• Aircraft power usually comes from engine driven units, with bigger aircraft having a dedicated unit for this – APU – Auxiliary Power Unit.

• APU will use same type of fuel as main engines.• Common to marine applications of APUs.• Some older small aircraft use a wind driven “generator”.• These units are often an add on unit, by major alteration process.• Note: Once unit installed may nullify qualification for Light Sport Aircraft.• Electromechanical generator may also be used as signal generator for such things as

tachometers, wheel speed sensors and synchronization components.• Power Sources - Electro-chemical• Electrochemical = same as battery.• Primary = one time use• Secondary means can be recharged and used more than once.• Typically used for starting systems, and to run basic equipment during non-engine run phases or

during emergencies.• Will also act as a buffer to stabilize power “grid” during various fluxuation events such as the high

load that occurs when starting.• Some very recent technologies use systems that directly convert simple hydrocarbon fuels into

electricity.• Fuel source must be critically clean, technology has a long way to mature and become

reasonably priced.• Upside is it can be very lightweight, clean, and quiet.• Power Sources - Alternate – solar, etc.• Solar power sources use photovoltaic qualities of some semiconductor technologies.• Essentially as photons strike the material enough energy is added to it that the electron is

knocked free.• The material is so arranged that the electrons must go in a uniform direction thereby becoming

current.• The basic unit of a photovoltaic cell silicon diode.• by doping two layers of silicon with phosphorus and boron, respectively, it will then trade

electrons to balance the atomic need.• But this leaves the barrier very polarized so that electrons easily jump the barrier one, but won’t

go the other way.• This is because like poles repel, unlike poles attract.• As electrons are added to the N side this will tip the balance between chemical force and

electrostatic towards negative on the N side so electrons will jump the barrier to the positive since opposite polarity attracts.

• When electrons are added to the P side the scale tip will be towards making the P side more negative forcing the electron away since like polarity repels.

• This is called a P/N junction.• If it is made in a manner that light can reach the junction it can generate current flow.• Then when photons hit an electron on the P side it gets enough energy to jump the barrier and

will do so if a circuit exists to allow the electrons to flow back around.• These tend to be fairly low power generators.• In part this is because they can only really use a narrow frequency band of of this spectrum.• Also, the substrate in which all this resides must be a semi-conductor for it to work, so therefore

won’t be the best of current carriers.• Power Sources - Alternate – solar, etc.• END of Section• AC theory• Alternating Current• Electrons move back and forth in circuit.• Works just like DC in a purely resistive circuit.• But no circuit is purely resistive.• AC theory

• Two primary reasons for using AC are;– Is simple to cause alternating electron motion via electro-mechanical means.– Signal transmission via electromagnetic spectrum.

• From the resistive perspective Ohm’s and Kirchhoff’s laws apply equally to AC and DC circuits.• But since the amount of current is changing all the time and there is always some magnetic

output from a conductor carrying current there will be an “impedance” to the changing. • This is primarily due to the fact that as current increases the magnetic field builds, as it decreases

the field collapses.• This since this field changing takes time it will lag the current changes some.• Since current can be made by magnetic fields passing through a conductor they will pass through

itself or other parts of the circuit like the other loops of a coil.• This will create an “Induced” voltage.• This induced voltage is opposite of the voltage causing the current change.• Therefore as the voltage increases, the current increases, causing the magnetic field to increase,

creating an induced voltage that is opposite in polarity to the original voltage.• No current change = no induced voltage, high rate of change = high induced voltage.• So as the rate of changing increases the inductive impedance increases.• Impedance is like resistance in an AC circuit in that it causes a loss of energy. • It can therefore be treated in a similar mathematical manner with the “Laws”.• Is properly called “Reactance”.• A circuit that has some capacitive aspect will allow AC to pass through the capacitor, but prevent

DC from passing.• DC is merely the absolute case of very slow AC.• So as the frequency of AC slows down the impedance to AC will increase in a capacitive circuit.• Called Capacitive Reactance this is the opposite of inductive reactance with respect to frequency.• But it is similar in that it will impede the “energy” of electron flow in an AC circuit.• Like inductive reactance, the “laws” can be applied.• Like resistance, reactance exists in any circuit where the current is changing.• These effects can be reduced in design by applying the “laws”.• But before they can be applied we must first understand how Alternating Current is generated,

and how we “model” that generation mathematically.• Power Generation• As stated in the previous section, “power” or current production is most commonly produced

using an Electromagnetic Generator.• Like most things this technology has changed some over the years.• But it still primarily falls into two groups of generators.• The first, or older group is simply an electric motor being spun by an outside force such as a

propeller in the wind.• The second group is similar in nature, but relies on solid state technology to control and convert

the current as needed.• In the DC world we commonly call these a generator and an alternator respectively.• In the AC world since we don’t convert to DC we call them generators.• Specifically they are all generators.• Power Generation• If a wire passes through a magnetic field current will flow.• It will flow in a direction that depends upon the direction of the flux and the direction relative

motion.• Left hand rule for generators will show this.• Thumb = direction of motion.• Index = lines of force, North to South• Middle Finger = EMF = Electromotive force = Electrons in Middle Finger. • The left hand rule for a wire will show the direction of current relative to the direction of flux.• It will also do this with respect to coils and magnetic polarity.• In a wire the thumb = current, and curled fingers are flux direction.• In a coil, fingers are current direction, and thumb is North pole.

• So using a loop of wire with either side of the loop rotating through two poles: each wire will be passing in opposite direction so the current will be in opposite direction of the respective sections of wire.

