start Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 OBJECTIVES: After studying Chapter 37, the reader should be able to: • Prepare for ASE Electrical/Electronic Systems • • • • (A6) certification test content area “A” (General Electrical/Electronic Systems) Explain capacitance Describe magnetism Describe electromagnetism Explain how electricity can create magnetism and how magnetism can create electricity Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 KEY TERMS: armature capacitance • condenser • counter electromotive force (CEMF) • dielectric e coil • electromagnetic induction • electromagnetic interference (EMI) • electromagnetics farads • flux density • high energy ignition (HEI) ignition coil • ignition control module (ICM) • induced voltage Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 KEY TERMS: left-hand rule • lenz’s law • leyden jar magnetic flux lines • magnetism • mutual induction permeability • polarity • pole • primary winding radio choke coil • radio-frequency interference (RFI) • relative motion • relay • reluctance • right-hand rule secondary winding • self-induced voltage turns ratio Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 CAPACITANCE The ability of an object or surface to store an electrical charge is  called capacitance.  Around 1745, Ewald Christian von Kliest and  Pieter van Musschenbroek independently discovered capacitance in an electric circuit, using a device,  now called a Leyden jar, made  from a glass jar filled with water,  with a nail piercing the stopper  and dipping into the water.  They connected the nail to an  electrostatic charge.  Figure 37–1 A Leyden jar can be used to store an electrical charge After disconnecting from the  charge, they found that a shock  could be felt by touching the nail Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 In 1747, John Bevis lined both the inside and outside of the jar with  foil. This created a capacitor with two conductors (the inside and  outside metal foil layers) equally separated by the insulating glass The Leyden jar was also used by Benjamin Franklin to store the  charge from lightning and was also used in other experiments The natural phenomenon of lightning includes capacitance because  huge electric fields develop between cloud layers or between clouds  and the earth prior to a lightning strike Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 CAPACITOR CONSTRUCTION AND OPERATION A capacitor consists of two conductive plates with an insulating  material between them, called a dielectric A dielectric is a substance that is a poor conductor of electricity and  can include air, mica, ceramic, glass, paper, plastic, or any similar  nonconductive material The dielectric constant is the relative strength of a material against  the flow of electrical current. The higher the number, the better the  insulating properties Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 DIELECTRIC CONSTANTS See the chart on Page 382 of your textbook.  Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 When a capacitor is placed in a closed circuit, the voltage source  (battery) forces electrons around the circuit Because electrons cannot flow through the dielectric, excess electrons  collect on what becomes the negatively charged plate.  Figure 37–2 This simple capacitor, made of two plates separated by an insulating material, is called a dielectric At the same time, the other plate loses electrons  and, becomes positively  charged Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Current continues until the voltage charge across the capacitor plates becomes the same as the source voltage At that time, the negative plate of the capacitor and the negative terminal of the battery are at the same negative potential See Figure 37–3 The positive plate of the capacitor and the positive terminal of the battery are also at equal positive potentials There is then a voltage charge across the battery terminals and an equal voltage charge across the capacitor plates The circuit is in balance, and there is no current An electrostatic field now exists between the capacitor plates because of their opposite charges It is this field that stores energy Figure 37–4 NOTE: Capacitors are also called condensers. This term developed be­ cause electric charges collect, or condense, on the plates of a capacitor much like water vapor collects and condenses on a cold bottle or glass Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Figure 37–30 Typical air-cooled epoxy-filled E coil Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Figure 37–31 Cutaway of a General Motors Type II distributorless ignition coil Note that the primary windings are inside of the secondary windings The primary windings  of the coil extend  through the case of the  coil and are labeled as  positive and negative.  The positive terminal  of the coil attaches to  the ignition switch,  which supplies current  from the positive  battery terminal.  Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 The negative terminal is attached to an ignition control module  (ICM or igniter), which opens and closes the primary ignition  circuit by opening or closing the ground return path of the circuit When the ignition switch is on, voltage should be available at both  the positive terminal and the negative terminal of the coil if the  primary windings of the coil have continuity The labeling of positive (+) and negative () of the coil indicates  that the positive terminal is more positive (closer to the positive  terminal of the battery) than the negative terminal of the coil. This  condition is called the coil polarity.  The polarity of an ignition coil is determined by the direction of rotation of the coil windings.  Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 What is a “Married” and “Divorced” Coil Design? An ignition coil contains a primary winding and a secondary winding These windings can be connected together at one end or kept separate Married Also called a tapped transformer design The primary winding is electrically connected to the secondary winding Common in older distributor-type ignition system coils, and many coil-on-plug designs The inductive kick, called flyback voltage, created when the primary field collapses is used by the PCM to monitor secondary ignition performance Divorced Called a true transformer design, used by most waste spark ignition coils to keep both primary and secondary winding separated Figure 37–32 Tapped- (married) type of ignition coil where the primary winding is tapped (connected) to the secondary winding Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 ELECTROMAGNETIC INTERFERENCE (EMI) SUPPRESSION Until the advent of the onboard computer, electromagnetic interference (EMI) was not  a source of real concern to automotive engineers.  