126 terms

Basic Automotive Electrical Cicuits

CM-22, # 509
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What are the 5 basic electrical circuits fin automotive electrical systems?
1. Charging circuit
2. Starting
3. Ignition
4. Lighting
5. Accessory
Which circuit supplies all of the electricity for a vehicle whenever the engine is running?
The charging circuit
What are the 4 basic parts of a charging circuit?
1. Batter
2. Alternator (generator)
3. Alternator Belt
4. Voltage regulator
What is the usual type of battery used in automotive equipment?
A lead-acid cell-type battery
How many batter elements are there in most automotive batteries?
6
What are the active materials which compose the charged negative and positive plates in each battery cell compartment?
Charged negative plates contain gray colored porous or spongy lead (Pb); Charged positive plates contain chocolate-brown colored lead peroxide PbO2
What color of paint is used to mark a positive battery terminal?
Red
What is the composition of the electrolyte solution used in a fully charged battery?
60% water and 40% sulfuric acid
What is the normal specific gravity of the electrolyte used in a fully charged lead-acid storage batter?
1.28 (at 80F)
What is the unit of measurement for the capacity of a battery?
Ampere-hour
What is the cold-cranking rating of a car battery?
It shows how much current (in amperes) the battery can deliver for 30 seconds at 0 degrees F while a terminal voltage for 7.2 volts is maintained
What are the 2 principal methods used for charging a battery?
The constant current method and the constant voltage method
What is the usual charging rate using the constant current charging method?
1 ampere per positive cell
When mixing electrolyte, should the water be poured into the acid, or acid into water?
The acid is ALWAYS poured into the water slowly and gently: Pouring water into sulfuric acid can cause an explosion or splattering
What type of water should be used to fill battery cells when the electrolyte level is low?
Distilled water only
What should battery terminals be coated with when reinstalling battery cables?
Petroleum or white grease, in order to keep acid fumes off of the connections and thus prevent corrosion
What should the hydrometer reading indicate for a fully charged battery?
1.265 or higher
What are the 3 basic types of hydrometers used to check the specific gravity of batteries?
1. Float
2. Ball
3. Needle
What reading indicates a bad battery which must be replaced using the cell voltage test?
Any reading on 1 or more cells which is 0.2 volts or more lower than the other cells
Which type of test is considered to be the best method for checking battery condition?
The battery capacity test, also called the battery load test
What is another name for the quick charge test?
The 3-minute charge test (the battery is charged for 3 minutes to 30-40 amps), which can determine whether or not the battery is sulfated
What are the principal components of a DC generator?
1. Armature
2. Field frame
3. Field coils
4. Commutator with brushes which establishes electrical contact with the rotating element
What is the purpose of the soft iron pole pieces (pole shoes) located within the field frame of a dc generator?
To develop the magnetic circuit between the poles
What are the brushes made of in a dc generator
Carbon
Which factors determine the output of a dc generator?
The armature rotation speed, the number of armature conductors, and the magnetic field strength
Which type of generator regulator operates when the electric load requirements are high and the battery is low?
The current regulator would operate in order to prevent generator output from exceeding the safe maximum
What should be used to sand or smooth a dc commutator if it is dirty or slightly rough?
Number 00 sandpaper (emery cloth should never be used)
When should the brushes in a dc generator be replaced?
When they have worn down to half of their original length
What condition is indicated when the test lamp light does not burn when testing a generator field?
The field is open-cicuited
What would an ohmmeter indicate if a field coil is short-circuited?
Near zero
What are the 2 most practical tests used to locate shorts, opens, and grounds in armatures?
The growler test, and bar-to-bar best
Why has the dc generator generally been replaced by the alternator?
Because the alternator is more efficient and is smaller, lighter, and more dependable
What are the principal components of an alternator?
1. Rotor assembly
2. Stator assembly
3. Rectifier assembly
What does the rotor assembly consist of?
1. Rotor shaft
2. Claw poles
3. Slip rings
4. Field windings
What are the field windings?
Wire is is wound into a coil that is placed over an iron core, and mounted on the rotor shaft
What are the 2 types of stators?
1. Y-type: yields good current output at low engine speeds
2. Delta-type: used in high-output alternators
What is another name used for the rectifier assembly?
Diode assembly
What is the purpose of the 6 diodes that make up a rectifier assembly?
To convert the stator ac output into dc current
How are the rectifier diodes mounted?
Either in a heat sink or a diode bridge
How can the amount of necessary alternator maintenance be minimized?
By using prelubricated and/or longer lasting brushes
What does an ohmmeter reading BELOW the manufacturer's specified resistance value indicate when testing a rotor by connecting the ohmmeter to both slip rings?
A short
What does an ohmmeter reading ABOVE the manufacturer's specified resistance value indicate when testing a rotor by connecting the ohmmeter to both slip rings?
An open
What would a high ohmmeter reading indicate when connected from any one of the leads to the stator frame?