• But due to the loop nature, this compounds, or adds the EMF.• To make the unit move more electrons we must add more loops, or make each loop into a bunch

of loops.• This is done by coiling the wire around a ferromagnetic core.• It can also be increased by adding more than one loop circuit per armature.• Since this unit is rotating the wires will quickly get wound up unless we make a conductive path

that allows “slipping”.• This is called a brush assembly, and is composed of “brushes” and “slip rings”.• The brushes (carbon) are spring loaded to ride on the slip rings (copper) mounted on the rotating

armature.• As the loop rotates, the wires will reverse so the current must reverse.• As the loop rotates the direction of wire travel changes which alters the amount of flux being cut.• This varies from none, to maximum, one time per current direction, or two times per loop

revolution.• This current can be plotted using a Descartes projection of X and Y axis.• The Y (vertical) axis depicts current (or voltage) and the X depicts degrees of rotation starting

from no current.• By adding more loops into coils one can make more voltage.• By adding a separate bundle of loops wired in series the voltage will increase.• or if wired in parallel the current will increase. • By adding more single loops and putting a switching set of brushes and commutator it will push

electrons through a loop, then switch to the next.• This is called a DC generator, but in fact the current in the rotor is switches direction in the wires

as they reverse.• But its not real AC because the current goes one way, stops, then the other, stops, etc. • The down side of this is its hard to make, and all the current generated must pass through the

brushes and commutator.• It can be voltage controlled with a regulator attached to the electromagnet.• The permanent type magnet generator must use a current sink or vary RPM to control voltage.• By making each loop out of thicker wire, and making the magnet stronger, and by spinning faster

we can get more current.• But this will get hot.• Additionally, due to histerysis and the concentrating effect of ferromagnetic materials the rotor will

“drag” the magnetism some, and it will produce a counter EMF which both serve to limit the output.

• As well this unit will best function at a specific RPM, but will decay in performance at lower RPMs greatly.

• Another approach to this would be to spin the electro magnet, using a much smaller amount of current for the field (typical 5 amps).

• The down side of this is without the switching of the commutator the output will be AC. • By making the magnet shaped with fingers one can alternate north and south at each finger.• This magnetic field can be made by using a permanent magnet.• Or by using an electro-magnet with a coil of wire wrapped around the center and slip

rings/brushes to feed it current.• Then if we take this “field” and put a bunch of coils around it it will make alternating current.• Like above we could put all the coils in series, or parallel, or we could do a combination of the

both.• Typically you will see 3 parallel circuits of multiple coil gangs.• These will be wound in either a WYE or Delta configuration.• But this will leave you with three or four output leads.• But we can partially use the coils by either going from neutral to the coil end with the Wye wound,

or from one corner to the next corner in the Delta wound.

• In the Wye wound if we jump from one branch to the next bypassing the neutral we will double the voltage.

• 110V vs 220V AC• If we use all three leads our output will need to be a three phase device.• Typically hard to get this as most streets are wired staggered so each unit only sees two of the

phases.• Another circuit would be a combining circuit that connects to all three leads. (The wye neutral is

grounded)• In this case such a circuit exists that will also convert the AC to DC• This is called a bridge rectifier.• But to understand how this works we must first plot the voltage of each coil and overlap them in a

phased array.• Each coil array will be phased equidistance from each other. • This causes a symmetrical overlapping of the voltage sine waves.• If we are then able to eliminate the reverse portion of the AC current the overlaps will act as a

pulsing DC.• We do this by installing a couple of one way check valves in each of the two lines leading from

each coil.• Then we bridge the output into two leads, current in, and out.• In the above example the check valves stop the reverse flow of current, but the bridging causes a

voltage overlap so with a volt meter of voltage scope we will only see the top portion of each wave.

• The rising voltage in the next phase masks the descending voltage of the previous one. • In this example the phases are 60 deg apart. This can be anything and is based upon how the

generator is wound.• The closer they are the less “bumpy” the DC will be.• Physically this unit looks mush like the commutator type generator.• But it easier to make, weighs less, runs cooler, and is self limiting to some degree, although most

are made light enough that they will burn up before self limiting if run to long at to high an output. • This layout will cause there to be many over lapping phases per rotor revolution.• In essence it compacts a bunch of the one loop generators into a small package.• For a DC system each winding is then fed into a bridge rectifier which converts it into DC.• This is an array of six diodes with three input legs, and two output legs, one + and one -.• The rectifier diodes allow the coils to push current to flow into one leg and pull current from the

other leg.• In the wye wound unit two coils form the circuit, in the delta wound unit one coil is used per

phase.• The rectified generator is self limiting.• As current in crease in both the field and the armature, for some RPM they will create opposing

magnetic fields that cancel any increase in output.• Unfortunately this output value is often much higher then the temperature limits of the unit.• Output control is a function of rotor RPM and Field current.• If either increase, output increases.• But output current must always match load or the voltage will vary greatly.• So voltage control is the control of choice.• In purely AC systems, frequency is also very important to control for many AC users.• So rotor RPM is held very constant, and field current is the sole controller.• In DC systems RPM is often not controllable because it’s a function of engine RPM.• So again, field current control becomes the sole means of controlling the unit.• The controller is usually a simple switch that turns the field off and on in varying amounts, at high

speed.• This switch can be between the power source and the field, or between the field and ground.• It can be a mechanical switching device, a solid state device, or an analog resistive device.• Voltage out from the V-Reg will be a digital signal of varying duty cycle.• The V-Reg can be internal or external to the alternator.

• Can be installed on the ground side of the field, but this is not common.• Automotive units often have an idiot light circuit.• The two common failures are a failed regulator, or a failed rectifier.• To test, bypass the regulator to “full field” the alternator.• This can be difficult on the internal type units.• System voltage should go up to 17-23V depending on RPM.• You must know how to bypass the reg, IE: is it on the positive or negative side of the field.• This can be very hard to tell when the unit is internally mounted.• In older commutated type generators the voltage regulator

– regulated voltage in a similar manner, – prevented excessive current, – prevented reverse current from motoring the generator.