NOTE: Radio­frequency interference (RFI) is a part of electromagnetic  The problem was mainly one of radio­frequency interference (RFI), caused primarily  interference (EMI), which affects radio reception by the use of secondary ignition cables containing a high­resistance, nonmetallic core  made of carbon, linen, or fiberglass strands impregnated with graphite Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 As the use of electronic and computerized components and systems  increased, the problem of electromagnetic interference increased Whenever there is current in a conductor, an electromagnetic field is  created. When current stops and starts, as in a spark plug cable or a  switch that opens and closes, field strength changes. Each time this  happens, it creates an electromagnetic signal wave If rapid enough, the high­frequency signal waves, or EMI, interfere  with radio and television or other electronic systems, such as those  under the hood; an undesirable side effect of electromagnetism Static electric charges caused by friction of the tires with the road, or  the friction of engine drive belts contacting their pulleys, also  produce EMI. Drive axles, driveshafts, and clutch or brake lining  surfaces are other sources of static electric charges Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 EMI Transmission  There are four ways of transmitting EMI, all of which can be found in a vehicle Conductive coupling is actual physical contact through  circuit conductors Capacitive coupling is the transfer of energy from one circuit  to another through an electrostatic field between two  conductors Inductive coupling is the transfer of energy from one circuit  to another as the magnetic fields between two conductors  form and collapse Electromagnetic radiation is the transfer of energy by the use  of radio waves from one circuit or component to another Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 EMI Suppression Devices  There are four general ways in  which EMI is reduced By the addition of resistance to conductors that suppresses  conductive transmission and radiation By the use of capacitors and radio choke coil combinations  to reduce capacitive and inductive coupling By the use of metal or metalized plastic shielding, which  reduces EMI radiation in addition to capacitive and inductive  coupling By an increased use of ground straps to reduce conductive  transmission Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Suppression Capacitors and Coils  Capacitors are installed across  many circuits and switching points to absorb voltage fluctuations.  Among other applications, they are used: Across the primary circuit of some electronic ignition modules Across the output terminal of most alternators Across the armature circuit of electric motors Radio choke coils reduce  fluctuations resulting from self­induction,  and are often combined with capacitors to act as EMI filter circuits.  Filters also may be incorporated in wiring connectors Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Resistance Suppression  Adding resistance to a circuit to suppress  RFI works only for high­voltage systems. This has been done by the  use of resistance spark plug cables, resistor spark plugs, and the  silicone grease used on the distributor cap and rotor of some  electronic ignitions Shielding  Metal shields, such as the ones used in breaker point  distributors, block the waves from components that create RFI  signals. The circuits of onboard computers are protected to some  degree from external electromagnetic waves by their metal  housings Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Figure 37–33 To help prevent underhood electromagnetic devices from interfering with the antenna input, it is important that the hood be grounded to the body to form one continuous metal covering around the engine compartment This is particularly important if the vehicle has a front fender-mounted antenna If necessary, add a braided ground strap as this Ford Mustang owner did to eliminate radio interference Ground Straps Ground or bonding straps between  engine and chassis help suppress  EMI conduction and radiation by  providing a low­resistance circuit  ground path.  Suppression ground straps are  often installed between rubber­ mounted components and body The strap has no other job than to  suppress EMI.  Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Cell Phone Interference A cell (cellular) phone emits a weak signal if it is turned on, even though it is not being used This signal is picked up and tracked by cell phone towers When the cell phone is called, the cell phone emits a stronger signal to notify the tower that it is on and capable of receiving a phone call It is this “handshake” signal that can cause interference in the vehicle Often this signal simply causes some static in the radio speakers even though the radio is off, but it can also cause a false antilock brake (ABS) trouble code to set These signals from the cell phone create a voltage that is induced in the wires of the vehicle Because the cell phone usually leaves with the customer, the service technician is often unable to verify the customer concern Remember, the interference occurs right before the cell phone rings To fix the problem, connect an external antenna to the cell phone This step will prevent the induction of a voltage in the wiring of the vehicle Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 SUMMARY Capacitors (condensers) are used in numerous automotive  applications. Because of their ability to block direct current  and pass alternating current, they are used to control radio­ frequency interference and are in­stalled in various electronic  circuits to protect and control changing current Most automotive electrical components use magnetism, and  the strength of the magnetism depends on both the amount of  current (amperes) and the number of turns of wire of each  electromagnet The strength of electromagnets is increased by using a soft­ iron core Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 SUMMARY (cont.) Voltage can be induced from one circuit to another Electricity creates magnetism and magnetism creates electricity Radio­frequency interference (RFI) is a part of electromagnetic  interference (EMI) Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 end Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458