Transcript Document
Electrical •Electricity •Fuses •Relays •Solenoids •Electrical Testing •Wiring Harnesses •Testing •Voltage Drop Testing •Test Procedures •Cables/Connections •Glow Plugs What is Electricity? • The flow of electrons from atom to atom in a conductor • Electricity is based on a theory- an “unseen” force because the energy itself cannot be seen, heard, touched, or smelled Fuses- devices used to protect the electrical circuit from too much current flow •A fuse is designed to open the circuit when the current reaches a predetermined level. •Fuses are rated in Amps •Do not install a fuse larger than is designed for the circuit Why Use Relays? •To direct electricity to a high current device like a starter motor, with the use of a light duty switch (key switch) •To control devices -A relay is a switch that changes states when voltage is applied to its input. The input connects to an electric coil. When voltage is replaced across the input, the coil magnetizes and moves a switch contact. Why Use Relays? •Relay we use has a single switch that is normally open (N.O.)- refers to the effect of the switch in its normal (non-energized state) 87A Electric symbol we use for these relays - the symbol shows the coil and switch 87 30 86 85 -When the coil is not energized a spring keeps the switch held open or OFF. When the coil is energized the magnetic field pulls the switch against the normally open contact thereby closing the switch. Starter motor solenoid or magnetic switch – Consists of a contact plate, plunger, plunger shaft, pull-in coil, hold in coil and return spring -When power is applied to coil terminal (key turned to start), current flows through pull in and hold in coils. Magnetic field pulls in plunger (the end of plunger has a contact disc). Disc makes contact with the two main contacts and an R terminal contact. Battery is connected to one main contact and the starter motor is connected to the other. Current flows between the battery and starter motor. Current also bypasses the pull in coil. The hold in coil continues to keep the solenoid energized until the key switch is opened. At that instant current no longer flows through the hold in coil and the contact disc is spring returned and starter motor quits turning. Solenoid- a coil of wire When voltage is placed across ends of coil, coil magnetizes (magnetism moves a plunger) Cut away view of coil commonly found on hydraulic control valves –Solenoids often take the place of what use to be done by mechanical linkages, levers and switches. -Common uses for solenoids are to control mechanical, hydraulic and electric circuits. Sensors •Sensors (referred to as senders) - devices that respond to a physical “stimulus” •Variable Resistive Sensors - as physical property changes, resistance of sensor changes •Variable Capacitance Sensors - (engine oil pressure and hydraulic oil charge pressure) –three wires to these sensors: ground lead, supply voltage lead and sensor signal –Variable Capacitance sensors- have a circuit built into them. The circuit converts the capacitance to an output voltage proportional to the pressure. As the pressure increases the voltage increases. Sensors Switch sensors (air filter and hydraulic filter) –close or open when the physical property reaches predetermined level Testing •Harnesses - Suspected defect in a wire –test for continuity with an ohm meter –after checking for continuity, check for a short to nearby pins, battery ground and battery positive •Switches - Test leads on correct pins –With wires disconnected from the switch, connect ohm meter across the switch –Switch can often be tested with a voltmeter in a live circuit -With the switch open you should read infinite ohms. With the switch closed you should read zero ohms. Anything other than these readings indicates a faulty switch. Testing •Relays - Test activation signal –May be able to test for activation signal by listening to the relay –Test switch output –same test for any other switch –activate the relay and check that the switch functions properly -Activation Signal- When activated and or deactivated, many relays make a clicking sound. If the clicking sound is present, you can generally assume that the activation signal is present. A more positive method is to check for ground and the correct activation signal at the relay using a volt meter. If you do not have the activation signal, the relay coil was shorted and should be replaced. If you do not have the activation signal, the cause for this must be found. Testing Relays – Quick Testing Tips •Replace relay with a known good relay • quick and effective •Remove relay and put a jumper across correct pins to simulate a closed switch –if output circuit functions, the circuit is ok Testing •Modules / Controllers •First, check for correct ground and power to module •If a known good module is available, replacement is the best test •Observe symptoms •Often controllers are expensive –casual controller replacement is not recommended -Because modules often are complex internally and perform many functions, it can be difficult to determine if a problem exists. Voltage Drop Testing •Voltage drop- the difference in voltage potential when measured across a circuit or component creating resistance -Voltage Drop- “Resistance decreases the amount of voltage available.” •Resistance- an opposing force, created by a circuit or component, to the flow of electrical current -Resistance- “There is a small amount of natural resistance when voltage flow through wires, switches, grounds or connections. The resistance increases beyond acceptable limits if corrosion develops, fittings become loose or wires fray. Resistance increases each time something, such as a wire, a switch, connections, or the ground are added to the circuit.” What Else Should be Tested –Each wire, ground, connector, switch, solenoid and the complete circuit should be tested –Each connection point is a potential source of increased resistance