• They can negatively or positively control the field.• Older, smaller units used a vibrating mechanical switch type regulator called a 3 unit regulator.• This handled all three needs, V-reg, current limiting and reverse current prevention.• But larger units would fry points at high current output so they used a carbon pile regulator.• This was wired in in the same manner, but the field current was control by a pile of carbon discs.• As this pile was compressed its resistance would go down.• And the Field gets stronger.• A voltage sensitive coil was used to decompress the coils as voltage increases.• When several generators are used there must also be devices which balance load.• This balancing circuit will then drive the dual regulators to regulate voltage while keeping load

balanced.• The commutated type generators are similar to the rectified units in that by passing the V-reg to

“full field” will determine if the V-reg is bad or the generator.• Type “B” wiring the V-reg is between + and the field = most common.• Type “A” wiring the V-reg is between the field and ground.• The brushes will wear, and if replaced need to be seated.• Note the insulator under cutting.• Offset or angled brush units should not be back spun.• Series Wound DC Generators = Field is in series with armature.

– Regulates voltage poorly but tends to self compensate for load.• Shunt wound DC Generators = Field and V-reg are in parallel.

– Regulates voltage well but V-reg must be very sensitive to be stable to load changes.• Compound wound DC Generators use the best of both worlds by having two field circuits, one in

series and one in parallel.• The series field is really unregulated in this unit. The output is controlled on the parallel wound

field.• Armature reaction is where the two magnetic fields drag each other rotationally.• It varies with RPM and load.• This can be countered using interpoles.• These are additional “leading” field poles that cancel the armature magnetism proportionally to

the load being generated.• The other means of reducing the arcing caused by reaction is to shift the brushes to a position

where the armature is not producing power when the brush breaks contact.• This only works well with a constant RPM unit.• Inductance, capacitance and resistance• As previously discussed inductors and capacitors create loads on a circuit.• This is called reactance.• It varies depending on current and frequency.• At no frequency, or DC there is no reactance.• At low frequency capacitors create the most reactance• At high frequency inductors create the most reactance• Since inductive reactance varies with frequency and inductance the formula for this is X l=2pfL

where f is frequency and L is Henrys and Xl is in Ohms.

• Ohms law for inductance is the same as that used to combine resistances in series and parallel circuits.

• An inductor will cause current to lag behind voltage because induced voltage resists current changes.

• Since capacitive reactance varies with frequency and capacitance the formula for this is Xc=1/(2pfC) where f is frequency and C is Farads and Xc is in Ohms.

• Ohms law for capacitance is inverted from that used to combine resistances in series and parallel circuits.

• A capacitor will cause voltage to lag behind current because at 0 volts charge the circuit will be at maximum current.

• Therefore capacitive and inductive reactance counter, or cancel each other.• Their effect on phase counters the other’s phase effect.• ELI the ICEman• E leads I with an L (inductor)• I leads E with a C (capacitor)• Since resistance doesn’t effect phase the net of the two reactances, with the lessor subtracted

from the greater, will act upon total impedance at 90° to resistance.• But since reactance is already expressed in the form of Ohms in a purely reactive circuit Ohms

laws applies normally for a purely inductive or capacitive circuit.• Since both reactance’s cause current to lead or lag by 90° they must be added to resistances

using the Pythagorean theorem.• C2 = A2 + B2 • Zt

2 = R2 + X(c-l or l-c)2

• Zt = the circuits total opposition to current flow.• If the circuit has no AC, or inductors and capacitors then Zt = Rt • Ohms law works for AC circuits with inductors, capacitors and resistances.• Series circuits solve for impedance first, in parallel solve for currents since the V-drop is the same

across each leg. • Resonance is when the frequency is such that a capacitor in series with an inductor cancel each

other’s reactance.• Similar resonance in a parallel circuit with an inductor and capacitor will have infinite resistance at

a resonant frequency.• Power factor is 100% in DC circuits.• It is the ratio of apparent power to true power.• Apparent Power is that derived from measuring voltage and current in an AC circuit and

multiplying them.• True power is the power actually used by the resistive load and does not contain the power lost to

reactance.• Power factor = 100 X True Power / Apparent Power• Transformers• A transformer is a set of two or more inductors in close proximity whose purpose is to exchange

voltage for current in an AC circuit.• If the voltage or current is incorrect for a given application it can be transformed up or down.• The catch is if one goes up, the other must go down.• The other catch is this will lose some power within the circuit.• Essentially one inductive coil will have thicker wire with fewer loops or turns than the other.• They can be high current or high voltage coils depending on what they need for output.• Generally a “step up” or “step down” transformer refers to the voltage being “stepped”.• The unit can include a rectifier to convert the output to DC.• It can have multiple coils tapped into at various points internally for a series of different outputs

from one unit.• They can be cooled, often in an oil bath.• They are limited by the apparent power being driven through them.• Excessive power input or output can overheat them.• They can have different cores from iron to air.

• They can fully isolate one part of a circuit from another such that electrons do not actually travel through the transformer.

• or they can be wired such that the circuit is not isolated.• They are very efficient, loosing a little power to heat and hysterisis.• But they are inductors so will effect the impedance of the AC circuit.• Transformers will cause the voltage of an AC circuit to be 180° out of phase between the primary

and secondary windings.• This is because the current is 90° out of phase with the primary voltage and the secondary

voltage is 90° out of phase with that current.• Consequently a circuit with multiple transformers must be designed to accommodate phase

effect.• Another neat feature of transformers is that they use almost no power when “idling” in an AC

circuit.• In other words when there is no load on the secondary circuit the counter EMF in the primary

cancels out almost all current flow in that winding.• They can be single dual or three phase.• Each winding will need a reciprocal winding.• Their cores will be laminated to reduce eddy current effects.• And they can have a core that moves into and out of the coil.• This makes it an adjustable transformer which can be used to tune a circuit.• Capacitors can also be made variable for the same reason.• Motors• Motors are electronic devices. If it operates by internal combustion it is properly called an engine.• Like a generator, the relationship of motion, current flow and direction of the magnetic lines of flux

will determine what an electric motor will do.• Since the left hand rule for generators defines current flow based upon motion direction a reverse

rule, the right hand rule for motors defines the motion direction based upon current flow.• Each respective finger remains the same with the index finger defining the lines of flux from north

to south, the thumb defines the motion force, and the middle finger points to the direction of current flow.