The windings are not grounded
What does a charging system output test measure?
System voltage and current under maximum load
What does a regulator voltage test measure?
It is used to check the calibration of the voltage regulator and to detect either a high or low setting
In what range do most voltage regulators operate?
Between 13.5 and 14.5 Volts
What is the purpose of a circuit resistance test?
To locate defective wiring, loose connections, partly burned wiring, corroded terminals, or similar problems
What is the maximum value which the voltmeter should read during a ground circuit resistance test?
No more than 0.1 V/electrical connection
What are other common names for the electric starting motor of an internal combustion engine?
Cranking motor or starter
What does the armature assembly or a starter consist of?
1. Armature shaft
2. Armature core
3. Commutator
4. Armature windings
What component of a starter includes the brushes, brush springs, and armature shaft bushing?
The commutator rend frame
What is the pinion gear in a pinion drive assembly?
It is a small gear located on the armature shaft that engages the ring gear on the flywheel
Which pinion drive design provides for the complete and positive meshing of the drive pinion and the ring gear before the starting motor is energized?
The DYER drive, which combines the principles of both the Bendix and the overrunning clutch type of drives
What type of engines is the DYER drive used on?
Heavy-duty engines
What are the functions of a starter solenoids?
1. To close the battery-to-starter circuit
2. To rush the starter pinion gear into mesh with the Ring gear
3. To bypass the resistance wire in the ignition circuit
What is the field coil (field winding)?
A stationary set of windings designed to create a strong magnetic field around the motor armature
How many teeth are there on the ring gear for every 1 on the pinion gear of a direct drive starter?
Between 10 and 6
What is the purpose of a neutral safety switch on a vehicle which is equipped with an automatic transmission?
It prevents the engine from being started unless the transmission shift selector is in either PARK or NEUTRAL
What does the starter current draw test measure?
The amount of amperage used by a starting circuit
What is the maximum amount of time that an engine should be cranked when starting, in order to avoid damage to the starter?
No more than 30 seconds
What does the ignition circuit provide at the spark plug electrodes?
High voltage arcs to start combustion (as high as 50,000 volts)
What are the 4 basic positions of an ignition switch?
1. Off
2. Accessory
3. Ignition On
4. Start
What is the ignition coil composed of?
2 sets of windings (primary and secondary); 2 primary terminals (low voltage connections); the iron core, which is a long piece of iron set inside the windings; and a high voltage terminal (coil wire connection)
Are the secondary windings in a ignition coil wound in the opposite direction of the primary windings?
Yes
What device actuates the ON/OFF cycles of current flow through the primary coil windings, and also causes the spark to occur at each spark plug earlier in the compression stroke as the speed increases?
The ignition distributor
How many volts are required for a spark to jump the rotor-to-cap gap in a distributor?
~4,000 volts
What is the spark plug gap?
The distance between the center and the side electrodes (normally between .030 and 0.06 inch)
What factors determine the spark plug heat range?
1. The length and diameter of the insulator tip
2. The ability of the spark plug to transfer heat into the cooling system
What do resistance spark plug wires consist of?
Carbon-impregnated strands made from rayon braid
What is the point dwell, or cam angle, in a contact point ignition system?
The amount of time that the points remain closed between each opening, given in degrees of distributor rotation
What are the basic components of an electronic ignition system?
1. Trigger wheel
2. Pickup coil
3. Electronic control uni amplifier
What type of rotor is used in a Hall-effect distributor?
A rotor with curved pates called shutters, which can pass through the air gap between the 2 poles of the magnetic sensor
Which method of ignition system timing is controlled by the engine speed?
Centrifugal advance
Which method of ignition system timing is controlled by intake manifold vacuum and engine load?
Vacuum advance
Which sensor in a computerized advance method of ignition timing allows the computer to retard the timing when the engine knocks or pings?
The detonation sensor
How does an oil-fouled spark plug appear?
It has wet oily deposits with very little electrode wear, which result from worn ring, leaking valve seals, or a scored cylinder
How do spark plugs appear that have preignition damage?
They have blistered or burned insulator tips and badly worn electrodes
What test is used to check a spark plug for sparks arcing through the insulation to ground?
The spark plug wire insulation test
What is a carbon trace on the inside of a distributor cap or on the outer edge of a rotor?
A small line of a carbon-like substance that conducts electricity and may short the coil voltage to ground or to the wrong terminal lug within the distributor cap
How are the distributor contact points aligned?
By bending the stationary contact bracket only; The movable contact arm should never be bent
How many degrees of dwell does an 8-cylinder engine require?
30
Which test is used to compare actual pickup coil resistance in an electronic ignition distributor with the manufacturer's specifications?
The pickup coil ohmmeter test (Pickup coil resistance varies between 250 and 1,500 ohms)
Does turning a distributor housing AGAINST the distributor shaft rotation advance or retard the timing?
