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AUT 242 Automotive Electricity II

AUT 242 Automotive Electricity II. Review for Final. Electricity. Three parts of electricity Voltage Current Resistance. Voltage. Definition: Voltage is the electrical pressure (potential) that causes the electrons to flow through a conductor .

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AUT 242 Automotive Electricity II

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  1. AUT 242Automotive Electricity II Review for Final

  2. Electricity • Three parts of electricity • Voltage • Current • Resistance

  3. Voltage • Definition: Voltage is the electrical pressure (potential) that causes the electrons to flow through a conductor. • If there is voltage on a circuit, there is the potential (possibility) for current flow. • A voltmeter is placed is used in “series” in a live circuit to measure voltage.

  4. Electron Flow (Current) • Electrical Current is the movement of free electrons, from atom to atom through a conductor to complete a circuit. • It is measured in Amperes (AMPs) • An ammeter must be place in series in a live circuit to measure amperage.

  5. Resistance to Current Flow • Resistance to the flow of current through a conductor • It is measured in OHMs • An ohmmeter is used to measure resistance and must be isolated from the power source of the circuit being tested.

  6. Ohm’s Law OHM’s LAW • Definition • An electrical law that states “It requires 1 volt (E) to push 1 ampere (I) through 1 ohm of resistance (R). • Use the following diagram to help with computations. E R I

  7. Computing Resistance • Series Circuits • Can be calculated by adding each resistance value within the circuit • Parallel Circuits • Can be calculated by treating each leg of the parallel circuit as a simple circuit. • Use the following formula RT =R1 + R2 R1 X R2 RT = R1 + R2

  8. Circuits • Circuit is a path that electrons travel from a power source, through a load and back to the power source. This example is a simple series circuit.

  9. Circuits • Circuit Components: Complete Automotive circuits will normally have the following components: • Power source • Protection (control device) • Conductor to load(insulated) • Electrical Load • Return path(ground)

  10. Simple Series Circuit 12 VDC L1 L2 L3 Series Circuits • Definition • A series circuit is a complete circuit that has more than one electrical load where all the current has only one path to flow through all the loads. • Voltage at each point will vary within the circuit.

  11. Simple Parallel Circuit 12 VDC L1 L2 Parallel Circuits • Definition • A Parallel Circuit is a circuit that has more than one path for current flow. • The voltage for each leg of a simple parallel circuit will be the same. • The current flow in a simple parallel circuit will be the sum of the current flow through each leg.

  12. SERIES-PARALLEL CIRCUIT L1 L2 L3 Series-Parallel Circuits • Definition • Series-Parallel circuits are a combination of series and parallel segments on one complex circuit.

  13. Electromagnetism Characteristics • Field strength increases as current flow through the coil increases. • Field strength increases if the number of coil turns increases. • If reluctance increases, field strength decreases.

  14. Factors That Affect Electromagnetic Voltage Output • The strength of the magnetic field • The speed at which the lines of flux are cut • The number of conductors • The closer the conductor and magnetic fields are at right angles with each other

  15. Magnetic Field Strength

  16. Charging System • Testing • Output test – Voltage and amperage under load. • Regulator voltage test - Testing for voltage regulator operation • Regulator bypass test (full field) – Bypassing the voltage regulator to produce maximum voltage. • Circuit resistance tests – Testing for poor conductors, connections and/or components within the charging circuit. • Voltmeter testing : See following slide.

  17. Voltmeter hookup to test the voltage drop of the charging circuit.

  18. Starting System • Basic components in a starter system and possible point sof failure. • NOTE: The neutral safety switch used only in cars equipped with an automatic transmission. Cars with manual transmissions use a safety switch mounted on the clutch linkage to prevent the starter from operating if the clutch is not disengaged.

  19. Battery Safety • Do not allow battery acid to come in contact with skin, eyes, or clothing. • Observe polarity when making connections to the battery. • Always disconnect the negative cable first. • Always connect the negative cable last.

  20. Purpose of the Ignition System • Create a spark strong enough to ignite the fuel air mixture. • Maintain the spark long enough to allow the for the combustion of all the air and fuel in the cylinders. • Deliver the spark at the right time during the compression stroke of each cylinder. • Maximum pressure should occur 10 to 25 degrees after TDC • Ignition must occur prior to TDC in order to complete the combustion cycle @ 10/25 dec ATDC.

  21. Factors That Affect Timing • Engine speed (rpm) • Less Time for the combustion cycle. • Engine load • More concentrated fuel air mixture which causes faster burning. • Firing order • Determined by the manufacturer • Numbered by cylinder. • Ignition system must be able to monitor the rotation of the crankshaft and the relative position of each piston to determine which piston is on the compression stroke.

  22. Ignition Systems • Primary Circuit (low voltage, system voltage or lower) • Power Source • Conductors • Switching device (Points and/or ignition module) • Primary coil. • Secondary Circuit (high voltage 10kV or higher.) • Secondary Coil • Distributor (depending on system) • Plug and or Distributor leads (as necessary) • Spark Plugs

  23. Primary and Secondary Circuits

  24. Creates a high voltage in the secondary winding by creating a magnetic field in the primary windings and causing that field to rapidly collapse. Note: This graphic does not include the capacitor/condenser in the primary ciruit.

  25. Mechanical Ignition Systems • Also called “Point and Coil. • Components • Power source • Distributor • Condenser • Contact Points • Cam • Rotor • Cap • Centrifugal advance (advances timing in relation to engine speed) • Vacuum advance/retard (uses manifold vacuum to determine engine load and advance timing under low load conditions and retard timing under high load conditions. • Coil • Primary and Secondary Circuits • May have a starting ballast or resistor • Spark Plug

  26. Ignition Summary • The ignition system supplies high voltage to ignite the air/fuel mixture. • The arrival of the spark is timed to coincide with the compression stroke of the piston. • The ignition system has two interconnected electrical circuits: a primary circuit and a secondary circuit. • The distributor may house the primary switching device plus centrifugal or vacuum timing advance mechanisms. • The secondary circuit carries high voltage surges to the spark plugs. • Ignition timing is directly related to the position of the crankshaft. • Computer-controlled ignition eliminates the need for centrifugal and vacuum timing mechanisms. • Nearly all of today’s engines are equipped with an EI system, which does not use a distributor. • There are primarily two different designs of EI systems, coil-on-plug and waste spark.

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