• This is because of the original left hand rule which describes the behavior of flux around a current carrying conductor.

• In this case the lines of force below the conductor are in the same direction and repel, while the lines above are opposite and attract.

• Since this force applied will vary depending on the direction the conductor travels, and since the direction varies since the conductor is on a rotating “armature” it would eventually hit neutral force and then begin to reverse force.

• So, more than one conductor is used, there is a switching commutator, and the armature has a lot of mass to ensure momentum.

• In some strategies they have more than one brush assembly riding on the commutator. • This allows more than one set of conductors to apply torque at the same time, but it will also

require a second set of field poles. • Motors, like anything, have different phases of operation, and different operating needs to meet

each specific application.• All will need special attention to start spinning, some make their power through high RPM and low

torque, other have a reverse need.• Some are also combined with a generator function. • Like generators there are permanent magnet and electro magnet motors. • Typically permanent mag motors are only used in small unit application.• Whereas high load/torque units usually utilize electro magnetic fields. • These can also be wired in series or parallel with the armature, or both with a split field.• Like generators, motors a have problems with armature reaction.• They also generate counter EMF as a result of their motion. • This is in fact what limits their maximum speed.• As a motor approaches this maximum no load speed it’s current flow will reduce to very little.

• If load is applied, RPM will reduce, current flow will increase attempting to reestablish EMF and counter EMF balance.

• As load is increased, RPM is decreased, and current is increased.• In a series wound motor all the current travels through both the field and armature.• This allows for a very high torque at low speeds.• This is a good design for high load low speed such as a starter motor.• But these don’t limit well and will go to very high speed if not loaded.• Field windings are heavy with fewer turns.• In a parallel, or shunt would motor the field is wound with finer wire since there is no armature in

line to provide resistance.• Consequently these motors don’t start well, but are fairly stable in “cruise” RPM.• These units are often known as constant speed motors, although they do vary RPM slightly due

to changes in load.• But, they will need some strategy to get started.• One is to unload them during start, another is to include a small series field to assist starting, or

they may have alternative starting strategies if they are an AC motor.• DC motors are easily reversible.• Just switch the lead polarity of either the field or the armature.• Switching the polarity of both will net the same direction of rotation due to the right hand rule. • This is very easy in a permanent magnet motor.• One way would be to have two opposite would fields in the motor, picking one for each direction.• This is common for things like landing gear or flap motors.• Brush, commutator and bearing maintenance is the same as that of a generator.• Brush arcing may be more of a problem in motors with a high variability of load. • Brush phase is critical to RPM and load due to armature reaction.• Some units incorporate the use of magnetic brakes and clutches.• This allows for a greater control during either starting or stopping the unit.• Can be used to prevent undue binding on the mechanical linkage connected to the motor or may

disengage the motor when not needed as in the case of the bendix drive used in starter motors.• They may also incorporate speed or thermal limiting devices.• Many motors are duty limited.• They can produce more heat then they can reject during a given period of operation.• Starter motors, and landing gear motors my be an example of this.• Not all motors are designed to output rotating motion.• Some put out linear motion.• The simplest of these is the solenoid which is a coil around a movable core.• A spring moves the core one way, and the energized field moves it the other way.• Another type does spin, but this spinning drives an internal worm gear which then gives high

torque linear motion.• This is also a torque increasing gear reduction system which is often used in both linear and

rotary motors.• Although the previous discussion pertains to both DC and AC motors, the two are very different.• The AC motor comes in tow main categories: the induction motor, and the synchronous motor.• These can be single, two, or three phase motors. (one could go with more phases but the added

complexity would not derive much benefit) • In general the advantage of AC is that one can get more power for less weight.• The down side is batteries don’t do AC without help.• They also don’t self start as well as DC units with equal torque load.• A third type, the universal motor, works on both AC and DC, but these are not efficient,

particularly at 400hz• In essence the induction motor self induces current in the armature, there are no brushes.• This is done by winding the fields with each phase of the AC generator in a staggered manner

much like the generator is wound.• This causes each respective field generated by the phase current to increase and decrease in a

manner that emulates a flow around the field perimeter.

• This is similar to a row of lights with each bulb sequentially turned on so that it looks like the ‘light’ moves along the path of bulbs.

• In truth, there is no flow, each bulb simply turns on and off in phase. • The rotor in this motor is a can shape with copper bars running the length connected together at

the ends via a ring.• As the current changes in the surrounding field it induces current in these copper bars.• The resultant flux will cause the bars to try to follow the field until it reaches neutral.• As such, higher “slip” causes more torque. • So, as the load is increased, RPM is decreased causing more slip, causing more rotor current,

causing more force to catch up with the field.• Self starting for AC motors is a challenge, particularly single phase units. • They are often coupled with a tickler winding that is wired in series with a large electrolytic

capacitor.• The capacitor splits the current phase from the normal one causing those windings to pull more at

zero to low RPM.• A centrifugal switch cuts out this winding.• Another strategy is to split the field poles slightly with a magnetically shaded side.• This in effect curves the magnetic lines causing them to pull at an angle slightly off from the