Advances
How many leads does a timing light usually have?
Three: 2 small leads connected to the battery, and 1 larger lead connecting the number 1 spark plug wire
What is a vehicle lighting circuit composed of?
1. The battery
2. Vehicle frame
3. All of the lights
4. The switches that control the lights
What is the basic type of lamp used on automotive equipment?
The small gas-filled incandescent lamp with a tungsten filament
What does the candlepower of a lamp measure?
Luminous intensity
What are the main parts of a sealed beam headlight?
A lens, 1 or 2 elements, and an integral reflector
How much more light output does a halogen headlight produce then a standard headlight?
25% more light (with no current increase)
What is the function of the rheostat (or variable resistor) on the headlight switch?
To adjust the brightness of the instrument panel lights
What switch controls the high and low headlight beams?
The dimmer switch
What is a headlight aiming screen?
A series of measured lines that are marked on an auto shop wall (or on an easel) for the purpose of aiming vehicle headlights
What is the hotspot of a headlight bean light ray?
The high intensity portion of the ray
What degree of lighting is provided by a blackout driving light?
A white light of 25 to 50 candlepower at a distance of 10 feet in front of the light
At what distance should blackout stop/taillights and marker lights be visible?
A horizontal distance of 800 feet, and they should not be visible beyond 1,200 feet
Which type of light combines the service stop, tail, and turn signals with the blackout stop and taillights?
The composite light, which is the standard light used on the rear of tactical military vehicles
What is the basic functional part of a turn signal flasher unit?
A bimetallic strip wrapped within a wire coil, which serves as 1 of the contact points
What are the main components of a backup light system?
1. Fuse
2. Gearshift- or transmission- mounted switch
3. Two backup lights
4. Wiring required to connect the components
What is the function of fuses?
They are safety devices located at specific places in electrical circuits in order to protect wires and electrical components from a heavy low of current
What is a fuse element made of?
A metal with a low melting point that forms the weakest point of a particular electric circuit
Which type of battery condition gauge is used to indicate the amount of current flowing to and from a battery?
Ammeter
What are the 2 ways that an indicator lamp be set up to indicate an electrical malfunction?
1. As a low-voltage warning lamp: to indicate a warning whenever the electrical system voltage drops below the normal operational range
2. As a no-charge indicator: to indicate a warning whenever the alternator does not produce current
What does the sending unit of a self-regulating thermostatic fuel gauge consist of?
A hinged arm with a float on the end: the arm movement controls a grounded point that makes contact with another point attached to an electrically heated bimetallic strip, which is linked to a pointer
What does a magnetic fuel gauge consist of?
A pointer mounted on an armature
What is the function of the 2 coils in a magnetic fuel gauge?
1 coil is connected directly to the battery and produces and constant magnetic field, while the other coil produces a variable field, the strength of which is determined by a rheostat-type tank unit
How are the 2 coils placed in relation to 1 another in magnetic fuel gauge?
90 degrees apart
What term is used for the C-shaped tube in a mechanical pressure gauge ?
The bourbon tube
What is a thermistor, which is used in the sending unit of an electric temperature gauge?
It is an electronic device whose resistance decreases proportionally with an increase in temperature
What vehicle speed units are indicated by speedometers?
MPH or KPH
What device is employed to measure engine speed in rpm ?
Tachometer
What device counters the rotation of the metal cup surrounding the rotating magnet in a mechanical speedometer?
A calibrated hairspring
What generally drives the signal generator for an electric speedometer?
The transmission output shaft through gears
From where does an electronic tachometer usually obtain the pulse signal?
From the ignition distributor as it switches the coil on and off
What type of motor in generally used for the windshield wiper motor?
A small shunt-mount dc motor
Which components transfer motion fro the wiper motor transmission to the wiper blades?
The wiper linkage and arms
What are the branches of a ground return system called?
One-wire circuits
What are the 2 wires of a 2-wire circuit?
1 wire from the electrical enegery source to the unit that it will operate; and 1 wire to complete the circuit from the unit back to the electrical power source
Are 2-wire circuits commonly used on equipment that is subjected to frequent heavy vibrations?
Yes
What are the 2 basic types of wiring assemblies?
Cable and Wiring harness
What are the 2 principal purposes or wiring harness assemblies?
1. To prevent any chafing or loosening of terminals and connections that are caused by vibrations and road shocks
2. To keep the wires in neat condition away from the moving parts of the vehicle
What types of binding materials are used with wiring harness assemblies?
1. Tape
2. Lacing cord
3. Wire ties
What color code is used on all M-series tactical equipment wiring?
Black only
What are wiring diagrams?
They are drawings that depict the relationship of the electrical components and wires in a circuit
What are the 2 major classes of wiring terminals?
Solder type and solderless type
What are other names used for the solderless types of wire terminals?
The pressure or crimp type
What should be used to protect wire that passes through holes in the metal members of a vehicle frame or body
Rubber grommets