(b) Photoelectric. When light strikes the surface of certain sensitive materials, such as selenium or cesium, electrons are released. (Solar Power) (c) Thermoelectric. Electron movement can be created by heating the connection of two dissimilar metals. If the two metals are connected to a voltage sensitive gauge, an increase in the temperature of the wire junction will increase the voltage reading. (d) Piezoelectric. Certain crystals become electrically charged when pressure is applied to the crystal. The potential difference produced increases with increased pressure. Piezoelectric are used in air pressure and fuel pressure sensors on computer-operated systems. (e) Magnetic induction. Magnetic induction occurs when is relative movement between a conductor and a magnetic field that causes the conductor to cut the lines of force surrounding the magnet. A difference of potential is set-up between the ends of the conductor and a voltage is induced. (f) Electrochemical. A battery is a chemical device that produces a voltage potential between two different metal plates submerged in an acid. Lead-acid batteries are of this type. (ON #21) (g) Voltage does not flow through a conductor; it is the pressure that “pushes” the electricity. However, voltage can be used as a signal – for example, difference in voltage levels, frequency of change, or when it is switching from positive to negative. (4) A digital voltage signal is in one of two states either on-off, yes-no, or high-low. The simplest generator of a digital signal is a switch. A is a sudden ON and OFF of electricity within a circuit. In its basic form, an on-off switch
(3) The diameter of the conductor: the smaller the cross-sectional area of the conductor, the higher the resistance. (4) Temperature: normally an increase of temperature of the conductor causes an increase in the resistance. (5) Physical condition of the conductor: if the conductor is damaged by nicks, cuts, or corrosion, the resistance will increase because the conductor’s diameter is decreased by these. (ON SLIDE #30) (6) Resistance (load) is required to change electrical energy to light, heat, or movement. There is resistance in any working device of a circuit, such as a lamp, motor, relay, or other load component. (ON #31) (7) There may be unwanted resistance in a circuit. This could be in the form of a corroded connection or a broken conductor. In these instances, the resistance may cause the load component to operate at a reduced efficiency or to not operate at all. (8) It does not matter if the resistance is from the load component or from unwanted resistance. There are certain principles that dictate its impact in the circuit: (a) Voltage always drops as current flows through the resistance. (b) An increase in resistance causes a decrease in current. (c) All resistance changes the electrical energy into another form of energy to some extent. (ON #32)
(ON SLIDE #206) c. Electrical Circuits of the Starting System. Any internal combustion engine must be cranked manually to start it running on its own. Early equipment was started by the driver through the use of a hand crank. A system of cranking the engine with an electric motor was developed as technology progressed. The modern electric starting system has reduced the task of starting an internal combustion engine to the turn of a key or the pushing of a button. To accomplish this task electrically, a typical starting system consists of the start and control circuits. (ON SLIDE #207) (1) Start circuit. The circuit that delivers the heavy current required to crank the engine with sufficient torque and speed to overcome the mechanical forces of friction and compression include: (a) A power source such as a battery or batteries capable of supplying the necessary electrical energy. (b) A starter motor able to change the electrical energy into the mechanical horsepower and torque required to start the engine. (c) A solenoid that closes the circuit between the motor and power source and shifts the drive mechanism into mesh with the starter ring gear on the flywheel or flex plate. (d) Heavy gauge wire to transmit the electrical energy between the power source, solenoid, and motor. (ON SLIDE #208) (2) Control circuit. One method of controlling the starter engagement is by a pushbutton on the instrument panel. Pushing the button closes the control circuit so that current can be supplied to the solenoid coil. Current practice, however, is to eliminate a separate pushbutton switch by incorporating a start position into the key switch. A relay is frequently used in the control circuit to supply current to the solenoid coils. Only