center of rotation.• These units are very low torque starting and have been replaced by the Cap start units.• A synchronous motor is one where the AC field is the same as the induction unit, but the

armature doesn’t self induce.• It has DC applied to the rotor so it will stay right in phase with the induction windings since it

needs no slip to induce rotor current.• Typically uses 3 phase current, with a rectifier to produce the rotor DC.• Rotor speed in an AC motor is a function of the AC hz, as well as the current being applied and

the load being driven.• Like their DC counterparts as the load increases current increases, heat generation increases

and melt down will eventually happen.• Schematics - Schematic devices and diagrams• Typically there are several types of schematics.• The primary type tries to depict the circuit in a simple format that shows the electrical relationship

between all the parts and circuits.• Typically wires are solid lines, and parts may be drawn using common symbols or a generic “box”

for more complex “units”• A set of diagrams may put certain types of information in a common area, like all the grounding

point locations may be drawn on one page.• Another may be all the connector/pin diagrams.• A third may include drawings of the various devices.• Another type of schematic is one that doesn’t depict circuits it depicts diagnosis decision making,

called a flow chart.• These can be useful, or not, but they will contain data about testing results.• This can include both known good and known bad values for a specific test.• In general component symbols are usually similar, with some attempt at showing function or

purpose.• In spite of that one must memorize some of them to be able to easily read a schematic.• Schematics - Schematic devices and diagrams• wire and wire intersections• Resistors• Capacitors• Switches• Batteries & antennas• Coils• Solid State Devices• In general if the arrow points from positive towards negative current will flow from negative to

positive.

• The straight line defines the cathode region, the arrow defines the anode region.• If the anode is positive and the cathode is negative current will flow.• Diodes• Junction Transistors• PNP NPN• Emitter is the arrowed leg and emits holes or inputs electrons• The Collector is the collector of holes or output of electrons• The base controls• If its an N region and goes negative, current will flow.• If its a P region and goes positive, current will flow.• In Junction Field Effect transistors there is a source, drain, and gate.• Current flows from source to drain.• Gate can either be P or N type channel• Is less sensitive to voltage and noise output is less but is slower and can’t handle as much

current.• Schematics - Logic theory• One last type of schematic is a block type that is designed to show logic flow.• It does not necessarily show current paths.• It often doesn’t show power and ground supplies.• The primary purpose is to show how the circuit processes decisions and information.• These can most often be used to determine when a component or module is bad, but are not that

great for diagnosing a specific failure within that module.• The basic building blocks for this are the and, or, nand, and nor gates as well as the amplifier and

the inverter.• These will almost always be packaged into a circuit “chip” called and integrated circuit.• The common form for these are either a multi-pin chip with pins on either side or the bottom.• Or they may be a SMT device (surface mount technology) that has pads which are soldered to a

“board”• This is often done by machine in mass.• Other than being fried, the most common failure of theses devices is broken solder joints due to

poor soldering technique or excessive vibration.• Wiring

– Connectors– Identification, routing and mounting

• Wiring – Connectors• There are as many different types of connection strategies as there are manufacturers.• They can be single pin, multi-pin, plastic, metal, clipped, positive locked, threaded, and sealed in

a myriad of ways.• A good connection is one that

– Provides continuity with little resistance– Is mechanically sound and unlikely to break the wire in the event of relative motion.– Prevents corrosion of the wire or connector components.– Is easily disconnectable, but won’t do so on its own. (excludes permanent cnxtns)

• AMP and Molex are the common players of many years, but they have a lot of competition.• In general the two types are male/female arrangements or contact pads with spring pins.• Typically the strategy will be to put the most protected side on the power side of the connection.• This will most often be the female pins, although the connector may appear to fit inside the male

pin housing.• The connector pins are either some derivative of copper, or they may be a gold plated type.• They can be crimp or solder type, and they can be pre-mounted solder leads or loose insert

types.• Most loose types will have some tools that allow one to “eject” the pin back out of the connector

housing.• These pins get bent easily, and the retention tangs break off when removed. • 90% of electrical failures occur at a connection.

• It may be bent pins, wire pull out from the pin, corrosion, misalignment of the pins, pin push back, mis-installed pins (wrong hole), pin crimped onto insulation, or pin crimped onto shield.

• Quality connectors provide a means to secure a good electrical connection that is different than the means to ensure a good mechanical connection.

• The connector housing may have screw plates that trap the wire bundle aft of the connection pins.

• Connectors may have various mounting features such as a bulkhead flange, pressurized or not.• Connectors may provide a means to maintain shielding through the connector.• In general use the right tool for the job.• All crimpers are specialized to a specific task, some more than others.• Trimming insulation is critical, and very difficult to get right.• Cut or nicked strands compromise the current and mechanical capacity of the wire.• Always test new connections with a pull and an Ohm meter.• Always re-verify connector pin-outs prior to the application of power. • Wiring - Identification, routing and mounting• The Advisory Circulars have great data about how to route, where to route and how to identify

wiring harnesses.• In general limit the number of wires in any bundle. This reduces heat, and provides redundancy in

the event a mechanical event destroys that one harness.• Identification is either alpha/numeric coding or by color.• This value can change at a connector.• There can be hidden connections within a harness such as a solder joint.• Identification can also be by size, IE, two red wires, one #10 and one #16.• Wire sizing relates to current being carried, length of run, and thermal capacity of run.• AC 43.13 1XXX has charts for bundled and unbundled sizes.• The typical mounting device for a harness is the adel clamp.• These come in sizes from 1/8” up to 4” or 5”, in 1/8” increments.• Two can be doubled to attach a harness to a tube structure.• In general routing should always include some sag between hard points.• Wires can be laced together, or zip tied into a harnesses.• Zip ties are not structural nor are they suitable for high heat environments.• Lacing does a much cleaner job, but is harder to service or install a new wire into.• Another method of securing wires into a bundle or harness is spiral wrap, or split tube “Spaghetti”.• These are easily installed and removed for reuse after a wire is added or removed.• Not good for any heated environment.• They do provide some mechanical protection.• Harness shields and stand offs are a common strategy to prevent mechanical or thermal damage.• Never run a harness under fluid devices or lines.• Keep wires bundled cleanly, with concentric turns, and even feeds in and out of the harness.• 90° turns between relative motion points such as an engine and mount provide room for motion.• Three or four loops in a hard wire bundle provide flexibility, EG a thermal-couple lead going to an

engine.• Route wires away from likely hand holds or stepping zones.• Twist wires if a paired circuit, eg wires to a landing light and back. This will help cancel inductive

effects from the wires.• Install an appropriate connector if often disconnected, eg device mounted on a cowl such as a

light.• Busses• Typically provide common distribution points for power and ground.• Must provide a means to mechanically secure connectors.• No more than four per lug.• Hardware specific to metals being used.• Not uncommon to have several power busses, eg one master, one for radio stack, panel lights,

etc

• Buss design and insulation will be appropriate to the voltage and current being carried on that system.

• Are often made from copper or plated copper.• Insulation block will be a hard phenolic composite.• Busses• The general use of a buss is to have a common point to shut down a group of devices at one

time.• The down side is they reduce redundancy.• If one thing in the group shorts, they all go down, unless independently protected.• Typical circuit will see power supply to shut off device for circuit, then to the buss and then a short

run to the circuit protection devices.• On the ground side it may be grounded right where its mounted, or the main ground may carry

back to some more significant point.• Is not the best practice to use metal structures for ground paths in aircraft.• This makes a lot of noise on those sensitive devices.• As well it can effect performance of the device load.• Radios, antenna leads and intercom/microphone circuits are very particular to noise.• Should always be fully separate and shielded as much as possible.• Controllers

– Mechanical– Solid State

• Controllers – Mechanical• These are typically switches such as a toggle or limit switch.• They will often be incorporated into a system of levers, cranks and pulleys.• They may be a little micro switch or a big rotary selector device.• Generally their maintenance is the same as any other mechanical device.• Properly secure and seal them, keep them lubricated and adjusted correctly.• Controllers - Solid State• Are most often a black magic box.• Will have inputs and outputs.• Inputs are usually analog devices and outputs are a mix of both.• Output control is often on the negative side of the circuit. • NPN Power Transistors generally drive outputs.• Repair is usually replacement.• Failure is often due to output device using too much current. (overloads the NPN driver)• Be sure to verify all outputs are good when replacing a bad solid state controller.• Heat, vibration, and broken solder joints are the common enemy of these critters.• Mis-installation of a power or ground source can buy one of these quickly.• Transient voltage/current spikes can do the same.• Static protection when working with these is sometimes called for.• Will be a grounding device for you, the unit, the aircraft, or all three.• Packaging/mounting may also be designed for this.• Controller location may be environmentally controlled.• Could be for cooling, or moisture content, or pressurization.• These units are generally not field repairable.• Circuit rating and protection• Circuit protection is just that, a device that protects the circuit.• Typically includes fuses and circuit breakers.• They only protect the circuit, not the load device in the circuit.• Any circuit must be so designed such that all its power sources and loads will not exceed the

current carrying capacity of the conductors, and the voltage insulation capacity of the insulation.• The voltage issue is not big for most insulation materials used unless you exceed several

hundred volts.• Other factors that may effect the choice of insulation will be mechanical protection, and thermal

characteristics of the material and the environment.

• Current carrying capacity is a function of material choice, cross sectional area, and length.• But, since any conductor provides some resistance there will be some loss in heat.• Circuit rating and protection• Since heat can effect a material’s resistance, as well as effecting the insulation, current capacity

will change if the wire is bundled or not and shrouded or not.• In general the designer will add up all the loads for that one circuit, the distances of the runs, and

then determine a wire size that won’t cause an unacceptable line loss.• Once these values are known, then the proper type and rating of circuit protection device can be

selected.• These devices are rated for voltage, current, and speed of activation.• Fuses are commonly designed to be either fast or slow blow.• This allows for balancing protection needs with a dirty circuit.• In most circuits a high flow of current won’t do damage if it occurs for a short period (milliseconds)• This might toast a load device, but the circuit will be OK as it takes time for it to heat up and let

the smoke out.• If a load device needs specific protection that should be integrated into its internal power supply.• This can be both voltage and current protection.• It can be on the input, power/grnd sources, and on the output side.• The power supply must be rated appropriately as well.• A 2 Amp/Hour Battery won’t cut the load of starting an engine.• The same is true with a generator.• Generator gauge (amps) can be wired between the buss and battery, or the buss and generator.• If on battery leg it will be called an amp meter.• It will read plus and minus for battery charge and discharge.• All system users (except starter) must not exceed 80% max Generator output.• This allows for battery load during recharge.• If on generator leg it will be called a load meter.• Will read plus only.• All system users (except starter) must not exceed 100% max Generator output.• Load devices• Electro-mechanical - Motors• Lights/heaters• Others• Load devices - Electro-mechanical – Motors• When engaged motors are typically the highest power consumer on most aircraft.• But, most motors have a limited duty cycle.• The one exception is fans and drive servos.• Fans have limited use on turbine aircraft because the engine provides a lot of customer air.• Drive servos can be in constant use particularly with autopilots and trim systems.• They are all inductors.• As such in a DC circuit one must design for inductive spikes.• In an AC circuit one must account for inductive reactance in the system design.• Most of these devices are not field repairable, but they may need servicing and adjustments.• Typical failures include overloading/fried, and worn brush/commutator assemblies.• Load devices - Lights/heaters• In the long run of time lights are probably the highest user of power on any vehicle.• Typical cruise ship will use 1/4 to 1/3 of total power production for lighting.• Although heaters are sometimes used, in most aircraft the engine provides plenty of heat

sources.• Some medium size aircraft do use a specialized combustion heater.• The electrical power these use is mostly for driving their blower fans.• Heat comes from a combustion process.• Lights are most often high intensity heaters that act like resistors and inductors in a circuit.• They can also function by exciting specialized gasses such that photons are emitted in a more

diffused manner over a larger area.

• In the case of lights, heaters and motors they all have what’s called In-Rush current.• Because of EMF, Counter EMF, and varying degrees of resistance due to temperature when

current is first applied to these devices it flows freely in high quantities.• It will do this until the device loads/heats up to operating parameters.• Since the circuit is turned on with this low relative resistance the switch will be conducting a lot of

current while it is making contact.• Load devices - Lights/heaters• For this reason all switches for these devices must be de-rated.• “In-rush” current generally calls for the switch to be rated at a higher voltage and a higher current

then the load device’s listed ratings.• As previously stated many load devices will also unload current when they are shut off.• For this reason there may be circuit devices to reduce impact.• EG: diodes used on master and starter solenoid relays, or the capacitor used in every ignition

circuit.• Load devices – Others• Heaters, motors and lights tend to be the greatest current users in most aviation circuits.• But devices such as transmitters use a lot of current when they are transmitting.• As such the circuit (and generator) must be rated for maximum output conditions.• Typical radios need about 5-8 amps so are often protected at 10 amps, with wiring to support 10

amps.• Avionics are often place on one common master buss so that they may all turned off during start,

but easily turned back on. • Most new age avionics use variable input power supplies of 10-33 volts.• They will give different current/power specs for the two common system voltages, 12/24• These units if stacked may produce a lot of heat.• They may need a cooling blower.• Many will have a 5/8 hose connector in their chassis for cooling air.• Typical stack chassis should have spacing between units for circulation. • Stack assembly of trays may be tied together to increase structure.• Typical installation should include 12/18 inches of service loop in all wiring.• Wire routing should separate signal lines from power/ground lines and from antenna lines. • Avoid any routing near magnetic sensing devices such as flux gates and compasses.• Many installations will require additional certification such as navigation or transponder devices.• Load devices• On a final note for load devices, many, if not most electrical installations are considered to be a

major alteration.• This is one area where it behooves the installer to check with your local FSDO Avionics Inspector

prior to the installation.• Circuit diagnosis• Plan of attack• Testing techniques and analysis• Verification• Failures – causes and patterns• Circuit Diagnosis - Plan of attack • In general the process of diagnosis is abut keeping facts and assumptions organized.• Never mistake the two.• Always use a plan.• Always record results.• Intermittent failures often a long take time to identify.• Always verify and re-verify.• A plan should start with verifying the problem, if possible.• In general the plan should isolate through process of elimination.• The plan should prioritize based upon ease of testing and likelihood of failure.• Always find out what was done most recently.• Often times known good data is hard to acquire.

• This can come from schematics, troubleshooting charts, other maintenance manuals, or other known good systems.

• This data can be various readings like voltages, resistances, or it can be O-Scope patterns, or data codes.

• But, effective diagnosis will not happen without good data.• Use various connectors, switches, or circuit breakers to isolate circuits or portions of circuits.• If a part proves bad, determine why if failed if possible.• Parts that smelled burnt often fail due to too much load for some other reason.• Avoid parts swapping unless its a last resort, this can get very expensive.• Always assume multiple problems, particularly if you are not the first one looking at it.• Be particularly alert if you see evidence of new parts currently installed.• If there are multiple symptoms look to see what is common between symptom areas.• Don’t always trust manufacturer’s data. • Things like wire color or numbers sometimes get changed without being documented.• Is very uncommon, so don’t readily assume this, but if it happens, it’ll drive you nuts.• Circuit Diagnosis - Testing techniques and analysis • Testing technique is also critical.• Make sure you are testing what you think you are.• Trying to read power source voltage from a ground won’t tell you much.• Or reading resistance with an unseen parallel path will nullify any results.• Be careful how you hook up test equipment.• A current test applied incorrectly can fry a lot of pricy stuff.• Make sure the circuit status is correct prior ro hook up, circuit off/circuit on/circuit devices running.

– Don’t use an Ohm or Amp meter for voltage tests.• Try to test at connectors without compromising their sealing capacity.• Penetrating insulation is bad at best, but if you must, reseal with a dab of electrician’s silicone

sealant. (Non-corrosive)• Circuit Diagnosis – Verification• Always verify testing repeatability under differing conditions.• Low voltage coupled with a voltage drop check can ensure accuracy.• Heated vs cooled testing is often done.• Once repaired re-verify circuit operation completely.• Check to be sure other circuits are also working.• In fixing one thing you may have loosened a poor connection somewhere else.• Be thorough, customer confidence is what pays the bills.• Always be in hyper-alert if other attempts have been made to rectify this problem.• Many are challenged electrically and will repair symptoms leaving the cause un-repaired.• They may also add new complications to your diagnosis/repair efforts. • Circuit Diagnosis - Failures – causes and patterns• There are only three types of failures within any circuit.

– An Open– A Short– A failed electromotive source– or a partial/combination of the above.

• An open is when there is a break in portion of the circuit cause the electrons to stop flowing.• A short is when the electrons are allowed to flow anywhere other than designed.• A failed source will depend upon the type of source.• In a chemical source either the source is internally shorted/open, or its chemically depleted.• In a magnetic source either there is an internal short/open, a loss of magnetism, a failed current

converter/regulator, or the unit has mechanically failed.• Circuit boards• Typically fail at solder joints.• Traces get fried.• If smoky there is a high current user that needs fixing.• Onboard component repair is rare but doable if you know the circuit.

• Connectors• Most common cause of electrical failures.• Pin misalignment, or pin push-back• Bad pin crimping• Full of H2O or corrosion• Idiots• If you are replacing a new part look for the idiot who didn’t diagnose the original problem, and

don’t join them.• Black vinyl electrical tape is a good sign of needing idiot intervention.• The stupid list is infinite!!!• Circuit repair• Component replacement • Soldering• Circuit repair – Component replacement• If at all possible know why a component failed before you replace it.• In general internal component repair should be done at the depot level.• Field level repair is usually component or inter-connection replacements.• Circuit repair - Soldering• The correct, and good quality tools are mandatory, do not use cheap unregulated irons.• Solder surfaces must be clean and kept that way.• Use flux minimally, and remove thoroughly.• Delicate components should have heat sink between heat source and part.• Heat source is wetted with solder to conduct heat quickly.• Parts are heated then solder is added. • Prefluxing is helpful with un-tinned parts.• Adequate heat is critical to avoid cold joints that crack after time.

– Solder cools too fast and pre-cracks due to shrinkage.• Plan for insulation prior to soldering (pre-install heat shrink or other mounting devices as needed)• Do not compromise heat sinks, reattach with proper hardware and bonding agents.• Do not overheat trace (delaminate it from board)• Do not create conductive bridges (joints should be concave but filled)

P-Lead Repair Notes

• AMT 110CAircraft Power PlantsLab

• Soldering• Generally use a 60/40 mix of tin to lead.• Allows for it to melt at a lower temp while still flowing out well and remaining moderately strong.• Common to see rosin or acid core.• This is the flux used to clean surfaces and “wet” out the solder into the joint surfaces.• General method is to start with a clean tip, that is at temp, and has been “tinned” properly.• Apply tip to joint, with just enough solder to make a good heat contact.• Apply solder to joint as it heats up and will flow the solder into the joint.• Multi-strand wire may not heat up evenly.• Use only the heat setting required to get a good joint, but use enough heat to get the job done

quickly before the heat “sinks” into other parts.• Many components can be destroyed by heat.• A good joint should look tapered, and some what lean.• Surfaces should be concave vs. convex• Exception is inline joint.• May use extra solder to smooth a surface.• But solder is not structural.• Larger components, over one gram, should be secured by anther means. (Hot glue/Epoxy/Etc.)• Acid core solder good for pipes, but bad for wires.• Generally do not need additional flux if using rosin core.• But pre-fluxing does make for a smoother lighter joint.• When soldering stranded wires, pre-tinning the wire helps it join the connector, quicker, and with

less heat.• Many solder type connectors will come pre-tinned.• Crimp type, solder-less connectors.• Come in many sizes and styles.• Most common are insulated butted or brazed ring sleeve.• Or double fold ring sleeve.• The connecting end comes in many different varieties. • Ring and spade are the most common.• Ring generally comes in various stud sizes.• Spade comes in a few sizes.• In either case when these are large they are often called “lugs”.• General method is to use proper crimpers and crush.• Crush is very critical.• Not enough causes a weak joint mechanically and electrically.• Too much will cut the wire, and/or the connector.• Better quality crimpers have a stop. Some even have an adjustable one.• A good joint, whether crimp or solder will be designed to electrically connect and mechanically

hold• These are often separate from each other.• In the non-insulated there will be one set of folding tangs that grab the stripped wire.• And another set that grab the insulation and wire.• These need to be properly folded in a “U” shape back inward into the wire.• Aviation brazed ring crimp lugs are not the same as is often used in automotive and home use.• Typically they will have a pinch for the electrical connection, then another one for the mechanical

connection that also traps the insulation.• They will have a liner sleeve between the outer insulation and the lug.• Insulation is rated to higher temperature.• For most:

• Yellow = 26-24 gauge• Red = 22-18 gauge• Blue = 16-14 gauge• Yellow = 12-10 gauge• General project will be to make a “P” Lead type connection.• Uses shielded #18 stranded wire with braided shield.• Removed 1 Inch out outer insulation.• This may take several steps• Generally it is best to cut through the insulation most of the way with the stripper, then re grip the

insulation above the cut and pull it off.• Most strippers will cut wires if used to cut and pull in one motion.• By pushing the shield back one can extract the core wore out.• You can also unbraid the shield as well.• Twist the braided into a clean wire, then trim the core insulation back 3/16”• Trim a two inch piece of #18 multistrand wire back 5/16”• Connect to braid as shown.• Solder as shown, also tin the core lead.• Trim as shown, to 3/16”• And double insulate with heat shrink.• Install terminals• 22-18 ring #10 stud non-insulated to braided lead• 16-14 ring #8 stud insulated to core lead.• Crimp leads correctly and add a small amount of solder to the non-insulated one.• Insulate it with a small piece of heat shrink.• Attach to studs as per proper method in 43.13-1B• Note: #10 stud should have a base nut, #8 stud should not for this project.• Base metal is as labeled on back of stud adaptor.• Next cut pigtail in middle, two inches from unfinished end.• Repair with solder and heat shrink, two different methods.• Trim shield insulation back ¾” on each lead.• Cut 5/16” off of each core lead.• Strip each core lead back 3/16”.• Twist, solder, smooth with file and insulate with heat shrink.• Wrap or tie braids together, with small dab of solder.• Alternate method is to make core leads slightly shorter, push together and solder, clean up,

insulate, and then overlap braids.• Do not do this kind of repair on any attenuated lead. (antenna wires, or sensor wires)• Typically is best to not repair shielded wire, replace it instead, or install connectors and coupling.• Any connectors will mean a loss of power, or signal strength.• Typical “P” lead is one case where this type of repair might be suitable as its sole purpose it to kill

magnetos after shut down.